Controllable bulk solvent-free melt ring-opening polymerization (ROP) of L-lactide catalyzed by Ni(II) and Ni(II)-Ln(III) complexes based on the Salen-type Schiff-base ligand

Abstract A monometallic (Ni 2+ , 1 ) and a series of bimetallic (Ni 2+ –Ln 3+ , Ln = Ce ( 2 ); Ln = Nd ( 3 ); Ln = Sm ( 4 ); Ln = Eu ( 5 ); Ln = Tb ( 6 ); Ln = Ho ( 7 ); Ln = Tm ( 8 )) complexes based on the Salen-type Schiff-base ligand H 2 L ( H 2 L  = N,N′-bis(3-methoxysalicylidene)ethylene-1,2-diamine) were synthesized and characterized by EA, FT-IR, ESI-MS and X-ray crystallography. The catalysis results showed that the two kinds of 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 series of bimetallic complexes 2 – 8 , the involvement of rare ions effectively passivated the catalytic behaviors on the ROP of l -lactide, while was in favor of the increase of polymeric molecular weights ( M w or M n ) and the polymerization controllability, and the type of rare ions was important and influential factor contributing to the catalytic behaviors.