Abstract
AbstractThe polymerization of 3,3′‐dihydroxybenzidine with the phenyl esters of phthalic, isophthalic, terephthalic, and 5‐chloroisophthalic acids yielded a series of aromatic polybenzoxazoles exhibiting high thermal stability. Melt polymerization afforded these polymers in quantitative yield with inherent viscosities in the range of 0.20–1.04 and thermal stability very similar to those obtained with the aromatic polybenzimidazoles. Homopolymerization of 3‐amino‐4‐hydroxybenzoic acid and 4‐amino‐3‐hydroxybenzoic acid was achieved through the preparation of an intermediate poly(ester‐amide) followed by thermal cyclization (at 250–300°C.) to the benzoxazole unit. Six model compounds containing the benzoxazole unit were prepared for use as standards of reference. These were 2‐phenylbenzoxazole, 2,2′‐p‐phenylene‐bisbenzoxazole, 2,2′‐m‐phenylene‐bisbenzoxazole, 2,2′‐o‐phenylene‐bisbenzoxazole, 2,2′‐(5‐chloro‐1,2‐phenylene)‐bisbenzoxazole, and 2,2′‐(diphenyl)‐6,6′‐bibenzoxazole.
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