Synthesis and kinetic analysis of 1,4-naphthalene-di(carboxylic acid) and hydroquinone diacetate based homopolyesters

Abstract

A variety of high temperature liquid crystalline polymers can be developed using the homopolyester of 1,4-naphthalene di(carboxylic acid) (1,4-NDCA) and hydroquinone diacetate (HQDA) as a spacer. In such cases the monomer 1,4 NDCA acts as a kink. Kinetic studies of the synthesis of homopolyesters by melt polymerization using 1,4-NDCA and hydroquinone diacetate (HQDA) are reported. The performance of two transesterification catalysts are estimated for this system. In this study, initial stage polymerization kinetics of the homopolyesters were examined. The side product, acetic acid, evolved in the homopolymerization of 1,4-NDCA and HQDA, was used to estimate the progress of the reaction. The polycondensations were found to obey second order kinetics, regardless of whether the reaction was catalyzed or uncatalyzed. A set of twelve differential equations containing four different rate constants, k1, k2, K3 and K4 has been developed and computed, to study the initial stage kinetics. The computed values of acetic acid are compared with the experimentally collected amounts, and the four rate constants are optimized using a differential algebraic optimization technique. The present model represents the data with an acceptable accuracy and with an average percentage error of less than 5% for the entire experimental range. The correlation coefficient values range from 0.95 to 0.99 for all experimental data. The kinetic constants and activation energy values are reported. Different scanning calorimetric (DSC) analysis of the homopolyesters indicate that 1,4 NDCA-HQDA had the highest melting temperature, around 350°C.