Random Copolymerization of ε-Caprolactone and Lactides Promoted by Pyrrolylpyridylamido Aluminum Complexes

The monomethylaluminum complexes 1 and 2, bearing pyrrolylpyridylamido as dianionic [-NNN-] tridentate ligands with general formula [NNN]AIMe, were synthesized and tested as initiators in the ring-opening polymerization (ROP) of epsilon-caprolactone, L-lactide, and D,L-lactide. In the presence of 1 equiv of alcohol, compounds 1 and 2 were highly active initiators in the ROP of epsilon-CL (TOF up to 4000 mol(CL) mol(Al-1) h(-1)), and they showed moderate activity in the ROP of lactides (TOF up to 1.7 mol(LA) mol(AL)(-1) h(-1)) The polymerization processes proceeded with a living mechanism; moreover, the obtained PLAs resulted isotactic-enriched with P-m values up to 76%. More interestingly, this class of catalysts promoted the random copolymerization of epsilon-caprolactone and lactides. In particular, compound 1 allowed excellently controlled random copolymerization of epsilon-caprolactone and D,L-lactide as indicated by both the values of the reactivity ratios of the two monomers (r(LA) = 1.17; r(CL) = 1.36) and the average lengths of the caproyl and lactidyl sequences (L-CL = 2.0; L-LA = 2.5).