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Graduate Theses and Dissertations Graduate School
11-3-2016
Synthesis and Characterization of NovelPolyurethanes and PolyimidesKenneth KullUniversity of South Florida, [email protected]
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Scholar Commons CitationKull, Kenneth, "Synthesis and Characterization of Novel Polyurethanes and Polyimides" (2016). Graduate Theses and Dissertations.http://scholarcommons.usf.edu/etd/6530
Synthesis and Characterization of Novel Polyurethanes and Polyimides
by
Kenneth Kull
A dissertation submitted in the partial fulfillment
of the requirements for the degree of
Doctor of Philosophy
Department of Chemistry
College of Arts and Sciences
University of South Florida
Major Professor: Julie P. Harmon, Ph.D.
Abdul Malik, Ph.D.
Shengqian Ma, Ph.D.
Jianfeng Cai, Ph.D.
Date of Approval:
September 9, 2016
Keywords: Polyetherdiamine, Polycarbonate Polyol,
Soft Thermoplastic Urethane, Phase Seperation
Copyright © 2016, Kenneth Kull
Dedication
This dissertation is dedicated to my family. In particular, to my children Kaleb and Kara. I
dedicate this dissertation as a reminder that all dreams and goals are possible. That with hard
work, dedication and perseverance, all you set out to accomplish can be achieved.
Acknowledgments
I would like to thank my Advisor, Dr. Harmon for guidance and tutelage. I appreciate
her sticking with me throughout this long and drawn out process. My committee members: Dr.
Abdul Malik, Dr. Shengian Ma and Dr. Jianfeng Cai. I would like to thank the Department of
Chemistry at USF and all those that helped with the paperwork and deadlines.
I would especially like to thank the late Dr. Ralph Moore for being the one who guided,
mentored and pushed me to start this journey. Ralph was a trusted friend who will forever be
missed.
I would like to thank the Klingel family for their support and understanding while
working full time and pursuing my degree. I would like to thank my current employer Brighvolt
for allowing me the time and providing many resources as I finished my degree. Many thanks to
Dr. Anaba Anani for his encouragement, guidance as well as his ability to help others understand
what it will take to finish my degree. Imalka Marasinghe Arachchilage
I would like to thanks all my past and present lab colleagues: Dr. Timofey Gerasimov,
Lanetra Clayton, Kadine Mohomed, Butch Knudsen, Garrett Craft, Alejandro Rivera-Nicholls,
Tamalia Julienne and Imalka Marasinghe Arachchilage.
i
Table of Contents
List of Tables ................................................................................................................................. iv
List of Figures ..................................................................................................................................v
List of Equations .......................................................................................................................... viii
Abstract .......................................................................................................................................... ix
Chapter 1: Introduction ...................................................................................................................1
Polyurethanes .......................................................................................................................1
Polyimides............................................................................................................................5
Chapter 2: New Generation of Ultrasoft Non-Blocking Polyurethanes with High Mechanical
Properties for Biomedical Applications ...........................................................................................8
Polyurethane Calculations ..................................................................................................9
One Shot Method ............................................................................................................. 13
Two Shot Method ............................................................................................................ 13
Particle Size Reduction ..........................................................................................14
Testing ...............................................................................................................................14
Instruments ........................................................................................................................15
Results and Discussion ......................................................................................................17
Hardness .................................................................................................................17
Tensile/Elongation .................................................................................................18
Molecular Weight Determination (GPC) ...............................................................21
FTIR .......................................................................................................................23
Small Angle Xray (SAXS) .....................................................................................29
Dynamic Mechanical Analysis, DMA ...................................................................30
Thermongravimetric Analysis (TGA) ....................................................................35
Differential Scanning Calorimetry, DSC ...............................................................40
Modulated Differential Scanning Calorimetry (MDSC) .......................................47
Atomic Force Microscopy (AFM) .........................................................................52
Scanning Electron Microscopy (SEM) ..................................................................53
USP Class VI Testing ............................................................................................54
Conclusions ........................................................................................................................55
Chapter 3: Synthesis and Characterization of Novel Melt Processable Polyimide .......................57
Materials and Methods .......................................................................................................57
TMMDA Synthesis and Characterization ..........................................................................57
FTIR .......................................................................................................................58
ii
Titration..................................................................................................................58
NMR ......................................................................................................................59
TMMDA Mechanism .............................................................................................62
General Procedure for Polymerization ...................................................................62
FT-IR......................................................................................................................65
Rheology ................................................................................................................65
Thermogravimetric Analysis (TGA) ......................................................................65
Tensile Test ............................................................................................................65
Microhardness Test ................................................................................................66
Results ................................................................................................................................66
Rheology ................................................................................................................66
Thermogravimetric Analysis .................................................................................68
Gel Permeation Chromatography ..........................................................................69
FTIR .......................................................................................................................70
Vickers Hardness ...................................................................................................70
Discussions ........................................................................................................................71
Gel Permeation Chromatography ..........................................................................71
Rheology ................................................................................................................71
Thermogravimetric Analysis .................................................................................72
Infrared Spectroscopy ............................................................................................72
Microhardness ........................................................................................................73
Conclusions ........................................................................................................................74
Chapter 4: Future Work .................................................................................................................76
Polyurethane and Nanoparticles ........................................................................................76
Current Target Areas ..........................................................................................................79
Threading the Nanoballs with Linear Polyurethanes .........................................................79
Short Term Objectives .......................................................................................................81
Research Plan .....................................................................................................................81
Polymerize Baseline Material ................................................................................81
Determine Solubility of Nanoballs ........................................................................81
Cap Hydoxylated Nanoballs ..................................................................................82
Fabrication of Polyurethane Capped Nanoball Composites ..............................................83
Thermoplastic Polyurethane Threaded Through the Capped Nanoballs ...............83
A Millable Polyurethane Rubber Threaded Through the Capped Nanoballs ........83
Thermoplastic Polyurethane Threaded Through the Capped Nanoballs ...............84
Fabrication of Cross-Linked Polyurethane Nanoball Composites .....................................84
Thermoplastic Polyurethane Cross-Linked By the Nanoballs ...............................84
Cast Polyurethane Cross-Linked By the Nanoballs ...............................................85
Millable Polyurethane Rubber Cross-Linked By the Nanoballs ............................85
Testing of the Urethane/Nanoball Composites ..................................................................86
Differential Scanning Calorimetry (DSC) .............................................................86
Dynamic Mechanical Analysis (DMA) .................................................................86
Thermal Gravimetric Analysis (TGA) ...................................................................86
UV Visible Spectroscopy .......................................................................................87
Atomic Force Microscopy .....................................................................................87
iii
Tensile Testing .......................................................................................................87
Abrasion Testing ....................................................................................................87
Polyimide ...........................................................................................................................88
References ......................................................................................................................................90
About the Author ............................................................................................................... End Page
iv
List of Tables
Table 1. Thermoplastic Polyurethane Physical Properties .........................................................19
Table 2. Thermoplastic Polyurethane Physical Properties .........................................................20
Table 3. Molecular Weight of TPU's .........................................................................................22
Table 4. Nomenclature, Composition and Process Type ...........................................................41
Table 5. Glass Transition and Melting Temperatures Observed from DSC
Thermograms ...............................................................................................................41
Table 6. Feedstock Stoichiometry of Polyimide ........................................................................63
Table 7. Onset and Temperature at 97% Starting Weight for the Polyimides Studied ..............67
Table 8. TGA Onset and Temperature at 97% Starting Weight for the Polyimides
Studied .........................................................................................................................68
Table 9. Mw, Mn and Polydispersity by GPC ...........................................................................69
Table 10. Vickers Hardness Values .............................................................................................70
v
List of Figures
Figure 1: Urethane Reaction Scheme ......................................................................................1
Figure 2: Segmented Polyurethane ..........................................................................................3
Figure 3: Formation of Polycarbonate Copolymer ..................................................................8
Figure 4: Urethane Polymerization Scheme ..........................................................................12
Figure 5: Molecular Weight Graph .......................................................................................22
Figure 6: FTIR Hydrogen bonding Depiction .......................................................................23
Figure 7: FTIR Hydrogen Bond N-H Stretch and Non Hydrogen Bonded N-H
Stretch ....................................................................................................................27
Figure 8: FTIR Hydrogen Bonded Carbonyl Stretch and Non Hydrogen Bonded
Carbonyl Stretch ....................................................................................................28
Figure 9: SAXS of PCPU 7 Days after Molding ...................................................................29
Figure 10: Dynamic Mechancal Analysis of PCPU ................................................................31
Figure 11: Apparent Activation Energy of the Beta Transition ..............................................32
Figure 12: WLF/Time Temperature Superposition fit at Tg from DMA data ........................33
Figure 13: TGA XP-2816 ........................................................................................................36
Figure 14: TGA XP-28203 ......................................................................................................37
Figure 15: TGA XP-28062 ......................................................................................................38
Figure 16: TGA XP-28221 ......................................................................................................39
Figure 17: DSC XP-162 1st Heat Cycle ..................................................................................42
Figure 18: DSC XP-28162 2nd Heat Cycle ............................................................................42
Figure 19: DSC XP-28203 1st Heat Cycle ..............................................................................43
vi
Figure 20: DSC XP-28203 2nd Heat Cycle ............................................................................43
Figure 21: DSC XP-28062 1st Heat Cycle ..............................................................................44
Figure 22: DSC XP-28062 2nd Heat Cycle ............................................................................44
Figure 23: DSC XP-28221 1st Heat Cycle ..............................................................................45
Figure 24: DSC XP-28221 2nd Heat Cycle ............................................................................45
Figure 25: MDSC XP-28062 1st Heat Cycle ..........................................................................48
Figure 26: MDSC XP-28062 2nd Heat Cycle .........................................................................48
Figure 27: MDSC XP-28203 2nd Heat Cycle .........................................................................49
Figure 28: MDSC XP-28203 2nd Heat Cycle .........................................................................49
Figure 29: MDSC XP-28162 1st Heat Cycle ..........................................................................50
Figure 30: MDSC XP-28162 2nd Heat Cycle .........................................................................50
Figure 31: MDSC XP-28221 1st Heat Cycle ..........................................................................51
Figure 32: MDSC XP-28221 2nd Heat Cycle .........................................................................51
Figure 33: AFM Tapping Mode Phase Images .......................................................................53
Figure 34: SEM Image x1000 .................................................................................................54
Figure 35: SEM Image x25000 ...............................................................................................54
Figure 36: TMMDA FTIR.......................................................................................................58
Figure 37: Carbon NMR ..........................................................................................................60
Figure 38: Hydrogen NMR .....................................................................................................61
Figure 39: TMMDA Mechanism .............................................................................................62
Figure 40: Synthetic Procedure Outline for the Formation of the Polyether Polyimide .........64
Figure 41: Rheology Temperature Sweeps .............................................................................66
Figure 42: Rheology Temperature Sweeps .............................................................................66
vii
Figure 43: TGA Thermograms for the Polyimides .................................................................68
Figure 44: Gel Permeation Chromatograms for the Polyimides .............................................69
Figure 45: FTIR Sprectrum of Polyimide ...............................................................................70
Figure 46: Calculated Nanoball Window Sizes (Angstroms) .................................................80
Figure 47: Mono Functional Isocyanates ................................................................................82
viii
List of Equations
Equation 1: Urethane Calculation .............................................................................................10
Equation 2: Prepolymer Calculation .........................................................................................10
Equation 3: Percent Hardsegment .............................................................................................11
Equation 4: Bragg's Law ...........................................................................................................29
Equation 5: Activation Energy ..................................................................................................31
Equation 6: WLF of Alpha Tranisitions ....................................................................................34
Equation 7: Activation Energy for the Glass Transition ...........................................................34
Equation 8: TMMDA % Purity .................................................................................................59
ix
Abstract
Four novel high performance soft thermoplastic polyurethane elastomers utilizing
methylene bis(4-cyclohexylisocyanate) as a hard segment, 1,4 butanediol as a chain extender and
modified low crystallinity carbonate copolymer as a soft segment were synthesized. The samples
were characterized by infrared spectroscopy (FTIR), tensile, elongation, hardness, abrasion
resistance and atomic force microscopy (AFM). SAXS data shows evidence of an interdomain
"center-to-center" distance of 45Å. DSC traces show evidence of one glass transition temperature
and a weak melting region. DMA analysis reveals a low temperature secondary relaxation and
the glass to rubber transition followed by a rubbery plateau. All samples demonstrated the
ability to maintain excellent physical and mechanical properties in hardness below 70 Shore A.
Thermoplastic polyurethanes in this study do not possess surface tackiness usually observed in
soft polyurethanes. Biocompatability testing showed no toxicity of these samples as indicated by
USP Class VI, MEM Elution Cytotoxicity and Hemolysis toxicology reports. This novel type of
polyurethane material targets growing markets of biocompatible polymers and can be utilized as
peristaltic pump tubing, balloon catheters, enteral feeding tubes and medical equipment gaskets
and seals.
Polyimides are a family of engineering polymers with temperature stability, high polarity
and solvent resistance. These high-performance materials are used in aerospace applications, in
the production of semi-dry battery binders, and in a host of other high temperature demanding
situations. However, their glass transition and melt temperatures are characteristically very high
x
and close to one another, making them difficult to melt process and limiting them to thin film
formulations from their polyamic acid precursors. Here, a new series of thermoplastic polyether-
polyimides (PE-PIs) are synthesized by incorporating a polyetherdiamine monomer to reduce
rigidity and break up an otherwise fully aromatic backbone as seen with most conventional
polyimides. It will be shown that control of the stoichiometric ratio between the aromatic 4,4'-
methylenebis(2,6-dimethylaniline) and aliphatic polyetherdiamines relative to PMDA
(pyromellitic dianhydride), along with the molecular weight of the polyetheramine, can be used
to tune the Tg to best balance between temperature performance and processability.
1
Chapter 1:
Introduction
Polyurethanes
Polymers have become widely used in many different industries for many different
applications. Two different types of polymers, a polyurethane and a polyimide will be discussed
regarding the synthesis, properties, processing and applications. Discussed will be specific target
end uses and the potential benefits of the novel polymers developed in this study.
Polyurethane polymers (can also be called carbamates) are formed when you react an
isocyanate (sometimes called the “A” side of the formula) and a hydroxyl group (called the “B”
side) as demonstrated in the below figure.
