PSEUDO-LADDER RIGID-ROD POLYMERS - DIHYDROXY PENDENT BENZOTHIAZOLE AROMATIC HETEROCYCLIC POLYMER AND COPOLYMERS

Anisotropic homopolymerization of 2,5-dihydroxyterephthalic acid (DHTA ) and 2,5-diamino-1,4-benzenedithiol dihydrochloride (DABDT.2HCl), and copolymerization of DHTA, terephthalic acid and DABDT.2HCl in polypho sphoric acid (PPA), afforded high molecular weight rigid-rod polymer a nd copolymers, with two hydroxyl groups as pendants per repeat unit. I n PPA, the lyotropic liquid crystalline behaviour of the homopolymer w as distinctly affected by the polymerization temperature. Spectroscopi c evidence strongly suggested a completely planar and ribbon-like stru cture, the consequence of the strong intramolecular hydrogen bonds bet ween the OH moieties and the N atoms of the nearby benzothiazole units . The homopolymer also exhibited the unusual capability, characteristi c of BBL-type ladder polymers, to form directly from its precipitate a n aggregated film which displayed little or no shrinkage when dried. A nisotropic dopes of the homopolymer (dihydroxy-polybenzothiazole (PBZT )) and certain dihydroxy-PBZT/PBZT copolymers were spun into fibres wi th typical tensile properties for modified PBZT polymers, but marginal compressive strength (4-30 ksi (1 ksi = 6.9 M Pa) for homopolymer and 16 61 ksi for the copolymers). The intrinsic conductivity for the as- spun fibre of the homopolymer was 2.2 x 10(-7) S cm-1 and that for hea t-treated (435-degrees-C) fibre was 5.6 x 10(-8) S cm-1.