Synthesis and Characterization of New Polyamides, Poly(amide-imide)s, Polyimides
and Polyurethanes Bearing Thiourea Moieties
A Dissertation Submitted to the Department of Chemistry, Quaid-i-Azam University, Islamabad, in partial fulfillment of the
requirements for the degree of
Doctor of Philosophy
In
Chemistry
By
Ayesha Kausar
Department of Chemistry Quaid-i-Azam University
Islamabad, Pakistan
(2011)
IN THE NAME OF ALLAH
THE MOST COMPASSIONATE &
MERCIFUL
“Allah will rise up, to ranks, those of you who
believe and who have been granted Knowledge.
And Allah is well-acquainted with all ye do”.
(AL-QURAN 58:11)
DECLARATION
This is to certify that the dissertation submitted by Ms. Ayesha Kausar is accepted in its present form by the department of Chemistry, Quaid-i-Azam University,
Islamabad, as satisfying the requirements for the award of degree of Doctor of Philosophy
in Chemistry.
Supervisor: ________________________ Dr. M. Ilyas Sarwar Associate Professor Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan Chairman: ________________________ Department of Chemistry Prof. Dr. Saqib Ali
Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan
Head of Section: ________________________ Inorganic/Analytical Chemistry Prof. Dr. Amin Badshah
Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan
External Examiner: ________________________
External Examiner: ________________________
DEDICATED
TO
MY MOTHER & LATE FATHER
ACKNOWLEDGEMENTS
All praises and glories to the Almighty Allah, Who bestowed the man with wisdom,
perception and intellect. Peace and blessings of Allah be upon the Prophet Muhammad who
urged mankind to pursue knowledge and cognizance.
An appreciation merely with a few words seems to be inappropriate to gratefully
acknowledge my research supervisor Dr. M. Ilyas Sarwar, Associate Professor, Department
of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan for his painstaking endurance
and direction during my doctoral program. He not only provided the indispensable guidance,
nevertheless encouraged an unrestrained approach to research that fostered an incredibly
creative environment for research, allowing me to broaden my knowledge in several areas of
polymer science.
I, indeed, would like to extend my profound sense of gratification to my foreign
supervisor Dr. Cafer T. Yavuz, Assistant Professor, Graduate School of EEWS, KAIST
(Korea Advanced Institute of Science & Technology), for providing me an opportunity to
work as a visiting research fellow in his group and allowing me an access to various required
instruments during my foreign research epoch.
I am deeply indebted to Prof. Dr. Saqib Ali, Chairman, Department of Chemistry, for
providing me research facilities during my research period.
I gratefully acknowledge the monetary support granted by Higher Education
Commission of Pakistan (HEC) under Indigenous 5000 PhD Fellowship Scheme Batch-III
(063-111354-Ps3-068)” and “International Research Support Initiative Program (IRSIP 16
PS-08)” to peruse my research work at Graduate School of EEWS, KAIST, Daejeon,
Republic of Korea.
It is also proud privilege to on record my sincere thanks to Prof. Dr. Zahoor Ahmad,
Faculty of science, Kuwait University, Kuwait, and Prof. Dr. Muhammad Ishaq, Department
of Chemistry, Quaid-i-Azam University, Islamabad, whose valuable discussions and advice
eased and strengthened the learning experience.
Especially worth mentioning is Dr. Sonia Zulfiqar for her continuous encouragement
and support throughout my doctoral program.
I would also like to thank Dr. Liaquat Ali for providing molecular weight analysis of
my polymer samples, and for his expertise with respect to GPC analysis.
Moreover, my heartfelt gratitude to Dr. Saima and all my lab fellows working at the
Department of Chemistry, Quaid-i-Azam University, Islamabad, for their polite and
considerate attitude during my reside in the department.
Last but not the least, special thanks to my family members: my mother, grand mother,
loving sister Dr. Maher, brothers Maj. Malik Hanif, Malik Umer, Malik Mustafa, Malik
Ibrahim and Dr. Malik Humanyun, bhabis, uncle Sajjad Kayani, and others for their
continuous love, support and cooperation throughout my academic career.
Though, many have not been mentioned, none is forgotten. Ayesha Kausar
Synthesis and Characterization of New Polyamides, Poly(amide-imide)s, Polyimides
and Polyurethanes Bearing Thiourea Moieties
By
Ayesha Kausar
Department of Chemistry Quaid-i-Azam University
Islamabad, Pakistan
(2011)
ABSTRACT This thesis primarily addresses the systematic modification of polyamides, poly(amide-
imide)s, polyimides and polyurethanes to yield high performance poly(thiourea-amide)s,
poly(thiourea-amide-imide)s, poly(thiourea-ether-imide)s, poly(phenylthiourea-azomethine-
imide)s, poly(urethane-thiourea)s, poly(urethane-thiourea-imide)s and poly(urethane-
azomethine-thiourea)s. The foremost goal of current research is the structural modification of
polymers exploiting the synthetic chemistry to attain excellent solubility via slightly disrupting
polymer chain regularity and packing. Various synthetic schemes were developed for the
inclusion of thiourea moieties along with other desired linkages in these polymers. The designed
monomers (dinitro, diamines, dicarboxylic acids, diacid chlorides, diols and diisocyanates)
bearing pre-formed linkages were then synthesized and employed for the preparation of novel
thiourea-based polymeric materials. The incorporation of different functional groups provides an
opportunity to control certain physical properties such as solvent miscibility, ηinh, crystallinity,
molecular weight, thermal stability and flame retardancy of the resulting polymers. The effect of
thiourea and other functional groups on the properties of newly synthesized polymers were
scrutinized together with their structure-property relationship. Major tools utilized for the
examination of polymer properties are FTIR, 1H NMR, solubility, viscometry, GPC, TGA, DSC
and XRD. Novel thiourea-based polymers demonstrated outstanding thermal stability without
deteriorating their organosolubility or processability. Another objective of the work was to
evaluate the expedient applications and potential relevance of these valuable high-performance
materials for advanced technologies. The processable poly(thiourea-amide)s, poly(thiourea-
amide-imide)s, poly(thiourea-ether-imide)s and poly(urethane-azomethine-thiourea)s were found
to have superior thermal stability as well as non-flammability. Poly(phenylthiourea-azomethine-
imide)s having C=S and –C=N– moieties can act as imminent contenders to fabricate certain
electrically conducting materials. Poly(thiourea-amide)s, in addition to the excellent solubility
and thermal resistance, can be employed as solid extracting phases for the elimination of
environmentally toxic metal ions from aqueous media. Prior to this effort, reported in peer-
reviewed journals, synthesis of high temperature polymers bearing C=S entity was an unexplored
area. Easy processability, high molar mass, heat and flame stability, electrical conductivity, etc,
depict their high adaptability in future, rendering them backbone materials in polymer science.
i
CONTENTS
A i
C ii
L xi
L xi
L xx
L xx
C
1. 1
1. 2
4
6
8
8
8
8
di
9
10
10
11
bstract
ontents
ist of Abbreviations ii
ist of Table x
ist of Schemes ii
ist of Figures vi
HAPTER 1
INTRODUCTION
1 Polyamides
1.1.1 Hydrogen bonding in polyamides
1.1.2 Crystallinity in polyamides
1.1.3 Synthetic routes to polyamides
1.1.3.1 Low-temperature polycondensation
1.1.3.2 Solution polycondensation of diamines and diacid chlorides
1.1.3.3 Interfacial polycondensation technique
1.1.3.4 Polyamides via direct polycondensation of dicarboxylic acids and amines
1.1.3.5 Polycondensation of diisocyanates and dicarboxylic acids
1.1.3.6 Polycondensation of N-silylated diamines and diacid chlorides
1.1.3.7 Microwave-assisted polycondensation
ii
11
11
12
13
15
15
16
17
18
20
22
1. 23
24
24
24
25
26
26
27
27
30
1. 33
34
1.1.3.8 Alternative polymerization methods
1.1.4 Structure-property relationship in polyamides
1.1.4.1 Flexible linkages in polyamides
1.1.4.2 Polyamides containing pendant alkyl or aryl group
1.1.4.3 Fluorinated polyamides
1.1.4.4 Substituted isophthalic acid monomers
1.1.5 Polyamides with specialty properties and applications
1.1.5.1 Optically active polyamides
1.1.5.2 Polyamides in membrane technologies
1.1.5.3 Polyamides with selective receptors and environmental applications
1.1.5.4 Polyamides with outstanding thermal stability and flame retardancy
2 Poly(amide-imide)s
1.2.1 Synthesis of poly(amide-imide)s
1.2.1.1 Amide-imide forming reaction
(a) Acid chloride or acid route
(b) Diisocyanate route
(c) Hydrazide route
1.2.1.2 Formation of imide linkage via monomers containing amide unit
1.2.1.3 Formation of amide linkage via monomers containing imide unit
1.2.2 Structure property relationship in poly(amide-imide)s
1.2.3 Poly(amide-imide)s with specialty properties and applications
3 Polyimides
1.3.1 Synthetic routes to polyimides
iii
34
34
35
37
37
38
1.
