Ring opening polymerization of lactide under solvent-free conditions catalyzed by a chlorotitanium calix[4]arene complex

A novel chlorotitanium calix[4]arene complex was synthesized and tested, without activator, as catalyst for the polymerization of L- and rac-lactide under solvent-free conditions. The catalyst displayed high activity, which depended on the monomer-to-catalyst molar ratio, and led to highly isotactic PLLA. Despite concomitant transesterification during the polymerization, polylactide formation was well-controlled, the molar mass distribution indexes remaining in the restricted range of 1.2-1.4.