Rational design of dual Chemo- and Thermo-responsive phase separation of Poly(4-hydroxystyrene) in non-aqueous media

Abstract

Dual stimuli-responsiveness in non-aqueous media could allow various molecular designs using a system that is not compatible with aqueous media. However, the difficulty in controlling the desolvation of the polymer chains in non-aqueous media for lower critical solution temperature (LCST)-type phase separation at ambient temperature has hindered the attainment of dual stimuli-responsiveness based on chemical stimuli. In this study, we rationally designed dual chemo- and thermo-responsive phase separations of poly(4-hydroxystyrene) in non-aqueous media. The LCST-type thermo-responsiveness of poly(4-hydroxystyrene) in 1,4-dioxane/toluene was considerably altered by the addition of small amounts of hydrogen-bonding molecules as chemical stimuli. Secondary amines or molecules containing two hydrogen-bonding functional groups formed stronger hydrogen bonds with the polymer chains than 1,4-dioxane, which altered the solvation state and induced the UCST-type thermo-responsiveness or insolubility of PHS. This dual stimuli-responsive system could serve as a chemical sensor to detect the presence of acids. Dual chemo- and thermo-responsive phase separations of poly(4-hydroxystyrene) in non-aqueous media were demonstrated. The addition of small amounts of hydrogen-bonding molecules as chemical stimuli caused a considerable change of LCST-type thermo-responsiveness of poly(4-hydroxystyrene) in 1,4-dioxane/toluene. Secondary amines or molecules containing two hydrogen-bonding functional groups could cross-link the polymer chains through the hydrogen bonds, which altered the solvation state and induced the UCST-type thermo-responsiveness or insolubility of the polymer. This dual stimuli-responsive system worked as a chemical sensor to detect the presence of acids.