38
40
1.fo
41
41
41
41
43
46
47
1. 47
48
49
53
53
54
54
1.3.1.1 Conventional two-step method via poly(amic-acid)s
(a) Thermal imidization of poly(amic-acid)s
(b) Chemical imidization of poly(amic-acid)s
(c) Solution imidization of poly(amic-acid)s
1.3.1.2 Polyimides via poly(amic-ester)s or poly(amic-amide)s precursors
1.3.1.3 Polyimides via polyisoimide precursors
3.1.4 Single-step imidization using high temperatures
1.3.1.5 Polyimides via reacting dianhydrides and diisocyanates
3.1.6 Metal catalyzed carbon-carbon coupling route to polyimide rmation
1.3.2 Structure-property relationship in aromatic polyimides
1.3.3 Applications of polyimides
1.3.3.1 Polyimides in fuel cell application
1.3.3.2 Polyimides in LCD technology
1.3.3.3 Polyimide membranes for bio-gas purification
1.3.3.4 Miscellaneous uses of polyimides
4 Polyurethanes
1.4.1 Hydrogen bonding in polyurethanes
1.4.2 Reactivity of isocyanate group
1.4.3 Synthetic methodologies for polyurethanes
1.4.3.1 Synthesis of [n]-polyurethanes using a versatile and mild reagent
1.4.3.2 Synthesis of AB type aromatic polyurethane via pyrolysis
1.4.3.3 Polyurethane via non-isocyanate synthetic method
iv
55
56
58
61
62
63
64
65
66
66
67
72
74
74
76
77
78
78
79
1 79
83
85
87
1.4.3.4 Polyurethane via ring opening polymerization (ROP)
1.4.3.5 Phosgenation route to polyurethanes
1.4.3.6 Synthetic methods for segmented polyurethane elastomers
1.4.4 Structure-Property relationship in polyurethanes
1.4.5 Applications of polyurethanes
1.5 Experimental techniques employed in present work
1.5.1 Fourier transform infrared (FTIR) Spectroscopy
1.5.2 Nuclear magnetic resonance (NMR) Spectroscopy
1.5.3 Elemental analysis
1.5.4 Solubility assessment
1.5.5 Inherent viscosity
1.5.6 Gel permeation chromatography (GPC)
1.5.7 Thermogravimetric analysis (TGA)
1.5.8 Differential scanning calorimetry (DSC)
1.5.9 Dynamic mechanical analysis
1.5.10 X-ray diffraction
1.5.11 Flame retardancy (Limiting Oxygen Index)
1.5.12 Solid-liquid extraction tests
1.5.13 Chemical resistance
.6 Present Work
1.6.1 Aromatic and aromatic-aliphatic poly(thiourea-amide)s
1.6.2 Poly(thiourea-amide-imide)s
1.6.3 Poly(thiourea-ether-imide)s and poly(phenylthiourea-azomethine-imide)s
v
90
94
95
95
ba
10
10
10
10
10
ph
11
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11
11
11
(P
11
11
11
12
12
1.6.4 Thiourea-derived polyurethanes
1.6.5 Novelty and scope of the current research endeavor
CHAPTER 2
2. EXPERIMENTAL
2.1 Chemicals
2.2 Synthesis of aromatic and semi-aromatic poly(thiourea-amide)s from thiourea-sed flexible diacid chlorides
2
2.2.1 General procedure for the preparation of diisothiocyanates (DITCs) 2
2.2.2 Synthesis of terephthaloyl bis(3-(3-carboxyphenyl) thiourea) (DACa) 2
2.2.3 Synthesis of terephthaloyl bis(3-(3-chlorocarbonylphenyl) thiourea) (DACLa)
6
2.2.4 Polyamide synthesis 9
2.3 Synthesis of poly(thiourea-amide)s using 1-(4-aminobenzoyl)-3-(3-amino- enyl) thiourea
2
2.3.1 Preparation of 4-nitrobenzoyl isothiocyanates (NBITC) 2
2.3.2 Synthesis of 1-(4-nitrobenzoyl)-3-(3-nitrophenyl) thiourea (NBNPT) 2
2.3.3 Synthesis of 1-(4-aminobenzoyl)-3-(3-aminophenyl) thiourea (ABAPT) 4
2.3.4 Synthesis of PAMs 7
2.4 Synthesis of novel aromatic and aromatic-aliphatic poly(thiourea-amide)s TAMs)
9
2.4.1 Procedure for the preparation of diisothiocyanates (DITCs) 9
2.4.2 Synthesis of terephthaloyl bis (3-(3-nitrophenyl) thiourea (BNPTa) 9
2.4.3 Synthesis of terephthaloyl bis (3-(3-aminophenyl) thiourea) (BAPTa) 2
2.4.4 Synthesis of PTAMs 5
vi
ph
13
13
13
13
13
13
13
ca
13
2
14
14
14
14
14
am
14
14
15
15
15
2.5 Synthesis of poly(thiourea-amide-imide)s using 1-(1,3-dioxo-2-(4-amino-enyl)isoindolin-5-yl)carbonyl-3-(4-aminophenyl)thiourea
0
2.5.1 Preparation of trimellitic anhydride isothiocyanate (TMAI) 0
2.5.2 Synthesis of 1-(1,3-dioxo-2-(4-nitrophenyl)isoindolin-5-yl) carbonyl-3- (4- nitrophenyl)thiourea (DNICNT)
1
2.5.3 Synthesis of 1-(1,3-dioxo-2-(4-aminophenyl)isoindolin-5-yl)carbonyl-3-(4 aminophenyl)thiourea (DAICAT)
3
2.5.4 Synthesis of PAIs 5
2.6 Synthesis of poly(thiourea-amide-imide)s using CPDITNC 7
2.6.1 Preparation of trimellitic anhydride isothiocyanate (TMAI) 7
2.6.2 Synthesis of 2-(3-(2-(3-carboxypyridin-2-yl)-1,3- dioxoisoindoline-5-rbonyl) thioureido)nicotinic acid (CPDITNA)
8
.6.3 Synthesis of 2-(3-(2-(3-(chlorocarbonyl)pyridin-2-yl)-1,3-dioxo- isoindoline-5-carbonyl)thioureido)nicotinoylchloride (CPDITNC)
0
2.6.4 Synthesis of PTAIs 1
2.7 Synthesis of poly(thiourea-ether-imide)s from 4,4'-oxydiphenyl bis(thiourea) 5
2.7.1 Synthesis of 4,4'-oxydiphenyl bis(thiourea) (ODPBT) 5
2.7.2 Preparation of polymers 7
2.8 Synthesis of poly(phenylthiourea-azomethine-imide)s based on N-(4-chloro-3-inobenzal)N'(4-aminophenyl)thiourea
9
2.8.1 Synthesis of N-(4-chloro-3-nitrobenzal)N'(4-nitrophenyl) thiourea (CNBPT)
9
2.8.2 Synthesis of N-(4-chloro-3-aminobenzal)N'(4-aminophenyl) thiourea (CABPT)
2
2.8.3 Preparation of polyimides 4
2.9 Synthesis of poly(phenylthiourea-azomethine-imide)s based on 1,4- phenylene bis((E)-1-(4-chloro-3-aminobenzylidene)thiourea)
6
vii
2.9.1 Synthesis of 1,4-phenylene bis((E)-1-(4-chloro-3-nitrobenzylidene-)th
5
15
16
16
16
16
16
17
17
17
17
17
17
((
17
17
18
18
18
2 18
(I
18
iourea) (PCNBT) 1 6
2.9.2 Synthesis of 1,4-phenylene bis((E)-1-(4-chloro-3-aminobenzyli- dene)thiourea) (PCABT)
9
2.9.3 Preparation of poly(phenylthiourea-azomethine-imide)s (PPTAIs) 2
2.10 Synthesis of poly(urethane-thiourea)s from thiourea-based diol chain extenders 3
2.10.1 Preparation of terephthaloyl diisothiocyanate (TDI) 3
2.10.2 Synthesis of thiourea-based chain extenders 4
2.10.3 Synthesis of segmented PURs (one-step procedure) 8
2.11 Synthesis of poly(urethane-thiourea-imide)s using IPCT 1
2.11.1 Synthesis of 1-(3-hydroxyphenyl)thiourea 1
2.11.2 Synthesis of 3-(3-((4-isocyanatophenyl)carbamoyl)thioureido)phenyl -4-isocyanatophenylcarbamate (IPCT)
1
2.11.3 Synthesis of isocyanate terminated prepolymer 3
2.11.4 Synthesis of segmented poly(urethane-thiourea-imide)s 4
2.11.5 Film casting 8
2.12 Synthesis of poly(urethane-azomethine-thiourea)s from 1,4-phenylene bis E)-1-(4-hydroxobenzylidene)thiourea)
8
2.12.1 Synthesis of 1,4-phenylene bis((E)-1-(4-hydroxobenzylidene) thiourea) (PBHBT)
8
2.12.2 Synthesis of segmented PUATs (one-step procedure) 1
2.12.3 Film casting 2
2.13 Synthesis of poly(urethane-thiourea)s from IBPCOT diisocyanate 4
.13.1 Preparation of isophthaloyl diisothiocyanate (IDI) 4
2.13.2 Synthesis of isophthaloyl bis (3-(3-hydroxoopyridyl) thiourea) BHPT)
4
viii
2.py
18
2. 18
19
19
fr
19
19
19
19
19
20
20
20
20
20
B
20
20
20
21
21
21
13.3 Synthesis of isophthaloyl bis (3-((4-isocyanatophenylcarbamoyloxy) ridyl) thiourea) (IBPCOT)
4
13.4 Synthesis of poly(urethane-thiourea)s (PUTs) 7
2.14 Measurements 1
CHAPTER 3
3. RESULTS AND DISCUSSION 3
3.1 Aromatic and semi-aromatic poly(thiourea-amide)s (PAMDs) derived om DACLa-d
3
3.1.1 Organosolubility of PAMDs 5
3.1.2 Viscometry and molecular weight measurements of PAMDs 6
3.1.3 Thermal analyses of PAMDs 7
3.1.4 X-ray powder diffraction of PAMDs 9
3.2 Poly(thiourea-amide)s (PAMs) based on ABAPT 0
3.2.1 Organosolubility of PAMs 1
3.2.2 Viscometry and molecular weight measurements of PAMs 2
3.2.3 Thermal stability and flame retardancy of PAMs 3
3.2.4 X-ray powder diffraction of PAMs 6
3.3 Aromatic and aromatic-aliphatic poly(thiourea-amide)s (PTAMs) derived from APTa-d
7
3.3.1 Organosolubility of PTAMs 7
3.3.2 Viscometry and molecular weight measurements of PTAMs 9
3.3.3 Thermal analyses of PTAMs 0
3.3.4 X-ray powder diffraction of PTAMs 4
3.3.5 Solid–liquid extraction of toxic metal ions by poly(thiourea-amide)s 6
ix
21
3 21
3 22
3 22
3 22
ba
22
3. 22
3. 22
3. 22
23
23
3. 23
3. 23
3. 23
3. 23
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24
