The effect of structure on the thermoresponsive nature of well-defined poly(oligo(ethylene oxide) methacrylates) synthesized by ATRP

Statistical copolymers of di(ethylene glycol) methyl ether methacrylate (MEO(2)MA) and tri(ethylene glycol) methyl ether methacrylate (MEO(3)MA) were synthesized by atom transfer radical polymerization (ATRP) providing copolymers with controlled composition and molecular weights ranging from M-n = 8,300-56,500 with polydispersity indexes (M-w/M-n) between 1.19 and 1.28. The lower critical solution temperature (LCST) of the copolymers increased with the mole fraction of MEO(3)MA in the copolymer over the range from 26 to 52 degrees C. The average hydrodynamic diameter, measured by dynamic light scattering, varied with temperature above the LCST. These two monomers were also block copolymerized by ATRP to form polymers with molecular weight of M-n = 30,000 and M-w/M-n from 1.12 to 1.21. The LCST of the block copolymers shifted toward the LCST of the major segment, as compared to the value measured for the statistical copolymers at the same composition. As temperature increased, micelles, consisting of aggregated PMEO(2)MA cores and PMEO(3)MA shell, were formed. The micelles aggregated upon further heating to precipitate as larger particles. (c) 2007 Wiley Periodicals, Inc.