Facile and Green Preparation of Superfast Responsive Macroporous Polyacrylamide Hydrogels by Frontal Polymerization of Polymerizable Deep Eutectic Monomers

Polymerizable deep eutectic monomers (DEMs) were prepared by mixing various molar ratios of acrylamide (AM) and choline chloride (ChCl). 1H NMR and Fourier transform infrared confirmed that there were strong hydrogen bonds between AM and ChCl in DEMs. The hydrogen bonds can effectively depress the crystallization of AM and ChCl. All DEMs can be used for sustainable thermal-induced frontal polymerization (FP) at 35 °C. It was found ChCl could accelerate the FP of DEMs. The front velocity (Vf) and the maximum front temperature (Tmax) of FP in DEM were much higher than those in dimethyl sulfoxide. The increase in the molar ratio of AM and ChCl and the amount of N,N′-methylenebisacrylamide (MBA) led to an increase in Vf and Tmax. When the polymerized DEM hydrogels were immersed in distilled water, water-soluble ChCl were washed out and the hydrogels were further freeze-dried. The macroporous polyacrylamide hydrogels with pores in an average diameter of about 150 μm were observed. They exhibited superfast reversible swelling and shrinkage in alternate water and acetone. The study implies a facile and green method to efficiently fabricate macroporous polyacrylamide hydrogels with superfast responsive properties via FP of DEMs in less than 6 min. The preparation method is also green, low-energy, and sustainable and possesses a good application prospect in the environmental and biomedical areas.