Lactide, β-butyrolactone, δ-valerolactone, and ε-caprolactone polymerization with copper diketiminate complexes

Pseudo-first-order rate constants for the polymerization of rac-lactide with dimeric (nacnac(Bn)Cu(mu-OiPr))(2) (nacnac(Bn) = deprotonated N,N'-dibenzyl-2-amino-4-imino-pent-2-ene), 1, in acetonitrile, THF, dichloromethane, and toluene are k(obs) = 2.4(1), 5.3(5), 3.6-4.4, and 10(1) min(-1), respectively (25 degrees C, 1.0 mmol L-1 1). A bimodal polymer molecular weight distribution is obtained in toluene, narrow polydispersities of 1.1 for THF and acetonitrile. Under the same conditions (25 degrees C, 1.0 mmol L-1 1, CH2Cl2), 1 polymerizes beta-butyrolactone, epsilon-caprolactone, and delta-valerolactone with rate constants of k(obs) = 3.0(1) x 10(-2), 1.2-2.7 x 10(-2), and 0.11(1) min(-1), respectively. Homopolymers showed narrow polydispersities of approximately 1.1. Sequential addition polymerizations showed evidence for transesterification if beta-butyrolactone or epsilon-caprolactone is introduced after a lactide block.