Process for the preparation of polyesters and poly(ester-carbonates)

Process for preparing polyesters and poly(ester-carbonates) comprising

• (a) preparing a reaction mixture of
• (1) an aromatic polycarbonate having an inherent viscosity of about 0.1 or more and (A) having the general formula ##STR6## wherein Ar is the residue remaining after the removal of the hydroxy groups from at least one aromatic diol and optionally the residue may be substituted with alkyl groups containing 1-4 carbon atoms or phenyl,
• (2) an ester of a dicarboxylic acid (B) having the general formula ##STR7## wherein R may be the same or different and is selected from aliphatic, cycloaliphatic and aryl groups containing up to 8 carbon atoms, and Y is the residue remaining after removal of the carboxyl groups from an aliphatic, cycloaliphatic or armatic dicarboxylic acid, and
• (3) a catalytic amount of a suitable ester exchange and polymerization catalyst,
• (b) initially heating said reaction mixture sufficiently to substantially reduce the melt viscosity of the reaction mixture,
• (c) increasing the temperature as required to keep the reaction mixture molten and to distill away the dialkyl or diaryl carbonate condensation by-product, and
• (d) reducing pressure to further remove said by-product and to increase the molecular weight of the polymer product.