Ring-opening polymerization of L-lactide by organotin(IV)alkoxides, R2Sn(OPri)2:: Estimation of the activation parameters

The ring-opening polymerization of L-lactide, L-LA, to give poly-L-lactide by R2Sn(OPri)(2) compounds, where R = Bu-n and p-XC6H4 (X = CF3, F, H, Me and OMe) has been studied in benzene over a temperature range. There is a relatively small variation in Delta H not equal as a function of R with all the values falling within the range 11 +/- 2 kcal mol(-1). The entropy of activation, Delta S not equal, is consistently large and negative, -50 +/- 5 eu, supporting the view that the ring-opening event, the enchainment step involves a highly ordered transition state. The crystal and molecular structures of the compounds Ph2Sn(OPri)(2), (p-FC6H4)(2)Sn(OPri)(2) and (p-Me2NC6H4)(3)SnOPri are also reported. While the latter compound is monomeric in the solid state the former are both dimeric with a pair of bridging OPri ligands. (c) 2007 Published by Elsevier Ltd.