Controlled synthesis and characterization of poly[ethylene-block-(L,L- lactide)]s by combining catalytic ethylene oligomerization with "coordination-insertion" ring-opening polymerization

Model poly[ethylene-block-(L,L-lactide)] (PE-block-PLA) block copolymers were successfully synthesized by combining metallocene catalyzed ethylene oligomerization with ring-opening polymerization (ROP) of L,L-lactide (LA). Hydroxy-terminated polyethylene (PE-OH) macroinitiator was prepared by means of ethylene oligomerization on rac-dimethyl- silylenbis(2-methyl-benz[e]indenyl)- zirconium(IV)-dichloride/methylaluminoxane (rac-MBI/MAO) in presence of diethyl zinc as a chain transfer agent, and subsequent in situ oxidation with synthetic air. Poly[ethylene-block-(L,L-lactide)] block copolymers were obtained via ring-opening polymerization of LA initiated by PE-OH in toluene at 100°C mediated by tin octoate. The formation of block copolymers was confirmed by ¹H NMR spectroscopy, fractionation experiments, thermal behavior, and morphological characterization using AFM and light microscopy techniques.