Polyhydropolyborates as polymerization catalysts

This invention relates to polyhydropolyborates useful as transesterification catalysts in melt polymerization reactions of dihydroxy aromatic compounds with diaryl carbonates. Suitable polyhydropolyborates are those which comprise alkali metal counterions. The invention further relates to a method for the preparation of polycarbonates using these polyhydropolyborates. The method provides a product polycarbonate comprising a lower level of Fries product than is provided by other known methods employing conventional melt transesterification catalysts. The present invention relates to a synthetic method comprising contacting at least one diaryl carbonate with one or more dihydroxy aromatic compounds in the presence of a transesterification catalyst under melt polymerization conditions to afford a product polycarbonate. The transesterifcation catalysts used according to the method of the present invention are polyhydropolyborates in combination with tetraalkylammonium or tetraalkylphosphonium compounds which serve as co-catalysts. The transesterification catalysts employed according to the method of the present invention provide polycarbonates having reduced levels of Fries rearrangement product relative to conventionally employed catalysts such as sodium hydroxide in combination with tetramethylammonium hydroxide co-catalyst.