RNCO
ISOCYAN
ROH
POLYO
RNHCOOR
URETHANEFigure 1: Urethane Reaction Scheme
2
An isocyanate contains a nitrogen atom (N), a carbon atom (C), and an oxygen atom (O) and is
represented as –N=C=O. The common “B” side is generally referred to as a polyol or a diol and
contains a hydroxyl group (-OH). In general, polyurethanes are produced using diisocyanates
and polyols containing two or more hydroxyl groups. There are two types of hydroxyl
containing groups. The polyol referred to above is generally a long chain molecule with a
molecular weight range between 700 – 4000 amu. These molecules are known for their ability to
flex and stretch. There are also diols called chain extenders which are much lower in molecular
weight. An example would be 1, 4 butanediol with a MW of 90 amu. Chain extenders, as their
name suggests link long, flexible portions of the urethane molecule and impart rigidity to the
polymer. The chain extender is part of the total “B” side but is a much smaller portion than the
long chain polyol. It is well known and has been extensively studied that thermoplastic
polyurethanes are linear segmented block copolymers made up of a hard segment (HS) and a soft
segment (SS). The hard segment is made from the diisocyanate and the short chain diol called
the chain extender. The soft segment consists of a long, flexible diol called a polyol and can be a
polyether, polyester or in our case a polycarbonate. The hard segment directly impacts the final
hardness of the polymer as well as imparts the excellent physical and mechanical properties. The
soft segment accounts for the elastic and flexible nature of the final polymer. The figure below
shows a representation of the hard and soft segments.
Polyurethanes were discovered in 1937 by Otto Bayer and were produced on a
commercial scale in the 1940’s. The first thermoplastic polyurethanes (TPU) became available
in the 1950’s, and by the 1960’s many TPU’s were available from companies such as DuPont
(Lycra®), B. F. Goodrich (Estane®), Mobay (Texin®), Upjohn (Pellethane®), Bayer
3
(Desmopan®), and Elastogran (Elastollan®) (Meckel 1987) (Hepburn 1987). Thermoplastic
polyurethanes are linear segmented block copolymers. Their unique mechanical properties result
from two phase morphology: the separation of hard segments made of the diisocyanate/chain
extender from the soft segment made of aliphatic oligomeric diol. The hard segments serve both
as reinforcement sites and physical crosslinks greatly influencing modulus, hardness and tear
strength of polyurethane. The soft segments contribute to both the elastic and mechanical
properties to polyurethanes (Kull, et al. 2015) (Meckel 1987) (Hepburn 1987) (Velankar 1998)
(Frick and Rochman 2004) (Culin, et al. 2004). A combination of properties such as high tensile
strength and ultimate elongation, excellent toughness, abrasion and tear resistance, low
compression and tensile set, low temperature performance, and resistance to oil have allowed
polyurethanes to be used in many demanding applications including: automotive, industrial and
printing rolls, cables and wires, sealants and adhesives (Kull, et al. 2015) (Meckel 1987)
(Hepburn 1987) (Wirpsza 1993). The polyaddition reaction can be easily adapted to produce a
wide variety of desired properties by adjusting hard and soft segment length and composition
(Wirpsza 1993) (Liaw 1997) (Sanches- Adsuar 2000)
LONG CHAIN DIOL (HIGH MOLECULAR WEIGHT)
(SOFT SEGMENT)
SHORT CHAIN (LOW MOLECULAR WEIGHT)
(CHAIN EXTENDER/CROSSLINKER)
REST OF THE DIISOCYANATE
URETHANE GROUP
HARD SEGMENT
Figure 2: Segmented Polyurethane
4
Excellent biocompatibility and biostability of TPU combined with their softness without
the use of potentially extractable plasticizers have made them an important part of the medical
device market. Beginning in the 1950’s they have been used in applications as diverse as medical
tubing, catheters, prosthetic valve leaflets, arteriovenous access grafts and electrical insulation on
pacemaker electrodes (Kull, et al. 2015) (Hsu and Lin 2004) (Ioan and Stanciu 2001) (Howard
2002) (Khan, et al. 2005) (Christenson, et al. 2004) (Wiggins, et al. 2003) (Tanzi, et al. 1996)
(Puskas and Chen 2004) (Hsu and Lin 2004). The first generation polyurethanes used in medical
industry consisted mostly of poly(ester urethanes) (Ioan and Stanciu 2001) (Howard 2002)
(Khan, et al. 2005). However, rapid hydrolysis of polyester soft segment made them useless for
long-term use. Second generation of biomedical polyurethanes is made of poly(ether urethanes)
and was extensively used in medical industry for the last 20 years (Kull, et al. 2015)
(Christenson, et al. 2004) (Wiggins, et al. 2003) (Tanzi, et al. 1996). TPU containing ether
linkage possess excellent hydrolytic stability but susceptible to oxidative degradation leading to
chain scission and crosslinking (Kull, et al. 2015) (Ioan and Stanciu 2001) (Christenson, et al.
2004) (Wiggins, et al. 2003) (Tanzi, et al. 1996). Poly(carbonate urethanes), a new class of
polyurethane elastomers that does not possess ether linkages have recently gained significant
interest as biomedical materials. Several studies have shown that poly(carbonate urethanes) are
more biostable than compatible poly(ether urethanes) while exhibiting good mechanical and
surface properties (Howard 2002) (Khan, et al. 2005) (Christenson, et al. 2004) (Wiggins, et al.
2003) (Tanzi, et al. 1996) (Puskas and Chen 2004) (Hsu and Lin 2004).
One of the barriers to wider use of poly(carbonate urethanes) has been the commercial
unavailability of soft grades (below 75 Shore A). This study focuses on the development of ultra
soft poly(carbonate urethane) using a novel soft segment (Moore, et al. 2003). A typical
5
polycarbonate polyol is a crystalline solid at room temperature. These types of polycarbonates
yield polyurethane elastomers that are tough, but also stiff; this is caused by the tendency of the
soft segment to crystallize. By the use of modified low crystallinity polycarbonate copolymer
diol depicted in Figure 1 we have been able to demonstrate the ability to maintain excellent
physical and mechanical properties in hardness ranges between 60 and 70 Shore A. The low
crystallinity of these novel polycarbonate copolymers allows for their use in systems that are
liquid at room temperature and prevents cold hardening of the resulting polyurethane. The
structure/property relationships of thermoplastic polyurethane elastomers based on polycarbonate
copolymer diols with 2,000 molecular weight were studied.
Polyimides
Polyimides are a class of high temperature resistant polymers that are most frequently used
for structural engineering purposes. The first description of araomatic polyimides was first
described by Endrey in 1962 and subsequently in several patents by Dupont (Endrey 1962) (A. L.
Endrey 1965). Indeed they are mechanically, chemically and also thermally resistant. Polyimides
are a class of thermally stable polymers that are often based on stiff aromatic backbones. They are
most frequently used because of their thermal stability and good mechanical properties. Polyimides
offer a mean to a higher dielectric constant material by the introduction of a polar group in the
polymer backbone and are thermally stable at temperatures exceeding °C. Their resistance is so
great that these materials often replace glass and metals like steel in highly demanding industrial
applications. Polyimides are also used in some everyday life applications. They are used for the
reinforcements and chassis in some cars, as well as for some parts located under the hood because
they support intense heat, corrosive lubricants, fuel, cooling liquid that requires a car. They are
also used in the construction of many appliances, as well as for some baking dishes for microwave
6
and for food packaging because of their thermal stability, resistance to oils, greases, fats and
transparent to microwave radiation. They can also be used for the plates of integrated circuits,
insulation, protective clothing fibers, composites and adhesives (Regnier and Guibe 1997) (Li, et
al. 1992) (Lua and Su 2006) (Yang, et al. 2012) (Ghosh 1996).
The chemistry of polyimides is in itself a vast area with a large variety of monomers
available and several methodologies available for synthesis. However, there has been considerable
debate on the various reaction mechanisms involved in different synthesis methods (Xia, et al.
2013) (Hsiao, Hsiao and Kung 2016) (Han, Fang and Zuo 2010). Although polymerization of a
dianhydride and a diamine to create the polyamic acid intermediate is generally simple, certain
monomer choices do not react well causing either a low molecular weight or the need for catalysts
and special reaction conditions to obtain product with measurable molecular weight (Han, Fang
and Zuo 2010) (Myung, Kim and Yoon 2002). They also have rather unique properties for small
ion or molecule diffusive transport. We have an interest in lithium ion transport in a conductive
separator matrix for batteries without short circuiting since these materials have low electrical
conductivities (Baldwin, et al. 2013) (Hsiao, Hsiao and Kung 2016). Also possible are materials
for selective gas transport and fuel cell membranes (Qi, et al. 2015) (Kiatkittikul, Nohira and
Hagiwara 2015). Although polyimides are relatively expensive compared to most polymer classes,
they can be tailored at the molecular level with a much broader combination of controllable
properties than any other class. This makes them very useful when a unique and specific target is
required. This review however, covers only the important fundamentals regarding the polyimide
synthesis. This review will discuss ‘aromatic’ polyimides as they constitute the major category of
such materials. The nature of these types of polyimides makes them very rigid with a very high
melting point which limits the processing options (Pei, et al. 2013) (Lua and Su 2006) (Li, et al.
7
2004) (Takassi, et al. 2015) (Regnier and Guibe 1997). We have designed polyimides that will
have a lower melting point using a range of molecular weight aliphatic diamines. A common
dianhydride, pyromellitic dianhydride (PMDA) is reacted with various aliphatic diamines to
produce lower melting, flexible polymers. Secondly, the properties of these polyimides can be
dramatically altered by minor variations in the structure. The subtle variations in the structures of
the dianhydride and diamine components have a tremendous effect on the properties of the final
polyimide. We have designed a series of polyimides that will have a lower melting point using a
range of molecular weight aliphatic diamines (Jeffamines D230, D400, D2000 and D4000). The
polyimide is composed of aromatic and aliphatic diamines to obtain the flexibility and rigidity
optimal for processing on conventional thermoplastic equipment such as injection molding or
extrusion. The stability seen in the conventional fully aromatic polyimides, however, comes at the
price of difficulty in processing for use in their myriad high-performance roles due to highly
elevated glass transitions or melt temperatures (Pei, et al. 2013) (Lua and Su 2006) (Li, et al. 2004)
(Takassi, et al. 2015). Typically, these conventional PIs are first synthesized as polyamic acids and
coated as thin films on a surface to be imidized ad hoc by heat treatment to form the finalized
polyimide (Noda, et al. 2014) (Takabayashi and Murakami 2014). To circumvent this shortcoming
we are reporting here the successful incorporation of polyetheramine backbone linkers which
provide flexibility and break up the otherwise rigid aromatic main chain of conventional
polyimides. The polyetheramine-polyimides synthesized in this work yield a functional
thermoplastic material which can be molded or extruded into shapes necessary for diverse uses,
thus negating the need for the highly limiting thin-film casting methodology of conventional PIs.
The glass transition temperatures can be controlled both with the stoichiometric ratio between
TMMDA and polyetheramine, along with the molecular weight of the polyetheramine itself.
8
Chapter 2
New Generation of Ultrasoft Non-Blocking Polyurethanes with High Mechanical
Properties for Biomedical Applications
Five thermoplastic polyurethane elastomers were synthesized and compared. The
isocyanate portion of the hard segment was methylene bis(4-cyclohexylisocyanate) (H12MDI or
Desmodur W) purchased from Bayer. Polyurethane elastomers based on H12MDI are known for
their excellent light stability and hydrolysis resistance (19). The chain extender was 1,4
butanediol purchased from Dupont.
Figure 3: Formation of Polycarbonate Copolymer. R is either x or y structure
9
The modified polycarbonate copolymer PES EX-619 (purchased from Hodogaya
Chemical Co., Ltd.) was used as soft segment. Reaction components were dried to less than
500ppm of water prior to mixing. No further purification techniques were used (Kull, et al.
2015).
Polyurethane Calculations
Polyurethane chemistry and the calculations used are not like other typical chemistry
calculations in that most chemical reactions are calculated using moles whereas urethane
chemical reactions use equivalence. When the molecular weight of a material is divided by the
number of places or functional groups on the molecule where reactions or bonding can take
place, this is known as the equivalent weight of the material. The equivalent weight tells you
how many grams of a material you need to have one equivalent of reactive groups. One
equivalent weight of isocyanate (-N=C=O) will always react with one equivalent weight of
hydroxyl (-OH). The functionality refers to the number of reactive sites per molecule. The
functionality is an average calculated using the molecular weight and the weight percent of each
material. The following formulas will demonstrate the process by which the required amounts of
diisocyanate and diol are determined. A typical urethane consists of a diisocyanate, one or more
long chain polyols and a short chain diol often referred to as the chain extender. Polyurethanes
can be prepared by two different paths, one called the one shot method and the other called the
two shot method.
In the one shot method, the isocyanate is used as received from the supplier and the
polyol parts by weight will include the chain extender. When the number of hydroxyl groups
equals the number of isocyanate groups you have a stoichiometric ratio of 1.0. It is typical to
10
over index the isocyanate to insure that all the hydroxyl groups get reacted. So in the formula,
there is a component to set the isocyanate at a ratio greater than one. It is typical to use an index
of 1.03
ONE SHOT FORMULA
Total Weight of Isocyanate required =
(index)(Isocyanate eq. wt.) [𝑝𝑏𝑤 𝑝𝑜𝑙𝑦𝑜𝑙 𝐴
𝐸𝑞.𝑤𝑡.𝑝𝑜𝑙𝑦𝑜𝑙 𝐴+
𝑝𝑏𝑤 𝑝𝑜𝑙𝑦𝑜𝑙 𝐵
𝐸𝑞.𝑤𝑡.𝑝𝑜𝑙𝑦𝑜𝑙 𝐵 + ⋯ +
𝑝𝑏𝑤 𝑝𝑜𝑙𝑦𝑜𝑙 𝑁
𝐸𝑞.𝑤𝑡.𝑝𝑜𝑙𝑦𝑜𝑙 𝑁+
𝑝𝑏𝑤 𝐻2𝑂
𝐸𝑞.𝑤𝑡.𝐻2𝑂 ]
Equation 1: Urethane Calculation
In the two shot method, the isocyanate percent is known and will be used to make a
prepolymer. If the isocyanate is 33% NCO and a 20% prepolymer is desired the calculation
below will yield the necessary amount of long chain diol needed to form the prepolymer.
