Preparation of macroporous polyvinyl alcohol formaldehyde based hydrogels and their dual thermo- and pH-responsive behavior

Abstract

Dual thermo- and pH-responsive polymer hydrogels have broad potential applications due to their unique responsive behavior to environmental stimuliregulatedby more than one mechanism. Herein, the dual thermo- and pH-responsive polyvinyl alcohol formaldehyde (PVF) based hydrogels were successfully prepared via redox grafting polymerization by incorporating respectively poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) moieties onto PVF backbone. These hydrogels retain an interconnected macroporous structure with high porosity (~83.0%), facilitating rapid penetration and diffusion of water molecules. The sizes of pore and pore walls are in micrometer scale, significantly reducing the characteristic time of swelling or deswelling. Besides, these hydrogels possess the thermo-responsiveness even in high grafting percentage of PAA (60.8%), overcoming the inhibition effect of PAA moieties in a high content on thermal sensitivity of traditional poly(NIPAM-co-AA) copolymers. Their pH-responsiveness and excellent repeated absorption performance are determined by measuring the absorption capacities of hydrogels in water and different buffer solutions. Moreover, these hydrogels exhibit rapid deswelling kinetics on the minute time scale by detecting water retention in pH 3 buffer solution at 50 °C. In addition, the deswelling behavior leads to the noticeable changes of macroscopic dimensions of hydrogels; we anticipate potential applications in dual thermal and pH sensors.