Polymerization in Micro-Layers to Ultrahigh Molecular Weight Nonlinear Polycarbonates

Ultra-high molecular weight bisphenol A polycarbonates (PC) have been synthesized in micro-layers of amorphous at pseudo-solid state polymerization conditions. The polymerization procedure consists of formulating a low molecular weight prepolymer precursor derived from bisphenol A and diphenyl carbonate in a melt transesterification process into thin polymer micro-layers on inert substrate surfaces, and carrying out the polymerization at temperatures where the polymer layer is in a rubbery state or a pseudo-solid state. The polymer layer containing lithium hydroxide monohydrate (LiOH×H₂O) catalyst maintains the amorphous state during the polymerization. The rate of polymerization in the amorphous polymer micro-layer has been found to be significantly faster than the conventional solid-state polymerization (SSP) in pre-crystallized spherical particles. At longer reaction times, the fraction of branched and partially cross-linked but solvent-soluble polymer increases without losing transparency. The presence of branched and cross-linking structures was confirmed and characterized by ¹H-NMR, pyrolysis-GC/MS, and Atomic Force Microscopy (AFM).

These nonlinear structured polymers are formed through Kolbe-Schmitt and Fries rearrangement reactions as well as radical-induced chain scission and hydrogen abstraction reactions. The final polymer molecular weights (M_w) of soluble polymers reached as high as 600,000 g/mol and the polycarbonate film obtained were optically transparent and ductile. In this presentation, we propose a mechanism of solvent-induced radical generation that leads to the nonlinear polymer chain structures and extensive experimental investigation results.