Total Weight of H12MDI required to make a 20% prepolymer
H12MDI = X + 𝑁(𝑋+𝑌)
(42
𝑋)−𝑁
Equation 2: Prepolymer Calculation
Where:
N = desired NCO of the prepolymer (expressed as fraction)
X = equivalent weight of the isocyanate
Y = eq. wt. of the polyol (or average equivalent weight of the polyol blend)
Total H12MDI needed = 132 + 0.2(132+1000)
(42
132)−0.2
= 2050.6 pbw H12MDI
So, 1000
1000+2050.6 x 100 = 32.8% Carbonate diol
11
And 2050.6
1000+2050.6 x 100 =67.2% H12MDI
Once the prepolymer is made, formula 1 is used to calculate the remaining amounts of
diols necessary to make the urethane. The key to making a soft thermoplastic polyurethane is to
control the hardsegment. As mentioned earlier, urethanes are segmented polymers consisting of
the hardsegment and the softsegment. It is important to know the amount of hardsegment in
each polymer as it directly affects the overall hardness of the final polymer. Using the
calculation below we are able to determine the percent hardsegment knowing it is comprised of
the diisocyanate and the short chain diol.
Calculate % Hard Segment
Assume 1000g batch
297.3 g prepolymer of which 199.79 is H12MDI
671.1 g polyol
31.6 g BDO
199.79 + 31.6 =231.39
% Hardsegment = 231.39
1000 = .23139 x 100 = 23.14
Equation 3: Percent Hardsegment
The thermoplastic polyurethanes were prepared either via a one shot reaction or by
preparing an isocyanate terminated prepolymer (the two shot method). The one shot method
consists of reacting the –OH or hydroxyl groups of the polycarbonate copolymer and chain
extender with the –NCO groups of the diisocyanate in the appropriate equivalent weight ratio in
one step. The two shot method consists of first making a prepolymer by reacting some of the –
12
OH or hydroxyl groups of the polycarbonate copolymer with the –NCO or diisocyanate groups
of the isocyanate to generate an –NCO terminated prepolymer having a certain % NCO. Then,
the remaining –OH or hydroxyl groups of the polycarbonate copolymer and chain extender are
reacted with the –NCO terminated prepolymer at the appropriate equivalent weight ratio. The
reaction scheme is shown in Figure 4.
Figure 4: Urethane Polymerization Scheme
The hard segment to soft segment ratios were varied from 20.4 to 27.6 % by weight in the
one shot method and the results compared. We also compare the one shot method verse the two
shot method while holding the hard segment content constant.
13
One Shot Method
Into a 2L reactor equipped with constant nitrogen blanketing and a heating mantle with
controlled temperature and mixing, the polycarbonate copolymer is charged and the temperature
is maintained between 60 and 80°C. The low molecular weight chain extender is then added and
mixed. The processing aids and stabilizers are added and the mixture is mixed until
homogenous. A small amount of catalyst (typically stannous octoate) is added. Once the
mixture is homogeneous, a slight stoichiometric excess of isocyanate is added to the mixture
while mixing. The resulting thermoplastic urethane is then placed in an oven at 107°C for two
hours for curing and then the temperature is dropped to 93° C for several days while post curing.
The post curing is continued until the absence of isocyanate groups absorption at 2264 cm-1 was
confirmed by FTIR spectrometry. All samples were aged seven days before continuing (Kull, et
al. 2015).
Two Shot Method
Step 1 - The isocyanate is charged into a 2L reactor equipped with constant nitrogen
blanketing and a heating mantle with controlled temperature and mixing. The
polycarbonate copolymer is then added to the isocyanate targeting a specific % NCO. A
small amount of catalyst (typically stannous octoate) is added. The mixture is heated to
100° C and allowed to react for several hours. The result is an isocyanate terminated
prepolymer.
Step 2 - The polycarbonate copolymer is charged into a 2L reactor equipped with
constant nitrogen blanketing and a heating mantle with controlled temperature and
mixing, and the temperature is maintained between 60-80°C. The low molecular weight
chain extender is then added and mixed. The processing aids and stabilizers are added
14
and the mixture is stirred until homogenous. A small amount of catalyst (typically
stannous octoate) is added. The prepolymer is then added to this mixture in a slight
stoichiometric excess and mixed thoroughly. The resulting thermoplastic urethane is
them placed in an oven at 107°C for two hours for curing and then the temperature is
dropped to 93°C for several days while post curing. The post curing is continued until
the absence of isocyanate groups absorption at 2264 cm-1 was confirmed by FTIR
spectrometry. All samples were aged seven days before continuing (Kull, et al. 2015).
Particle Size Reduction
The TPU made by both processes was guillotined into small chunks and frozen at-18° C.
The frozen chunks were then ground and dried in a vacuum oven at 55°C for 12 hours. Tensile
sheets and compression buttons were produced by injection molding. The molded samples were
aged for seven days before testing.
Testing
Standard physical property tests were performed using the ASTM methods common in
the US:
- Hardness: ASTM D2240 Shore A hardness
- Tensile stress/strain properties at 23° C: ASTM D412C, tensile strength at break, tensile strength
at 100%, 200% and 300% elongation, elongation at break and tensile set at break.
- Tear Strength: ASTM 624 - 00
- Melt Flow ASTM D123 8
- Density ASTM 274
15
- Abrasion Resistance (Rotary Drum Abrader): ASTM D5 963-97a, volume loss in mm3
- GPC – Molecular Weight
- Small Angle Xray (SAX) Rigaku MicroMax-002+ generator and Cu anode tube.
- FTIR – Fourier Transform Infrared Spectroscopy
- Differential Scanning Calorimetry (DSC): ASTM D3418-03
- Modulated Differential Scanning Calorimetry MDSC Q200
- Thermogravimetric analyzer TGA Q500/50 –
- Dynamic Mechanical Analyzer (TA Instruments) -2980
- Hemolysis – Rabbit Blood: ISO 10993-4,2002
- MEM Elution Cyytotoxicity USP 27, NF 22, 2004, ISO 17025, 1999
- Class VI Plastics – USP 27, NF 22, 200
Instruments
Hardness measurements were done using Pacific Tranducer Corp. Durometer Model
470.
A Tensiometer measured tear strength, tensile, elongation and modulus and were all
done with Alpha technologies tensiometer 10K.
Melt Flow measurements were done with Tinus-Olsen Extrusion Plasto Meter Model UE-
4-78.
16
Abrasion resistance was measured with Hampden Din Abrator.
Gel Permeation Chromatagraphy (GPC) was determined using a PerkinElmer LC
200 with using THF as the Eluent and standard polystyrene as the reference
Infrared spectroscopy scans were collected with a PerkinElmer Spectrum 2000 using an
ATR cell to scan thin film samples from 4000 to 600 cm-1 at a resolution of 4 cm-1.
SAXS data was collected on a Rigaku with a MicroMax-002+ generator, a Cu anode
tube and a 120mmDET detector and a wavelength of 1.45Å. Two traces were recorded. One
trace was recorded 7 days after compression molding; a second trace was recorded 32 days after
after molding.
A 2980 Dynamic Mechanical Analyzer (TA Instruments) was used for the dynamic
mechanical analysis (DMA). The loss and storage moduli, E” and E' respectively were probed.
The sample was run in tension with 5mm displacement at frequencies between 1 and 100Hz at a
temperature range of -150 to 150°C. The frequency sweep was conducted at 5 degree increments.
The sample size was 12.9mm length, 5.3mm width, 1.2mm thick.
The Q500/50 TGA is a research grade thermogravimetric analyzer, whose leading
performance arises from a responsive low-mass furnace; sensitive thermobalance, and efficient
horizontal purge gas system (with mass flow control).
The Q2000 DSC is a research-grade with unmatched performance in baseline flatness,
precision, sensitivity, and resolution. Tzero™ and Modulated DSC® technologies, a reliable 50-
position autosampler, and multiple new hardware and software features
17
The DSC 2920 differential scanning calorimeter (TA Instruments) was used to
characterize the thermal behavior of the samples. Dry nitrogen gas with a flow rate of 75 ml/min
was purged through the sample cell. Cooling was accomplished with the liquid nitrogen cooling
accessory (LNCA). Indium was used for temperature calibration. For all DSC experiments a
temperature ramp of 5C/min was used. Experimental data was recorded from the second heat to
erase previous thermal history of the samples.
Atomic Force Microscopy Surface studies were performed with Digital Instruments
atomic force microscope using tapping mode and phase imaging. The images were acquired
under ambient conditions with standard silicon tapping tip on a beam cantilever. Thin films used
for AFM studies were prepared by casting from 1% bwt. THF solutions. Several drops of
polymer solution were placed on glass slides and dried in a vacuum oven at 60ºC for 24 hours.
Results and Discussion
Hardness
The Shore A hardness of the PCPU is 64. This is an unusually low value considering the
fact that the polymer did not exhibit blocking as described below. One of the barriers to wider
use of PCPUs has been the availability of soft grades (below 75 Shore A). Our research focuses
on bridging this gap by synthesizing a soft PCPU with a <70 Shore A value by utilizing the soft
segment derived from the modified poly(carbonate) polyol [17] combined with effects of
incorporating 4,40-diisocyanate dicyclohexylmethane into the hard segment. By using the
modified, low crystallinity polycarbonate copolymer diol we have been able to demonstrate the
ability to maintain excellent physical and mechanical properties in hardness ranges between 60
and 70 Shore A. The low crystallinity of these novel polycarbonate diols allows for their use in
18
systems that are liquid at room temperature and prevents cold hardening of the resulting
polyurethane. Kultys et al. [80] summarized hardness properties of PCPUs as they relate to
structure. Soft PCPUs with low moduli of elasticity are obtained in commercially aliphatic
H12MDI/butane diol hard segment polymers. The ChronoFlex_ polymers referenced however
still have Shore A hardness values that range from 75 to 80. Despite the relative softness our
sample did not show the typical tendency to fuse together usually referred to as blocking when
virgin surfaces were merged. TPU’s which are made in soft grades (75 Shore A or less) have a
tendency to permanently fuse or block to themselves. Our results for this test determined that the
surface force for the TPU is <0.44 N, the minimum force resolution of the instrument, showing
that there is no tack between the surfaces. This is due to the fact that high surface free energy
hydrogen bonding sites move into the matrix after sample preparation as described above.
Tensile/Elongation
Thermoplastic polyurethanes studied in this paper demonstrate softness with Shore A
values of 70 or lower. These materials are the first commercially available TPU’s that have
shown no tendency to fuse together, usually referred to as blocking. The grades discussed in this
paper do not possess the very high degree of surface tackiness observed in previous soft
polyurethanes. The standard test procedure for testing surface tackiness is the BFGoodrich tack
test. This procedure requires the surfaces of the sample be forced together with the contact area
controlled. The applied force is held constant for a given dwell period. After the dwell period
the surfaces are separated at a controlled rate and this separation force is recorded. The
minimum force resolution is 0.1 lbf. An independent testing lab has determined that the TPU is
<0.1 lbf and concluded that there is no tack between the surfaces. Despite their softness,
however, the thermoplastic polyurethanes described in this paper retained excellent thermal and
19
mechanical properties (Abraham, Frontini and Cuadrado 1997) (Gorman, et al. 1997) which are
summarized in Table 3.
Table 1: Thermoplastic Polyurethane Physical Properties
Experiment number Units
28062 28162 28172 28203 28221
Composition: polyol
PES EX619 PES EX619
PES
EX2000 PES EX619 PES EX619
isocyanate
DES W DES W DES W DES W DES W
% hard segment
25.7 20.4 23 23 23
Process type
One shot One shot One shot Two shot One shot
Durometer Shore A
70 60 65 64 66
Tensile Strength Psi
1792 1497 1866 3067 1574
100% Modulus Psi
380 283 330 357 328
200% Modulus Psi
579 349 468 534 475
300% Modulus psi
862 443 653 813 680
20
Table 2: Thermoplastic Polyurethane Physical Properties
Experiment number Units 28062 28162 28172 28203 28221
Elongation at break % 452 549 576 492 506
Glass Transition (Tg), °C -29.2 -24.1 -29.9 -23.2 -24.6
Tensile Set, % 97 96 98 97 97
Tear Strength, Die C, pli 155 176 218 208 214
Specific Gravity Ratio 1.12 1.12 1.15 1.13 1.14
Abrasion Resistance, mm3 loss 38.0 32.4 32.5 36.0 32.8
Melt Flow Rate, Condition 228/2.16 g/10min 10.8 9.98 9.10 10.9 10.6
Despite their softness, however, the urethanes described in this paper retained excellent
thermal and mechanical properties which can be varied by adjusting the concentration of hard
segment, soft block composition, and processing techniques to finely tune to the desired
properties of the end product. As was expected, an increase in hard segment concentration
results in an increase in tensile strength of corresponding thermoplastic polyurethanes. In
addition, polyurethane produced by a two-shot method yields higher tensile strength value due to
the more even distribution of hard segment within the polymer matrix. When comparing the two
shot method verse the one shot method while holding the percent hard segment constant we see a
two-fold increase in tensile strength while maintaining nearly the same hardness and elongation.
21
The tensile strength at intermediate elongation values such as 100 or 300% (often
referred to as modulus) was measured for all samples. For polymers with the same composition
of soft block the modulus depended directly on the concentration of hard segment. The two-shot
sample exhibited higher modulus, but this is a consequence of the sample’s high tensile strength.
The EX2000 sample showed slightly lower modulus than that of EX619 sample with the same
hard segment concentration, even though the ultimate tensile strength for EX2000 sample is
significantly higher.
Tensile set is the primary tool used to determine a polymer’s elastic properties. All
samples showed excellent recovery to their original dimensions after break with tensile set
values ranging from 96 to 98%. The most important mechanical property is the abrasion
resistance, which measures the ability of polymer to work under friction for prolonged time
periods and becomes especially vital for soft polyurethanes used in medical tubing. The abrasion
resistance numbers (in mm3) range from 32 to 38. These abrasion resistance values approach
values that are equal to or better than other urethanes that are much harder.
It can be seen that in all examples, the 300% modulus is less than 50% of the ultimate
tensile strength and some samples approach 25%. Due to the high resistance to abrasion and
other superior properties, such as high burst strength, it may be possible to make tubes with
much thinner walls without sacrificing performance.
Molecular Weight Determination (GPC)
A series of thermoplastic polyurethanes having a weight percent hardsegment ranging
between 20 and 25% were synthesized using hydrogenated MDI and a 2000 molecular weight
polycarbonatediol. The molecular weights were determined and are listed in the following table.
