synthesis and characterization of new polyamides, poly...

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

11

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-dioxoisoindoline-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-aminobenzylidene)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

23

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

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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 diisothiocyanates.

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 2.23: 1H NMR spectra of PTAM 1 a-d [296]. 129



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 3.16: 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

synthesis and characterization of new polyamides, poly...

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