The ring-opening polymerization (ROP) of epsilon-caprolactone (g-CL), 4-methyle-caprolactone (4-MeCL), and 6-methyl-epsilon-caprolactone (6-MeCL) with a single-site chiral initiator, R,R'-(salen) aluminum isopropoxide (R,R'-[1]), was investigated. The kinetic data for the ROP of the three monomers at 90 degrees in toluene corresponded to first-order reactions in the monomer and propagation rate constants of k epsilon-CL > k(4-MeCL) >> k(6-MeCL). A notable stereoselectivity with a preference for the R-enantiorner was observed in the ROP of 6-MeCL with R,R'-[1], whereas for 4-MeCL, no stereoselectivity was found. (c) 2006 Wiley Periodicals, Inc.