ATRP synthesis of thermally responsive molecular brushes from oligo(ethylene oxide) methacrylates

Molecular brushes consisting of 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 grafting from poly(2-(2-bromoisobutyryloxy)ethyl methacrylate (PBIEM) macroinitiators using atom transfer radical polymerization (ATRP) providing copolymers with controlled composition and molecular weights ranging from M-n=601 500 to 2 731 000 with polydispersity indexes (M-w/M-n) between 1.06 and 1.20. The lower critical solution temperature (LCST) of the brushes increased with the mole fraction of MEO(3)MA in the side chain, and the hysteresis between the heating and cooling cycles decreased with the length of the side chain. Brush copolymers with different graft density were also prepared, and the average hydrodynamic diameter, measured by dynamic light scattering (DLS), varied with temperature above the LCST, and the maximum diameter of the aggregates increased according to the graft density of side chain along the brush backbone. These two monomers were also incorporated into side chain block copolymer brushes by ATRP. The cloud point of the block brushes solution displayed two stages of aggregation during heating, exhibiting the results of both intermolecular and intramolecular aggregation. This behavior was strongly dependent on the sequence of the side chain segments. As the temperature increased, particles consisting of collapsed PMEO(2)MA and PMEO(3)MA segments aggregated upon further heating to precipitate as larger particles.