Copolymerization of CO2 and 1,2-Cyclohexene Oxide Using a CO2-Soluble Chromium Porphyrin Catalyst

The copolymerization of 1,2-cyclohexene oxide (CHO) with carbon dioxide was performed, using supercritical carbon dioxide (scCO2) as both solvent and reactant, to produce an aliphatic polycarbonate. A CO2-soluble catalyst, tetra(pentafluorophenyl)porphyrin chromium(III) chloride (CrTFPPCl), was synthesized and used to catalyze the polymerization in the presence of 4-(dimethylamino)pyridine (DMAP) as cocatalyst. The best yields for the copolymerization (up to ∼75%) were obtained in the temperature range 95−110 °C over a period of 18 h, with a molar ratio of catalyst to monomer of 2.6 × 10-3. High catalyst efficiencies (3.9 kg of polymer/g of Cr) were observed under these conditions. The copolymers consisted predominantly of carbonate linkages (90−97%), and the chain microstructure was analyzed by 1H NMR and 13C NMR spectroscopy. Gel permeation chromatography revealed number-average molecular weights (M n) of the order of 3500. In contrast to previous studies involving supercritical CO2, narrow polymer molecular weight distributions were observed throughout (M w/M n < 1.4).