GB1026151A - Process for accelerating the transesterification process for the production of high molecular weight thermoplastic polycarbonates - Google Patents

Abstract

In the manufacture of polycarbonates by effecting a transesterification between (a) an ester of carbonic acid and (b) a dihydric phenol or a mixture thereof with a dihydric alcohol, the transesterification is carried out in the presence of an unstable monomeric and/or polymeric ester which evolves carbon dioxide. The latter acts as an entraining agent for the removal of monohydroxy compounds from the reaction melt. A mixture of unstable esters may be used which decompose at different temperatures. The unstable esters may be added at the beginning or during the transesterification and may be certain dialkyl, dicycloalkyl or diaryl carbonates or similar mixed dicarbonates, or may be certain biscarbonates of dihydric phenols and monohydric alcohols. Alternatively, there may be added to the reaction mixture substances capable of forming by transesterification unstable carbonates or polycarbonates, suitable substances being certain aliphatic or cycloaliphatic mono- or dihydric alcohols. The diaryl carbonates used for the transesterification may be diaryl carbonates or bis-phenyl carbonates of dihydric phenols. Examples describe the manufacture of polycarbonates by reacting (1)-(4) and (6) bisphenol A with diphenyl carbonate in the presence of hexylene-1:6-bis-phenyl carbonate, hexane - 1:6 - diol, n - dodecyl alcohol, n-stearyl alcohol, 2:2-bis-(4 - (beta - hydroxyethoxyphenyl) - phenyl) - propane, 1:4 - dimethyl - butylene - 1:4 - bis - (phenyl carbonate) or 3 - methyl - propylene - 1:3 - bis-(phenyl carbonate); (5) bisphenol A and hydroquinone with diphenyl carbonate in the presence of 1:6-hexylene-bis-(phenyl carbonate).