Effects of monomeric sequence distributions on physical properties of thermotropic liquid crystalline copoly(ester-imide)s

Abstract

Thermotropic liquid crystalline copoly(ester-imide)s were synthesized from n-(omega-carboxyalkylene) trimellitic imide, 2,6-dihydroxynaphthalene, and p-hydroxybenzoic acid. The synthesized polymers were abbreviated as PEIM, CPHA, CPHB, CPHC, and CPHD, corresponding to mole fractions of p-hydroxybenzoic acid (PHB) to PEIM varied from 0 to 1/3, 1/2, 2/3, and 3/4. We investigated the monomeric sequence distributions by high resolution C-13 NMR and their effects on the thermal, viscoelastic properties and molecular orientation of copoly(ester-imide)s. The solids of CPHA and CPHB with short runs of PHB blocks in a main chain preserved a nematic glassy state during the cooling process because of the slow crystallization. The low degree of crystallinity and slow crystallization rate were considered to be caused by the absence of long runs of PHB blocks. But CPHC with long runs of PHB blocks showed a high tendency to crystallize and, therefore, the hysteresis of viscoelastic properties in heating and cooling was observed. The residual crystallites of CPHC were considered to hinder the molecular orientation during melt spinning.