A Novel Use of Ti-POSS as Initiator of L-Lactide Ring-Opening Polymerization

The efficacy of a metal-silsesquioxane, namely, hep- taisobutyl (isopropoxyde)titanium-polyhedral oligomeric silses- quioxanes (Ti-POSS), as initiator of the ring-opening polymerization of L-lactide (LLA) has been assessed. Indeed, as demonstrated by proton nuclear magnetic resonance (1H NMR) spectroscopy and gel permeation chromatography (GPC) measurements, a well-controlled polymerization occurs via a coordination-insertion mechanism. Moreover, the above reac- tion leads to the direct insertion of the silsesquioxane molecule into the polymer backbone, thus producing a hybrid system. Differential scanning calorimetry measurements demonstrated that in comparison with a commercial poly-L-lactide (PLLA), the polymers prepared with Ti-POSS exhibit a higher crystallinity. Indeed, the presence of silsesquioxane molecules, attached to one end of the polymer chains, has been found to appreciably affect the crystal nucleation density.