Syntheses of Biodegradable and Biorenewable Polylactides Initiated by Aluminum Complexes Bearing Porphyrin Derivatives by the Ring-Opening Polymerization of Lactides.

Three aluminum alkyl complexes bearing porphyrin derivatives were synthesized by pyrrole derivatives and benzaldehyde derivatives. These complexes were characterized by NMR and elemental analysis. These complexes are used for racemic-lactide polymerization. In the ring-opening polymerization of racemic lactide, complex 3(2,3,7,8,12,13,17,18-octamethyl-5,10,15,20-tetraphenylporphyrin aluminum methyl, R1 =H, R2 =Me in Scheme 2) with isopropanol showed the highest stereoselectivity, and an isotactic polylactide with a Pm of 0.68 was obtained. The polymerization kinetics with complex 3 as catalyst was studied in detail. The kinetics of the polymerization data indicated that the rate of polymerization initiated by complex 3 had first-order dependency on monomer and catalyst. There is a linear relationship between lactide conversion and the number average molecular weight of PLA.