Synthesis of versatile poly(PMMA-b-VI) macromonomer-based hydrogels via infrared laser ignited frontal polymerization

In this work, poly((PMMA-b-VI)-co-AA) (MMA = methyl methacrylate; VI = 1-vinylimidazole; AA = acrylic acid) hydrogels and poly((PMMA-b-VI)-co-AA)/TPU (TPU = thermoplastic polyurethane) IPN (interpenetrating polymer networks) hydrogels have been fabricated via versatile infrared laser ignited frontal polymerization by using poly(PMMA-b-VI) macromonomer as the mononer. The frontal velocity and T_max (the highest temperature that the laser beam detected at a fixed point) can be adjusted by varying monomer weight ratios, the concentration of BPO (BPO = benzoyl peroxide) and the amount of TPU. Moreover, the addition of TPU enhances the reactant viscosity to suppress the "fingering" of frontal polymerization (FP) and decrease T_max of the reaction, providing a new inert carrier (TPU) to assist FP. Through the characterization of Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and differential scanning calorimetry (DSC), the desired structure can be proved to exist in the IPN hydrogels. Furthermore, poly((PMMA-b-VI)-co-AA)/TPU IPN hydrogels possesses more excellent mechanical behaviors than hydrogels without IPN structure. Besides, the poly((PMMA-b-VI)-co-AA) hydrogels present splendid sensitive properties toward substances of different flavor including sourness (CA, citric acid or GA, gluconic acid), umami (SG, sodium glutamate), saltiness (SC, sodium chloride), sweetness (GLU, glucose), enabling their potential as artificial tongue-like sensing materials.