Rheological Design of Sustainable Block Copolymers

Alex MannionAdvisors: Frank Bates, Chris Macosko

Final Oral ExaminationAugsut 4th, 2016

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Safety moment: proper hand washing

jst.umn.edu

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Rheological design

Paint

Food

CosmeticsBiological systems

“The rheological behavior of block copolymers is perhaps the least understood of all categories of

complex fluids…” – Professor Ron Larson, Dept. of

Chemical Engineering, U. of Michigan1

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Block copolymers

AB diblock copolymer

AB diblock copolymer ABA triblock copolymer

ABABA… multiblock copolymer

Morphology

Architecture

1. “Structure and Rheology of Complex Fluids,” Oxford University Press, Ronald G. Larson, 1999.

Dalsin, S. J.; Bottlebrush Polymers: Synthesis, Rheology, and Self-Assembly, 2016

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Sustainability

Ellen MacArthuer Foundation, “The New Plastics Economy: Rethinking the Future of Plastics,” 2016

Past… Future…

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Thesis Outline

Chapter 2 Chapter 4 Chapter 6

Chapter 3 Chapter 5 Chapter 7

Chewing Gum Branched Multiblock Copolymers Practical Materials

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Goal:• Replace conventional chewing gum ingredients

with new materials to simplify formulation• Maintains the same sensory profile

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Next generation chewing gum

What is chewing gum’s rheological fingerprint?

Morgret, L., Science-Based Design of High Performance Bubblegum, 2005

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Gum materials

Important deformation regimes1

• shear strains: 10-1000%• shear rates: 10-100 s-1

• shear stresses: >104 Pa

1. Anderson et al., J. Oral Rehabil., 2002; Steffe J., Rheological Methods in Food Processing Engineering, 1992

Chewing gums Bubble gums Sample preparation

Mouth chewing

Ralph DeLong, UMN, Dentistry

S (Pa-sn) n GR (Pa) (s)30100 0.228 24300 0.0440

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Linear viscoelasticity (LVE): oscillatory shear

S: stiffness n: strength of gel network

Critical gel equations1

Fitting parameters

Rouse model equations

S (Pa-sn) n30100 0.228

1. Chambon et al., J. Rheol, 1987

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Start up of steady uniaxial extension

L0L

Constant Hencky strain rate:

Uniaxial extension:

Transient extensional viscosity:

Large strains at break ( > 4.0) correlate with desirable sensory feelLarger stresses at break for bubble gums stabilizes bubble blowing

Chewing gums Bubble gums

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Block copolymer blends for chewing gum applications

What is chewing gum’s rheological fingerprint?

Fragile critical gel fluid with high extensibility

Goal: Next generation chewing gum

Block copolymers

• Microphase separate tunable solids• Precise control over molecular architecture

Glass

Rubber

ABA triblock AB diblock

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High extensibility Softener, “critical gel” behavior

Why use block copolymers?

Mn (kg/mol) wPLAAB 7.4 0.41ABA 95.1 0.36

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Mn (kg/mol) wPLAAB 7.4 0.41ABA

A = poly(D,L-lactide)B = poly(cis-1,4-isoprene)

ABA triblock/AB diblock blends: extension

Lee, S. Structure and Dynamics of Block Copolymer Based Soft Materials, 2011

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Three component system

Investigated effects of• Polymer composition• Molecular weight

AA B

BA

BA

Poly(D,L-lactide) (L)Glassy, Tg ≈ 50 °C

Poly(ε-decalactone) (D)Rubbery, Tg ≈ -50 °C

dimethanolbenzene

Sn(Oct)2toluene110 °C, 4 h

ε-decalactone

Sn(Oct)2130 °C, 12 h

D,L-lactide

Benzyl alcohol

Synthesis

Advantages:• High conversion, well-controlled• Scalable• Renewable/FDA approved materials

