Swelling Characteristics of pH- and Thermo-Sensitive Crosslinked Poly(Vinyl Alcohol) Grafts

Grafting of N-isopropylacrylamide, NIPAAm, onto partially and fully hydrolyzed poly(vinyl alcohol–g-maleic anhydride), PVA–MA, was carried out in presence of ammonium persulfate as initiator. The crosslinked PVA–MA–NIPAAm copolymers were prepared in presence of different weight percentages of methylene bisacrylamide, MBA, as crosslinker and N,N,N,N′-tetramethylethylenediamine, TMEA, as accelerator. Crosslinked PVA–MA–NIPAAm copolymers were prepared at two different temperatures 5 and 55 °C. The structural features of these grafts were confirmed by ¹H NMR analysis. Solution behaviors of both PVA–MA and PVA–MA–NIPAAm were evaluated from viscosity measurements. The swelling ratios of the crosslinked polymers were measured at different temperatures and pH values. The phase transition of the crosslinked gels was measured from DSC analysis. Crosslinked PVA–MA–NIPAAm grafts show different pH and temperature sensitivity. The swelling behaviors of PVA–MA–NIPAAm were referred to formation of hydrogen bonding between amide and carboxylic groups and also to hydrophobic aggregation of NIPAAm grafts.