Thermotropic polyesters: structure of poly(chloro-1,4-phenylene terephthalate) and its copolymers

Structures of poly(chloro-1,4-phenylene terephthalate) and two series of nematogenic copolymers with reduced chain rigidity, viz. poly(chloro-1,4-phenylene terephthalate- co-4,4′-oxybisbenzoate)s containing an ether oxygen disruptor, and poly(chloro-1,4-phenylene terephthalate- co-4,4′-hexamethylenedioxybisbenzoate)s containing a hexamethylenedioxy flexible spacer, are investigated by wide-angle X-ray techniques. The chain packing density in crystals of the parent rigid-chain ‘homopolymer’ is similar to those of unsubstituted polyesters containing 1,4-phenylene moieties. In contrast, the parent ‘homopolymers’ of reduced chain rigidity have crystal structures with increased interchain spacings. Copolymers with the ether oxygen disruptor contain crystallites of the less rigid parent ‘homopolymer’ while those with the flexible spacer contain crystallites of both parent ‘homopolymers’. This is attributed to the combined effects of chain cross-sectional areas and melting temperatures of the parent ‘homopolymers’.