Nematogenic block copolymers of rigid and flexible aromatic units. I. Synthesis and characterization

Abstract

AbstractThree types of wholly aromatic block copolymers were synthesized using the phosphorylation reactions of Yamazaki and Higashi. Each copolymer contained blocks of rigid and flexible units. The first copolymer, PBA/PABH‐T, contains blocks of poly(p‐benzamide) and the polyterephthalamide of p‐aminobenzhydrazide. The second copolymer, PBA/MPD‐I, contains blocks of poly(p‐benzamide) and poly(p‐phenylene isophthalamide), whereas the third, PPD T/MPD‐I, contains blocks of poly(p‐phenylene terephthalamide) and poly(m‐phenylene isophthalamide). Three synthetic routes were used for the preparation of the block copolymers. In the two‐step polycondensation (A), monomers of the flexible block are added to the rigid prepolymer. The multistep method (B) differs in that the rigid prepolymer is carboxy‐terminated prior to addition of the monomers of the flexible block. Carboxy‐terminated prepolymer of the rigid block is reacted with amine‐terminated prepolymer of the flexible block in the two‐pot condensation (C). The presence of a considerable amount of the flexible homopolymer is indicated by viscosity, extraction, and NMR studies, particularly when methods A and C were used. The flexible homopolymer can be extracted by using a nonsolvent for the rigid blocks. Extraction of the rigid homopolymer (which may also be presumed to be produced) entails a more elaborate procedure. In principle, one can use these methods to obtain pure block copolymer for study of mixtures with the rigid and flexible homopolymers. Phase studies of some of these systems will be reported in a following paper.