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 = Bun 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 ΔH≠ as a function of R with all the values falling within the range 11 ± 2 kcal mol−1. The entropy of activation, ΔS≠, 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)2Sn(OPri)2 and (p-Me2NC6H4)3SnOPri 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.

Studies of the ring-opening polymerization of l-lactide by RLSn(OPri)2 compounds where R = Bun and p-XC6H4 (X = CF3, F, H, Me and OMe) over a temperature range in benzene reveals activation parameters ΔH≠ = 11 ± 2 Kcal mol−1 and ΔS≠ = − 50 ± 5 eu. The consistently large and negative value of ΔS≠ is taken to imply a highly ordered transition state for the ring-opening (enchainment) event.Figure optionsDownload as PowerPoint slide