Polycarbonates (PCs) prepared by melt transesterification processes from bisphenol A (BPA) and diphenyl carbonate (DPC) typically contain significant levels of uncapped chains (7 – 50 %) compared to PCs prepared by interfacial processes. The resulting free OH end groups may sometimes have an impact on properties of the resins. For this reason, it may be desirable to use compounds with a higher capping efficiency than DPC in a post-polymerization endcapping process. Endcapping reagents often are carbonate or ester derivatives of phenol; however, such reagents release the byproduct phenol, which then rapidly re-equilibrates with the polymer to limit the achievable molecular weight and endcap level. Unfortunately very long reaction and devolatization times are required to counteract this effect, and such long residence times may themselves negatively affect the PC properties.
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