Solution Properties of Amphiphilic Alternating Copolymers of N-Ethylmaleimide and 2-Hydroxyethyl Vinyl Ether: Thermoresponsiveness in Alcohols and Cosolvency Phenomenon in Binary Ethanol/Water Solutions

Abstract

We discovered unique solution properties, including cosolvency of an amphiphilic alternating copolymer comprising hydrophobic N-ethylmaleimide (EMIm) and hydrophilic 2-hydroxyethyl vinyl ether (HEVE). The solubility of polymers is greatly affected by the balance of polymer−polymer interaction and polymer−solvent interaction, and an amphiphilic alternating sequence is attractive for achieving unique solubility. We synthesized the alternating copolymers P(EMIm/HEVE) by reversible addition-fragmentation chain transfer polymerization to investigate the solubility in a variety of solvents. The obtained polymers exhibited the upper-critical-solution-temperature-type miscibility behavior in various alcohols, and the insoluble-to-soluble transition temperature varied depending on the alcohol structure: bulkier and more hydrophobic alcohol resulted in a higher transition temperature. Furthermore, P(EMIm/HEVE) was shown to be soluble in the mixture of ethanol and water, despite being insoluble in each solvent at room temperature. This cosolvency phenomenon was probably due to the change in the local composition of ethanol and water around the polymer.