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-C-60 ((PMEO(2)MA-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(2)MA-stat-POEGMA(300) increased from 42 to 95 degrees 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(2)MA-stat-POEGMA(300))-C-60 also increased with methanol content, however it was lower than PMEO(2)MA-star-POEGMA(300) for all methanol/water compositions. The CMC of (PMEO(2)MA-stat-POEGMA(300))-C-60 increased with increasing methanol content, suggesting that methanol is a better solvent for PMEO(2)MA-stat-POEGMA(300) segment. The amphiphilic (PMEO(2)MA-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 similar to 0.75 to similar to 1.0. We believe that the (PMEO(2)MA-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. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.