Synthesis of Ultrahigh Molecular Weight PLAs Using a Phenoxy-Imine Al(III) Complex.

l- and d-lactide polymerization kinetics using phenoxy-imine ligands of the type MeAl[O-2-Bu-6-(CFN=CH)CH] in the presence of -butanol and benzyl alcohol by ring-opening polymerization into polylactide are investigated. Effects of initiator concentration, catalyst concentration, polymerization temperature, and time on the molecular weight of poly-l-lactide are also investigated. Purification and drying of l-lactide are found to significantly influence the polymerization kinetics and the final molecular weight achieved. Ultrahigh molecular weight poly(l-lactic acid) PLLA ( = 1.4 × 10 g/mol with = 1.8) and ultrahigh molecular weight poly(d-lactic acid) PDLA ( = 1.3 × 10 g/mol with = 2.0) are obtained when polymerization is performed with a molar ratio of monomer to catalyst (LA/Al) of 8000 for 72 h at 120 °C in the presence of benzyl alcohol with conversions of 96 and 91%, respectively. We report for the first time the synthesis of ultrahigh molecular weight poly-l- and d-lactide using the MeAl[O-2--Bu-6-(CFN=CH)CH] catalyst. The identified catalyst is found to be suitable for the synthesis of a broad range of molecular weights.