22
Table 3: Molecular Weight of TPU's
Figure 5: Molecular Weight Graph
Sample ID Mw Polydispersity Mw/Mn
28162 256507 1.86
28172 203239 1.94
28221 172801 1.78
28203 268264 2.16
28062 180223 1.66
23
All polymers were cured in an oven at 190°C until no additional molecular weight growth was
seen via gel permeation chromatography technique described.
FTIR
Excellent mechanical properties may partially result from the strong hydrogen bonding in
polyurethane molecules. In polycarbonate-polyurethane segmented copolymers, the urethane N-
H can bond to urethane C=O groups or to –C=O and –O- groups of polycarbonate as depicted in
the following illustration (Yen and Hong 1997) (Furukawa, Shiiba and Murata 1999) (Wilhelm
and Gardette 1998) (Furukawa and Wakiyama 1999).
Figure 6: FTIR Hydrogen Bonding Depiction
24
This creates physical cross-links between both hard segment molecules and hard
segment-soft segment molecules increasing the overall performance of polymer. Hydrogen
bonding in polyurethanes is observed by means of IR spectroscopy which exhibits separation of
free and bonded –N-H and –C=O groups (Yen and Hong 1997) (Furukawa, Shiiba and Murata
1999) (Wilhelm and Gardette 1998) (Furukawa and Wakiyama 1999). An IR study of five
polyurethane samples presented in this paper revealed free and bonded –N-H stretch absorptions
at 3379 cm-1 and 3305 cm-1, respectively. Carbonyl absorptions also showed a separation into
free and bonded state at 1739 cm-1 and 1710 cm-1, respectively. Unfortunately, it is not possible
to separate urethane and carbonate –C=O absorptions. However, DSC data suggests partial
mixing of hard and soft segments which in turn will open possibility for hydrogen bonding
between molecules of different segments.
Hydrogen bonding in polyurethanes has been thoroughly studied via FTIR in the C=O
and N-H stretching regions (Hwang, et al. 1984) (Tanaka, Yokoyama and Yamaguchi 1968)
(Seymour, Estes and Cooper 1970) (Martin, et al. 1996) (Tsai, Yu and Teng 1998) (Kim, et al.
1999). IR absorption of hydrogen bonded carbonyl groups occurs at lower frequencies than that
of free urethane carbonyl groups. Hydrogen bonded carbonyl groups in PUs absorb from 1695 to
1719 cm_1, whereas free carbonyl groups absorb from 1731 to 1733 cm_1 (Tsai, Yu and Teng
1998). N-H hydrogen-bonded-stretching occurs at 3329–3324 cm_1, while stretching in free N-H
occurs at 3446–3441 cm_1 (Tsai, Yu and Teng 1998). In PCPUs the carbonate C=O vibrations
occur at 1737–40 cm_1; this masks free carbonyl group stretching in the urethane groups (Fare, et
al. 1999) (Eceiza, et al. 2008) (Ma, et al. 2011) (Kultys, Rogulska and Pikus 2012). Kultys et al.
formulated PCPUs containing poly(hexane-1,6-diyl carbonate) diol (PHCD), 4,40
diphenylmethane diisocyanate and novel methylenebis(1,4-phenylenemethylenethio)dialcanol
25
chain extenders (Kultys, Rogulska and Pikus 2012). At 20% PHCD, they observed non-
hydrogen-bonded urethane carbonyl stretching at 1734–1731 cm_1 and hydrogen bonded
urethane carbonyl stretching at 1706 cm_1. Carbonate carbonyl stretching was negligible. At
higher carbonate concentrations the absorption of carbonate carbonyl at 1743–39 cm_1 masked
the non-hydrogen-bonded carbonyl stretching.
Hydrogen-bonded urethane carbonyl stretching diminished as the polycarbonate diol
increased. The diminishing hydrogen bonding was attributed to the fact that the polycarbonate
diol exhibits a low degree of phase separation in the urethane as compared to similar
formulations made with poly(oxytetramethylene) diol (Eceiza, et al. 2008). A synthesized
PCPUs containing 4,4-diphenylmethane diisocyanate, 1,4-butanediol chain extender with
polyhexamethylene carbonate diols and polyhexamethylene–pentamethylene carbonate diols
(Eceiza, et al. 2008). Here, again, the free carbonyl stretching is masked by the polycarbonate
stretching at 1737 cm_1. Disordered hard segment domains are accompanied by carbonyl
stretching vibrations observed at 1718 cm_1 in polymers containing polyhexamethylene
carbonate soft segments. These are thought to be due to hydrogen bonds between carbonate
carbonyl groups near the hard segments and -NH groups in the hard segments. The number of
these hydrogen bonded group’s increases as the molar mass of the soft segment decreases. The
ability of the carbonate carbonyl groups to hydrogen bond with the -NH groups is much higher in
formulations containing polyhexamethylene carbonate soft segments than in those containing
poly hexamethylene–pentamethylene carbonate soft segments. This is attributed to the fact that
there is a better fit between carbonate carbonyl groups and –NH groups in polymers with even
numbers of carbon atoms in both the soft and hard segments. Indeed, Pongkitwitoon et al., report
larger interdomain spacings in PCPUs containing even numbers of carbon atoms (140 Å) that we
26
report for our PCPU containing odd–even numbers of carbon atoms (45 Å) (Pongkitwitoon, et al.
2009). Fig. 7 show FTIR data for the -NH and AC=O absorptions. As observed in the research
described above, carbonate carbonyl absorption is noted at 1740 cm_1 while the absorption peak
at 1718 cm_1, due to associated groups in somewhat disordered regions can be interpreted, in
light of Ref. (Eceiza, et al. 2008)to be due to hydrogen bonding between -NH groups in the hard
segments and nearby carbonate carbonyl groups. The polyol used in this research contains an
odd number of methylene groups; however, there is still evidence of hydrogen bonding with the
hard segment -NH. N-H hydrogen-bonded-stretching occurs at 3340 cm_1, while stretching in
free N-H occurs at 3380 cm_1. A shifting of N-H bonded stretching to higher wavenumbers
indicates a disruption in H-bonding in polycarbonate containing urethanes as compared to
nonpolycarbonate systems (Tsai, Yu and Teng 1998). All of this reflects the fact that hydrogen
bonding occurs between the soft and hard segments and that phase separation is diminished in
PCPU structures at low hard segment contents. The domain structure of 45 Å observed in SAXS
is likely a hybrid due to partial hard and soft segment mixing. This ultrasoft PCPU may undergo
segmental diffusion and hydrogen bond formation during the self-healing process. The lack of
well-defined crystalline domains and ample mobility may be responsible for the partial self-
healing.
29
Small Angle Xray (SAXS)
Figure 9: SAXS of PCPU 7 Days after Molding
The SAXS data (Figure 9) revealed a peak at 0.14 Å-1. According to the Bragg’s Law,
2dsinθ = nλ
Equation 4: Bragg's Law
and then d = 2π/q where d is the estimated interdomain spacing and q is the scattering vector.
When q=0.14 Å-1, d=44.88 Å. The data for the sample aged 32 days exhibited at peak at 0.14 Å-1
as well. However the intensity increased slightly from 0.06476 intensity units to 0.06832 upon
aging for 32 days. The SAXS data evidences an interdomain "center-to-center" distance of 45Å.
Interdomain spacings in polyurethanes are usually of the order of 100Å. For example,
Pongkitwitoon et al, studied polymers made from 4,4-methylenediphenyl diisocyanate and 1,4-
butanediol, and soft segments from an aliphatic polycarbonate [poly(1,6-hexyl 1,2-ethyl
carbonate)] (Pongkitwitoon, et al. 2009). They reported interdomain spacings of about 140 Å
near room temperature. It is known that polyurethanes, in general, have microphases containing
0.01
0.1
1
0 0.05 0.1 0.15 0.2 0.25 0.3
I co
un
ts/m
2-s
ec
q (A-1)
30
mixed hard and soft segments (Eceiza, et al. 2008). This is especially true of PCPUs which often
exhibit a high degree of mixing in the phases due to hydrogen bonding between urethane groups
and carbonate groups in the soft segments (Gunatillake, et al. 1998) (Trovati, et al. 2010)
Dynamic Mechanical Analysis, DMA
DMA was used to characterize the viscoelastic properties of the polymer. Figure 7
depicts traces of tan δ, E’ and E” versus temperature. Two transitions which are identified by
peaks in the tan δ and E” traces. Note that the low temperature moduli exceed 1010 Pascals.
This is uncommon in organic polymers and is likely due to machine compliance
problems encountered at low temperatures. The data does depict reasonable transition data and is
not intended for an accurate determination of moduli in this low temperature region. Fig. 7. E',
E” and tan delta vs. temperature. The higher temperature relaxation due to large scale chain
slippage occurs at the glass transition region [61]. At lower temperatures a secondary relaxation
is noted as well. McCrum discusses relaxations noted in polyurethanes (McCrum, Read and
Willeams 1967). Three relaxations are noted, a relaxation and two secondary relaxations, b and
g. The higher temperature b relaxation at -100 to -50 °C is attributed to absorbed water
molecules and was not observed in our studies. A secondary relaxation is noted in figure 7 near -
120 °C in the E” and tan(delta) traces. Time-temperature superposition software was used to plot
shift factor versus temperature and the resulting linear graph in figure 8 is evidence of Arrhenius
behavior. Equation 3 was used by the software to calculate activation energy where log(aT) is
the shift factor, Ea is the activation energy, R is the universal gas constant, To is initial
temperature in Kelvin and T is temperature in Kelvin.
31
2.303 log (aT) = -Ea/R [1/T0 – 1/T]
Equation 5: Activation Energy
The activation energy is 51.5 kJ/mol (12.4 kcal/mol). The g relaxations in polyurethanes
described by McCrum occur near -120°C and are thought to arise from local motion in the
carbon chains of the soft segments (McCrum, Read and Willeams 1967). The reported observed
activation energies for this local motion are from 50-63 kJ/mol (12-15 kcal/mol) and in the
range our value, 51.5 kJ/mol (12.3 kcal/mol), figure 11.
Figure 10: Dynamic Mechancal Analysis of PCPU
34
Alpha transitions that follow WLF behavior are traditionally analyzed via equation 4 (Wilkes
1975).
log (aT)=− C
1(T − T
g)
C2+ (T− T
g)
Equation 5: WLF of Alpha Tranisitions
Where C1 and C2 are material constants, aT is the shift factor, R is the universal gas
constant, T is temperature and Tg is the glass transition temperature, both in Kelvin. Here, the
reference peak is Tg, and experimental values for C1 and C2 (18.6 and 81.4 respectively) were
found by plotting the log(aT) vs. temperature (figure 12) using a time-temperature superposition
program. The apparent activation energy for the glass transition, ΔEa, is calculated from Eq 6:
Δ Ea= (− 2.303)(
C1
C2
)RT 2
Equation 6: Activation Energy for the Glass Transition
The Tg showed WLF behavior and from this the apparent activation energy of the alpha
transition was calculated using equation 4 is 255 kJ/mol (61 kcal/mol) and is indicative of the
energy required to induce large segmental slippage associated with the glass transition and
similar to that reported for a series of polyurethanes made from vegetable oil polyols, where the
apparent activation energies varied from 179-209kJ/mol (Ma, et al. 2011). It is significant to note
that the storage modulus ranged from 1.5 X106 – 5.6 106 Pa at temperatures up to 423K (150°C)
depending on the frequency. The tan delta remained relatively constant in this region and this
indicates that the material was still a solid network physically cross-linked by hydrogen bonding
35
within and possibly reinforced by the weakly ordered moieties. Additionally, DMA data
indicates that rehealing studies presented below take place in a matrix with minimal phase
separation and that it is possible that physical crosslinks can break with stress and reform.
(Hwang, et al. 1984) (Martin, et al. 1996) (Tsai, Yu and Teng 1998) (Kim, et al. 1999)
Thermongravimetric Analysis (TGA)
TGA is an analytical method where the mass of a substance is observed and data
recorded as a function of temperature or time as the sample is subjected to a programmed
temperature profile while in a controlled environment. TGA simply records a samples weight as
it is subjected to temperature variations. This allows for the quantification of such properties as
water loss, pyrolysis, oxidation and decomposition.
Thermogravimetric Analysis of the decomposition temperature will aid in determining
the test temperature’s in other thermal techniques such as DSC and Rheometry. The following
graphs shows the results from TGA is a thermal analysis technique used to determine chemical
and physical changes in a materials property. All samples were tested by increasing the
temperature at 10°C/Min from ambient to 650°C which helps determine the decomposition
temperature. The determination of the decomposition temperature aids in the testing conditions
of other techniques such DSC and Rheology.
36
Figure 13: TGA XP-2816
102.2%(8.948mg)
314.48°C
192.26°C
466.34°C
346.55°C
-0.5
0.0
0.5
1.0
1.5
2.0
De
riv.
We
ight
(%/°
C)
-20
0
20
40
60
80
100
120
We
igh
t (%
)
0 100 200 300 400 500 600
Temperature (°C)
Sample: XP-28162Size: 8.7520 mg
Universal V4.3A TA Instruments
37
Figure 14: TGA XP-28203
97.39%(8.600mg)
317.38°C
196.19°C
435.29°C
345.92°C
-0.5
0.0
0.5
1.0
1.5
2.0
De
riv.
We
ight
(%/°
C)
0
20
40
60
80
100
120
We
igh
t (%
)
0 100 200 300 400 500 600
Temperature (°C)
Sample: XP-28203Size: 8.8310 mg
Universal V4.3A TA Instruments
38
Figure 15: TGA XP-28062
103.2%(8.571mg)
306.52°C
204.17°C
500.07°C
340.72°C
-0.5
0.0
0.5
1.0
1.5
2.0
Deriv. W
eig
ht (%
/°C
)
-20
0
20
40
60
80
100
120
Weig
ht (%
)
0 100 200 300 400 500 600 700
Temperature (°C)
Sample: XP-28062Size: 8.3070 mg
Universal V4.3A TA Instruments
39
Figure 16: TGA XP-28221
93.81%(8.873mg)
312.79°C
200.22°C
449.85°C
342.94°C
-0.5
0.0
0.5
1.0
1.5
2.0
Deriv. W
eig
ht (%
/°C
)0
20
40
60
80
100
120
Weig
ht (%
)
0 100 200 300 400 500 600
Temperature (°C)
Sample: XP-28221Size: 9.4590 mg
Universal V4.3A TA Instruments
40
Differential Scanning Calorimetry, DSC
Four poly(carbonate)urethanes were synthesized by traditional one- and two-shot
techniques. The composition and nomenclature of these samples is summarized in Table 1. The
differential scanning calorimetry has been carried out. DSC thermograms are shown on Figure 3.
