Solid state polymerization of bisphenol A polycarbonate: Effect of the crystallization method and polymerization conditions

A study on the effect of the crystallization method on the solid state polymerization (SSP) process of bisphenol A polycarbonate has been performed. Prepolymer samples were crystallized via four different techniques (solvent induced, shear induced, organic salt induced, and thermal crystallization) and SSP progress was checked by measuring the molecular weight increase. The fastest polymerization rate was obtained with prepolymers crystallized with acetone. The reaction rates were correlated with the crystallinity and plasticization of solvents, which both affected the chain mobility. The experiments conducted using different sweep gas flow rates and different particle sizes showed that, for the acetone-crystallized prepolymers, the reaction rate was limited by the by-product diffusion inside the polymer particles and from the surface of the particles into the sweep gas. 1H-nuclear magnetic resonance analysis proved that polymers prepared through a solid state process had a consistently lower content of Fries rearrangement by-products with respect to commercial samples obtained by standard melt polycondensation methods