3. 24
3. 24
3. 24
24
3. 24
3.4 Poly(thiourea-amide-imide)s (PAIs) from DAICAT 8
.4.1 Organosolubility of PAIs 9
.4.2 Viscometry and molecular weight measurements of PAIs 0
.4.3 Thermal stability and flame retardancy of PAIs 2
.4.4 X-ray powder diffraction of PAIs 4
3.5 Poly(thiourea-amide-imide)s (PTAIs) bearing C=S and pyridine moieties in the ckbone
5
5.1 Organosolubility of PTAIs 6
5.2 Viscometry and molecular weight measurements of PTAIs 7
5.3 Thermal analyses of PTAIs 9
3.5.4 X-ray powder diffraction of PTAIs 1
3.6 Poly(thiourea-ether-imide)s (PTEIs) 2
6.1 Organosolubility of PTEIs 3
6.2 Viscometry and molecular weight measurements of PTEIs 4
6.3 Thermal stability and flame retardancy of PTEIs 5
6.4 X-ray powder diffraction of PTEIs 8
3.7 New generation of poly(phenylthiourea-azomethine-imide)s (PIs) 9
3.7.1 Organosolubility of PIs 0
7.2 Viscometry and molecular weight measurements of PIs 1
7.3 Thermal stability of PIs 2
7.4 X-ray powder diffraction of PIs 4
3.8 Poly(phenylthiourea-azomethine-imide)s (PPTAIs) 5
8.1 Organosolubility of PPTAIs 6
x
3. 24
3. 24
3. 25
25
3. 25
3. 25
3. 25
3. 25
25
3. 25
3. 25
3. 26
3. 26
3. 26
26
3. 26
3. 26
3. 26
3. 27
3. 27
3. 27
27
3. 27
8.2 Viscometry and molecular weight measurements of PPTAIs 7
8.3 Thermal stability of PPTAIs 7
8.4 X-ray powder diffraction of PPTAIs 0
3.9 Poly(urethane-thiourea)s (PURs) derived from TBHPT/TBNT 1
9.1 Organosolubility of PURs 2
9.2 Viscometry and molecular weight measurements of PURs 3
9.3 Thermal stability of PURs 3
9.4 XRD powder analysis of PURs 6
3.10 Poly(urethane-thiourea-imide)s (PUTIs) 7
10.1 Organosolubility of PUTIs 8
10.2 Viscometry and molecular weight measurements of PUTIs 8
10.3 Thermal stability of PUTIs 0
10.4 Crystallinity of PUTIs 3
10.5 Chemical resistance of poly(urethane-thiourea-imide)s 4
3.11 Poly(urethane-azomethine-thiourea)s (PUATs) from PBHBT 5
11.1 Organosolubility of PUATs 6
11.2 Viscometry and molecular weight measurements of PUATs 7
11.3 Thermal analysis of PUATs 7
11.4 Flame retardancy of PUATs 0
11.5 Crystallinity of PUATs 0
11.6 Chemical resistance of poly(urethane-azomethine-thiourea)s 0
3.12 Poly(urethane-thiourea)s (PUTs) from IBPCOT 1
12.1 Organosolubility of PUTs 2
xi
3. 27
3. 27
3. 27
27
27
28
12.2 Molecular weight analyses of PUTs 3
12.3 Thermal stability of PUTs 4
12.4 XRD powder analysis of PUTs 6
3.13 Brief outline of distinctive features of poly(thiourea-amide)s 7
3.14 Brief outline of distinctive features of poly(thiourea-amide-imide)s 9
3.15 Brief outline of distinctive features of poly(thiourea-ether-imide)s 0
3.16 Brief outline of distinctive features of poly(phenylthiourea-azomethine-imide)s
28
28
28
28
28
32
0
3.17 Brief outline of distinctive features of thiourea-based polyurethanes 1
3.18 Conclusions 3
3.19 Future prospects 8
REFERENCES 9
LIST OF PUBLICATIONS 6
xii
LIST OF ABBREVIATIONS
ABA 3-Aminobenzoic acid
ABAPT = 1-(4-Aminobenzoyl)-3-(3-aminophenyl) thiourea AP Adipoyl chloride
Ac2O Acetic anhydride
BAPFDS 9,9-Bis(4-aminophenyl) fluorene-2,7-disulfonic acid
BTDA Benzophenonetetracarboxylic dianhydride
BTB 1,3-Bis(trimellitimido)-2,4,6-trimethyl benzene
BMDI 4,4-Diphenyl methane diisocyanates
BABPI N,N'-Bis(4'-amino-4-biphenylene) isophthalamide
CaCl2 Calcium chloride CO2 Carbon dioxide CABPT = N-(4-chloro-3-aminobenzal)N'(4-aminophenyl)thiourea
CDA Cardo diamine
CHCl3 Chloroform
CHP 1-Cyclohexyl-2-pyrrolidinone
CH4 Methane CH2Cl2 Dichloromethane CDA Cardo diamine
CPDITNA 2-(3-(2-(3-Carboxypyridin-2-yl)-1,3-dioxoisoindoline-5-carbonyl)-thioureido)nicotinic acid
CPDITNC = 2-(3-(2-(3-(Chlorocarbonyl)pyridin-2-yl)-1,3-dioxoisoindoline-
5-carbonyl)thioureido)nicotinoyl chloride
CNBPT N-(4-chloro-3-nitrobenzal)N'(4-nitrophenyl)thiourea
xiii
CuS Copper sulfide
DADO 1,8-Diamino-3,6-dioxaoctane
DAICAT = 1-(1,3-Dioxo-2-(4-aminophenyl)isoindolin-5-yl)carbonyl-3-(4-a-minophenyl)thiourea
DAN 1,5-Diamino naphthalene DAM 2,4-Diamino mesitylene DCC N,N-Dicyclohexylcarbodiimide DBTDL Dibutyltin dilaurate DITCs Diisothiocyanates DMF Dimethylformamide
DMSO Dimethylsulfoxide
DMAc N,N′-Dimethylacetamide
DPA Diphenylmethane diamine
DNICNT = 1-(1,3-Dioxo-2-(4-nitrophenyl)isoindolin-5-yl)carbonyl-3-(4-nit-ro phenyl)thiourea
DMDB 2,2'-Dimethyl-4,4'-diamino biphenyl DMA Dynamic mechanical analysis DMTA Dynamic mechanical thermal analysis DSC Differential scanning calorimetry Et-OH Ethanol FTIR Fourier Transform Infrared GPC Gel-permeation chromatography HDI 1,6-Hexamethylene diisocyanate HMPA Hexamethylphosphoramide H12MDI 4,4'-Diisocyanato dicyclohexylmethane HCl Hydrochloric acid H2S Hydrogen sulphide
xiv
IBHPT Isophthaloyl bis (3-(3-hydroxoopyridyl)thiourea) IBPCOT Isophthaloyl bis (3-((4-isocyanatophenylcarbamoyloxy)pyridyl)
thiourea)
IDI Isophthaloyl diisothiocyanate ITO Indium tin oxide IPC Isophthaloyl chloride IPCT 3-(3-((4-Isocyanatophenyl)carbamoyl)thioureido)phenyl 4-iso-
cyanatophenylcarbamate
KF Potassium flouride
KSCN Potassium thiocyanate
KOH Potassium hydroxide
LAD Linear aromatic diamines LCAL Liquid crystal alignment layer LC Liquid crystal LCD Liquid crystals display LiCl Lithium chloride LOI Limiting Oxygen Index
MDA Methylene dianiline MDI Methylene diisocyanate Mn Number average molecular weight Mv Viscosity molecular weight Mw
Mw/Mn Weight average molecular weight
Polydispersity index MW Microwave radiation Mz Size average molecular weight NaCl Sodium chloride NBITC 4-Nitrobenzoyl isothiocyanate
xv
NBNPT 1-(4-Nitrobenzoyl)-3-(3-nitrophenyl)thiourea NMP N-methylpyrrolidone NMR Nuclear magnetic resonance OAP Optically active polymers ODA 4,4'-Oxydianiline ODPA 4,4'-Oxydiphthalic anhydride ODADS 4,4'-Diaminodiphenyl ether-2,2'-disulfonic acid ODPBT 4,4'-Oxydiphenyl bis(thiourea) PAIs Poly(amide-imide)s PBD 1,4-Polybutadienediol
PBHBT = 1,4-Phenylene bis((E)-1-(4-hydroxobenzylidene)thiourea)
PCABT 1,4-Phenylenebis((E)-1-(4-chloro-3-aminobenzylidene)- thiourea)
PCNBT = 1,4-Phenylene bis((E)-1-(4-chloro-3-nitrobenzylidene)thiourea)
PCP p-Chlorophenol PDA 1,4-Phenylene diamine PDI Polydispersity index PE Polyethylene PEEK Poly(ether ether ketone) PEG Polyethylene glycol PEO Polyethylene oxide PI Polydispersity index PIB Polyisobutylene
PMDA
PPA Pyromellitic dianhydride
Polyphosphoric acid PPO Polypropylene oxide
xvi
PP Polypropylene PS Polystyrene PSF Polysulfone PTEIs Poly(thiourea-ether-imide)s PTMO Polytetremethylene oxide
PUR Polyurethanes PUATs Poly(urethane-azomethine-thiourea)s PUTIs Poly(urethane-thiourea-imide)s PVC Polyvinyl chloride Py Pyridine RI Refractive index RMA Rosin-maleic anhydride RO Reverse osmosis ROP Ring opening polymerization SC Sebacoyl chloride SEC Size exclusion chromatography STN Super twisted nematic TBHPT Terephthaloyl bis(3-(2-hydroxopyridyl) thiourea) TBNT Terephthaloyl bis(3-(5-naphtholyl) thiourea) TDI Toluene diisocyanate TEM Transmission electron microscopy
TFDB 2,2'-Bis(trifluoromethyl)-4,4′-diamino biphenyl TGA Thermogravimetric analysis Tg Glass transition temperature THF Tetrahydrofuran
Tm Crystalline melting point TMA Thermal mechanical analysis
xvii
TMAC Trimellic anhydride chloride TMAI Trimellitic anhydride isothiocyanate TMB Trimellitimide-N-benzoic acid TMC Trimesoyl chloride TMU Tetramethylurea TN Twisted Nematic TPC Terephthaloyl chloride TPP Triphenyl phosphite UV Ultraviolet
WAXD Wide angle X-ray diffraction
XRD X-ray diffraction
xviii
LIST OF TABLES
Table 1.1: Few representative substituted isophthalic acid monomers. 16
Table 1.2: Representative monomers for organosoluble poly(amide-imide)s. 28
Table 1.3: Typical polyimides used as alignment layers for LCDs. 45
Table 1.4: Chemical structures of typical polyol soft segment. 59
Table 1.5: Novel monomers containing thiourea groups synthesized in the present work.
