Copolymerization of CO2 and cyclohexene oxide using a lysine-based (salen)Cr(III)Cl catalyst.

A new, natural lysine-based (salen)Cr(III)Cl ((lys-salen)Cr(III)Cl) complex was prepared and its catalytic activity for the copolymerization of CO(2) and cyclohexene oxide (CHO) was described in the presence of PPNCl (PPN(+) = bis(triphenylphosphoranylidene)ammonium) as cocatalyst. The influence of the reaction time, operating temperature and the molar ratio of the catalyst components on the copolymerization was investigated in detail. The results showed that the (lys-salen)Cr(III)Cl, synthesized from non-ortho-diamine, could effectively catalyze the alternating copolymerization (carbonate linkages = 94.6-99.0%). The selectivity was >95%, and was less sensitive to the temperature and the molar ratio of catalyst components, compared to that of the copolymerization catalyzed by traditional salen-metal complexes. The ESI-MS analyses of oligomer and (lys-salen)Cr(III)Cl indicated that a possible chain-transfer reaction had taken place, which might be induced by the water coordinating to the central metal ion.