Synthesis and Water Absorption Transport Mechanism of a pH-Sensitive Polymer Network Structured on Vinyl-Functionalized Pectin

Polysaccharide-structured copolymer hydrogel having excellent pH-sensitivity was developed from N,N-dimethylacrylamide (DMAc) and vinyl-functionalized Pectin (Pec). The Pec was vinyl-functionalized by way of chemical reaction with glycidyl metacrylate (GMA) in water under acidic and thermal stimuli. C-13 NMR, H-1 NMR, and FT-IR spectra revealed that the vinyl groups coming from the GMA were attached onto backbone of the polysaccharide. The hydrogels were obtained by polymerization of the Pec-vinyl with the DMAc. C-13-CP/MAS NMR and FTIR spectra confirmed that the gelling process occurred by way of the vinyl groups attached on Pec-vinyl backbone. The values of apparent swelling rate constant (k) decreased appreciably for pH greater than 6, demonstrating the swelling process of the hydrogel becomes slower at more alkaline conditions. There was an increase of diffusional exponent (n) with increasing pH of the surrounding liquid. This means the water absorption profile becomes more dependent on the polymer relaxation in basified swelling media. In this condition, a longer water absorption half-time (t(1/2)) was verified, suggesting the polymer relaxation mechanism of the hydrogel would have a considerable effect on the t(1/2).