Thermal cleavage of hydrogen bond-induced LCST-type phase separation of PHEMA and related poly(hydroxyalkyl (meth)acrylate)s in mixed organic solvents

Abstract

Molecular design exhibiting LCST-type phase separation in water has been widely accepted as desolvation of water-soluble amphiphilic polymers with a small alkyl group triggered by heat. However, for organic media, molecular design is not yet achievable due to the difficulty in designing the entropy-driven exothermic desolvation. In this report, we demonstrate LCST-type phase separations of poly(2-hydroxyethyl methacrylate) (PHEMA) and related poly(hydroxyalkyl (meth)acrylate)s in an organic medium at ambient temperature. Our design is based on the utility of a binary solvent mixture of hydrogen-bonding solvents for solvation and non-polar solvents for desolvation. The thermal cleavage of the hydrogen bond between the hydroxy group of the polymer chain and the hydrogen-bonding group of the solvent easily induced the LCST-type phase separation. We revealed a correlation between the critical molar ratio for LCST-type phase separation and the length of the alkyl groups both in the polymer side chain and 1-alcohol good solvents. These findings led to the development of a reliable molecular design strategy that could facilitate the development of smart materials in organic solvents.