Mechanism for the Amine-Catalyzed Formation of Polycarbonate Cyclics

Abstract

The importance of cyclic precursors for the preparation of polyamides, aliphatic polyesters, silicones, and epoxide thermosets by ring opening polymerization has been well documented. 1 However, use of cyclic aromatic polyesters or polycarbonates has been limited not only by low-yielding procedures for their preparation, 2 but also by the high melting points of the individual cyclics produced in these reactions.3 Recently, we have reported several high yielding procedures for preparing oligomeric cyclic polycarbonates, polyarylates, and polyimides for use in ring opening polymerizations.4 The low melt viscosity of these oligomeric cyclics together with the very high molecular weights which are achievable upon polymerization promise to make these polymer intermediates very useful in a variety of applications. We report herein mechanistic and process studies which have led to the high yielding procedure for preparing bisphenol A cyclic polycarbonates under interracial reaction conditions. The role of the tertiary amine catalyst will be addressed in detail. Many of the concepts developed in this work are applicable to interracial polycarbonate forming reactions in general and should provide utility in both novel and traditional polycarbonate syntheses. Although several procedures already exist for preparing cyclic polycarbonates, the interracial process described herein is the only one known which selectively affords cyclics with almost total exclusion of low MW linear oligomers (< 0.1% of oligomers with molecular weights < 5000). The presence of linear oligomers must remain low to ensure the formation of high MW polymer upon ring opening polymerization.