Ultrahigh molecular weight nonlinear polycarbonates synthesized in microlayers

Ultrahigh molecular weight bisphenol A polycarbonate (BPAPC) with nonlinear chain structures has been synthesized by solid-state polymerization in microlayers at 230 C. It has been found that the molecular weights of the microlayers of low molecular weight prepolymers with thickness ranging from 5 to 35 μm increased rapidly to ultrahigh molecular weight (300,000-600,000 g/mol) without any discoloration. The amorphous prepolymers exhibited much higher reaction rate than the partially crystallized prepolymers. Although the reactive end group mole ratios of the prepolymers prepared by semibatch melt polycondensation deviated significantly from the stoichiometric value, branching and partial cross-linking reactions have been found to occur to rapidly increase the polymer molecular weight. These nonlinear chain structures observed were due to Fries rearrangement, Kolbe-Schmitt rearrangement reactions, and radical-induced scission/cross-linking reactions. The microstructures of the high molecular weight polymers have been analyzed by ¹³C NMR, ¹H NMR, pyrolysis-gas chromatography mass spectrometry, and atomic force microscopy.