Ring‐opening polymerization of substituted ε‐caprolactones with a chiral (salen) AlOiPr complex

The ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL), 4‐methyl‐ε‐caprolactone (4‐MeCL), and 6‐methyl‐ε‐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° in toluene corresponded to first‐order reactions in the monomer and propagation rate constants of kε‐CL > k4‐MeCL ≫ k6‐MeCL. A notable stereoselectivity with a preference for the R‐enantiomer was observed in the ROP of 6‐MeCL with R,R′‐[1], whereas for 4‐MeCL, no stereoselectivity was found.