Synthesis and Characterization of Poly(L-lactide-co-ε-caprolactone) Copolymers: Effects of Stannous Octoate Initiator and Diethylene Glycol Coinitiator Concentrations

A series of approximately 50:50 mol % poly(L-lactide-co-ε-caprolactone) copolymers were synthesized by bulk copolymerization of L-lactide (LL) and ε-caprolactone (CL) using stannous octoate (Sn(Oct) 2 ) and diethylene glycol (DEG) as the initiating system. The resulting P(LL-co-CL) copolymers were characterized by various analytical techniques including dilute-solution viscometry, GPC, H/C NMR and DSC. It was found that both the Sn(Oct) 2 and DEG concentrations exerted important but different effects on the molecular weight (average and distribution), chain microstructure and temperature transitions of the copolymer formed. Whereas the Sn(Oct) 2 initiator mainly affected the molecular weight distribution and comonomer sequencing, the DEG coinitiator was more influential on the average molecular weight. The results are discussed in the light of current theories of the coordination-insertion mechanism of cyclic ester ringopening polymerization.