Patent ID: 6414106
Filing Date: 2002-07-02
Classification: C07C

Abstract:
A method of preparing polycarbonate by the melt process, comprising:combining a thermally stable organic base selected from the group consisting of tetraalkyl phosphonium hydroxides, tetraorganophosphonium carboxylic acid salts, or a mixture thereof with a crude dihydric phenol in the presence of a sulfonic acid compound and in the absence of an alkali metal compound or an alkaline earth metal compound to form a dihydric phenol; melting the dihydric phenol and a diester of carbonic acid for a time and at a temperature sufficient to form a melt product; combining the melt product with a catalyst comprising the alkali metal compound, the alkaline earth metal compound, a quaternary ammonium compound, a quaternary phosphonium compound, or a combination thereof; oligomerizing the melt product for a time and at a temperature sufficient to form a number average molecular weight of less than 8,000; and polymerizing the melt product to a number average molecular weight of about 10,000 to about 65,000.