The selective transformation of CO(2) and epoxides to afford completely alternating copolymers remains a topic of much interest for the potential utilization of carbon dioxide in chemical synthesis. The use of salicylaldimine (salen)-metal complexes and their saturated (salan)-metal versions have proven to be the most effective and robust single-site catalyst for these processes. Herein, we report on mechanistic aspects of the copolymerization of alicyclic and aliphatic epoxides with CO(2) in toluene solution and in neat epoxides in the presence of a (salan) CrCl/onium salt catalyst system. The activation barriers for both cyclohexene oxide(CHO)/CO(2) and propylene oxide(PO)/CO(2) were shown to be significantly higher in toluene solution than those previously reported for reactions carried out under solventless conditions. Terpolymerization of CHO/vinylcyclohexene oxide/CO(2) was shown via Fineman-Ross analysis at 60 degrees C to proceed with little monomer selectivity, for example, r(CHO) = 1.03 and r(VCHO) = 0.847. On the other hand, terpolymerization of CHO/PO/CO(2) occurred at 25 degrees C with a propensity for incorporation of PO in the polymer. However, at 40 degrees C, Fineman-Ross analysis revealed r(CHO) and r(PO) values of 0.869 and 1.49, thereby affording a terpolymer with a more equal distribution of monomers. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 127-133, 2012