Bulk ring-opening polymerization (ROP) of L-lactide catalyzed by Ni(ii) and Ni(ii)-Sm(iii) complexes based on a salen-type schiff-base ligand

A monometallic (Ni2+, 1) and a bimetallic (Ni2+-Sm3+, 2) complexes based on the Salen-type Schiff-base ligand H2L (H2L = N,N'-bis(3-methoxysalicylidene)ethylene-1,2-diamine) were synthesized and characterized by FT-IR, ESI-MS and X-ray crystallography. The catalysis results showed that the two complexes with different active species, could efficiently catalyze the bulk solvent-free melt ring-opening polymerization (ROP) of L-lactide with moderate molecular weights and narrow molecular weight distributions. Especially, for the bimetallic complex 2, the involvement of rare ions effectively passivated the catalytic behavior on the ROP of L-lactide, while was in favor of the increase of polymeric molecular weights (M-n) and the polymerization controllability.