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]AlMe, were synthesized and tested as initiators in the ring-opening polymerization (ROP) of ε-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 ε-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 ε-caprolactone and lactides. In particular, compound 1 allowed excellently controlled random copolymerization of ε-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).