A novel use of Ti-POSS as initiator of L-lactide ring-opening polymerization

The efficacy of a metal-silsesquioxane, namely, heptaisobutyl (isopropoxyde)titanium-polyhedral oligomeric silsesquioxanes (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 reaction 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.