Poly(lactide-co-ε-caprolactone) copolymers prepared using bis-thioetherphenolate group 4 metal complexes: Synthesis, characterization and morphology

Titanium and zirconium complexes 1-3 (1 = (t-BuOS)(2)Ti(O-i-Pr)(2); 2 = (t-BuOS)(2)Zr(O-t-Bu)(2); 3 = ((OS)-O-Cum)(2)Zr(O-t-Bu)(2)) supported by two phenolate bidentate ligands (t-BuOS-H = 4,6-di-tert-butyl-2-phenylsulfanylphenol and (OS)-O-Cum-H = 4,6-di-cumyl-2-phenylsulfanylphenol) promoted the copolymerization of L-lactide with epsilon-caprolactone. The reactivity displayed by the two monomers during the copolymerization experiments and the microstructure disclosed by C-13 NMR analysis indicated a gradient distribution of the two monomers along the polymer chain. Copolymers with high epsilon-caprolactone content showed a large scale formation of crystalline spherulites prone to perfection of the crystallinity upon thermal annealing at 50 degrees C. Differently L-lactide rich copolymers revealed a thin film morphology consisting of small rigid domains of L-lactide segments of about 15 nm embedded in a soft matrix of the counterpart. Copolymers with comparable mole fractions of the two monomers were entirely amorphous.