80
Table 2.1: Monomers used for the synthesis of various series of poly(thiourea-amide)s.
96
Table 2.2: Monomers used for the synthesis of different thiourea-based poly(amide-imide)s.
97
Table 2.3: Monomers employed for the synthesis of thiourea-based polyimides. 98
Table 2.4: Monomers employed for the synthesis of thiourea-based segmented polyurethanes.
99
Table 2.5: Other chemicals and solvents used in the present work. 100
Table 2.6: FTIR data of different PTAMs [296]. 127
Table 3.1: Solubility behavior of poly(thiourea-amide)s [294]. 195
Table 3.2: ηinh , Mw, PDI and % yield of PAMDs [294]. 196
Table 3.3: Thermal analyses data of various PAMDs [294]. 198
Table 3.4: Solubility behavior of PAMs [295]. 201
Table 3.5: ηinh , Mw, PDI and % yield of PAMs [295]. 202
Table 3.6: Thermal analyses data of PAMs [295]. 203
Table 3.7: Solubility behavior of PTAMs [296]. 208
Table 3.8: ηinh , Mw, PDI and % yields of PTAMs [296]. 209
xix
Table 3.9: Thermal analyses data of various PTAMs [296]. 211
Table 3.10: Solid–liquid extraction of various metal cations from aqueous solution by solid PTAM 1b and 2b [296].
217
Table 3.11: Solubility behavior of PAIs [297]. 220
Table 3.12: ηinh, Mw, PDI and % yield of PAIs [297]. 221
Table 3.13: Thermal analyses data of different PAIs [297]. 222
Table 3.14: Solubility behavior of PTAIs [298]. 227
Table 3.15: ηinh, Mw, PDI and % yield of PTAIs [298]. 228
Table 3.16: Thermal analyses data of different PTAIs [298]. 230
Table 3.17: Solubility behavior of PTEIs [299]. 234
Table 3.18: ηinh, Mw, PDI and % yield of PTEIs [299]. 235
Table 3.19: Thermal analyses data of different PTEIs [299]. 236
Table 3.20: Solubility behavior of PIs [300]. 240
Table 3.21: ηinh, Mw, PDI and % yield of PIs [300]. 242
Table 3.22: Thermal analyses data of different PIs [300]. 243
Table 3.23: Solubility behavior of PPTAIs [301]. 247
Table 3.24: ηinh, Mw, PDI and % yield of PPTAIs [301]. 248
Table 3.25: Thermal analyses data of different PPTAIs [301]. 249
Table 3.26: Solubility behavior of PURs [302]. 252
Table 3.27: ηinh, Mw, PDI and % yield of PURs [302]. 254
Table 3.28: Thermal analyses data of different PURs [302]. 255
Table 3.29: Solubility behavior of PUTIs [303]. 258
Table 3.30: ηinh, Mw, PDI and % yield of PUTIs [303]. 259
xx
Table 3.31: Thermal analyses data of different PUTIs [303]. 261
Table 3.32: Chemical resistance behavior of PUTIs [303]. 264
Table 3.33: Solubility behavior of PUATs [304]. 266
Table 3.34: ηinh, Mw, PDI and % yield of PUATs [304]. 267
Table 3.35: Thermal analyses data of different PUATs [304]. 268
Table 3.36: Chemical resistance behavior of PUATs [304]. 271
Table 3.37: Solubility behavior of PUTs. 272
Table 3.38: ηinh, Mw, PDI and % yield of PUTs. 273
Table 3.39: Thermal analyses data of PUTs. 275
xxi
LIST OF SCHEMES Scheme 1.1: Solution polycondensation of a diamine and a diacid chloride. 8
Scheme 1.2: Interfacial polycondensation of diamine and diacid chloride. 9
Scheme 1.3: Direct polycondensation leading to polyamide using TPP and Py. 10
Scheme 1.4: Condensation of N-silylated amine and acid chloride. 11
Scheme 1.5: Synthesis of fluorine-containing aromatic polyamides. 15
Scheme 1.6: Optically active polyamides using aromatic diacids and diisocyanates.
17
Scheme 1.7: Synthesis of 5-isocyanato-isophthaloyl chloride for RO membranes. 19
Scheme 1.8: Polychloro-substituted aromatic polyamides. 22
Scheme 1.9: Phosphorous-containing flame retardant polymers. 23
Scheme 1.10: Earliest route to poly(amide-imide)s. 25
Scheme 1.11 Poly(amide-imide)s derived from 2,4-bis(N-trimellitoyl)triphenylamine. 31
Scheme 1.12: Synthesis of Rosin derivative. 32
Scheme 1.13: Preparation of Kapton® polyimide. 35
Scheme 1.14: Mechanism of thermal imidization. 35
Scheme 1.15: Chemical dehydration of poly(amic acid). 36
Scheme 1.16: Mechanism for back conversion of amic acid to anhydride and amine. 37
Scheme 1.17: Polyimides via polyisoimide precursors. 39
Scheme 1.18: Polyimides via 7-membered cyclic ring intermediate. 40
Scheme 1.19: Polyimides via metal-catalyzed carbon-carbon coupling reaction. 41
Scheme 1.20: BAPFDS-based polyimides for fuel cell application. 42
xxii
Scheme 1.21: ODADS-based polyimides for fuel cell application. 43
Scheme 1.22. Formation of carbamic acid derivative. 50
Scheme 1.23: Urethane linkage formation. 51
Scheme 1.24: Urea linkage formation. 51
Scheme 1.25: Reaction between water and isocyanate. 51
Scheme 1.26: Formation of allophanate and biuret. 52
Scheme 1.27: Dimerization and trimerization of isocyanate. 53
Scheme 1.28: Formation of carbodiimides. 53
Scheme 1.29: Synthesis of [n]-polyurethanes (R= (CH2)4-12). 54
Scheme 1.30: Synthesis of AB type aromatic polyurethane. 54
Scheme 1.31: Synthesis of polyurethane via non-isocyanate synthetic method. 55
Scheme 1.32: Synthesis of polyurethane via ROP. 56
Scheme 1.33: Synthesis of toluene diisocyanate. 57
Scheme 1.34: Synthesis of diphenylmethylene diisocyanate. 57
Scheme 1.35: Two-step prepolymer method for synthesis of polyurethane. 61
Scheme 1.36: General scheme for the synthesis of aromatic/semiaromatic diisothio- cyanates.
84
Scheme 1.37: A synthetic route to poly(thiourea-amide)s from thiourea-based aromatic/aromatic-aliphatic diacid chlorides.
84
Scheme 1.38: Synthesis of anhydride-ring bearing isothiocyanate. 87
Scheme 1.39: A synthetic route to poly(thiourea-amide-imide)s from thiourea- and imide-ring bearing diacid chlorides.
87
Scheme 1.40: Synthesis of 1,4-phenylene bis(thiourea) using ammonium thiocyanate. 88
Scheme 1.41: Synthetic route to poly(thiourea-ether-imide)s from diamine bearing thiourea and ether moieties.
89
xxiii
Scheme 1.42: A synthetic route to poly(phenylthiourea-azomethine-imide)s. 90
Scheme 1.43: Synthesis of poly(urethane-thiourea)s. 91
Scheme 1.44: Synthesis of poly(urethane-thiourea-imide)s. 92
Scheme 1.45: Synthesis of poly(urethane-azomethine-thiourea)s. 93
Scheme 2.1: Scheme for the synthesis of diacid chloride monomers [294]. 103
Scheme 2.2: Scheme for the synthesis of PAMDs [294]. 109
Scheme 2.3: Scheme for the synthesis of ABAPT [295]. 115
Scheme 2.4: Scheme for the synthesis of PAMs [295]. 117
Scheme 2.5: Scheme for the synthesis of BAPTa-d [296]. 123
Scheme 2.6: Scheme for the synthesis of PTAMs [296]. 126
Scheme 2.7: Scheme for the synthesis of DAICAT [297]. 131
Scheme 2.8: Scheme for the synthesis of PAIs [297]. 136
Scheme 2.9: Scheme for the synthesis of CPDITNC [298]. 141
Scheme 2.10: Scheme for the synthesis of PTAIs [298]. 143
Scheme 2.11: Scheme for the synthesis of ODPBT and PTEIs [299]. 147
Scheme 2.12: Scheme for the synthesis of CABPT [300]. 152
Scheme 2.13: Scheme for the synthesis of PIs [300]. 154
Scheme 2.14: Scheme for the synthesis of PCABT [301]. 159
Scheme 2.15: Scheme for the synthesis of PPTAIs [301]. 161
Scheme 2.16: Scheme for the synthesis of diol monomers [302]. 165
Scheme 2.17: Scheme for the synthesis of PURs [302]. 169
Scheme 2.18: Scheme for the synthesis of monomer and prepolymer [303]. 174
Scheme 2.19: Scheme for the synthesis of poly(urethane-thiourea-imide)s [303]. 176
xxiv
Scheme 2.20: Scheme for the synthesis of PBHBT [304]. 179
Scheme 2.21: Scheme for the synthesis of PUATs [304]. 182
Scheme 2.22: Scheme for the synthesis of IBPCOT. 185
Scheme 2.23: Scheme for the synthesis of PUTs. 190
Scheme 3.1: Hydrogen-bonding in poly (thiourea-amide)s [294]. 194
xxv
LIST OF FIGURES
Figure 1.1: Enhancement of polymer processability via several approaches. 4
Figure 1.2: Amide to amide hydrogen bonding found in polyamides (nylon 6,6). 5
Figure 1.3: Folded chains in polymer crystallite. 7
Figure 1.4: Polyamides from bis (p-phenylthio) dibenzoic acid and various diamines. 12
Figure 1.5: Polyamides from aromatic diamine bearing adamantyl moiety.
13
Figure 1.6: Polyamide of 2,5-bis(4-aminophenyl)-3,4-diphenyl thiophene and IPC. 14
Figure 1.7: Copolyamide from 2,5-bis(4-chloroformyl phenyl)-3,4-diphenyl thiophene and diamines.
