Self-assembly of thermo-responsive poly(oligo(ethylene glycol) methyl ether methacrylate)-C₆₀ in water-methanol mixtures

Well-defined statistical copolymer of poly (di(ethylene glycol) methyl ether methacrylate–stat-oligo(ethylene glycol) methyl ether methacrylate-C₆₀ ((PMEO₂MA-stat-POEGMA₃₀₀)-C₆₀) was synthesized via atom transfer radical polymerization (ATRP) reaction and atom transfer radical addition (ATRA) processes. The lower critical solution temperature (LCST) of PMEO₂MA-stat-POEGMA₃₀₀ increased from 42 to 95 °C when the amounts of methanol was increased from 0 to 30 vol%, beyond which the LCST could not be quantified. Similarly, the LCST of (PMEO₂MA-stat-POEGMA₃₀₀)-C₆₀ also increased with methanol content, however it was lower than PMEO₂MA-stat-POEGMA₃₀₀ for all methanol/water compositions. The CMC of (PMEO₂MA-stat-POEGMA₃₀₀)-C₆₀ increased with increasing methanol content, suggesting that methanol is a better solvent for PMEO₂MA-stat-POEGMA₃₀₀ segment. The amphiphilic (PMEO₂MA-stat-POEGMA₃₀₀)-C₆₀ structure formed spherical micelles in water/methanol mixture, and larger micelles were formed at higher methanol content. The hydrodynamic radius (Rₕ) remained constant at temperature below the LCST. It increased dramatically at temperature greater than the LCST, and the (Rg/Rₕ) increased from ∼0.75 to ∼1.0. We believe that the (PMEO₂MA-stat-POEGMA₃₀₀) coronas dehydrate at higher temperature, and the micelles associate to form larger aggregates. In water/methanol mixtures, core-shell micelles and large compound micelles are produced below and above the LCST respectively.