Polylactones: 31. Sn(II)octoate-initiated polymerization of L-lactide: a mechanistic study

Abstract The polymerization of L-lactide was catalysed with Sn(II)2-ethylhexanoate (SnOct 2 ) in the presence or absence of benzyl alcohol. The molecular weights parallel the lactide/benzyl alcohol ratio, but never the lactide/Sn ratio. 1 H n.m.r. spectroscopy revealed the existence of benzylester and −CH(CH 3 )OH end-groups. Polymerizations conducted at low lactide/catalyst ratios in the absence of an alcohol yield polylactide with a low content of 2-ethylhexanoate end-groups. 1 H and 119 Sn n.m.r. spectroscopy of CHCl 3 solutions also demonstrated that SnOct 2 forms strong complexes with both benzyl alcohol and ethyl lactate and weaker complexes with lactide. A similar but weaker complexation was also detected for Bu 2 SnOct 2 in combination with either benzyl alcohol or lactide. A new polymerization mechanism is discussed, assuming the reaction between lactide and OH end-groups bound to a Sn atom via two sp 3 d 2 orbitals.

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