Impact of Contaminant Comonomers on the Various Conformational and Thermodynamic Properties of Poly (hydroxybenzoic acid) Liquid Crystals

Abstract

A conformational study of poly(hydroxybenzoic acid -co- hydroxynaphthoic acid) copolyesters was conducted to examine the effect of randomly positioning naphthoic units along the backbone of the poly(hydroxybenzoic acid) liquid crystals. This is usually done to bring down the processing temperature of the liquid crystal to practical working ranges. The COMPASS forcefield used throughout this study was developed particularly using ab - initio calculations to improve upon existing forcefields. Energy contour maps for both comonomers indicated a similar conformational behavior for the benzoic and naphthoic units. The radial distribution function calculated for the homopolymers and the copolyesters indicated a disruption of the short-range order in the copolyesters influenced by the greater length of the naphthoic units over that of the benzoic units. The important configurational properties such as the end-to-end distance and the radius of gyration show a linear dependence on the amount of the naphthoic units in the copolyester. Both the Kuhn segment parameters and the persistence lenth calculations indicate an increase in the stiffness of the chains with the increase in the amount of the naphthoic units. The Hildebrand solubility parameter evaluated from the cohesive energy densities of the copolyesters indicates, however, a constant value for the thermodynamic parameter across the entire compositional range of the copolyester.