Temperature/pH dual sensitive N-isopropylacrylamide/polyurethane copolymer hydrogel-grafted fabrics

Vinyl-capped polyurethane anionomer(VPUA) was synthesized from isophorone diisocyanate, polyoxytetramethylene glycol, 2,2-dimethylol propionic acid and 2-hydroxyethyl methacrylate. VPUA and N-isopropylacrylamide were graft copolymerized onto the nonwoven fabrics by ammonium persulfate initiation. Fourier transform infrared spectroscopy and X-ray photoelectron spectrometry confirmed the occurrence of grafting reaction. The measurement of weight indicated that the percentage of grafted polymer was strongly dependent on the monomer concentrations. At lower concentrations, only a small amount of poly(N-isopropylacrylamide) (PNIPAAm) and polyurethane (PU) was grafted onto the fabrics; at higher concentrations, the fabrics were coated with thin or thick layers of hydrogel, as verified by scanning electron microscope imaging. The differential scanning calorimetry results revealed that the incorporation of PU did not vary the phase transition temperature of PNIPAAm. The equilibrium water content of the grafted fabrics could be tuned by adjusting environmental temperature and pH and furthermore, the temperature sensitivity of PNIPAAm/PU hydrogel-grafted fabrics was reversible. In addition, the typical syneresis of PNIPAAm hydrogel was hindered to some extent by copolymerization with PU.