Morphotropic phase boundary (MPB) has been demonstrated in various ferroelectric polymers near which piezoelectric coefficient d33 is substantially enhanced. However, all these ferroelectric polymers contain expensive trifluoroethylene while the Curie temperature Tc remains low, limiting their practical applications. Here, MPB is explored in trifluoroethylene-free poly(vinylidene fluoride-co-tetrafluoroethylene) copolymer by grafting design. We find that grafting induces order-to-disorder structural evolution mediated by the formation of MPB reminiscent of composition- and irradiation-induced MPB in trifluoroethylene-contained ferroelectric polymers. Meanwhile, we show that local conformational disorder is pinned by head-head defects inherent to tetrafluoroethylene, which is essential to maintain high Tc. Consequently, markedly improved d33 of -41.6 pC N-1 and high Tc of over 130°C are concurrently achieved in graft poly(vinylidene fluoride-co-tetrafluoroethylene) copolymers, outperforming currently existing ferroelectric polymers with high Tc. These findings add a trifluoroethylene-free member into MPB family, which offers a solution to address the long-standing inverse d33-Tc relationship in ferroelectric materials.
Keywords: ferroelectric polymers; grafting modification; morphotropic phase boundary; piezoelectricity.
© 2026 The Author(s). Advanced Science published by Wiley‐VCH GmbH.