Synthesis and characterization of amphiphilic triblock copolymers by iron-mediated atom transfer radical polymerization

摘要

The atom transfer radical polymerization of methyl methacrylate (MMA) and n-butyl methacrylate (n-BMA) was initiated by a poly(ethylene oxide) chloro tele-chelic macroinitiator synthesized by esterification of poly(ethylene oxide) (PEO) with 2-chloro propionyl chloride. The polymerization, carried out in bulk at 90 degrees C and catalyzed by iron(II) chloride tetrahydrate in the presence of triphenylphosphine ligand (FeCl2 - 4H(2)O/PPh3), led to A-B-A amphiphilic triblock copolymers with MMA or n-BMA as the A block and PEO as the B block. A kinetic study showed that the polymerization was first-order with respect to the monomer concentration. Moreover, the experimental molecular weights of the block copolymers increased linearly with the monomer conversion, and the molecular weight distribution was acceptably narrow at the end of the reaction. These block copolymers turned out to be water-soluble through the adjustment of the content of PEO blocks (PEO content > 90% by mass). When the PEO content was small [monomer/macroinitiator molar ratio (M/I) = 300], the block copolymers were water-insoluble and showed only one glass-transition temperature. With an increase in the concentration of PEO (M/I = 100 or 50) in the copolymer, two glass transitions were detected, indicating phase separation. The macroinitiator and the corresponding triblock copolymers were characterized with Fourier transform infrared, proton nuclear magnetic resonance, size exclusion chromatography analysis, dynamic mechanical analysis, and differential scanning calorimetry. (c) 2005 Wiley Periodicals, Inc.