The glass transition temperatures of the soft segments as well as the melting temperatures of the
hard segments observed on these thermograms are tabulated in Table 2. The soft segments
exhibit well defined glass transition temperatures around -25C. The variations in soft segment
Tg due to the change in hard segment content are minimal indicating good phase separation in the
samples (Frick and Rochman 2004) (Ioan and Stanciu 2001) (Gunatillake, et al. 1998) (Fujiwara
and Wynne 2004). However, the glass transition temperatures of polyurethane samples are about
25C higher than that of pure carbonate polyol (-50C) recorded at the same experimental
conditions. This indicates that there is some mixing of hard segment in soft segment microphase
(Gunatillake, et al. 1998) (Fujiwara and Wynne 2004). The temperatures of well pronounced
endothermic peaks at about 65-80C are assigned to the melting point of the hard segment
domain and serves as an indicator of a high crystalline order material. The position change for
hard segment melting peak does not correlate directly to the hard segment content and can be
attributed to differences in hard segment sequence length (Li, et al. 1992). Upon heating above
the Tm hard segment dissolves completely in the soft segment matrix resulting in an amorphous
melt (Li, et al. 1992) (Ryan, Macasko and Bras 1992) (Brunette, et al. 1981). Fast cooling of the
amorphous melt with liquid nitrogen freezes the structure in its state resulting in the
disappearance of hard segment melting peaks from the second heating curves of DSC (Li, et al.
1992) (Ryan, Macasko and Bras 1992) (Brunette, et al. 1981). Upon careful examination, a
weak endotherm at about 20 °C between the Tg of the soft segment and the Tm of the hard
41
segment can be noticed. It is usually attributed to the partial mixing of the short-range ordered
hard segment (Ryan, Macasko and Bras 1992) (Chen, Shieh and Chui 1998) (Brunette, et al.
1981) (Yoon and Han 2000).
Table 4: Nomenclature, Composition and Process Type
Table 5: Glass Transition and Melting Temperatures Observed from DSC Thermograms
Units 28162 28221 28203 28062
Polyol PES EX619 PES EX619 PES EX619 PES EX619
Diisocyanate Desmodur W Desmodur W Desmodur W Desmodur W
% Hard segment 20.4 23.0 23.0 25.7
Process type One shot One shot Two shot One shot
Sample 28162 28221 28203 28062
Tg soft segment (C) -26.2 -26.0 -26.3 -27.2
Tm hard segment (C) 74.8 73.9 75.6 67.0
42
Figure 17: DSC XP-162 1st Heat Cycle
Figure 18: DSC XP-28162 2nd Heat Cycle
-2 6 .1 8 °C ( I)
-3 0 .8 8 °C
-2 0 .5 0 °C
7 4 .8 0 °C
6 0 .1 5 °C
3 .9 7 9 J /g
F irs t H e a t
-0 .6
-0 .4
-0 .2
0 .0
He
at
Flo
w (
W/g
)
-9 0 -4 0 1 0 6 0 1 1 0 1 6 0 2 1 0
T e m p e ra tu re (°C )
S a m p le : X P -2 8 1 6 2
S iz e : 9 .0 4 0 0 m g
E xo U p U n iv e rs a l V 4 .3 A T A In s t ru m e n ts
-25.82°C(I)
-30.22°C
-18.43°C
81.00°C
56.67°C0.9809J/g
Second Heat
-0.6
-0.4
-0.2
0.0
He
at
Flo
w (
W/g
)
-90 -40 10 60 110 160 210
Temperature (°C)
Sample: XP-28162Size: 9.0400 mg
Exo Up Universal V4.3A TA Instruments
DSC Analysis of XP 28162: 1st Heat Cycle
DSC Analysis of XP 28162: 2nd Heat Cycle
43
Figure 19: DSC XP-28203 1st Heat Cycle
Figure 20: DSC XP-28203 2nd Heat Cycle
First Heat
-26.32°C(I)
-31.61°C
-20.71°C
75.56°C
61.32°C4.606J/g
-0.5
-0.3
-0.1
He
at
Flo
w (
W/g
)
-90 -40 10 60 110 160
Temperature (°C)
Sample: XP-28203Size: 8.9300 mg
Exo Up Universal V4.3A TA Instruments
DSC Analysis of XP 28203: 1st Heat Cycle
DSC Analysis of XP 28203: 2nd Heat Cycle
44
Figure 21: DSC XP-28062 1st Heat Cycle
Figure 22: DSC XP-28062 2nd Heat Cycle
First Heat
Crystalline melt
Glass transition
-27.15°C(I)
66.61°C
52.96°C4.404J/g
-25.84°C(I)
67.00°C
51.13°C5.592J/g
Enthalpic relaxation
-0.10
-0.05
0.00
No
nre
v H
ea
t F
low
(W
/g)
-0.15
-0.10
-0.05
0.00
0.05
Re
v H
eat
Flo
w (
W/g
)
-0.15
-0.10
-0.05
0.00
0.05
He
at
Flo
w (
W/g
)
-90 -40 10 60 110
Temperature (°C)
Sample: XP 28062Size: 5.5800 mg
Exo Up Universal V4.3A TA Instruments
Second Heat
-24.90°C(I)
-31.02°C
-16.12°C
78.24°C
58.95°C0.8507J/g
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
He
at
Flo
w (
W/g
)
-90 -40 10 60 110 160 210
Temperature (°C)
Sample: XP-28062Size: 8.7800 mg
Exo Up Universal V4.3A TA Instruments
DSC Analysis of XP 28062: 1st Heat Cycle
DSC Analysis of XP 28062: 2nd Heat Cycle
45
Figure 23: DSC XP-28221 1st Heat Cycle
Figure 24: DSC XP-28221 2nd Heat Cycle
-26.02°C(I)
-32.19°C
-21.18°C
73.90°C
59.58°C4.805J/g
Anomaly not related to sample.Possibly a vibration from the bench top
First Heat
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
He
at
Flo
w (
W/g
)
-100 -50 0 50 100 150 200 250
Temperature (°C)
Sample: XP-28221Size: 9.1400 mg
Exo Up Universal V4.3A TA Instruments
-25.84°C(I)
-31.47°C
-16.78°C
79.46°C
61.27°C0.6021J/g
Second Heat
-0.5
-0.4
-0.3
-0.2
-0.1
Heat F
low
(W
/g)
-90 -40 10 60 110 160 210
Temperature (°C)
Sample: XP-28221Size: 9.1400 mg
Exo Up Universal V4.3A TA Instruments
DSC Analysis of XP 28221: 1st Heat Cycle
DSC Analysis of XP 28221: 2nd Heat Cycle
46
The PCPU with 23.0% hard segment was produced by the described two-shot method
and it is thought that this method produces material with more random structure leading to less
microheterogeneity (Peebles 1974). DSC results are shown. We did not observe two glass
transition temperatures when the sample was scanned to 165°C. An additional run was taken to
200 °C and this verified that there was not a second glass transition temperature above 165 °C.
The glass transition temperature of the PCPU decreased slightly from -26.3°C to – 25.6°C from
the first to second heating cycle. The presence of one glass transition temperature indicates that
there is some mixing of hard segments within the soft segment microphase (Gunatillake, et al.
1998) (Li, et al. 1992) (Liu, et al. 2003) (Chen, Shieh and Chui 1998) (Wilkes 1975) (Aklonis,
MacKnight and Shen 1972) (McCrum, Read and Willeams 1967) (Ma, et al. 2011) (Xu and
Zhang 2007) (Wu, Meure and Dolomon 2008) (Jud and Kausch 1979) (Boiko, Guerin and
Marikhin 2001). The high degree of mixing in some PCPUs has been attributed to the hydrogen
bonding between urethane groups in the hard segment and carbonate groups in the polyol
(Gunatillake, et al. 1998). Further, Baer reported that when phase separations are of the order of
a few tens of Angstroms, separate glass transition temperatures are not evident (Liu, et al. 2003).
The Tg of the PCPU sample is higher than that of pure carbonate polyol (-50°C) recorded under
the same ramp rate. This is thought to be due to both the presence of hard segments in the soft
phase and to inhibited movement caused by hard segments where the ends of the soft segments
are pinned (Pongkitwitoon, et al. 2009). Additionally, one diffuse melt region was noted around
80 °C. Fast cooling of the sample with liquid nitrogen resulted in a significant peak area decrease
in the melt in the second heating curve. The endotherm is barely visible and occurs in a lower
temperature range in the second run. This has been observed in polyurethane studies in the past
and is attributed to the partial mixing of the short-range ordered hard segment (Li, et al. 1992)
47
(Chen, Shieh and Chui 1998). This indicates that aging and processing conditions influence the
microstructure of the polymer. This is well known and documented in the literature (Wilkes
1975). Additionally, we did not observe endotherm increases in DSC traces after samples were
deformed. The fact that ordered structure was observed in the deformed structure in XRD, figure
4, but not easily detected by DSC indicates that our polymer does not contain well ordered,
distinct hard segment regions. SAXS data did clearly depict an interdomain structure (45Å) that
is attributed to hard segment-soft segment association.
Modulated Differential Scanning Calorimetry (MDSC)
Is a technique similar to DSC but has the advantages of allowing for the optimization of
both sensitivity and resolution in a single test by allowing for a slow average heating rate
(optimizing resolution) and a fast changing heating rate (optimizing sensitivity). A sinusoidal
modulation is overlaid on the conventional linear temperature ramp. This yields a heating profile
which is continuously increasing with time, but in an alternating heating/cooling program. This
allows for the Separation of complex transitions into individual components. It increases the
sensitivity for weak transitions. It increases the resolution without loss of sensitivity and gives a
direct measurement of heat capacity. In addition, Modulated DSC shows Enthalpy Relaxation
Endotherm or the physical ageing of a material. Amorphous materials can age or relax over
time. The physical properties of amorphous materials can change with time as the sample
relaxes. Aged materials show decreased physical and chemical reactivity compared to unaged
materials. As a material ages, its density increases while the free volume decreases. Blue is
reversible and Red in non-reversible. Green is Heat capacity (Cp). Heat capacity is the amount of joules
energy needed to increase the temperature of 1 gram of material by 1°C. These materials have two
phases: amorphous and crystalline. The two phases are clearly seen in the first heat, no
48
recrystallization is observed in the cool cycle. A glass transition and very little crystallinity is
observed in the second heat. It can be seen that the enthalpic relaxation (physical ageing) is
removed after the first heat cycle.
Figure 25: MDSC XP-28062 1st Heat Cycle
Figure 26: MDSC XP-28062 2nd Heat Cycle
First Heat
Crystalline melt
Glass transition
-27.15°C(I)
66.61°C
52.96°C4.404J/g
-25.84°C(I)
67.00°C
51.13°C5.592J/g
Enthalpic relaxation
-0.10
-0.05
0.00
Nonre
v H
eat F
low
(W
/g)
-0.15
-0.10
-0.05
0.00
0.05
Rev H
eat F
low
(W
/g)
-0.15
-0.10
-0.05
0.00
0.05
Heat F
low
(W
/g)
-90 -40 10 60 110
Temperature (°C)
Sample: XP 28062Size: 5.5800 mg
Exo Up Universal V4.3A TA Instruments
MDSC Analysis of XP 28062: 2nd
Heat Cycle
MDSC Analysis of XP 28062: 1st
Heat Cycle
Second Heat
-21.88°C(I)
-33.81°C
-13.26°C
-23.74°C(I)
-30.68°C
-14.63°C
Very little crystalline melt is observed in the second heat
Enthalpic recovery
75.11°C
57.32°C0.7089J/g
75.11°C
59.74°C0.2074J/g
0.000
0.002
0.004
0.006
Nonre
v H
eat F
low
(W
/g)
-0.12
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
Rev H
eat F
low
(W
/g)
-0.12
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
Heat F
low
(W
/g)
-80 -30 20 70 120
Temperature (°C)
Sample: XP 28062Size: 5.5800 mg
Exo Up Universal V4.3A TA Instruments
49
Figure 27: MDSC XP-28203 2nd Heat Cycle
Figure 28: MDSC XP-28203 2nd Heat Cycle
First Heat
-28.48°C(I)
-25.66°C(I)
67.61°C
53.15°C4.576J/g
67.86°C
51.81°C6.312J/g
-0.006
-0.004
-0.002
0.000
0.002
Nonre
v H
eat F
low
(W
/g)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
Rev H
eat F
low
(W
/g)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
Heat F
low
(W
/g)
-90 -40 10 60 110
Temperature (°C)
Sample: XP 28221Size: 6.0500 mg
Exo Up Universal V4.3A TA Instruments
Second Heat
-23.79°C(I)
-25.97°C(I)
-25.97°C(I)
74.15°C
56.42°C0.6180J/g
0.5
1.0
1.5
He
at
Cap
acity (
J/(
g·°
C))
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
Re
v H
eat
Flo
w (
W/g
)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
He
at
Flo
w (
W/g
)
-80 -30 20 70 120
Temperature (°C)
Sample: XP 28203Size: 5.9200 mg
Exo Up Universal V4.3A TA Instruments
MDSC Analysis of XP 28203: 1st
Heat Cycle
MDSC Analysis of XP 28203: 2nd
Heat Cycle
XP28203
50
Figure 29: MDSC XP-28162 1st Heat Cycle
Figure 30: MDSC XP-28162 2nd Heat Cycle
68.19°C
54.61°C2.912J/g
-28.34°C(I)
68.96°C
54.11°C3.804J/g
First Heat
-0.005
0.000
0.005
Nonre
v H
eat F
low
(W
/g)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
Rev H
eat F
low
(W
/g)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
Heat F
low
(W
/g)
-80 -30 20 70 120
Temperature (°C)
Sample: XP 28162Size: 6.2500 mg
Exo Up Universal V4.3A TA Instruments
-24.91°C(I)
-23.54°C(I)
74.10°C
51.63°C0.8162J/g
0.5
1.0
1.5
He
at
Cap
acity (
J/(
g·°
C))
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
Re
v H
eat
Flo
w (
W/g
)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
He
at
Flo
w (
W/g
)
-80 -30 20 70 120
Temperature (°C)
Sample: XP 28162Size: 6.2500 mg
Exo Up Universal V4.3A TA Instruments
MDSC Analysis of XP 28162: 1st
Heat Cycle
MDSC Analysis of XP 28162: 2nd
Heat Cycle
51
Figure 31: MDSC XP-28221 1st Heat Cycle
Figure 32: MDSC XP-28221 2nd Heat Cycle
-25.72°C(I)
-28.58°C(I)
67.84°C
52.81°C4.216J/g
67.61°C
53.15°C4.551J/g
-0.006
-0.004
-0.002
0.000
0.002
Nonre
v H
eat F
low
(W
/g)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
Rev H
eat F
low
(W
/g)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
Heat F
low
(W
/g)
-80 -30 20 70 120
Temperature (°C)
Sample: XP 28221Size: 6.0500 mg
Exo Up Universal V4.3A TA Instruments
Second Heat
-23.44°C(I)
-25.27°C(I)
-25.27°C(I)
74.14°C
59.19°C0.5001J/g
0.5
1.0
1.5
Heat C
apacity (
J/(
g·°
C))
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
Rev H
eat F
low
(W
/g)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
Heat F
low
(W
/g)
-80 -30 20 70 120
Temperature (°C)
Sample: XP 28221Size: 6.0500 mg
Exo Up Universal V4.3A TA Instruments
MDSC Analysis of XP 28221: 1st
Heat Cycle
MDSC Analysis of XP 28221: 2nd
Heat Cycle
52
Atomic Force Microscopy (AFM)
Free surface AFM images of the polyurethane with highest hard-segment content we
acquired to further investigate the phase separation. It is believed that surface of the
polyurethane is dominated by more hydrophilic soft segment (Garrett, Siedlecki and J. 2001)
(Aneja and Wilkes 2003) (McLean and Sauer 1997) (Tan, et al. 2004) (Revenko, Tang and
Santerre 2001). Thus, simple topography imaging usually yields featureless image of smooth
surface. However, by using tapping mode imaging with increased tapping force (A/A0 = 0.7) it is
possible to obtain a phase-separated phase image reflecting the presence of near-surface hard
domains. AFM images indicate that sample’s morphology consists of randomly oriented domains
with lateral diminutions of about 10nm. This data is compatible with domain sizes reported for
solution cast thin urethane films (Garrett, Siedlecki and J. 2001) (Aneja and Wilkes 2003)
(McLean and Sauer 1997) (Tan, et al. 2004) (Revenko, Tang and Santerre 2001). The images in
Figure 35 are 500x500 nm (top) and 100x100 nm (bottom). The phase scale is 20° for the
500nm image and 10° for the 100nm image.
