Dual-responsive reduced graphene oxides prepared by radiation-initiated living radical grafting polymerization

Temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) was grafted onto the surface of graphene oxide (GO) via reversible addition-fragmentation chain transfer polymerization initiated by γ-ray radiation. Raman spectroscopy and X-ray photoelectron spectroscopy analyses indicated that GO was reduced synchronously upon the radiation grafting polymerization of NIPAAm in an aqueous solution. A pulse radiolysis study demonstrated that NIPAAm reacted with both hydrated electrons (eaq-) and hydroxyl radicals (OH) produced by water radiolysis of which the reaction rate constants were 1.0×1010 L/(mol∙s) and (4.3±0.2)×109 L/(mol∙s), respectively. The addition reaction between NIPAAm and OH produces a radical at the unsaturated double bond of NIPAAm, which initiates the free radical polymerization of the monomers. Meanwhile, the reaction between NIPAAm and eaq- not only consumes strongly reductive eaq- but also produces weakly reductive radical anion intermediates, which decreases the reduction degree of rGO. The residual oxygen-containing groups on the surface of rGO with a low degree of reduction degree, such as carboxyl groups, endowed rGO-g-PNIPAAm with good pH responsiveness. Compared to pristine GO without PNIPAAm grafting, rGO-g-PNIPAAm which prepared with an absorbed dose of 3.6 kGy for radiation grafting polymerization exhibited a 30% higher photothermal conversion efficiency under near-infrared LASER irradiation. This study provides a convenient and controllable method for preparing photothermal conversion materials with pH and temperature dual responsiveness.