14
Figure 1.8: Aromatic polyisophthalamides for gas separation membranes. 20
Figure 1.9: Polyamides with host moieties for the extraction of cations. 21
Figure 1.10: Different types of cardo groups. 29
Figure 1.11: Poly(amide-imide)s by direct polycondensation of imide-containing diamines with aromatic diacids.
31
Figure 1.12: Assembly symbolizing a standard TN display. 44
Figure 1.13: Hydrogen bonding interaction in polyurethanes and polyureas. 49
Figure 1.14: Resonance structures of isocyanate group. 50
Figure 1.15: Urea and carbonate monomers for copolymerization. 55
Figure 1.16: Phenoxycarbonyloxymethyl ethylene carbonate. 56
Figure 1.17: Common diisocyanate building blocks for polyurethane. 58
Figure 1.18: Polyurethane chain extenders. 60
Figure 1.19: Plot of ηinh or ηred vs. change in concentration. 70
xxvi
Figure 1.20: Ubbelohde viscometer. 71
Figure 1.21: Schematic diagram representing GPC. 72
Figure 1.22: DMA analyzer. 76
Figure 1.23: The glass transition (Tg) in the storage modulus and tan δ. 77
Figure 2.1: FTIR spectra of DACa and DACLa [294]. 104
Figure 2.2: 1H NMR spectrum of DACa [294]. 104
Figure 2.3: 13C NMR spectrum of DACa [294]. 105
Figure 2.4: 1H NMR spectrum of DACLa[294].. 107
Figure 2.5: 13C NMR spectrum of DACLa [294]. 107
Figure 2.6: FTIR spectra of PAMDs [294]. 111
Figure 2.7: 1H NMR spectra of PAMDs [294]. 111
Figure 2.8: FTIR spectra of NBNPT and ABAPT [295]. 112
Figure 2.9: 1H NMR spectrum of NBNPT [295]. 113
Figure 2.10: 13C NMR spectrum of NBNPT [295]. 114
Figure 2.11: 1H NMR spectrum of ABAPT [295]. 116
Figure 2.12: 13C NMR spectrum of ABAPT [295]. 116
Figure 2.13: FTIR specta of PAMs [295]. 118
Figure 2.14: 1H NMR spectra of PAMs [295]. 118
Figure 2.15: FTIR spectra of BNPTa and BAPTa [296]. 120
Figure 2.16: 1H NMR spectrum of BNPTa [296]. 120
Figure 2.17: 13C NMR spectrum of BNPTa [296]. 121
Figure 2.18: 1H NMR spectrum of BAPTa [296]. 124
xxvii
Figure 2.19: 13C NMR spectrum of BAPTa [296]. 124
Figure 2.20: FTIR spectra of PTAM 1a-d [296]. 127
Figure 2.21: FTIR spectra of PTAM 2a-d [296]. 128
Figure 2.22: FTIR spectra of PTAM 3a-d [296]. 128
Figure 2.23: 1H NMR spectra of PTAM 1 a-d [296]. 129
Figure 2.24: 1H NMR spectra of PTAM 2 a-d [296]. 129
Figure 2.25: 1H NMR spectra of PTAM 3 a-d [296]. 130
Figure 2.26: FTIR spectra of DNICNT and DAICAT [297]. 132
Figure 2.27: 1H NMR spectrum of DNICNT [297]. 133
Figure 2.28: 13C NMR spectrum of DNICNT [297]. 133
Figure 2.29: 1H NMR spectrum of DAICAT [297]. 134
Figure 2.30: 13C NMR spectrum of DAICAT [297]. 135
Figure 2.31: FTIR spectra of PAIs [297]. 136
Figure 2.32: 1H NMR spectra of PAIs [297]. 137
Figure 2.33: FTIR spectra of CPDITNA and CPDITNC [298]. 138
Figure 2.34: 1H NMR spectrum of CPDITNA [298]. 139
Figure 2.35: 13C NMR spectrum of CPDITNA [298]. 139
Figure 2.36: 1H NMR spectrum of CPDITNC [298]. 142
Figure 2.37: 13C NMR spectrum of CPDITNC [298]. 142
Figure 2.38: FTIR spectra of PTAIs [298]. 144
Figure 2.39: 1H NMR spectra of PTAIs [298]. 144
Figure 2.40: FTIR spectrum of ODPBT [299]. 145
xxviii
Figure 2.41: 1H NMR spectrum of ODPBT [299]. 146
Figure 2.42: 13C NMR spectrum of ODPBT [299]. 146
Figure 2.43. FTIR spectra of PTEIs [299]. 148
Figure 2.44: 1H NMR spectra of PTEIs [299]. 149
Figure 2.45: FTIR spectra of CNBPT and CABPT [300]. 150
Figure 2.46: 1H NMR spectrum of CNBPT [300]. 151
Figure 2.47: 13C NMR spectrum of CNBPT [300]. 151
Figure 2.48: 1H NMR spectrum of CABPT [300]. 153
Figure 2.49: 13C NMR spectrum of CABPT [300]. 153
Figure 2.50: FTIR spectra of PIs [300]. 155
Figure 2.51: 1H NMR spectra of PIs [300]. 156
Figure 2.52: FTIR spectra of PCNBT and PCABT [301]. 157
Figure 2.53: 1H NMR spectrum of PCNBT [301]. 158
Figure 2.54: 13C NMR spectrum of PCNBT [301]. 158
Figure 2.55: 1H NMR spectrum of PCABT [301]. 160
Figure 2.56: 13C NMR spectrum of PCABT [301]. 160
Figure 2.57: FTIR spectra of PPTAIs [301]. 162
Figure 2.58: 1H NMR spectra of PPTAIs [301]. 163
Figure 2.59: FTIR spectra of diols [302]. 164
Figure 2.60: 1H NMR spectrum of TBHPT [302]. 166
xxix
Figure 2.61: 13C NMR spectrum of TBHPT [302]. 167
Figure 2.62: 1H NMR spectrum of TBNT [302]. 167
Figure 2.63: 13C NMR spectrum of TBNT [302]. 168
Figure 2.64: FTIR spectra of PURs [302]. 170
Figure 2.65: 1H NMR spectra of PURs [302]. 170
Figure 2.66: FTIR spectrum of IPCT [303]. 172
Figure 2.67: 1H NMR spectrum of IPCT [303]. 172
Figure 2.68: 13C NMR spectrum of IPCT [303]. 173
Figure 2.69: FTIR spectrum of prepolymer [303]. 175
Figure 2.70: 1H NMR spectrum of prepolymer [303]. 175
Figure 2.71: FTIR spectra of PUTIs [303]. 177
Figure 2.72: 1H NMR spectra of PUTIs [303]. 178
Figure 2.73: FTIR spectrum of PBHBT [304]. 180
Figure 2.74: 1H NMR spectrum of PBHBT [304]. 180
Figure 2.75: 13C NMR spectrum of PBHBT [304]. 181
Figure 2.76: FTIR spectrum of PUAT 1 [304]. 183
Figure 2.77: 1H NMR spectrum of PUAT 1 [304]. 183
Figure 2.78: FTIR spectrum of IBHPT. 186
Figure 2.79: 1H NMR spectrum of IBHPT. 186
Figure 2.80: 13C NMR spectrum of IBHPT. 187
Figure 2.81: FTIR spectrum of IBPCOT. 188
xxx
Figure 2.82: 1H NMR spectrum of IBPCOT. 188
Figure 2.83: 13C NMR spectrum of IBPCOT. 189
Figure 2.84: FTIR spectrum of PUT 1. 189
Figure 2.85: 1H NMR spectrum of PUT 1. 191
Figure 3.1: TGA curves of PAMDs at a heating rate of 10 oC/min in N2 [294]. 198
Figure 3.2: DSC thermograms of PAMDs at a heating rate of 10 oC/min in N2 [294]. 199
Figure 3.3: X-ray diffraction patterns of PAMDs [294]. 199
Figure 3.4: TGA curves of PAMs at a heating rate of 10 oC/min in N2 [295]. 205
Figure 3.5: DSC thermograms of PAMs at a heating rate of 10 oC/min in N2 [295]. 205
Figure 3.6: X-ray diffraction patterns of PAMs [295]. 206
Figure 3.7: TGA curves of PTAM 1a-d at a heating rate of 10 oC/min in N2 [296]. 212
Figure 3.8: TGA curves of PTAM 2a-d at a heating rate of 10 oC/min in N2 [296]. 212
Figure 3.9: TGA curves of PTAM 3a-d at a heating rate of 10 oC/min in N2 [296] . 213
Figure 3.10: DSC thermograms of PTAM 1a-d at a heating rate of 10 oC/min in N2[296]. 213
Figure 3.11: DSC thermograms of PTAM 2a-d at a heating rate of 10 oC/min in N2 [296]. 214
Figure 3.12: DSC thermograms of PTAM 3a-d at a heating rate of 10 oC/min in N2 [296]. 214
Figure 3.13: X-ray diffraction patterns of PTAM 1a-d [296]. 215
Figure 3.14: X-ray diffraction patterns of PTAM 2a-d [296]. 215
Figure 3.15: X-ray diffraction patterns of PTAM 3a-d [296]. 216
Figure 3.16: TGA curves of PAIs at a heating rate of 10 oC/min in N2 [297]. 223
Figure 3.17: DSC thermograms of PAIs at a heating rate of 10 oC/min in N2 [297]. 223
Figure 3.18: X-ray diffraction patterns of PAIs [297]. 224
Figure 3.19: TGA curves of PTAIs at a heating rate of 10 oC/min in N2 [298]. 230
xxxi
Figure 3.20: DSC thermograms of PTAIs at a heating rate of 10 oC/min in N2 [298]. 231
Figure 3.21: X-ray diffraction patterns of PTAIs [298]. 231
Figure 3.22: TGA curves of PTEIs at a heating rate of 10 oC/min in N2 [299]. 237
Figure 3.23: DSC thermograms of PTEIs at a heating rate of 10 oC/min in N2 [299]. 237
Figure 3.24: X-ray diffraction patterns of PTEIs [299]. 238
Figure 3.25: TGA curves of PIs at a heating rate of 10 oC/min in N2 [300]. 243
Figure 3.26: DSC thermograms of PIs at a heating rate of 10 oC/min in N2 [300]. 244
Figure 3.27: X-ray diffraction patterns of PIs [300]. 245
Figure 3.28: TGA curves of PPTAIs at a heating rate of 10 oC/min in N2 [301]. 249
Figure 3.29: DSC thermograms of PPTAIs at a heating rate of 10 oC/min in N2 [301]. 250
Figure 3.30: X-ray diffraction patterns of PPTAI 1 [301]. 251
Figure 3.31: TGA curves of PURs at a heating rate of 10 oC/min in N2 [302]. 255
Figure 3.32: DSC thermograms of PURs at a heating rate of 10 oC/min in N2 [302]. 256
Figure 3.33: X-ray diffraction patterns of PURs [302]. 256
Figure 3.34: TGA curves of PUTIs at a heating rate of 10 oC/min in N2 [303]. 262
Figure 3.35: DSC thermograms of PUTIs at a heating rate of 10 oC/min in N2 [303]. 262
Figure 3.36: Variation of loss tangent (tanδ) with temperature for PUTIs at 5 Hz [303]. 263
Figure 3.37: X-ray diffraction patterns of PUTIs [303]. 263
Figure 3.38: TGA curves of PUATs at a heating rate of 10 oC/min in N2 [304]. 269
Figure 3.39: DSC thermograms of PUATs at a heating rate of 10 oC/min in N2 [304]. 269
Figure 3.40: X-ray diffraction patterns of PUATs [304]. 270
Figure 3.41: TGA curves of PUTs at a heating rate of 10 oC/min in N2. 275
Figure 3.42: DSC thermograms of PUTs at heating rate of 10 oC/min in N2. 276
xxxii
Figure 3.43: X-ray diffraction pattern of PUT 1. 276
xxxiii
1
Chapter1
INTRODUCTION
Organic polymers afford one of the most imperative and versatile group of materials.
