Summary: Bisphenol‐A was polycondensed with diphosgene and excess pyridine in a mixture of dry dichloromethane and 1,4‐dioxane. The stoichiometry was varied to optimize the molecular weight. According to MALDI‐TOF mass spectra the fraction of cyclic polycarbonates increased with higher molecular weights. Analogous results were obtained with triphosgene. When pyridine was replaced by triethylamine, diethyl carbamoyl chloride was formed and an excess of diphosgene (plus triethylamine) yielded polycarbonates having one or two diethylcarbamate endgroups. However, the content of cycles increased again with the molecular weight and peaked for the sample with the maximum molecular weight. 1H NMR endgroup analyses confirmed the interpretation of the MALDI‐TOF mass spectra. SEC measurement indicated high polydispersity indices (around 7) for samples rich in cycles. magnified image
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Kricheldorf et al. (2005) studied this question.
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