Small dop of comonomer, giant shift of cloud point: Thermo-responsive behavior and mechanism of poly(methylacrylamide) copolymers with an upper critical solution temperature
writer：Jianlei Lu, Xionglin Zhou, Jialin Sun, Mengdi Xu, Mingming Zhang, Chuanzhuang Zhao
keywords：Thermo-responsive polymer, UCST, Molecular design, Polymethacrylamide
source：期刊
specific source：Journal of Polymer Science
Issue time：2021年
Poly(methylacrylamide) (PMAM) is a thermo-responsive polymer with an upper critical solution temperature (UCST). Its cloud point (Tcp) is around 60 ℃, unsuitable for certain biomedical and industrial applications. This study brought up a copolymerization strategy to tune the T-cp 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 similar to 69 to similar to 0 ℃. 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.