Design of temperature-responsive polymers with enhanced hysteresis: α,α-disubstituted vinyl polymers

Three temperature-responsive polymers which are R,R-disubstituted vinyl polymers having two amphiphilic groups (ethylamide or ethylester) per monomeric unit were designed. Two of these polymers showed unusually large hysteresis in their phase transition temperatures between a heating and a cooling process. This hysteresis resulted from the extremely slow kinetics of the dissolution process of the aggregated polymer chains in the cooling process due to intraand interchain interactions including hydrogen bonding and hydrophobic interaction. The high density of the amphiphilic substituents on the polymer chain due to the α,α-disubstituted structure enhanced these intra- and interchain interactions. The large hysteresis was also observed in the volume change of a corresponding hydrogel. These new classes of temperature-responsive polymers are interesting materials because their large hystereses can be regarded as erasable memory function.