Polycarbonates, cyclic

Poly(bisphenol-A-carbonate) under pseudoideal reaction conditions was investigated, and the cyclic polycarbonate was obtained as the main product. In the system, the interface of the water/toluene mixture might have favored the cyclization reaction between the polar end groups [88]. Cyclic carbonates during the (Salen)CrCl catalyzed CCh/cyclohexene oxide copolymerization process in the presence of ionic initiators was also obtained [89]. The cyclic carbonate is produced via the backbiting mechanism, and the process is assumed to take place via a metal alkoxide (polymer chain) intermediate. Subsequent ring-opening of the cyclic carbonate with concomitant formation of polyether and CO2 was fast at the reaction temperatures from 80 to 100 °C). 

MALDI-TOF spectra of commercial polycarbonates display peaks due to open-chain macromolecules along with peaks due to cyclics. Polycarbonates containing porphyrin or fullerene units in the main chain fullerene are easily analyzed by MALDI-TOF. ... 

The MALDl-TOF mass spectra exclusively revealed peaks of cyclic polycarbonates detectable up to masses around 55 kDa after fractionations (Figs. 7.7 and 7.8). Similar results were obtained, when the hydrolytic polycondensation of bi-sphenol-A bischloroformiate was optimized [23]. The large fraction of cyclic polycarbonates including high molar masses indicates that the reaction conditions of the best experiments were close to the optimum. 

Furthermore, polycondensations of bisphenol-A and diphosgene were performed in a homogeneous phase with pyridine as catalyst and HCL acceptor. The excess of diphosgene was varied to compensate for the loss due to side reactions. After optimization of the reaction conditions the MALDl-TOF mass spectra displays again an almost exclusive formation of cyclic polycarbonates, but the highest Mn amounted only to 15 kDa. In other words, the interfacial polycondensations... 

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