53
Figure 33: AFM Tapping Mode Phase Images
Scanning Electron Microscopy (SEM)
The scanning electron micrographs of the fractured surface of the two shot soft
thermoplastic urethane is shown below. It is well known that thermoplastic urethanes exhibit a
two phase morphology. Moreover the separation of the soft segment and the hard segment is
known to occur (Paul, et al. 1999). Our SEM studies show no evidence of phase separation most
likely due to extremely small segment size and surface domination by the hydrophilic soft
segment.
54
Figure 34: SEM Image x1000
Figure 35: SEM Image x25000
USP Class VI Testing
The Class VI is designed to determine the biological response of animals to direct and
indirect contact with the test article or injection of the test article extract. The study conformed
to all applicable laws and regulations. Specific regulatory requirements included the current
FDA, 21 CFR, Part 58 – Good Laboratory Practice for Non clinical Laboratory Studies;
AAALAC, International; “Guide for the Care and Use of Laboratory Animals, “National
55
Research council, 1996. (NIH) (OLAW), “Public Health Service Policy on Humane Care and
Use of Laboratory Animals, “Health Research Extension Act of 1985 (Public Law 99-158
November 20, 1985, Reprinted 1996; USDA, Department of Agriculture, Animal and Plant
Health Inspection Service, 9 CFR Ch. 1 (1/1/95 edition), Subchapter A – Animal Welfare.
The 0.9% USP Sodium Chloride for injection (NaCl), Cottonseed Oil, 1 in 20 dilution of
ethanol in NaCl and Polyethylene Glycol 400 (PEG) extracts of the test article, and the test
article, XP28221 did not produce a biological response following intramuscular implantation in
rabbits, intracutaneous injection in rabbits, or systemic injection in mice. Therefore, the test
article meets the requirements of USP 27, NF 22, 2004, for Class VI Plastics – 70°C. Due to the
cost of this evaluation only one of the samples were tested.
Conclusions
A set of novel ultra-soft thermoplastic polyurethanes using low crystallinity carbonate
polyol was synthesized and characterized. All samples showed softness on or below 70 Shore A
while at the same time retaining excellent mechanical properties. This includes excellent tensile
strength and elongation properties and superior tensile set at break with recovery of 97%. All
samples exhibited excellent abrasion resistance of 32-38 mm3 loss which is attributed to the high
degree of hydrogen bonding both within hard segment and between segments. In addition tack
testing for all of the samples showed no indication of sample surfaces fusing together. Testing
showed high biocompatibility and low toxicity of polyurethanes discussed in this paper with no
signs of biological reactivity or toxic reaction as indicated by USP Class VI, MEM Elution
Cytotoxicity and Hemolysis toxicology reports. These novel polyurethane materials are
currently being tested as performance enhancing substitutes for many high demand biomedical
56
applications including but not limited to peristaltic pump tubing, balloon catheters, enteral
feeding tubes and medical equipment gaskets and seals.
57
Chapter 3
Synthesis and Characterization of Novel Melt Processable Polyimide
Materials and Methods
Pyromellitic dianhydride (PMDA), 4,4’-Methylenebis (2,6-dimethylaniline) (TMMDA),
gamma- butyrolactone (GBL) were used as received, and kindly donated from BrightVolt, Inc.
(Lakeland, FL). Jeffamine® D230, D400, D2000 and D4000 were provided by Huntsman, Inc.
(The Woodlands, Texas). Tin (II) ethyl hexanoate (catalyst), Sigma Aldrich.
TMMDA Synthesis and Characterization
Tetramethymethyene Dianaline was synthesized by the author in house. A purity
titration, FTIR and carbon and hydrogen NMR were used to verify structure and purity. The
reaction procedure is typically 2,6-dimethylaniline hydrochloride dissolved in warm 2M
hydrochloric acid solution into which ½ equivalent of formalin is added slowly. Some heat of
reaction is evolved and the mixture crystallizes out the hydrochloride salt of the product. A thick
slurry is obtained after about four hours at 80C. The hydrochloride salt is filtered first to
remove the excess acid and unreacted material. The salt will be almost white. The
hydrochloride salt is suspended in a large volume of water and then 1.2 equivalents of NH4OH
per hydrochloride to convert the product to the free amine. The diamine is essentially insoluble
in 1 M ammonia solution. Filter to recover. The recrystallization is accomplished with
ethanol/water containing some ammonia. The final crystals of diamine must be vacuum dried to
be completely dry (Oleinik, et al. 2009).
58
FTIR
FTIR is the instrumental technique most often applied to structure determination of
organic compounds. Although it is not as revealing of the structure as NMR spectroscopy, it is
useful in identifying the presence of certain functional groups. The FT-IR spectrum below was
used to confirm the TMMDA structure (Figure 36). The Tetramethyl Methylene Dianaline
(TMMDA) exhibited the characteristic N-H aromatic stretch, the primary amines produce two
N-H stretch absorptions at 3392 and 3461 cm-1. NH2 scissoring and deformation vibrations are
seen at 1625 cm−1. There are characteristic bands of aromatic rings at 1489 cm−1 for C-C
stretching vibrations. Alkyl C-H Stretch vibration are seen ranging from 2851 and 3052 cm−1
(Rouchaud, et al. 1989) (NIST Chemistry Webbook 2016)
Figure 36: TMMDA FTIR
Titration
The total amount of functional end groups as diamines is titrated with standardized 0.1N
perchloric acid while the milivolt reading is recorded. The TMMDA must be dried to below 500
ppm prior to performing the titration. Dissolve approximately 500 mg into acetic acid using a
59
four place analytical balance. While mixing, immerse the probe in the solution and begin
titrating using the 0.1N perchloric acid recording the millivolt readings according to the
following
a. 0 ml – 20 ml in 5 ml increments
b. 20 ml - 30 ml in 2 ml increments
c. 30 ml – 35 ml in 1 ml increments
d. 35 ml – 40 ml in 0.5 ml increments
e. 40 ml – 45 ml in 1 ml increments
Enter results into the table in the excel spreadsheet named TMMDA to determine the end point
making an ordinary titration curve. The first derivative is then computed. The first derivative of
the graph represents the slope of the graph at any particular point. The equivalence point of the
titration is the point of highest slope on the titrations curve, or where the curve changes from
concave to convex. The slope can be approximated by the discreet rise over run values
calculated from each pair of data points. So the endpoint volume is equal to the equivalence
point and N is the normality of the standardized perchloric acid.
100).(
)(int%
SamplegWt
mlVolumendpoTitrationeNpurityTMMDA
Equation 7: TMMDA % Purity
NMR
The 13C-NMR of TMMDA shows 6 individual product peaks for the TMMDA (due to
symmetry) as well as a reference peak from the deuterated chloroform solvent. In the aromatic region, 4
distinct peaks are seen (140 ppm, 131ppm, 128 ppm, 121 ppm) displaying the symmetry within the
aromatic ring and the symmetry of TMMDA itself. The peak at 40 ppm corresponds to the methylene
bridge, and the right most peak at 17.68 ppm is the combination of 4 methyl signals on the two anilines.
60
The 1H-NMR of 4,4'-methylenebis(2,6-dimethylaniline), or TMMDA further confirms the
structure, showing only 4 distinct peaks due to the symmetry of TMMDA. The aromatic region (furthest
left) is condensed into a very finely coupled set of peaks (a) corresponding to 4 proton signals between
the two aniline rings. The second peak from the left, at 3.73, corresponds to the methylene bridge
between the two anilines. The broad singlet seen at 3.46ppm integrates for 4 protons and matches with the
typical shift in literature for the NH2 on an aniline ring. The furthest peak to the right, and the largest
peak, is standard for a set of 4 equivalent methyl groups on the TMMDA, integrating for 12 protons in
total. This NMR matches that of previously published characterization of TMMDA 4,4'-
Methylenebis(2,6-dimethylaniline) (3k): Yellow oil. 1H NMR (CDCl3, 400 MHz) δ 6.87 (s, 4H), 3.79 (s,
2H), 3.50 (s, br, 4H), 2.23 (s, 12H). 13C NMR (CDCl3, 100 MHz) δ 140.6, 131.7, 128.7, 121.9, 40.4,
17.7 (Barluenga, et al. 1980).
Figure 37: Carbon NMR
62
TMMDA Mechanism
Methods
General Procedure for Polymerization
A 1L three necked glass reactor equipped with Teflon® blades as a mechanical mixer and
nitrogen purge was charged with Jeffamine®. TMMDA is then dissolved in GBL and charged
Figure 39: TMMDA Mechanism
63
into the glass reactor. The diamine solution is warmed to 30ºC and homogenized for 20 minutes
with mechanical stirring, with Tin (II) ethyl hexanoate added to catalyze the polymerization.
PMDA is then separately dissolved in GBL and charged into the glass reactor. The reaction is
kept under an inert nitrogen atmosphere for 4 hours before the temperature is increased to 80°C
and a vacuum is strip off the GBL and water resulting from imidization of the polyamic acid
backbone. The reaction remains under vacuum and 80°C for 24 hours. Subsequently, the wet
polyimide is placed in a vacuum oven at 100ºC to further dry the polymer and ensuring that
imidization is complete. Table 6 shows the varying amounts of diamine used in each formula.
Table 6: Feedstock Stoichiometry of Polyimide
Name
TMMDA
mol%
PMDA mol
%
D230 mol
%
D400 mol
% D2000 mol %
PI-1 11.0% 50.0% 38.8% 0.0% 0.2%
PI-2 11.0% 50.0% 35.4% 3.0% 1.4%
PI-3 11.0% 50.0% 39.4% 0.0% 0.0%
PI-4 11.0% 50.0% 0.0% 39.4% 0.0%
P-I5 25.0% 50.0% 0.0% 23.8% 1.4%
65
FT-IR
Thin film samples were prepared from a heated Carver hydraulic press. The thin films
were analyzed using a Perking Elmer Spectrum One FT-IR equipped with ATR. The resulting
data was analyzed using Spectrum software.
Rheology
A rectangular solid sample measuring 50mm x 10mm x 3mm was molded in a heated
Carver hydraulic press at 3 metric tons to temperatures between 150 and 170°C are reached, with
quick cooling under 5 metric tons until room temperature. Isothermal strain sweeps were
performed on the rectangular samples to determine the regions of linear viscoelasticity (LVE)
with an AR2000 rheometer from TA instruments at three temperatures (-50ºC, 25ºC and 100ºC).
The highest strain percent within the measured LVE common to the three temperatures was
chosen to characterize the sample with a temperature ramp under that controlled strain from -
50ºC to 125ºC at 5ºC/min with liquid nitrogen used for active cooling. Resulting modulus data
were analyzed with software available from TA Instruments.
Thermogravimetric Analysis (TGA)
A 10mg sample from each polymer formulation was assayed for temperature stability
with a TGA Q50 from TA instruments. The samples was heated from 25ºC to 800ºC with a ramp
rate of 10ºC per minute. The results were analyzed using a TA Data Analysis software.
Tensile Test
A sample of 120mm by 30mm by 3mm was molded in a heated press. Then carved using
a FREEMAN die STYLE D638 TYPE 4. The samples were pulled at 2.50cm per minute in a
Shimatdzu® AGS-J and analyzed using a TrapeziumX software.
66
Microhardness Test
Rectangular solid samples were prepared in a matter analogous to those used in rheology.
Ten replicate 15 second indentations were obtained (5 per side of rectangular sample) under 500
gf using a Leica VMHT equipped with Vickers diamond indenter, with averages and their
standard deviations computed.
Results
Rheology
Figure 41: Rheology Temperature Sweeps
Figure 42: Rheology Temperature Sweeps
Overlay
Overlay
67
Table 7: Onset and Temperature at 97% Starting Weight for the Polyimides Studied
Storage, loss and damping moduli vs temperature are shown. The upper rheology trace
shows the shift in glass transition temperature with varying amounts of Jeffamine
(polyetherdiamine lengths. The lower rheology trace shows the shift in glass transition
temperature with varying the amounts of aromatic diamine (TMMDA). Temperature sweeps
under constant strain within the LVE (determined from strain sweeps) illustrate beta and alpha
transitions. The alpha (glass) transition can be seen as a drop in storage modulus (G’), an
increase in dampening (Tan δ) and a peak in the loss modulus (G’’). Figure 41 shows an increase
in the glass transition temperature with a decrease in the molecular weight of the
polyetherdiamine linker. Figure 42 shows an increase in glass transition temperature with
increase in the molar feedstock of the aromatic diamine (TMMDA).
