Polycarbonate prpen. from dipheonl and carbonate ester - by polycondensn. of intermediate crystalline oligocarbonate in presence of boiling liq. entraining agent, used in electrical industry

摘要

The prepn. of aromatic polycarbonates of wt. average mol. wt. (Mw) 15,000-200,000 and OH end-gp. content below 250 ppm (I) from diphenols, carbonate diesters and opt. branching agents, comprises (i) transesterifying in the melt to give oligo-carbonates (II) of Mw 2,000-10,000 and OH end-gp. content 20-50 mol.% followed by crystallising; and (ii) solid-phase polycondensing the crystalline (II) in the presence of a boiling organic solvent (III) which acts as entraining agent for the cleavage prods. from polycondensn. but does not dissolve or melt the oligomer (II). USE/ADVANTAGE - (I) are used e.g., in the electrical industry and in motor vehicle prodn.. The process enables the removal of cleavage prods. from (II) without using large amts. of gaseous entraining agent and without the high cost associated with high vacuum processes (cf prior-art processes). In an example, a mixt. of 684.9g Bisphenol A, 661.3g diphenyl carbonate and 8mg Na bisphenolate was melted at 250 deg.C with stirring, then the pressure was reduced to 1 mbar over 90 mins. (with a continuous rate of distn.) to give an oligomer (II) of relative soln. viscosity (RSV) 1.080, which was crushed and crystallised from acetone. 20g (II) was heated with 180g undecane for 1 hr. at 180 deg.C and 7 hrs. at 200 deg.C in an appts. fitted with a reflux condenser and an extractor contg. 10g zeolite K-Y. The prod. was a crystalline, colourless polycarbonate of RSV 1.254 (0.5% in CH2Cl2).