Crystallization of bisphenol-A polycarbonate induced by organic salts: Chemical modification of the polymer. III. Reaction mechanism

In the presence of a sodium arylcarboxylate or arylphenoxide, bisphenol-A polycarbonate (PC) undergoes complex chemical modifications at high temperatures. The reaction mechanism is similar to the one previously established for model systems. Initially, the salt reacts with the carbonate groups of the polymer. This lowers the number-average molecular weight and produces ionic chain ends of the phenoxide type. A fast transesterification reaction is then induced by a continuous exchange between the phenoxide and the carbonate groups, affecting the molecular distribution until an equilibrium is attained. In the presence of CO₂, the phenoxide-terminated PC undergoes further chemical modifications (formation of phenyl salicylate and phenyl phenoxybenzoate groups) leading to progressive crosslinking of the polymer.