Ferroelectric relaxation dependence of poly(vinylidene fluoride-: Co -trifluoroethylene) on frequency and temperature after grafting with poly(methyl methacrylate)

Poly(vinylidene fluoride) (PVDF) based ferroelectric fluoropolymers have attracted considerable attention in high energy density pulse capacitors application for the tunable and tight composition dependence of their ferroelectric performances. Grafting poly(methacrylate esters) (ca. poly(methyl methacrylate) (PMMA)) onto the side chain of P(VDF-TrFE-CTFE) (TrFE refers to trifluoroethyelene and CTFE is chlorotrifluoroethylene) has been shown to be an effective route to tailor the ferroelectric performance of P(VDF-TrFE-CTFE). The resultant grafted copolymers possess advantages including well maintained high energy density and remarkably reduced energy loss. To further disclose the influence of a PMMA side chain on ferroelectric relaxation of a P(VDF-TrFE-CTFE) main chain, a set of P(VDF-TrFE-CTFE)-g-PMMA copolymers bearing PMMA content from 10 wt% to 32 wt% were synthesized and well characterized in this work. The dielectric and energy storage performance of the grafted copolymers were systematically investigated under increased electric field, testing temperature, and frequency. The PMMA side chain was found to exhibit great influence with ferroelectric performance under varied conditions by impeding crystallization and formation of the ferroelectric phase of the P(VDF-TrFE-CTFE) main chain along with increasing the Young's modulus of amorphous phase. As a result, the grafted copolymer with optimized PMMA content shows excellent stability with testing frequency, temperature, and electric field. That allows them to store and discharge energy consistently, which is rather important for energy storage capacitors working under varied conditions. With respect to promising energy storage performances together with low performance dependence during working conditions, the PMMA grafted P(VDF-TrFE-CTFE) copolymer may offer a great candidate material for high energy density pulse capacitors.