Self-assembly of thermo-responsive poly(oligo(ethylene glycol) methyl ether methacrylate)-C 60 in water-methanol mixtures

Abstract

Well-defined statistical copolymer of poly (di(ethylene glycol) methyl ether methacrylate–stat-oligo(ethylene glycol) methyl ether methacrylate-C 60 ((PMEO 2MA-stat-POEGMA 300)-C 60) was synthesized via atom transfer radical polymerization (ATRP) reaction and atom transfer radical addition (ATRA) processes. The lower critical solution temperature (LCST) of PMEO 2MA-stat-POEGMA 300 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 (PMEO 2MA-stat-POEGMA 300)-C 60 also increased with methanol content, however it was lower than PMEO 2MA- stat-POEGMA 300 for all methanol/water compositions. The CMC of (PMEO 2MA-stat-POEGMA 300)-C 60 increased with increasing methanol content, suggesting that methanol is a better solvent for PMEO 2MA-stat-POEGMA 300 segment. The amphiphilic (PMEO 2MA-stat-POEGMA 300)-C 60 structure formed spherical micelles in water/methanol mixture, and larger micelles were formed at higher methanol content. The hydrodynamic radius (R h) remained constant at temperature below the LCST. It increased dramatically at temperature greater than the LCST, and the (R g/R h) increased from ∼0.75 to ∼1.0. We believe that the (PMEO 2MA- stat-POEGMA 300) 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.