Synthesis of poly(vinylidene fluoride-cochlorotrifluoroethylene)-g-poly(methyl methacrylate) with low dielectric loss by photo-induced metal-free ATRP

The grafting of poly(methacrylate ester) or polystyrene onto the side chain of poly(vinylidene fluoride) (PVDF)-based fluoropolymers maintains their high energy density and remarkably reduces the energy loss due to the confinement (or insulation) effect, which has potential application in high-pulse capacitors. The graft copolymers were previously synthesized from C-Cl bonds via the transition metal-catalyzed atom transfer radical polymerization (ATRP) process. To overcome the negative influence of the residual metal ions from the catalyst on the dielectric properties of the resultant copolymers, in the present contribution, a facile strategy is reported for photo-mediated ATRP using organic-based photoredox catalysts to directly synthesize a poly(methyl methacrylate) (PMMA)-grafted copolymer from the commercial poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)). The graft copolymerization is efficiently activated and deactivated with light and exhibits first-order kinetics. The detailed structural information of the graft copolymer, including average grafting density and side chain length, are also determined by converting the uninitiated Cl atoms into H atoms. When compared with the traditional Cu-catalyzed ATRP process, the current photo-induced ATRP method used for preparing the graft copolymer results in improved dielectric performances such as reduced dielectric loss at low frequency and high temperature, decreased conduction loss, and enhanced breakdown strength.