Small dop of comonomer, giant shift of cloud point: Thermo‐responsive behavior and mechanism of poly(methylacrylamide) copolymers with an upper critical solution temperature

Abstract

AbstractPoly(methylacrylamide) (PMAM) is a thermo‐responsive polymer with an upper critical solution temperature (UCST). Its cloud point (Tcp) is around 60 °C, unsuitable for certain biomedical and industrial applications. This study brought up a copolymerization strategy to tune the Tcp of PMAM with hydrophilic comonomers. Surprisingly, with a small portion of hydrophilic monomer doped, the Tcp of the PMAM copolymer can be significantly shifted. For instances, with ≤7 mol% of acrylamide or 1 mol% of oligo(ethylene glycol) methacrylate, the Tcp can be shifted in a wide range from ~69 to ~0 °C. Microdifferential scanning calorimetry demonstrated that the enthalpic effect during the phase transition of the solutions is indistinctive, while fluorescence measurement with pyrene as a probe revealed that the hydrogen‐bonding within polymer chains is enhanced by the hydrophobic aggregation of methyl groups. Therefore, the doped hydrophilic monomer could remarkably alter the ordering of water‐molecules and the extent for the aggregation of methyl groups, leading to the pronounced shifting in the Tcp of the copolymers. This work would facilitate the application of PMAM as smart polymer materials and guide the inventions of functional materials based on UCST polymers.