Swelling/deswelling, thermal, and rheological behavior of PVA-g-NIPAAm nanohydrogels prepared by a facile free-radical polymerization method

A novel method of synthesizing poly(vinyl alcohol)g-N-isopropylacrylamide (PVA-g-NIPAAm) nanohydrogels under crosslinker-free conditions at high dilution and elevated temperature is presented. Hydrogen peroxide (H2O2), used as an initiator, decomposes to hydroxyl radicals at high temperature, which causes the abstraction of hydrogen from PVAchains, resulting in NIPAAm-grafting polymerization. Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) confirmed the grafting polymerization of NIPAAm onto PVA chains. The effects of the NIPAAm/PVA feed composition ratio, the amount ofH(2)O(2), and both pH and temperature on the swelling properties of the nanohydrogels obtained were investigated. An investigation of the swelling/deswelling kinetics and oscillatory swelling behavior of the nanohydrogels indicated that they have high swelling ratios with fast response rates and good reversibilities, and are sensitive to both pH and temperature. Elemental analysis revealed that the NIPAAm content increases with increasing NIPAAm/PVA ratio and H2O2 concentration, which leads to a remarkable increase in the nanohydrogel swelling ratio. Rheological studies demonstrated that the samples with higher PVA contents had enhanced elastic responses. The phase-transition temperatures and size distributions of the nanohydrogels were also studied. It appears that that these fast-responding nanohydrogels with properties that are sensitive to both pH and temperature, and which are obtained by a relatively simple and convenient polymerization method, could be potential candidates for drug-delivery carriers.