SYNTHESIS OF POLY(PARA-PHENYLENETEREPHTHALAMIDE) BY SOLID-PHASE POLYMERIZATION

Poly(p-phenyleneterephthalamide) (PPTA) chain extension reactions, notably the catalyzed condensation of diphenyl terephthalate with p-phenylenediamine, are severely limited, at reaction temperatures up to at least 400-degrees-C, by immobilization of the growing macromolecules at modest molecular weight (MW) levels. This is characteristic of the stiff, extended nature of the polymer chains and their high propensity to crystallize. However, the phenolysis reaction can proceed very rapidly above a threshold temperature of about 475-degrees-C such that very high MW (eta(inh) = 5-9 dL/g in H2SO4) is achievable by brief heating at about 530-degrees-C. Novel techniques have been devised to subject the material to be polymerized (a monomer-catalyst mixture or a low-MW oligomer) to high temperatures for a very short time. The threshold temperature is believed to signal the level beyond which the PPTA chains develop considerable segmental mobility such that interchange of amino ends with adjacent amide groups can occur freely. Ultimately an amino end will interchange with a phenyl ester group to liberate phenol which can diffuse out of the system for a net gain of one amide group. The effects of catalysts, byproduct elimination rate, and heat-up rate are considered. In all cases polymerization was accompanied by some branching which, while not detectable by most conventional analytical procedures, caused major adverse changes in the viscosity and shear sensitivity of sulfuric acid solutions. A consideration of model compound reactions attributed branching to disproportionation of two amide groups to form an amidine branch point.