Abstract: A process for producing a low-particle-content transparent thermoplastic resin solution, which comprises centrifuging a solution of a transparent thermoplastic resin containing free water to separate it into a resin solution phase, an aqueous phase and an intermediate layer, and separating the resin solution phase from the aqueous phase and the intermediate layer. By this process, the number of particles having a size of at least 0.5 .mu.m in the resin solution can be decreased to 10,000 or less, preferably substantially zero, per gram of the transparent thermoplastic resin.

Abstract: A process for preparing polycarbonate oligomers by reacting phosgene with an alkaline aqueous solution containing an alkali metal salt or alkaline earth metal salt of a dihydric phenol in the presence of an inert organic solvent, which comprises previously cooling said alkaline aqueous solution to not higher than 0.degree. C., reacting the cooled aqueous solution with phosgene to perform a phosgenation reaction and also to absorb the heat of the phosgenation reaction by the quantity of heat that said cooled aqueous solution has, thereby to adjust the phosgenation reaction system substantially to not higher than 10.degree. C., and then oligomerizing the phosgenation product at a temperature of 15.degree. C. or higher.

Abstract: A process for producing polycarbonate oligomers by the reaction of dihydroxy compounds with phosgene, which comprises contacting a mixture of a dihydroxy compound and an aqueous alkali solution with phosgene in the presence of an organic solvent in a tubular reactor to perform a first-stage reaction, introducing the first-stage reaction mixture into a tank-type reactor equipped with a stirrer and containing the aqueous alkali solution and a solution in the organic solvent of a polycarbonate oligomer formed by the reaction of the first-stage reaction product in a second stage, and performing the second-stage reaction while stirring the reaction mixture in the tank-type reactor and maintaining it at a predetermined temperature by sufficient removal of the heat of reaction.

Abstract: High molecular weight polycarbonates are prepared by the reaction of phosgene with a dihydroxydiaryl alkane in the presence of an acid acceptor, a solvent and at least one member selected from specified monohydric alcohols, haloformates, monothiols, halothioformates, monocarboxylic acids and halides, salts, quaternary ammonium salts and anhydrides thereof.