Synthesized polymers

Sample Mn*

[kg mol-1]fPLA Đ#

DL-S1 5.6 0.15 1.11

DL-S2 8.0 0.33 1.13

DL-S3 9.0 0.41 1.18

DL-M1 32 0.09 1.05

DL-M2 38 0.21 1.06

DL-M3 46 0.32 1.06

LDL-1 102 0.05 1.07

LDL-2 112 0.11 1.09

LDL-3 133 0.23 1.06

Targeted a range of PLA weight fractions for three sets of polymers:

*calculated from end-group analysis of 1H-NMR #determined from room-temperature size-exclusion chromatography (SEC) †determined from differential scanning calorimetry (DSC)

LL D

Three polymer species

D L

D L

Produced 24 blends80% diblock20% triblock

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Effect of triblock composition

(DL-S2)

(LDL-1, LDL-2, or LDL-3)

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LL DD L

Vary PLA weight fraction

80 wt.% 20 wt.%

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Effect of diblock molecular weight

LL D

20 wt.%

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80 wt.%

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Vary diblock ratio (2:0, 1:1, or 0:2)

D LD L

Small angle X-ray scattering

Exact morphology does not matter!

(DL-S2) (DL-M2)

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Blends for chewing and bubble gums

Best blends: Key rheological parameters:

LL D

D L

Polymer LDL-2

…with short DL diblocks

Future work• Increase strain at break with multiblock architecture

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Thesis Outline

Chapter 2 Chapter 4 Chapter 6

Chapter 3 Chapter 5 Chapter 7

Chewing Gum Branched Multiblock Copolymers Practical Materials

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Blown film extrusion

Shear viscosity low at high rates

Extensional viscosity high at high rates

Goals:• Stable bubble• Controlled thickness• Fast through-put

Rheological targets:

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One commercial success story: poly(lactide) (PLA)

lactic acid lactide polylactidesugar

- H2O catalyst

• ~$1 per lb• Mechanically similar to

polystyrene• Compost 100% in ~45 days

Natureworks.com

ApplicationsProperties

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Deficiencies of commercial PLA

Poor mechanical propertiesPoor melt strength

TD

MD

Extensional rheology

Blown film extrusion

Tensile testingMachine direction (MD)

Transverse direction (TD)

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Toughening PLA with multiblock architecture

Poly(D,L-lactide)Tg ≈ 50 °C

Elastomeric blockTg

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Tuning processability with long chain branching

Long chain branching can lead to strain hardening1

Long chain branch

Short branch

1. Meissner et al., J. Appl. Polym. Science, 1972

1) Polymer composition2) Block lengths (~Mc) 3) Accessible TODT

Versatile and robust platform:

Linear multiblock(DL)n

Star diblockDL-4

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Branched multiblock(DL-4)n

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Linear triblockLDL

Strategy

couple

xx

couple

xx

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Synthesis and characterization

dimethanolbenzene

Sn(Oct)2toluene110 °C, 4 h

toluenepyridine25 °C, 2 h

ε-decalactone

Sn(Oct)2130 °C, 12 h

Sample MW[kg/mol]$

fPLA* І

LDL linear triblock 18.4 -- 0.72 1.14

DL-4 star diblock 39.7 -- 0.73 1.10

(DL)n linear multiblock 159 5.6 0.72 1.92

(DL-4)n branched multiblock 151 2.3 0.73 2.00

*calculated from 1H-NMR end group analysis $determined with SEC in room temp THF with a MALS detector †determined with SEC in room temp THF with a RI detector

sebacoyl chloride

D,L-lactide

pentaerythritol

Linear BranchedSize exclusion chromatography (SEC)Synthesis

= number of subunits in final multiblock

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Estimating branching from SEC with multi-angle light scattering (MALS)

Contraction factor:

Hyperbranched

Linear chain: g = 14-arm star: g = 0.63

“Comb-like”

High molecular weight species resemble a comb polymer

SEC-MALS

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Key advantages of branched multiblock

Strain hardening due to branching

(DL)n linear multiblock (DL-4)n branched multiblock

Multiblocks have increased toughness

Tensile testingExtensional rheology

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Key limitation: gelation

couple

… leads to a gel

Too much coupling agent… Gel point equation: Af + Bg

2 3 4 5

2 ∞ 3.0 2.0 1.73 4.0 2.0 1.6 1.4

4 3.0 1.8 1.5 1.4

5 2.7 1.7 1.4 1.3

fEgE

Values of at gel point:

