Patent ID: 6870013

Claim:
A method for preparing a copolyorganosiloxanecarbonate which comprises: contacting at least one dihydroxyaromnatic compound with phosgene, the molar ratio of phosgene to dihydroxyaromatic compound being in the range of about 0.3-0.85:1, in an alkaline mixed aqueous-organic liquid at a pH in the range of about 9-12, in the presence of at least one tertiary amine as the only catalytic species present and, optionally, at least one monohydroxyaromatic compound or chloroformate thereof as chain termination agent, thereby producing an oligomeric aromatic polycarbonate mixture; combining said mixture with a reagent consisting essentially of at least one polyorganosiloxane bis(aryl)chloroformate at a pH in the range of about 10.5-13.5, optionally with additional introduction of at least one of (1) phosgene and (2) at least one monohydroxyaromatic compound or chloroformate thereof as chain termination agent, thereby forming a copolyorganosiloxanecarbonate oligomer mixture; and adding phosgene and, optionally, chain termination agent to said copolyorganosiloxanecarbonate-containing mixture to afford a copolyorganosiloxanecarbonate of a desired molecular weight.