NEW POLYMER SYNTHESES .50. WHISKERS OF POLY(4-HYDROXYBENZOATE) BY CONDENSATION OF TRIMETHYLSILYL 4-ACETOXYBENZOATE

Polycondensations of various aprotic derivatives of 4-hydroxybenzoic acid were conducted in Marlotherm-S at 350 or 400-degrees-C. The following potential monomers were studied: phenyl 4-(trimethylsiloxy)-benzoate; trimethylsilyl 4-(trimethylsiloxy)benzoate; ethyl 4-acetoxybenzoate; phenyl 4-acetoxybenzoate; trimethylsilyl 4-acetoxybenzoate. Only the latter monomer gave acceptable yields (up to 60%) of poly(4-hydroxybenzoate). When concentration, reaction time, and temperature were varied, a whiskerlike morphology was found under most circumstances. Slablike crystals were never found even at a high monomer concentrations (0.4 mol/L). Hydrolysis, DSC, and WAXS measurements prove that the whiskers prepared at 400-degrees-C represent chemically and physically rather perfect crystals of poly(4-hydroxybenzoate), whereas those obtained at 350-degrees-C are physically less perfect. At 400-degrees-C fibrous whiskers with lengths above 100-mu-m and aspect ratios up to 100:1 can be synthesized.