Abstract

AbstractThe solubility and mesophase behavior are investigated for block copolymers of poly(p‐benzamide) (PBA), the polyterephthalamide of p‐aminobenzhydrazide (PABH‐T), and PBA and poly(m‐phenylene isophthalamide) (MPD‐I) dissolved in N,N‐dimethylacetamide (DMAc) containing 3% LiCl. The block copolymers, whose synthesis and characterization were described in the previous paper in this series, included samples prepared by the two‐step and multistep copolycondensations. The first of these methods yields a considerable amount of the flexible homopolymer (PABH‐T) and also some of the rigid homopolymer. The flexible homopolymer can be removed from the block copolymer by extraction with dimethyl sulfoxide (DMSO), whereas precipitation may offer a way to remove the rigid homopolymer. The results observed for the block copolymers are compared with those for the homopolymers and mixtures of homopolymers. The apparent solubility of the PBA/PABH‐T block copolymers obtained by the two‐step method is unusually large but decreases toward the value observed for mixtures after the flexible homopolymer had been extracted with DMSO. Labile adducts involving PABH‐T and/or the block copolymer appear to be capable of forming a single mesophase. This offers a most interesting approach to the preparation of composite materials involving rigid and flexible polymers.

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