Sample Tan δ Tg (at 10Hz) G'' Tg (at 10Hz)
PI-1 120.10 80.03
PI-2 105.06 65.08
PI-3 125.02 100.03
PI-4 40.08 20.06
PI-5 105.04 N/A
68
Thermogravimetric Analysis
Figure 43 TGA Thermograms for the Polyimides
Table 8 TGA Onset and Temperature at 97% Starting Weight for the Polyimides Studied
0
20
40
60
80
100
120
Weig
ht (%
)
0 200 400 600 800
Temperature (°C)
PI-1––––––– PI-2––––––– PI-3––––––– PI-4––––––– PI-5–––––––
Universal V4.5A TA Instruments
Sample Onset Temperature (ºC) Temperature (ºC) at 97% wt.
PI-1 366.97 349.01
PI-2 363.02 342.86
PI-3 377.95 305.35
PI-4 361.99 352.76
PI-5 362.98 347.16
69
Gel Permeation Chromatography
Figure 44 Gel Permeation Chromatograms for the Polyimides
Table 9 Mw, Mn and Polydispersity by GPC
Sample Mw (g/mol) Mn (g/mol) Polydispersity (PD)
PI-1 31062 13026 2.3846
PI-2 33301 14428 2.3081
PI-3 28553 11992 2.3793
PI-4 35182 16310 2.2145
PI-5 N/A N/A N/A
70
FTIR
Figure 45 FTIR Sprectrum of Polyimide
Vickers Hardness
Table 10 Vickers Hardness Values
Samples HV Standard Deviation (HV) MPa
PI-1 17.6 0.95 172.6
PI-2 14.4 1.25 141.2
PI-3 17.6 1.37 172.6
PI-4 N/A N/A N/A
PI-5 9.8 0.85 96.11
Date: Friday, May 20, 2016
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 650.0
17.0
30
40
50
60
70
80
90
100
105.0
cm-1
%T
2972.20
2871.69
1771.05
1714.35
1456.92
1372.84
1354.40
1095.84
1039.30
917.53
828.02
761.32
730.65
71
Discussions
Gel Permeation Chromatography
Gel Permeation Chromatography (GPC) data (Figure 44) was obtained and yielded
weight-averaged molecular weights (Mw) ranging from approximately 28500 to 3500Da,
number-averaged molecular weights (Mn) ranging from approximately 12000 to 15900 Da, and
polydispersity indices (Mw/Mn) ranging from 2.21 to 2.38, as summarized in Table 9.
Rheology
Rheological analysis was performed on rectangular solid samples under linear
viscoelasticity (LVE) strains determined from previous isothermal strain sweeps as described in
the Methods section. Temperature sweep data under these LVE-determined strains yielded alpha
and beta transitions, with glass (alpha) transitions showing as precipitous drops in the storage
modulus (G’), and peaks in both the loss modulus (G’’) and dampening (Tan δ). It can be seen
that the storage modulus, representing the elastic properties of the material and its recoverable
energy, drops as the sample nears its alpha transition and becomes more rubbery (viscous). The
concomitant increase in the loss modulus (G’) is due to a shift in the material’s elastic (storage)
modulus to a more viscous, rubbery material, as the main chains obtain enough degrees of
freedom and thermal energy to exhibit segmental slippage seen at the glass transition. The ratio
of the loss to storage modulus (known as dampening, or Tan δ) will be used to compare the glass
transition temperatures.
72
Thermogravimetric Analysis
The thermal stability and dryness of the polyimide were evaluated by TGA measurements
under nitrogen atmosphere. The thermograms of the polyetheramine-polyimides are shown in
Figure 43. The corresponding temperature at 3% weight loss and the onset temperature are
reported in Table 8. Polyimides typically have higher temperature stability (Takassi, et al. 2015)
(Li, et al. 2004) (Lua and Su 2006) as their backbone is linear, well-ordered, rigid and aromatic.
The polyetheramine-polyimides synthesized in this paper show thermoplastic properties at the
expense of relatively degraded thermal stability. The stability at the onset temperature represents
a relation between the lengths of the different aliphatic diamines in the repeat unit vs. the
temperature (Baldwin, et al. 2013) (Li, et al. 2004). As the aliphatic linkers increase in length,
the temperature stability decreases due to the presence of longer aliphatic linkages that makes it
more flexible and less heat resistant. Even though there is a decrease in thermal stability the
difference is not large enough between the larger links in PI-4 and the shorter links in PI-3.
Further, the thermal stability of the polyetheramine-polyimide is conserved. The results provided
by the TGA show that the majority of the samples have conserved a 97% of their mass up to
300ºC. The diamine monomers and the lactone solvent both have boiling points around 205ºC
which can explain the minimal loss of mass around that temperature. The onset temperature was
above 360ºC for each formulation. The information provided by TGA testing also allows the
determination of appropriate temperature regimes for rheology.
Infrared Spectroscopy
FT-IR spectroscopy was used to confirm polyimide formation and complete ring closure
(imidization) from the polyamic acid backbone. The novel polyetheramine-polyimides studied
here exhibited characteristic imide group absorptions around 1771 cm-1 and 1716 cm-1 typical of
73
imide carbonyl asymmetrical and symmetrical stretching arising from the anhydride ring of
PMDA, with 1355 - 1373 cm-1 being the characteristic C-N aromatic stretch. The disappearance
of amide carboxyl absorbencies around 1540 cm-1 (–NHCO- stretch) indicated a virtually
complete conversion of the polyamic acid (PAA) precursor into polyimide. NH2 symmetric and
asymmetric stretching and deformation vibrations are seen at 3474 cm−1. There are characteristic
bands of aromatic rings at 1565 cm−1 for C-C stretching vibrations. Alkyl C-H Stretch vibration
are seen at 2871 and 2972 cm−1 (Georgiev, et al. 2014) (Hsiao, Hsiao and Kung 2016).
Microhardness
During the micro hardness test, the holding time for the indentation was set as 15s with
an indentation load of 500 gf. The indentations were measured with a Leica VMHT apparatus.
Multiple indentations were done on different side of the sample to understand the entire
composition of the polymer and to account for anisotropy. The random conformations of the
polymer does not show different regions of varying hardness, implying an isotropic composition.
Four polymers of the series were tested for micro hardness, as PI-4 was too soft for the Vickers
scale. The results of the indentations are presented in Table 10. Overall, those samples with
larger amounts of Jeffamine D230 show higher hardness, ranging from 17.6 Hv to 14.4 Hv (PI-1
through PI-3), as compared to the sample with a large amount of Jeffamine D400 (PI-5) with a
rather low hardness of 9.8 HV. Particularly, PI-1 and PI-3 both composed of the shorter
Jeffamine D230, along with it being the major diamine of those polymers, appear to have similar
Vickers Hardness values of 17.6 Hv. However, once the longer diamine is added the value
decreases to 14.4 Hv as was seen in PI-2. Thus, the hardness appears to be governed by the
aliphatic diamine size and concentration, and is also correlated with Tg due to polymer’s degrees
of freedom and segmental slippage with applied force (Chandler 1999). This hardness-Tg
74
relationship is seen in the Tg of PI-1 being 120.1ºC and its hardness of 17.6Hv. While in PI-2,
its Tg is 105.06ºC and hardness of 14.4Hv. PI-3 has a Tg of 125.02 ºC and a hardness of 17.6Hv.
The results for PI-4 and PI-5, in particular, are governed by the large size of the aliphatic
Jeffamine D400. In this chase, PI-4 was too soft to be measured using a Vickers indenter and
when related to the Tg the value drops from 105.04ºC in PI-5 to 40.08ºC in PI-4.
Conclusions
The synthesis and subsequent characterization of the polyetheramine-polyimides
described in this work serve as a proof of concept for their formulation to yield the desirable
properties. Fully aromatic polyimides are well known to exhibit high thermal stability and
resistance to solvents, and as a consequence they are typically unable to be processed with
conventional thermoplastic equipment. By using long chain aliphatic polyether diamines we
were able to impart into the backbone flexible components making our polyimides melt
processable using typical thermoplastic techniques such as compression molding, injection
molding and extrusion. Thermal and mechanical properties such as glass transition and
decomposition temperatures were also characterized. The molecular weight and polydispersities
were elucidated from gel permeation data and low in comparison to typical polymers high
performance polymers such as the polyurethanes reported in chapter 2.
Rheological analysis of rectangular solid samples showed glass transition temperatures
(Tg) ranging from approximately 40°C to 125°C according to tan δ peaks at 10Hz. It can be seen
from Figure 41 and 42 and Table 6 and 7 that with approximately equivalent amounts of
Jeffamine D230 that the glass transitions can be tuned by the addition of varying sizes of the
aliphatic polyetherdiamines, with larger, higher MW aliphatic diamines reducing the glass
75
transition temperature. Conversely, the aromatic diamine shows a significant influence on glass
transition temperature.
76
Chapter 4
Future Work
Polyurethane and Nanoparticles
The future research proposal will be to develop novel polyurethane nanocomposites with
increased heat resistance and improved mechanical properties using the novel polycarbonate diol
in chapter one. This work encompasses the understanding, design and testing polyurethane
elastomer nanocomposites. The effect of nanoparticles on the properties of polyurethanes has
attracted significant attention lately and the definition of nanocomposite materials has broadened
to encompass a large variety of systems. This future work will focus on a specific class of
nanoparticles, metalorganics. Metalorganic nanoballs will be processed with polyurethanes to
yield nanocomposites with improved thermal and mechanical properties, chemical resistance,
optical clarity, and optimum gas barrier properties as compared to those of unmodified polymers.
The incorporation of self-assembled nanoparticles like nanoballs into linear polyurethane chains
will give rise to a mechanically cross-linked network resulting in a novel high performance
polyurethane.
It is proposed that a novel class of polyurethane composite materials will be developed.
We will investigate both thermoset and thermoplastic types. These polymers will be synthesized
via polyaddition polymerization. We will investigate both aliphatic and aromatic hard segments
77
during the polymerization process. The ultimate goal will be to develop high performance
polyurethane composite materials that will outperform those currently available to industry.
Polyurethane elastomers of the TPU and rubber type have always had degradation
problems at elevated temperatures. The intellectual merit of this work will be based on the
premise that the addition of nano size structures will improve their physical properties by
incorporating nanoballs linked via threading by the linear urethane or by crosslinking the
hydroxylated nanoballs with the urethane thus increasing the thermal stability of these classes of
materials. The interest given to this technology will allow entrance to industrial markets
previously off limits due to the thermal degradation. The primary objective is to advance the
knowledge of combining polyurethanes with nano structured materials with the ultimate goal of
providing materials that can be used in real world applications.
The broader impact of this work represents the opportunity to develop a polymer that
may be used in military tracked vehicles. The new tanks are heavier and faster than their
predecessors, weighing over 54,400kg and traveling at speeds of up to 72km/hr. The track pad
and bushings have a high rate of wear and failure and thus the military is constantly looking for
materials to improve the lifetime of these components (Dwight and Lawrence 1987). Due to the
military’s increased presence in desert climates, a thermally stable polyurethane would be of
great interest and cost savings. There are also other industrial applications that could benefit
such as automobile tires, high speed rollers and wear resistant tennis shoes.
Just in the last few years, nanostructured materials and nanotechnologies have received
much attention from the scientific community owing to the novel properties that arise in ordinary
matter when its size is reduced to a nanometric scale range (Carotenuto 2002). In 1960, Nobel
Laureate Richard Feynman, predicted that by the year 2000 products would be built one
78
molecule or one atom at a time. This shift is referred to today as the “nanotechnology
revolution” and many people consider Dr. Feynman’s quote the birth of nanotechnology. The
National Science Foundation predicts that by 2010 nanotechnology will pervade virtually every
corner of the economy and represent $1 trillion in goods and services. The term
“nanotechnology” is based on the root nanos, meaning one billionth. It refers to technology that
uses components or features that measure 100 nanometers or less. The definition of nano-
composite material has broadened significantly to encompass a large variety of systems such as
one-dimensional, two-dimensional, three-dimensional and amorphous materials, made of
distinctly dissimilar components and mixed at the nanometer scale. The general class of
nanocomposite organic/inorganic materials is a fast growing area of research. Just in the last
couple of years, nano-sized materials and the technologies associated have received a great deal
of attention. These systems show great promise and have generated significant industrial interest.
The interest being given to this technology is owed to the improvement in thermal, mechanical,
chemical resistance, optical clarity and gas barrier properties compared to those of pristine
polymers. It is important to recognize that nanoparticle loading adds significant improvements at
very low levels whereas traditional microparticle additives require much higher loading levels to
achieve similar performance, such as weight reduction, greater strength for similar structural
dimensions and improved barrier performance for materials of a similar thickness. There are a
wide variety of nanoparticles available. A significant amount of research has been devoted to
carbon nanotubes which can be single walled or multi-walled (Harada 1998) (Gong, Ji, et al.
1998) (Auten and Petrovic 2002) (Moulton, et al. 2001) (Abourahma, et al. 2001) (Srikanth, et
al. 2003) (McManus, Wang and Zaworotko 2004) (Mohomed, Abourahma, et al. 2005).
Recently we shifted our focus to include novel metalorganic nanoballs (Mohomed, Gerasimov, et
79
al. 2005) (Moulton, et al. 2001) (Abourahma, et al. 2001) (Srikanth, et al. 2003) (McManus,
Wang and Zaworotko 2004) (Mohomed, Abourahma, et al. 2005). This proposal will focus on
developing high performance polyurethane elastomers using self-assembled hydroxylated
nanoballs as fillers.
Current Target Areas
The properties of these novel polyurethane nanocomposites can be tailored to fulfill the
requirements of different applications like flex foam for cushions and bedding, rigid foam for
insulation, urethane coating for auto exterior, resilient elastomers for skate wheels or industrial
rollers, films or fibers and automotive molded seats and window encapsulates, medical device
and military tank tracks. Polyurethane is a very general term which is utilized for a significant
number of different polymers. Polyurethanes are formed by polyaddition polymerization.
