Tuning the upper critical solution temperature behavior of poly(methyl methacrylate) in aqueous ethanol by modification of an activated ester comonomer

Abstract

A statistical copolymer of methyl methacrylate (MMA) and pentafluorophenyl methacrylate (PFPMA, 6 mol%) exhibits upper critical solution temperature (UCST) behavior in aqueous ethanol solutions tunable by post-polymerization modification with different amines. The phase transition behavior of the obtained copolymers in aqueous ethanol was evaluated in detail. As expected, all copolymers reveal an upper critical solution temperature with 55 vol% or higher ethanol content. Furthermore, the solubility in aqueous ethanol of the copolymer can be increased by the introduction of hydrophilic moieties. When hydrophobic substituents are introduced a decrease in solubility was observed with low content of ethanol and an increase in solubility when adding more ethanol. As such, the thermoresponsive behavior of PMMA can be significantly altered by post-modification of 6 mol% of the reactive comonomer units. The hysteresis of the polymer phase transitions between heating and cooling was found to be strongly dependent on the polarity of the amine substituent and the ethanol/water ratio. The metastability of the hysteresis is addressed based on isothermal turbidity studies.