SYNTHESIS AND CHARACTERIZATION OF BLOCK-COPOLYMERS CONTAINING RIGID LIQUID-CRYSTALLINE AND FLEXIBLE BUTYLENE TEREPHTHALATE SEGMENTS

A series of novel thermotropic block copolyesters based on poly(tetramethylene 4,4'-(terephthaloyldioxy)dibenzoates) (Triad-4) and poly(butylene terephthalate) (PBT) were synthesized by high-temperature polycondensation in solution to minimize sequence randomization by transesterification. Three different schemes were examined in order to facilitate the systematic variation of block length and block content. All reaction schemes predict the formation of tetramethylene 4-(terephthaloyloxy)benzoate (Diad-4) moieties in the block copolymers. Diad-4 homopolymer and its block copolymers with PBT were synthesized and characterized and were compared to Triad-4-co-PBT block copolymers. The compositions of all block copolymers were determined from H-1 NMR spectroscopy. The DSC thermogram of a typical block copolymer revealed the presence of two major melting transitions, corresponding to the separate melting of PBT and Triad-4 domains. During the cooling cycle separate and distinct crystallization exotherms were also observed. Polarizing optical microscopy showed that all block copolymers were liquid crystalline and exhibited a nematic texture.