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

Abstract

Titanium and zirconium complexes 1–3 (1 = (^t-BuOS)₂Ti(O-i-Pr)₂; 2 = (^t-BuOS)₂Zr(O-t-Bu)₂; 3 = (^CumOS)₂Zr(O-t-Bu)₂) supported by two phenolate bidentate ligands (^t-BuOS-H = 4,6-di-tert-butyl-2-phenylsulfanylphenol and ^CumOS-H = 4,6-di-cumyl-2-phenylsulfanylphenol) promoted the copolymerization of L-lactide with ε-caprolactone. The reactivity displayed by the two monomers during the copolymerization experiments and the microstructure disclosed by ¹³C NMR analysis indicated a gradient distribution of the two monomers along the polymer chain. Copolymers with high ε-caprolactone content showed a large scale formation of crystalline spherulites prone to perfection of the crystallinity upon thermal annealing at 50 °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.