Owing to the intrinsic flexibility of molecular chains, these polymers exhibit extreme
sensitivity towards temperature due to their low softening points. Many of the principal
advances in polymeric materials engross desirable properties through the control of polymer
structure. Over the past decade, polyamides, poly(amide-imide)s, polyimides and
polyurethanes have occupied a significant place among high performance materials and
found a wide range of applications in aerospace, electronics and several other industries
because of their excellent thermal and mechanical properties. Nevertheless, these polymers
exhibit poor processability and limited solubility in organic solvents owing to strong
interchain interactions, high structural regularity and rigidity of the backbones. Numerous
efforts have been made to chemically modify the structure of these polymers with without
sarificing their organosolubility. So, an extensive variety of modified processable high
performance polymers have been synthesized. In this regard, several approaches have been
exploited to alter the polymer structure including the introduction of flexible spacers, bulky
side groups and bent units along the main chain. The rigid-chain structure of these polymers
can be modified via incorporation of meta or ortho-oriented phenylene linkages for distortion
of molecular symmetry. Moreover, the peculiar crystal structure of polymers is controlled by
the interchain hydrogen bonding that provides them with attractive physical properties.
Hydrogen bonding plays an important role not only in determining the crystal structure but
also in the overall performance of the polymers.
This thesis contributes to a rather abandoned area of research, particularly as it covers a
range of polymers bearing thiourea moieties in their repeat units. Generally, it has been a
long-desired goal to synthesize soluble polymers without appreciable loss in their thermal
properties. Relatively easy and economical routes were employed to prepare the monomers
2
having structural characteristics with improved properties such as solvent miscibility and
specifically thermal stability. Therefore, thiourea-based polyamides, poly(amide-imide)s,
polyimides and polyurethanes were prepared having good processability from appropriate
synthesized/commercial monomers. Effects of C=S functional group on the properties of
polymers such as solubility, processabilty, molecular weight, thermal stability and
crystallinity were studied. This synthetic research effort is directed toward the structural
modifications of polymers via disturbing their regularity and chain packing, thus providing
better processability. This chapter principally deals with various topics relevant to this
dissertation; including synthetic routes for the fabrication of different kind of high
performance polymers, the reaction chemistry involved and their essential characteristics
along with key relevances. An introduction to different techniques (elemental analysis, FTIR
and NMR spectroscopy, solubility tests, flame retardancy studies, viscometery, gel
permeation chromatography, solid-liquid extraction tests, chemical resistance investigation,
thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis
and X-ray diffraction) employed for the exploitation of structure and properties of the
monomers and polymers is also portrayed. Furthermore, a brief preface of the novel
polymers synthesized, poly(thiourea-amide)s, poly(thiourea-amide-imide)s, poly(thiourea-
ether-imide)s, poly(phenylthiourea-azomethine-imide)s, poly(urethane-thiourea)s,
poly(urethane-thiourea-imide)s and poly(urethane-azomethine-thiourea)s, together with an
overview of current work is also specified in the succeeding section.
1.1 Polyamides
These are the polymers bearing recurring amide groups
N
H
C
O
n as an integral part of the main chain. Polyamides inhabit an eminent position amongst the
synthetic high performance polymers. As significant industrial materials, these polymers are
widely used because of their exceptional comprehensive performance. For instance,
3
polyamides generally show excellent resistant at high temperatures while maintaining their
structural integrity along with outstanding combination of chemical, physical and mechanical
properties. Polybenzamide was the first synthetic polyamide prepared by Harbordt in 1862
[1, 2]. Prior to the 1920's organic chemists failed to recognize the importance of polymeric
materials, concentrating their efforts on producing low molecular weight compounds. During
the 1920’s, Staudinger conceded the existence of polymeric material by relating solution
viscosity to molecular weight. Upto 1929, a great controversy still existed as to whether
polymers were long chain molecules, colloids or aggregates of cyclic compounds. In early
1930s, Carothers suggested that diamines could condense with dicarboxylic acids to form
polymers such as polyamide-6,6. He also, for the first time, wrote a short review on two main
polymerisation reactions known as ‘chain growth’ (addition) and ‘step growth’
(condensation) polymerization. Hence, nylons were one of the early polymers developed
commercially. A range of aliphatic polyamides have been synthesized with varying
properties dependant upon molecular structure of the repeat units. Polyamides are tough,
flexible, thermally stable, impact and abrasion resistant materials [3–5] whose characteristic
physical properties are mainly determined due to hydrogen bonding.
Wholly aromatic polyamides (aramids) are considered to be high-performance organic
materials due to their outstanding thermal and mechanical resistance. Their properties arise
from their aromatic structure and amide linkages, which result in stiff rod-like
macromolecular chains that interact with each other via strong and highly directional
hydrogen bonds. These bonds create effective crystalline microdomains, resulting in a high-
level intermolecular packing and cohesive energy. First commercially produced aromatic
polyamide was poly(m-phenyleneisophthalamide), also known as Nomex® (Du Pont, 1967)
[6]. In the early seventies, development in the preparation of poly(phenyleneterephthalamide)
led to commercialization of para product, also known as Kevlar® (DuPont) [7]. Aramids
have been known for their high heat resistance and strength [8, 9]. Although, aramids are of
great commercial importance, the fabrication of unsubstituted aromatic polyamides has in
general proved to be difficult because of their tendency to decompose during or even before
melting and insolubility in common organic solvents. Thus, their intractability limits their
applications [10, 11]. Interest in the synthesis of polyamides, with various substituents or
4
structural irregularities in order to improve their processability, is continuesly growing.
Furthermore, aromatic-aliphatic polyamides [12–14] have been derived from aliphatic
primary and secondary diamines, cycloaliphatic secondary diamines and N-substituted
aliphatic-aromatic series. Structural modification (Figure 1.1) of polyamides through the
introduction of
i. Bulky pendant substituent [15, 16]
ii. Flexible alkyl spacers [17, 18]
iii. Non-coplanar biphenylene moieties [19]
iv. Nature of the parent chain (types of linkages and aromatic units) [20, 21]
have been reported to augment their solubility and to reduce phase transition temperatures.
Rigid rod like linear polymer backbone
Flexible polymer chain
Polymer spine with bulky pendant side groups
Bent units along polymer sequence
Figure 1.1: Enhancement of polymer processability via several approaches.
1.1.1 Hydrogen bonding in polyamides
Hydrogen bonding plays a vital role in the behaviour of polyamides. Covalent bonds
have energies in the order of 300 kJ/mol, while the much weaker van der Waals forces have
energies of 1 kJ/mol. Hydrogen bonds are intermediate in strength (around 20–50 kJ/mol)
5
and are electrostatic in nature. These bonds develop when hydrogen atom is covalently
bonded to a highly electronegative group (O, N or F), that has drawn some of the charge
from hydrogen atom. This makes hydrogen atom partially positive in charge; thus,
electronegative atom in another molecule is weakly attracted to hydrogen atom, forming a
hydrogen bridge. In polyamides, likewise, nitrogen atoms in amide linkages are highly
electronegative, withdrawing some of the charge from attached hydrogen atom. Normally,
oxygen atom of carbonyl in another amide group elsewhere in the polymer chain or from
another molecule is attracted towards hydrogen to form N–H…..O hydrogen bond, as shown
in Figure 1.2.
NN
N
O
O
O
H
H
H
NN
N
O
O
O
H
H
H
NN
N
O
O
O
H
H
H
Figure 1.2: Amide to amide hydrogen bonding found in polyamides (nylon 6,6).
In general, there are weak and strong hydrogen bonds. Nevertheless, those involved in
polyamides are considered moderate to strong. Hydrogen bond formation is implicit in the
determination of physical properties of polyamides. Besides, polyamide crystallization is
more complicated compared with many polymers, since hydrogen bonding constrains the
crystallographic possibilities beyond the steric considerations. Hydrogen bonds in
polyamides are persistent, being substantially consummated in the amorphous state and are
even present at a significant level in the melt [22]. In fact, these bonds are the driving force
that locks the crystallizing lamella into one or another crystalline form. Hydrogen bonding, is
therefore, a reason for very high melting temperature of polyamides as they provide stability
to their structures. Other molecules can also be incorporated into the polymer structure such
as water, which plasticizes and weakens polyamides by displacing hydrogen bonds.
6
1.1.2 Crystallinity in polyamides
Following features of polyamides can be exploited to gain a better understanding of
their crystallinity and the part hydrogen bonding plays in their properties:
i. Orientation of non-symmetric amide groups in polyamide chains.
ii. Steric limitations between the molecular chain segments lying next to each other and
between different molecules in a lamella.
iii. Exact type of polyamide because of the limited combinations of the way hydrogen
bonds can be formed within the molecules between amide groups.