Threading the Nanoballs with Linear Polyurethanes
These high performance polyurethanes will incorporate carbon nanoballs by threading the linear
urethane backbone though the nanoball which are termed rotaxanes (Gong, Ji, et al. 1998) (Gong and
Gibson, Controlling Polymer Topology by Polymerization Conditions Mechanical Linked network and
Branched Polyurethane Rotaxanes with Controllable Polydisperity 1997) (Nagapudi, et al. 1999) (Gong,
Glass and Gibson 1998) (Shen and Gibson 1992). High molecular weight polyol – a polar and highly
flexible molecule is expected to thread through the nanoball windows. Estimated diameter for linear poly
tetrahydrofuran polyol which is a standard component of modern high performance urethanes is about 0.3
nm (Gong, Ji, et al. 1998) (Gong and Gibson, Controlling Polymer Topology by Polymerization
Conditions Mechanical Linked network and Branched Polyurethane Rotaxanes with Controllable
Polydisperity 1997) (Nagapudi, et al. 1999) (Gong, Glass and Gibson 1998) (Shen and Gibson 1992).
Hydroxylated nanoballs created in Dr. Zaworotko’s laboratory are rhombi hexahedral in shape and
possess functional hydroxyl groups on the surface. They have average sizes of 2.6 to 3.1 nm window
80
sizes ranging from 0.9 to 1.2 nm as measured by X-ray crystallography and shown in Figure 2. thus,
allowing polyol molecules to enter the interior cavity of the nanoball efficiently creating a threaded
mechanical link.
A true polyrotaxane has the threaded molecule confined between two blocking groups preventing
the threaded molecule from slipping off. Upon formation of polyurethane a rigid MDI-based hard
segment is added to flexible polyol molecule which is threaded through the nanoball. MDI-based hard
segment is a less polar unit with significantly bigger diameter. Both factors should prevent the nanoball
from slipping off the polyurethane molecule. Since the nanoball is confined between two blocking groups,
the two components are mechanically linked thus making it thermally stable. Since the hydroxyl group is
half of the urethane reaction it will be necessary to either cap them or incorporate them into the reaction
as a cross link function. In this proposal we will consider both approaches.
Figure 46 Calculated nanoball window sizes
(angstroms)
81
Short Term Objectives
The short term research objectives are listed below in chronological order:
a. Determine base polyurethane polymers
b. Determine the solubility of nanoballs.
c. Cap hydoxylated nanoballs.
d. Incorporate the polyurethane polymers and nanoballs
e. Test the polyurethane nanoball composites to obtain the mechanical, thermal
and chemical properties.
Research Plan
Polymerize Baseline Material
We will carry out preliminary experiments by polymerizing and testing model thermoplastic
polyurethane and millable polyurethane rubber. The formulations are similar to those presented in chapter
1.
Determine Solubility of Nanoballs
We will test the solubility of the untreated nanoballs in various solvent systems to establish best
conditions for capping the nanoballs. In a separate study we will test the solubility of nanoballs in polyols
so that threading or crosslinking reaction can be done in the absence of a solvent. Our experience in
formulating polyurethanes leads us to believe that the selected materials will function to produce
compatible systems.
82
Cap Hydoxylated Nanoballs
The hydroxyl units on the surface of the nanoballs are reactive with isocyanate groups and would
thus interfere with the linear urethane reaction desired. We will cap the hydroxyl groups with a
monoisocyanate. Typical examples would be the following
Figure 47 Mono functional Isocyanates
83
Untreated hydroxylated nanoballs are dissolved in optimized solvent system and placed into a 100 ml
round bottom flask equipped with stirrer, heater and nitrogen blanket. A calculated equivalent amount of
monoisocyanate is added drop wise under stirring. The equivalent weight tells you how many grams of a
product you need to have one equaivalent of reactive groups. For an isocyanate, the reactive group is
N=C=O (NCO), and its concentration is measured by weight percent NCO.
Example: Isocyanate Equivalent Weight = 4,200 ÷ %NCO (g/eq)
Necessity of catalysts will be determined experimentally for each isocyanate used. Extent of reaction
will be monitored by either FTIR spectroscopy or hydroxyl group titration.
Fabrication of Polyurethane Capped Nanoball Composites
Thermoplastic Polyurethane Threaded Through the Capped Nanoballs
Into a 200 ml round bottom flask equipped with constant nitrogen blanketing and a heating
mantel with controlled temperature and stirring, the mixture of monoisocyanate-capped nanoballs in 50
ml of THF is added. A pre-determined amount of polytetrahydrofuran is added to the mixture which is
stirred overnight at 70°C to allow threading between nanoballs and linear species. At the end of the
threading period, calculated amounts of chain extender and butanediol are added and mixed. A small
amount of catalyst is added (typically stannous octoate), and the mixture is mixed until homogeneous.
Once homogeneous, in case of the thermoplastic polyurethane a slight stoiciometric excess of methylene
bis(diphenyldiisocyanate) is added to the mixture while mixing.
A Millable Polyurethane Rubber Threaded Through the Capped Nanoballs
Into a 200 ml round bottom flask equipped with constant nitrogen blanketing and a heating
mantel with controlled temperature and stirring, the mixture of monoisocyanate-capped nanoballs in 50
ml of THF is added. A pre-determined amount of polytetrahydrofuran is added to the mixture which is
stirred overnight at 70°C to allow threading between nanoballs and linear species. At the end of the
84
threading period, calculated amounts of chain extender and butanediol are added and mixed. A small
amount of catalyst is added (typically stannous octoate), and the mixture is mixed until homogeneous.
Once homogeneous, in the case of the polyurethane rubber a slight stoiciometric deficiency of methylene
bis(diphenyldiisocyanate) is added to the mixture while mixing.
Thermoplastic Polyurethane Threaded Through the Capped Nanoballs
Into a 200 ml round bottom flask equipped with constant nitrogen blanketing and a heating
mantel with controlled temperature and stirring, the mixture of monoisocyanate-capped nanoballs in 50
ml of THF is added. A pre-determined amount of polytetrahydrofuran is added to the mixture which is
stirred overnight at 70°C to allow threading between nanoballs and linear species. At the end of the
threading period, calculated amounts of chain extender and butanediol are added and mixed. A small
amount of catalyst is added (typically stannous octoate), and the mixture is mixed until homogeneous.
Once homogeneous, in the case of the cast polyurethane a slight stoiciometric excess of methylene
bis(diphenyldiisocyanate) is added to the mixture while mixing.
Fabrication of Cross-Linked Polyurethane Nanoball Composites
Thermoplastic Polyurethane Cross-Linked by the Nanoballs
Into a 200 ml round bottom flask equipped with constant nitrogen blanketing and a heating
mantel with controlled temperature and stirring, a pre-determined amount of polytetrahydrofuran is
added. A calculated amount of untreated nanoballs in a minimum amount of THF is added to the reaction
mixture which is stirred until homogenous. In this reaction hydroxylated nanoballs act as both
crosslinkers and chain extenders. A small amount of catalyst is added (typically stannous octoate) and the
mixture is mixed. Once homogeneous, a slight stoiciometric excess (based on pre-determined hydroxyl
content of both polyol and nanoballs) of methylene bis(diphenyldiisocyanate) is added to the mixture
while mixing. When all the components are added and sufficiently mixed stirring is stopped and reaction
85
temperature is maintained at 80° C for another 48 hours. Extent of the polymerization will be monitored
by FTIR spectroscopy.
Cast Polyurethane Cross-Linked by the Nanoballs
Into a 200 ml round bottom flask equipped with constant nitrogen blanketing and a heating
mantel with controlled temperature and stirring, a pre-determined amount of polytetrahydrofuran is
added. A calculated amount of untreated nanoballs in a minimum amount of THF is added to the reaction
mixture which is stirred until homogenous. In this reaction hydroxylated nanoballs act as both
crosslinkers and chain extenders. A small amount of catalyst is added (typically stannous octoate) and the
mixture is mixed. Once homogeneous, a slight stoiciometric excess (based on pre-determined hydroxyl
content of both polyol and nanoballs) of methylene bis(diphenyldiisocyanate) is added to the mixture
while mixing. When all the components are added and sufficiently mixed stirring is stopped and reaction
temperature is maintained at 80° C for another 48 hours. Extent of the polymerization will be monitored
by FTIR spectroscopy.
Millable Polyurethane Rubber Cross-Linked by the Nanoballs
Into a 200 ml round bottom flask equipped with constant nitrogen blanketing and a heating
mantel with controlled temperature and stirring, a pre-determined amount of polytetrahydrofuran is
added. A calculated amount of untreated nanoballs in a minimum amount of THF is added to the reaction
mixture which is stirred until homogenous. In this reaction hydroxylated nanoballs act as both
crosslinkers and chain extenders. A small amount of catalyst is added (typically stannous octoate) and the
mixture is mixed. Once homogeneous, a slight stoiciometric excess (based on pre-determined hydroxyl
content of both polyol and nanoballs) of methylene bis(diphenyldiisocyanate) is added to the mixture
while mixing. When all the components are added and sufficiently mixed stirring is stopped and reaction
temperature is maintained at 80° C for another 48 hours. Extent of the polymerization will be monitored
by FTIR spectroscopy.
86
Testing of the Urethane/Nanoball Composites
Differential Scanning Calorimetry (DSC)
A TA Instruments 2920 DSC will be used to determine glass transition, Tg, and melt
temperature, Tm. After calibration with an indium standard the second heating of each sample
will used in order to earase any previous thermal history. Each sample will be heated at 3 C
/min with dry nitrogen gas flowing at a rate of 75 ml/min purged through the sample cell.
Cooling will be accomplished with the liquid nitrogen cooling accessory (LNCA), provided with
the 2920.
Dynamic Mechanical Analysis (DMA)
Rectangular samples with dimensions of 30mm × 5mm × 1mm will be compression
molded using 20 ton Carver press. TA Instruments DMA 2980 will be used to find tensile moduli
for different samples. Data will be recorded at different frequencies from –150 C to temperatures
at which the samples are unable to bear loads. This will define the useable temperature for the
materials.
Thermal Gravimetric Analysis (TGA)
5 mg samples will be scanned on a TA Instruments QA 50 TGA at a scanning rate of 5
C/min under nitrogen and air. Thermal stability will be determined based on weight loss. The
samples was heated from 25ºC to 800ºC with a ramp rate of 10ºC per minute. The results were
analyzed using a TA Data Analysis software.
87
UV Visible Spectroscopy
Samples will be compression molded in 10mm diameter disk molds with a thickness of 5mm.
Transmission spectra will be recorded with an 8452A Hewlett-Packard UV/Visible Spectrophotometer.
These tests will show that nanoballs may have on transparency properties of polyurethanes.
Atomic Force Microscopy
Surface studies will be performed with Digital Instruments atomic force microscope using
tapping mode and phase imaging. The images will be acquired under ambient conditions with standard
silicon tapping tip on a beam cantilever. Thin films used for AFM studies will be prepared by casting
from 1% bwt. THF solutions. Several drops of polymer solution will be placed on glass slides and dried
in a vacuum oven at 60ºC for 24 hours.
Tensile Testing
Tensile Modulus and Tensile Strength: Dog-bone shaped samples will be compression
molded. An Instron 2980 will be used to determine the modulus and strength of the samples.
Samples will be deformed at a cross head speed of 0.5 inch/min.
Abrasion Testing
Abrasion testers use an abradant to be applied to the surface of a test specimen. Test
compounds are usually compared on a volume loss basis which is calculated from the weight loss
and density of the material. ISO 4649 refers to the DIN Abrader. The test specimen is put in a
holder that traverses a rotating cylinder covered with the specified abradant paper. By allowing
the sample holder to move the test piece across the drum as it rotates, there is less chance of
material buildup on the abradant paper (Gong, Ji, et al. 1998).
88
Polyimide
A polymers molecular weight and polydispersity are important properties and are
measured using a technique known as gel permeation chromatography or size exclusion
chromatography. Since all polymers are polydisperse it is better to refer to it as the average
molecular weight. It would be more accurate to call it “average relative molecular weight” as a
standard such as polystyrene with known molecular weights is used. A series of varying
molecular weight polystyrene samples are used and their elution then determine the average
molecular weight of the polymer sample being analyzed. The average molecular weight of a
polymer directly affects the physical and mechanical properties and solubility and brittleness of
the polymer. All the polyurethane polymers studied in chapter two had average molecular
weights in the range of two hundred thousand Daltons whereas the polyimide polymers studied
in chapter three had average molecular weight in the range of thirty thousand daltons. There will
be an attempt to increase the average molecular weight of the polyimide formulas either by
adjusting the reaction conditions such as temperature and time or chemically by adding in short
chain extenders or increasing/changing the type of catalyst used. Once the molecular weights
have been increased significantly the properties will be studied and compared to those polymers
discussed in chapter three.
It is well known that 13C-NMR spectroscopy is a promising analytical and identification
tool. H-NMR and C-NMR should be studied to confirm the structure of the polyimide. As well
an analytical method should be developed for the spectral analysis of polyamic acids and
polyamides. Developing a method to determine the full completion of ring closure would help
confirm the finished polyimide has no remaining open rings.
89
Polyimides are a class of high temperature resistant polymers that are most frequently
used for structural engineering purposes. They also have rather unique properties for small ion
or molecule diffusive transport. This is the area that industry can most effectively serve. We
have an interest in lithium ion transport in a conductive separator matrix for batteries. Also
possible are materials for selective gas transport and fuel cell membranes. Although polyimides
are relatively expensive compared to most polymer classes, they can be tailored at the molecular
level with a much broader combination of controllable properties than any other class. This
makes them very useful when a unique and specific target is required. Using the polyimides
discussed in chapter 3 as a separator layer will demonstrate a useful application.
90
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About the Author
Kenneth Kull received a B.A. Degree in Chemistry from Wayne State University in
Detroit Michigan in 1995. He was admitted to the graduate degree program in the spring of 2001
at The University of South Florida and immediately joined Dr. Julie Harmon’s polymer materials
research lab.
Kenneth has worked fulltime in industry since receiving his degree from Wayne State
in1995, working for companies such as BASF, TSE Industries, Saint Gobain and currently at
Brightvolt. He took seven coursed earning 21 GPA hours for an overall GPA of 3.23. Kenneth
has authored two publications and coauthored two publications in various peer-reviewed
scientific journals. Ken has also presented at several subject matter relevant conferences such as
FAME, TOPCON, HEXAGON and The CASTLE CONFERENCE.