Copolymerization of carbon dioxide and propylene oxide using various zinc glutarate derivatives as catalysts

Various zinc dicarboxylate catalysts were synthesized by the reaction of zi nc oxide with eleven different glutaric acid derivatives, and their coordin ation characteristics were investigated by infrared spectroscopy. The elect ronic nature and steric hinderance of substituents influenced the coordinat ion of the carboxylate and the zinc metal ion. The coordination characteris tics were classified into three categories: i) compounds exhibiting bridgin g bidentate coordinating bonding modes, such as syn-anti and syn-syn bridgi ng; ii) compounds with only unidentate coordination; and iii) compounds wit h mixed coordinations of unidentate and bridging bidentate. All the zinc ca rboxylate catalysts produced poly(propylene carbonate)s (PPCs) by the copol ymerization of carbon dioxide and propylene oxide. The first category of ca talysts produced relatively higher yields than the other categories. Zinc g lutarate without any substituent, which is a catalyst in the first category , produced PPC with the highest yield and the highest molecular weight. The catalytic activity of zinc glutarate was suppressed by incorporation of su bstituents. The suppression of the catalytic activity might be due to the v ariation in the Lewis acidity of the zinc site as well as changes in the mo rphological structure caused by the substituents. Methylaluminoxane was als o evaluated as a catalyst for the copolymerization, but it produced copolym ers containing a large amount of ether linkages.