Over fifty years ago, it was found that different types of polymers are able to enter a
partially crystalline state. This can happen for the polymers with slower cooling conditions or
if solid amorphous polymer allows a solid-state crystallization to take place. At this instant,
the degree of crystallinity depends on thermal and mechanical history of the sample and can
range from zero to 90 %. For instance, polyamide-4,6 can crystallise up to 70 % by volume
under favourable conditions. Consequently, crystallization adds to the mechanical stability of
many manufactured plastic articles. Usually, as cooling rate during crystallization increases,
the percentage in amorphous state increases and so crystallinity decreases. Lamellae are
crystalline regions within the polymer structure, having thickness of 5–10 nm, called
crystallites (Figure 1.3). Long polymer chains are generally considered [22, 23] to fold
backwards and forwards into place across the edge faces of lamellae crystallizing from the
melt or solution. In addition, lamellae formed in solution are usually more perfect than those
formed in the melt, since; there is more opportunity for polymer chains to easily orient
themselves correctly by displacing the smaller solvent molecules. In the lamellae, polymer
chains are reptating like snakes to produce more thermodynamically stable thicker
configuration. The ends of molecules withdraw from their initial place in the lamella during
this process. Thickening of polymer lamellae is also observed if they are later annealed for
some time at temperatures below the melting temperature. Lamellar thinning also occurred
with some semirigid polymers, including polyamides [24]. The lamellar thickness generally
depends on the temperature of crystallization in polymers. Typically, the lamellar thickness
increases with molecular weight and the melting temperature also increases. The lamellae
7
can often form in different crystallographic structures. The order caused by polymer chains
aligning themselves means regularity in the structure of atoms, allowing Bragg reflections to
be seen with X-Rays. Whether a crystallizable polymer solidifies purely with an amorphous
structure or certain extent of crystallization depends upon range of parameters that can also
affect the crystallographic form. Thermal history and the molecular weight also play a crucial
role.
amorphous regioncrystal nucleus
lamellar fibrils
Figure 1.3: Folded chains in polymer crystallite.
Linear polyamides, one of the most important classes of natural polymers, are known
as proteins or polypeptides to biochemists and biologists. Some of the similarities between
the polyamides and proteins have been pointed out. The peptide linkage is identical to the
amide linkage that occurs in synthetic linear polyamides [25]. A better comprehension of
polyamide crystallinity in different environments could potentially lead to improved
understanding of the way in which proteins fold. Proteins can form molten globules before
crystallizing out fully [26] and this concept is relevant to the way in which polyamides
crystallize from the melt or solution. A study on the formation of crystallites in molten
polymers by Olmsted et al. [27] further supported this concept.
8
1.1.3 Synthetic routes to polyamides
1.1.3.1 Low-temperature polycondensation
Polycondensation reaction of a diamine and diacid chloride < 100 °C in an amide
solvent such as hexamethylphosphoramide (HMPA), N-methylpyrrolidone (NMP) or N,N′-
dimethylacetamide (DMAc) is known as low-temperature polycondensation. This is a
convenient method for the synthesis of polyamides. The polycondensation route, developed
by Du Pont, has been used experimentally and commercially for the preparation of high
molecular weight polyamides [28, 29].
1.1.3.2 Solution polycondensation of diamines and diacid chlorides
Solution polycondensation involves the reaction of a diamine and a diacid chloride
in an amide solvent such as HMPA, NMP, DMAc, or tetramethylurea (TMU) (Scheme 1.1).
R NH2H2Nn R' CC
OO
ClClamide solvent
HClR NN C R' C
O
H H
O n
n
Scheme 1.1: Solution polycondensation of a diamine and a diacid chloride.
The solvent allows maximum solubility of the polymer formed at the early stage of
polycondensation. The solvation properties of amide solvents can usually be increased by the
addition of some salts (LiCl, CaCl2, etc) [30, 31].
1.1.3.3 Interfacial polycondensation technique
Another promising route for the preparation of polyamides is interfacial or two-
phase polycondensation, which is an adaptation of well known Schotten-Baumann reaction.
In low-temperature solution methods, the monomers are dissolved and reacted in a single
solvent phase. Alternatively, the two-phase process is involved with the reaction of diacid
chlorides and diamines in water-immiscible solvent media of low polarity and yields
polyamides of low molecular weight due to rapid precipitation. In this method, two fast
reacting intermediates are dissolved in a pair of immiscible liquids, one of which is
9
preferably water. Generally, the water phase contains diamine and usually an inorganic base
to neutralize the byproduct acid. The other phase encompasses the acid chloride in an organic
solvent such as CH2Cl2, toluene or hexane (Scheme 1.2).
R NH2H2Nn R' CC
OO
ClClorganic solvent
R NN C R' C
O
H H
O n
nH2O base
Scheme 1.2: Interfacial polycondensation of diamine and diacid chloride.
Thus, monomers are brought to react at the interface of the two phases. The two-phase
system is agitated vigorously to obtain high molecular weight polymers. Low temperature is
necessitated to minimize the side reactions, and the polymers which are unstable at high
temperatures can be synthesized [32, 33]. Since, chief disadvantage of this technique is the
broad molecular weight distribution of polymers making them unsuitable for fibers or films
fabrication.
1.1.3.4 Polyamides via direct polycondensation of dicarboxylic acids and diamines In direct or high temperature polycondensation of aromatic dicarboxylic acids and
aromatic diamines, aryl phosphites are used in the presence of pyridine. In early 1970’s,
Ogata and co-workers [34, 35] reported the phosphorylation polycondensation reaction. This
reaction has been extensively applied to polyamide synthesis because of its convenience.
Later on, Mitsuru and co-workers [36–38] successfully used this method for the fabrication
of polyamides. This technique employs triphenyl phosphite (TPP) and pyridine as
condensing agents to synthesize polyamides directly from aromatic diamines and aromatic or
aliphatic dicarboxylic acids, and the reaction proceeds through N-phosphonium salts of
pyridine. The reaction involves the formation of a complex of the acid with TPP in NMP and
pyridine, which further reacts with diamine to give the product (Scheme 1.3). CaCl2 and LiCl
are used along with NMP to improve the molecular weight of polymers. These are supposed
to form complexes with pyridine and are more soluble than the salts alone. Thus, solvent
with a higher content of metal salt can effectively solubilize polyamide formed in
the reaction medium, leading to high molecular weight products [39, 40]. As a result, this
10
synthetic approach has proved to be more efficient and convenient as compared to the acid
chloride route. The phosphorylation reaction has also extended successfully to the synthesis
of high molecular weight poly(amide-imide)s from imide containing dicarboxylic acids and
aromatic diamines.
R1COOH P(OPh)3N
N
P OCOR1
OPh
H
PhO
R1CONHR2 HP(OPh)2 PhOH
O
OPh
R2NH2
Scheme 1.3: Direct polycondensation leading to polyamide using TPP and Py.
1.1.3.5 Polycondensation of diisocyanates and dicarboxylic acids
The reaction of aromatic diisocyanates and dicarboxylic acids is also employed for
the synthesis of polyamides. The direct formation of polyamides via this route involves the
elimination of CO2 without using any condensing agents. Hence, several polyamides and
copolyamides have been prepared by this method [41, 42].
1.1.3.6 Polycondensation of N-silylated diamines and diacid chlorides
Although, most of the synthetic efforts leading to high molecular weight polyamides
incline towards the activation of diacids, there are few reports available on the activation of
diamine components. According to this method, diamines can be activated by reacting with
trimethylsilyl chloride. Undeniably, high molecular weight polyamides have been
synthesized by low temperature polycondensation of N-silylated aromatic diamines with
aromatic diacid chlorides [43]. The subsequent two-step nucleophilic addition-elimination
mechanism has been predicted for the acyl substitution of an acid chloride with an N-
silylated amine (Scheme 1.4).
11
C
O
Cl
Ar' N
H
SiMe3
Ar C
O
Cl
Ar'HN Ar
SiMe3
C
Cl
Ar' O
SiMe3
NHAr
CAr' NHAr
O
Me3SiCl
Scheme 1.4: Condensation of N-silylated amine and acid chloride.
1.1.3.7 Microwave-assisted polycondensation
High-temperature solution procedure was recently modified by the introduction of
microwave-assisted polycondensation. Microwave radiation (MW) is a nonconventional
energy source, now widely used in organic chemistry, employed to promote chemical
reactions fastly. The MW-assisted synthesis of polyamides is usually carried out through the
condensation of aromatic diacids and diamines under Yamazaki conditions. The conventional
heating system, i.e., temperature control oil bath, is replaced by the MW system, which
reduces the reaction time from 4 h to approximately 2 min [44, 45]. The polymers obtained
by both the methods have comparable inherent viscosities. MW has also been used to
promote the rapid polycondensation (less than 5 min) of diacids with aliphatic and aromatic
diisocyanates, yielding semiaromatic polyamides and aramids [46].
1.1.3.8 Alternative polymerization methods
Organic chemistry provides a wide set of synthetic methods to develope aromatic or
aliphatic–aromatic amide linkages, and some of them have been used to prepare polyamides.
It is not feasible to cover all of these procedures; a summary of reaction methods can be seen
in literature reported by Gaymans [47].
1.1.4 Structure-property relationship in polyamides
Over the past decades, polyamides have attracted a great deal of interest from polymer
scientists and technologists owing to their high thermal stability and excellent mechanical
properties. There has been an increasing indigence for processable high performance
12
polyamides having moderately high softening temperatures and good solubility in organic
solvents. To alleviate this intricacy, a number of approaches were adopted to synthesize
processable polyamides without significantly affecting their properties. In view of that,
introduction of flexible bonds or bulky pendant groups along the main chain of polyamides is
known to increase their solubility. Moreover, the substitution of halogen atoms in the
backbone enhanced Tg of polymers and it has a direct dependence on the size of halogen.
High structural regularity and rigidity of polyamide backbone can also be disturbed by the
introduction of m-oriented phenyl rings to decrease interchain interactions and improve
solubility.
