Controlled homoand copolymerization of ε-caprolactone and d,l-lactide in the presence of Ti^IV complexes

Titanium complexes with dialkanolamine (1, 2) and salen ligands (3), as well as titanium alkoxide containing two fragments of an unsaturated alcohol (cis-but-2-ene-1,4-diol) asε-ligands (4), were studied in the anionic ring-opening bulk polymerization of ɛ-caprolactone (CL) at 80–130 °,C. All the catalysts involved initiate controlled polymerization and afford polyesters with a number-average molecular weight up to Mn = 20 000 g mol−1, which can be regulated by adjusting the [monomer]: [catalyst] ratio. Among the catalysts studied, complex 2 is most efficient in CL polymerization and affords polyesters with the narrowest molecular weight distribution (Mw/Mn < 1.2). In addition, complex 2 initiates the controlled polymerization of d,l-lactide (LA) and is effective in the synthesis of random and block copolymers of CL and LA.