Synthesis and Characterization of Polyamides, Polyimides and Polyesters Containing Flexibilizing Groups A thesis submitted to the UNIVERSITY OF PUNE For the degree of DOCTOR OF PHILOSOPHY In CHEMISTRY By ANJANA SARKAR Polymer Science and Engineering Division National Chemical Laboratory Pune-411008 February 2005 i Dedicated To My Parents ii Form ‘A’ Certified that the work incorporated in the thesis entitled “Synthesis and Characterization of Polyamides, Polyimides and Polyesters Containing Flexibilizing Groups” submitted by Anjana Sarkar was carried out under my supervision. Such material as has been obtained from other sources has been duly acknowledged in the thesis. February, 2005 P. P. Wadgaonkar Pune (Research Guide ) iii Abstract High performance / high temperature polymers such as polyimides, poly(amideimide)s, polyamides, polyesters etc are characterized by their excellent balance of thermal and mechanical properties which makes them useful materials for engineering applications. However, these polymers particularly those with para- substituted rings exhibit poor processability and limited solubility in organic solvents. Therefore, many efforts have been made to chemically modify the structure of these polymers with the aim of improving their solubility in organic solvents and / or lowering their transition temperatures to a range which facilitates their processing in the melt. The main goal of the present research was the synthesis of polyimides, poly(amideimide)s, polyamides and polyesters with improved processability by incorporation of pendent flexible alkoxy chains along the polymer backbone making use of appropriate difunctional monomers. Another objective of the work was to evaluate the applications of selected polymers as alignment layers for liquid crystal display devices and as membrane materials for gas separations. Thus, our synthetic research effort was directed towards structural modifications designed to disturb regularity and chain packing via meta- catenation and internal plasticization thus providing better processability to the polymers. A series of 5-alkoxyisophthalic acids, 5-alkoxyisophthaloyl dichlorides, 5-alkoxy-1,3- phenylene diisocyanates, and 5-alkoxyisophthalic acid dihydrazides were synthesized. Aromatic diamines containing pre-formed amide linkages and aromatic diamines containing pre-formed ester linkages and possessing pendent flexible alkoxy chains were designed and synthesized. By relatively easy and inexpensive chemical routes, these monomers could be prepared that provide the structural characteristics needed for the improvement of properties such as processability, and specifically properties like pretilt angle and gas permeability. The length of pendent side chains iv was varied in order to study the effects of chain length on the properties of polymers, such as, solubility, thermal stability, Tg and processabilty. A series of polyimides and poly(amideimide)s containing pendent flexible alkoxy groups was synthesized from 5-alkoxy-1,3-phenylenediisocyanates, 5- alkoxyisphthalic acid dihydrazides and aromatic diamines containing pre-formed amide linkages by polycondensation with commercially available aromatic dianhydrides. Polyimides and poly(amideimide)s were of moderate to reasonably high molecular weights and could be cast into tough, transparent, and flexible films. The incorporation of pendent flexible alkoxy groups resulted in lowering of glass transition temperature. A large window between glass transition and polymer degradation temperature was observed. This gives an opportunity for these polyimides and poly(amideimide)s to be melt - processed or compression molded. It was demonstrated that improvement in solubility could be achieved by incorporation of pendent alkoxy chains along the backbone of rigid chain polymers and by proper selection of the comonomers (dianhydride). Wide angle X-ray diffraction analysis revealed that layered structures were formed for polyimides and poly(amideimide)s with long pendent alkoxy chains. The application of organo-soluble polyimide derived from 5-octyloxy-1,3- phenylene diisocyanate and 4, 4’- oxydiphthalic anhydride(ODPA) as alignment layer for liquid crystal display was evaluated in brief. A pretilt angle of 2.97o was observed which is adequate for display applications. Poly(amideimide)s containing octyloxy and hexadecyloxy side chains exhibited a good rubbing processability and excellent performance in controlling of both the alignment and the pretilt of LC molecules in the LC cell. The pretilt angle of LC molecules was easily achieved in a wide range of 3.8 – 17.5o depending upon the rubbing density as well as the length of the alkoxy chain. These values are in the desirable range for super twisted nematic (STN) LCD devices. High