METHOD FOR MAKING POLYCARBONATE

摘要

Polycarbonates having a high level of endcapping and containing a low level of Fries rearrangement product are prepared from dihydroxy aromatic compounds, such as bisphenol A, and diaryl carbonates such as diphenyl carbonate in a two stage process involving a tetraalkyl phosphonium carboxylate catalyzed oligomerization of the reactants in a first reaction stage followed by the addition of an alkali metal hydroxide co-catalyst in the second stage of the polymerization reaction. The late addition of the co-catalyst provides improved polymerization reaction rates as judged by higher polycarbonate molecular weights. The amount of alkali metal hydroxide co-catalyst is small thus avoiding the formation of excessive amounts of Fries product. The method has been used to provide Fries product levels between 200 and 1000 parts per million in polycarbonates having Mn values of at least 7,500 Daltons.