1.1.4.1 Flexible linkages in polyamides
Aromatic polymers are generally difficult to process because of limited solubility in
organic solvents. One approach to improve solubility of these polymers without appreciable
loss of thermal stability is the introduction of polar and flexible linkages into the backbone
[48]. For that reason, aromatic polyamides containing sulfide, sulfone, and ketone groups
have been synthesized (Figure 1.4). Joseph et al. carried out direct polycondensation of bis(p-
phenylthio) dibenzoic acid, 4,4'-sulphonyl bis(p-phenylthio) dibenzoic acid and 4,4'-
[carbonyl bis(p-phenylthio)]dibenzoic acid with various aromatic diamines in triphenyl
phosphite-pyridine systems [49].
NH
CC
n
NH
Ar
SO2
Ar:
O O
CH2 SO2
C
O
C
CH3
CH3
C
CH3
CH3
C
CH3
CH3
O OSO2
O O
Figure 1.4: Polyamides from bis (p-phenylthio) dibenzoic acid and various diamines.
13
1.1.4.2 Polyamides containing pendant alkyl or aryl group
Pendant groups have been introduced into the main chain [50–52] as an efficient
means of enhancing solubility with retention of ample thermal stability [53]. Such groups
influenced the mechanical properties to a small extent; however, thermal properties were
adversely affected. Espeso et al. [54, 55] reported the preparation of aromatic polyamides
based on an aromatic diamine with an adamantyl moiety in the lateral structure, namely 4-(1-
adamantyl)-1,3-bis(4-aminophenoxy)benzene (Figure 1.5). The direct reaction under
phosphorylation condensation of this diamine with various diacids produced amorphous
polymers at high yields, having weight average molecular weight 37–93×103 g/mol. Polymer
Tg's were measured between 240–300 ºC, while T10's were around 450 ºC. Films cast from
the polymers exhibited good mechanical properties with tensile strength in the range 77–92
MPa and tensile moduli between 1.5 and 2.5 GPa. A phenyl group ortho to carboxyl caused
increase in solubility and introduced flexibility into the polymer spine. Polyisophthalamides
containing pendant benzoyloxy groups were synthesized from 5-(benzoyloxy)isophthaloyl
chloride and aromatic diamines [56]. The incorporation of benzoyl group brought about a
decrease in Tg by 10–30 °C relative to unmodified polymers.
O O
NH
NH
CAr
C
O O
n
O C
CF3
CF3Ar:
C
CF3
CF3OO
H3CCH3
CH3
CH3
OO
H3C
CH3
CH3
CH3
H3C CH3
Figure 1.5: Polyamides from aromatic diamine bearing adamantyl moiety.
14
Cimecioglu and Weiss [57] prepared polyisophthalamides using 5-benzamido-
isophthalic acid by direct polyamidation, leading to soluble polymers without adversely
affecting thermal properties. Polyamides based on substituted bulky monomers containing
3,3-substituted binaphthyl and biphenyl group have also been reported [56]. Highly soluble
and thermally stable aramids containing biphenyl-2,2'-diyl and 1,1-binaphthyl-2,2-diyl were
also synthesized by low-temperature polycondensation of diacid chlorides of 2,2'-bis(p-
carboxyphenoxy) biphenyl and 2,2'-bis(p-carboxyphenoxy)-1,1'-binaphthyl with aromatic
diamines [58]. Furthermore, highly phenylated heterocyclic diamines and diacid chlorides
were used to achieve high solubility and retain thermal stability [59, 60].
C C
O O
NHS
HN
n Figure 1.6: Polyamide of 2,5-bis(4-aminophenyl)-3,4-diphenyl thiophene and IPC.
Soluble polyamide (Figure 1.6) having high Tg of 280–325 °C, has been prepared by
polymerizing 2,5-bis(4-aminophenyl)-3,4-diphenylthiophene with isophthaloyl chloride in
DMAc [61]. Besides, soluble polyamides and copolyamides were derived from 2,5-bis(4-
chloroformyl phenyl)-3,4-diphenyl thiophene [60] as shown in Figure 1.7. Low-temperature
polycondensation of 4,4'-oxydianiline was also used to synthesize soluble
coterephthalamides [62].
CS
C
n
N
O
HAr
HN C C
OO
HNAr'
HNAr
O
Figure 1.7: Copolyamide from 2,5-bis(4-chloroformyl phenyl)-3,4-diphenyl thiophene and diamines.
15
1.1.4.3 Fluorinated polyamides
Fluorinated polymers exhibit exceptional mechanical strength, film-forming
properties, improved melt flow, increased solubility in addition to flame, chemical and
radiation resistance. Maji and Banerjee [63] synthesized a series of fluorine containing
aromatic polyamides by the direct polycondensation of various fluorine-containing aromatic
diamines [64] and 5-t-butyl isophthalic acid (Scheme 1.5). The polyamides were
semicrystalline and soluble in polar aprotic solvents and in THF. The molar masses were
determined to be 152×103. Moreover, these polyamides exhibited good thermal stability up
to 489 ºC (T10 in N2) and maximum Tg up to 273 ºC. The polymers gave flexible films, which
exhibited moderate tensile strength (72 MPa) with initial modulus (1.39 GPa).
H2N
CF3
O NH2
F3C
OAr
HOOC
C(CH3)3
COOH
HN
CF3
OHN
F3C
OAr
C(CH3)3
C
O
C
O n
NMP/CaCl2Py/ TPP/ 90OC
C
CH3
CH3
C
CF3
CF3Ar:
Scheme 1.5: Synthesis of fluorine-containing aromatic polyamides.
1.1.4.4 Substituted isophthalic acid monomers
The processability of polyamides is often complicated because of their high
crystallinity, structural regularity and rigidity attributable to the presence of para-phenylene
structure in the backbones. One of the aspects to improve processability is the use of
substituted isophthalic acid monomers (meta-catenation). Few examples of substituted
16
isophthalic acids are listed in Table 1.1. Kajiyama et al. [68] studied the effect of perfluoro
alkyl group on the properties of polyisophthalamides. A decrease in Tg with increase in
carbon chain length was also observed in such polyamides.
Table 1.1: Few representative substituted isophthalic acid monomers.
No. Diacid Ref
No. Diacid Ref
1
NO2
65 4
RR= C4F9, C8F17
68
2
X
X= F, Cl, Br, I
66 5
OAr
Ar= PhCF3, Ph(CF3)2
69
3 CH3C
CH3
CH3
67 6
ORR= C11H23-C18H37
70
7
R
R=
COOHHOOCNH C
O
(CH2)X N
O
O
71
1.1.5 Polyamides with specialty properties and applications
The use of polyamides is prevalent in modern society and their applications continue
to grow. Many of the important advances in this area involve imparting desirable properties
through the control of polymer structure. In recent years, the area of high performance
17
polyamides is intensely focused; where tailoring polymer structure to give specific set of
properties is paramount.
1.1.5.1 Optically active polyamides
Numerous highly important naturally occurring polymers, such as proteins, DNA,
and polysaccharides are optically active. Most of the drugs, we use, are derived from natural
sources and are chiral. Therefore the design, characterization, and preparation of chiral
polymers are of particular interest [72]. Some applications of optically active polymers
(OAP) include the assembling chiral media for asymmetric synthesis, chiral stationary phases
(L-leucine)
NH2
O
OH
(L-isoleucine)
R
R=MeEt
O
O
O
SOCl2
i)
ii)iii) HOOC
NH2
COOH
HOOC
HN
COOH
R
OO
O
N
C
HN
C
R
OO
O
N
OHN
O
R'HN
x
R' NCOOCN
CH2
CH3 CH3
CH2
H3C CH3
R':(CH2)6
Scheme 1.6: Optically active polyamides using aromatic diacids and diisocyanates.
18
for resolution of enantiomers in chromatographic techniques, chiral liquid crystals in
ferroelectrics, nonlinear optical devices, etc. [73]. Mallakpour et al. [73] synthesized pendant
polyisophthalamides having a lateral L-isoleucine core group. Various polyamides were
prepared from two methods (the conventional high-temperature solution method and MW)
using aromatic diacids and diisocyanates (Scheme 1.6) [74]. Both methods were employed
using different catalysts (dibutyltin dilaurate (DBTDL), pyridine, triethylamine, or no
catalysts). The best results were obtained with DBTDL, under MW radiation as well as
conventional heating polymerization. The polymers showed optical rotation [α], which
verified their optical activity. Polyamides prepared by different methods showed different
optical rotation, and this fact was attributed to the dependence of the optical rotation on the
overall structure and regularity of the resulting polymer chains. The authors claimed that
since these polymers are optically active and have amino acids in the polymer architecture,
they are likely biodegradable, and are therefore, classified as environment friendly polymers.
In addition, they have the potential for use as the chiral stationary phase in gas
chromatography (GC) for the separation of racemic mixtures.
1.1.5.2 Polyamides in membrane technologies
Reverse osmosis (RO) is a water purification technique that reduces the quantity of
dissolved solids in solution [75]. Aromatic polyamides have been used for many years in RO
membranes. Aramids usually form the active layer, and exhibit high salt rejection and water
permeability. The thin layer is obtained by interfacial polycondensation of trimesoyl chloride
(TMC) with m-phenylene diamine (MPD), and polymerization takes place on a microporous
polysulfone membrane. Among other applications, these membranes are used in water
treatment, seawater desalination, and dialysis. Mohamed and Al-Dossary [76] prepared flat
sheet asymmetric reverse osmosis membranes comprised of a wholly aromatic polyamide-
hydrazides, using either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenz-
hydrazide having equimolar amounts of either terephthaloyl or isophthaloyl chlorides (TPC
or IPC), or mixtures of both, in the solvent DMAc. Polymers made using various ratios of
para- to meta-phenylene moieties were analyzed. The effects of various processing
parameters on membrane transport properties were investigated by varying the temperature
and the solvent evaporation time of the cast membranes, the coagulation temperature of the
19
thermally treated membranes, the annealing of the coagulated membranes, casting solution
composition, membrane thickness, and the operating pressure. For example, the salt rejection
was measured above 80 % within the required level of permeability. Polyamides having a
higher content of m-phenylene rings exhibited higher salt rejection. The introduction of other
chemical functional groups in the active layer of RO membranes can improve the
performance of the membranes over the standard m-phenylenediamine–trimesoyl chloride
(MPD–TMC) membranes. Thu