molecular weight (Mn 101050- 399400, GPC PS Standard) polyesters were synthesized by interfacial polycondensation of 5-alkoxyisophthaloyl dichlorides v with aromatic diols namely BPA and HFBPA. Polyesters could be cast into tough, transparent and flexible films from their solution in chloroform. Thermal degradation kinetics of polyesters revealed that degradation obeyed first order kinetics. The relationship between the chemical structure of polyesters and their thermal degradation behaviour was established. Polyesters based on 5-alkoxy isophthaloyl dichlorides and BPA showed increase in permeability and decrease in selectivity as length of pendent alkoxy group increases. However, HFBPA- based polyesters behaved differently owing to the presence of bulky hexafluoroisopropylidene group. The permeability behaviour of poly(amideimide) series was similar to that of BPA – polyester series. The marked increase in CO2 permeability than permeability of other gases tested namely He, O2 and N2 indicated potential of these membrane materials for CO2 – based separation applications. Polyamides were synthesized from 5-alkoxyisophthalic acids and 4,4’- oxydianiline employing Yamazaki- Higashi reaction conditions. Polyamides containing pendent alkoxy groups were soluble in DMF, DMAc, NMP and pyridine. Tough, transparent, and flexible films could be cast from DMAc solution of polyamides. Overall, internal plasticization through the incorporation of pendent alkoxy groups was shown to be successful in improving solubility and processability characteristics of polyimides, poly(amideimide)s, polyamides and polyesters with a compromise on thermal stability. Poly(amideimide)s and a polyimide were proved to be suitable as alignment layers for liquid crystal display devices. vi CONTENTS Description Page No. * Abstract i * List of Tables iv * List of Schemes vii * List of Figures ix CHAPTER 1 Introduction and literature survey 1.1 Introduction 1 1.2 Polyimides 4 1.2.1 Synthesis of polyimides 5 1.2.1.1 Classical two-step method via poly(amic acid)s 5 1.2.1.2 One-step high temperature solution synthesis of polyimides 16 1.2.1.3 Other synthetic routes to polyimides 17 1.2.1.3.1 Polyimides via derivatized poly(amic acid) 17 precursors 1.2.1.3.2 Polyimides via polyisoimide precursors 19 1.2.1.3.3 Polyimides from diester-acids and diamines 21 (Ester-acid route) 1.2.1.3.4 Polyimides from tetracarboxylic acids and 21 diamines 1.2.1.3.5 Polyimides from dianhydrides and diisocyanates 22 1.2.1.3.6 Polyetherimides via nucleophilic aromatic 26 substitution reactions 1.2.1.3.7 Other routes to polyimide formation 27 1.2.2 Structure-property relationship of aromatic polyimides 28 1.2.2.1 Liquid crystal displays 29 1.2.2.2 Polyimides for LCD Application 31 1.2.2.3 Applications of polyimides 36 1.3 Poly(amideimide)s 37 1.3.1 Synthesis of poly(amideimide)s 38 1.3.2 Structure- property relationship in poly(amideimide)s 38 1.3.3 Applications of poly(amideimide)s 38 1.4 Polyamides 39 1.4.1 Synthetic methods for the preparation of aromatic polyamides 40 1.4.1.1 Low temperature polycondensation of diamines and diacid 40 chlorides 1.4.1.2(a) Solution polycondensation of dicarboxylic acids and 41 diamines 1.4.1.3(b) Interfacial polycondensation of diamine and diacid chloride 41 1.4.1.4 High temperature solution polycondensation of dicarboxylic 42 acids and diamines 1.4.1.5 Polycondensation of N-silylated diamines and diacid 43 chlorides 1.4.1.6 Polycondensation of diisocyanates and dicarboxylic acids 44 1.4.1.7 Transition metal catalyzed polycondensation of aromatic 45 diamines,dihalides and carbon monoxide 1.4.2 Structure- property relationship of aromatic polyamides 45 1.4.3 Applications of polyamides 48 1.5 Polyesters 48 1.5.1 Synthesis of polyesters 49 1.5.1.1 Acid chloride route 49 1.5.1.1.1 Interfacial polycondensation 49 1.5.1.1.2 Low temperature solution polycondensation 51 1.5.1.1.3 High temperature solution polycondensation 52 1.5.1.2 Transesterification route 52 1.5.1.2.1 Phenyl ester route 52 1.5.1.2.2 Phenol acetate route 53 1.5.1.2.3 Phenyl ester and phenol acetate route 54 1.5.1.3 Other routes for polyester synthesis 55 1.5.1.3.1 Phenol silyl ether route 55 1.5.1.3.2 Direct esterification route 55 1.5.1.3.3 Palladium-catalyzed carbonylation of aromatic 57 dibromides and bisphenols 1.5.2 Structure- property relationship in polyesters 57 1.5.2.1 Gas separation 58 1.5.2.2 Polyarylates for gas separation 61 1.5.3 Applications of polyarylates 62 References 65 CHAPTER 2 Scope and Objectives 82 CHAPTER 3 Synthesis and Characterization of Difunctional Monomers Containing Pendent Flexible Alkoxy Groups 3.1 Introduction 88 3.2 Experimental 103 3.2.1 Materials 103 3.2.2 Measurements 103 3.3 Preparations 104 3.3.1 Preparation of dimethyl-5-hydroxyisophthalate