Fluorine-free strongly dipolar polymers exhibit tunable ferroelectricity

Current research on ferroelectric polymers centers predominantly on poly(vinylidene fluoride) (PVDF)-based fluoropolymers because of their superior performance. However, they are considered "forever chemicals" with environmental concerns. We describe a family of rationally designed fluorine-free ferroelectric polymers, featuring a polyoxypropylene main chain and disulfonyl alkyl side chains with a C3 spacer: -SO₂CH₂CHRCH₂SO₂- (R = -H or -CH₃). Both experimental and simulation results demonstrate that strong dipole-dipole interactions between neighboring disulfonyl groups induce ferroelectric ordering in the condensed state, which can be tailored by changing the R group: ferroelectric for R = -H or relaxor ferroelectric for R = -CH₃. At low electric fields, the relaxor polymer exhibits electroactuation and electrocaloric performance comparable with those of state-of-the-art PVDF-based tetrapolymers.