Amphiphilic block copolymers of high-molecular-weight poly(ethylene oxide) and either epsilon-caprolactone or gamma-methyl-epsilon-caprolactone: Synthesis and characterization

Ethylene oxide (EO) has been block-polymerized with both epsilon-caprolactone (epsilon-CL) and gamma-methyl-epsilon-caprolactone (MCL) through the combination of the anionic polymerization of EO and the ring-opening polymerization (ROP) of epsilon-CL and MCL. omega-Hydroxyl poly(ethylene oxide) has been reacted with triethylaluminum (OH/Al = 1) and converted into a macroinitiator for ROP of epsilon-CL and MCL. In toluene at room temperature, this polymerization leads to a bimodal molecular weight distribution as a result of monomer insertion in only some of the aluminum alkoxide bonds. However, in a more polar solvent (methylene chloride) added with 1 equiv of a Lewis base (pyridine), the expected diblock is formed selectively, and this indicates that aggregation of the active species in toluene is responsible for a macroinitiator efficiency of less than 1. A series of amphiphilic diblock copolymers with poly(epsilon-caprolactone) (semicrystalline) and poly(gamma-methyl-epsilon-caprolactone) (amorphous) as the hydrophobic blocks have been prepared and characterized with size exclusion chromatography, H-1 NMR, IR, and wide-angle X-ray scattering.