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Process for the neutralization of residual acid species in crude dihydric phenols

  • US 6,576,801 B2
  • Filed: 02/25/2002
  • Issued: 06/10/2003
  • Est. Priority Date: 03/02/2001
  • Status: Expired due to Term
First Claim
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1. A method of preparing polycarbonate by the melt process, comprising:

  • combining a thermally stable organic base 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; and

    polymerizing the melt product.

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