Two ester-functionalized cyclohexene oxide monomers (3,4-cyclohexene-oxide-1-carboxylic acid methyl ester (1) and 3,4-cyclohexene-oxide-1-carboxylic acid phenyl ester (2)) could be copolymerized with CO2 using the ß-diketiminato zinc catalyst (EtBDI)ZnOEt (EtBDI = 2-(2,6-diethylphenyl)amido-4-(2,6-diethylphenyl)imino-2-pentene) under mild conditions. MALDI-ToF-MS microstructure analyses of the formed aliphatic polycarbonates revealed the occurrence of chain transfer reactions to both monomer and polymer as a result of zinc-catalyzed transesterifications. As a consequence, branched and cyclic polymer structures were formed, which limited the molecular weight development and led to an increase in the polydispersity. The zinc catalyst is also capable of transesterifying carbonate functionalities, albeit that the transesterification rate is considerably lower than that for ester functionalities and only becomes visible at high conversion. This was supported by independent catalytic transesterification reactions of esters and carbonates. Transesterification of carbonate functionalities at the end of the polymerization reaction might explain the observed bimodal behavior for the intrinsically living ß-diketiminato zinc catalyst.
Duchateau, R., Meerendonk, van, W. J., Yajjou, L., Staal, B. B. P., Koning, C. E., & Gruter, G. J. M. (2006). Ester-functionalized polycarbonates obtained by copolymerization of ester-substituted oxiranes and carbon dioxide: A MALDI-ToF-MS analysis study. Macromolecules, 39(23), 7900-7908. https://doi.org/10.1021/ma0610313