Polymerization, morphology, and crystal structure of poly(p-benzamide)

Isothermal polymerization of acetaminobenzoic acid at various temperatures in bulk and solution was monitored by acetic acid evolution. The polymeriza tion took place initially in a homogeneous phase, but it soon changed to he terogeneous as the polymer precipitated from the melt or solution. The reac tion course consisted of a short induction period, followed by a fast secon d-order reaction and a third slow, also second-order, reaction. The differe nt polymerization rates in the second and third stage were due to polymer p recipitation. The degree of polymerization of the resulting polymer was gen erally low, usually less than 5. The polymer was highly crystalline and pro ne to decarboxylation at temperatures above 300 degreesC. Sample structure and morphology were characterized by various lamellar formations similar to those seen previously in many aromatic polyesters. Epitaxial solution poly merization/crystallization on mica resulted in three different morphologies , the most unique being shish kebab-type structures. Polybenzamide [poly(p- aminobenzoate)] is polymorphic; the most frequently seen hk0 electron diffr action patterns were similar to those from phase I of aromatic polyesters. Phase II of polybenzamide was seen only rarely. Simulation, using Cerius(2) , suggested equal agreement with [001], [100], and fiber electron diffracti on (ED) patterns and X-ray powder patterns for two different orthorhombic u nit cells (a = 7.71, b = 5.35, c = 12.94 Angstrom, rho = 1.55 g/cm(3)); bot h have a parallel packing of adjacent molecules, but in one, successive phe nyl rings along a given chain are parallel, while in the other they are twi sted at +/- 30 degrees. For both unit cells, neighboring molecules were dis placed by +/-0.14 Angstrom along c to obtain better agreement with the obse rved patterns. The [010] patterns could distinguish between the two cells, but were not obtainable.