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New approach: A2 + B2/B3

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A2PLA diol,

19 kg mol-1

Approach

oo B2

B3

Theory

SEC

Coupling Branching

Amount of B3

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Estimating branching from SEC with multi-angle light scattering (MALS)

SEC-MALS

High molecular weight species becoming increasingly branched

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Extensional behavior

bPLA-95 bPLA-90 bPLA-80 bPLA-50

Extensional rheology

Temperature: 120 °C

Amount of B3

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B3

Easily adoptable to triblock copolymers

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Outlook

+A2

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Approach

With A2 + B2/B3 reaction, can easily tune:

• Coupling extent ()

• Amount of branching• Viscosity Applicable to reactive

extrusion

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Thesis Outline

Chapter 2 Chapter 4 Chapter 6

Chapter 3 Chapter 5 Chapter 7

Chewing Gum Branched Multiblock Copolymers Practical Materials

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CollaboratorsBranched Multiblock Polymers• Dr. David Giles• Dr. Debbie Schneiderman• Matt Irwin• Maxwell Nagarajan

Pressure Sensitive Adhesives• Dr. Tessie Panthani• McKenzie Coughlin• Joel Updyke

Blown Film Extrusion• Dr. Mike Manno• Tuoqi Li• Liangliang Gu• Jacob Wright• Joseph Schaefer

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Acknowledgements

CollaboratorsChewing Gum• Prof. Marc Hillmyer• Prof. Sangwoo Lee• Prof. Randy Ewoldt• Dr. Luca Martinetti• Dr. Mark Martello• Dr. Debbie Schneiderman• David Giacomin• Renxuan Xie• Willy Voje• Tao Yang• Les Morgret• Rafael Bras• Niku Tseng

FundingL.E. and D.H. Scriven Fellowship

Facilities• Minnesota Characterization Facility• Polymer Characterization Facility• Hillmyer Group

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Acknowledgements, part 2

Bates Group MacoskoGroup

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Acknowledgements, part 3

Maxwell Nagarajan

(MIT)

Sangwoo Lee (RPI)

Frank Bates Chris Macosko

Mentors Army of undergraduate researchers

Team Foam

Willy Voje(U. Washington)

Marc Hillmyer

Joel Updyke

McKenzie Coughlin

Jacob Wright

Joseph Schaefer

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Acknowledgements, part 4

Fellow graduate students

Mannion Clan

Matt IrwinTessie Panthani Debbie Schneiderman

Jeff TingSid Chanpuriya

Meghan Peter Brian a.k.a. “Dad”

Elizabeth a.k.a. “Mother”

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Acknowledgements, part 5

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Thesis Outline

Chapter 2 Chapter 4 Chapter 6

Chapter 3 Chapter 5 Chapter 7

Chewing Gum Branched Multiblock Copolymers Practical Materials

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Rheological Design of Sustainable Block CopolymersSafety moment: proper hand washingRheological designBlock copolymersSustainabilityThesis OutlineNext generation chewing gumGum materialsLinear viscoelasticity (LVE): oscillatory shearStart up of steady uniaxial extensionBlock copolymer blends for chewing gum applicationsABA triblock/AB diblock blends: extensionThree component systemSynthesized polymersEffect of triblock compositionEffect of diblock molecular weightBlends for chewing and bubble gumsThesis OutlineBlown film extrusionOne commercial success story: poly(lactide) (PLA)Deficiencies of commercial PLAToughening PLA with multiblock architectureTuning processability with long chain branchingSynthesis and characterizationEstimating branching from SEC with multi-angle light scattering (MALS)Key advantages of branched multiblockKey limitation: gelationNew approach: A2 + B2/B3Estimating branching from SEC with multi-angle light scattering (MALS)Extensional behaviorOutlookThesis OutlineAcknowledgementsAcknowledgements, part 2Acknowledgements, part 3Acknowledgements, part 4Acknowledgements, part 5Thesis Outline