Propylene Oxide Homopolymerization and Copolymerization with Carbon Dioxide by γ-Alumina-Supported Zinc Coordination Catalysts

Propylene oxide was homopolymerized and copolymerized with carbon dioxide in the presence of catalysts based on ethylzinc phenoxide or ethylzinc 1-phenoxy-2-propoxide and/or diethylzinc and γ-alumina as a support. The propylene oxide homopolymerization yielded poly(propylene oxide) with an average molecular weight of about 20 × 103, and consisting of the prevailing amorphous fraction and the crystalline fraction. The copolymerization of propylene oxide and carbon dioxide produced poly(propylene carbonate) with an average molecular weight of about 30 × 103 and was accompanied by the formation of propylene carbonate. The polymeric products obtained were characterized by means of elemental analysis, IR, UV, 1H-NMR and 13C-NMR spectroscopy, and molecular weight determinations. On the basis of these studies, especially those concerning the polymer end-groups and the chain microstructure, a possible structure of the active sites in γ-alumina-supported zinc coordination catalysts and a possible mechanism of the initiation and propagation reactions in propylene oxide homopolymerization and copolymerization with carbon dioxide are presented.