Copolycarbonates containing such structural units as birefringence-reducing or “soft block” units are prepared by conducting a reaction, such as melt polymerization or equilibration, between a precursor polycarbonate and a monomer, polycarbonate oligomer or high molecular weight polycarbonate which is a source of other structural units. The crystallinity of the resulting precursor copolycarbonate or one of the reagents employed in its preparation is enhanced and the precursor copolycarbonate is subjected to solid state polymerization.