Poly(vinylidene fluoride/trifluoroethylene/hexafluoropropylene) terpolymers were synthesized by bulk polymerization process at ambient temperature based on alkyl borane/oxygen initiator. The ferroelectric and dielectric properties were investigated and compared with those of poly(vinylidene fluoride/trifluoroethylene) copolymer. The DSC, X-ray and FT-IR results suggest that the third comonomer in the polymer chain breaks the large polar domains into smaller domain size and reduces the crystallinity of terpolymer. As a result, both the ferroelectric-paraelectric phase transition and melting process take place at lower temperature. The smaller domain makes the dipoles reversal at lower electric field and reduces the polarization hysteresis as well as polarization level. High electrostrictive strain (2.5%) was obtained at low electric field for terpolymer with small quantity of HFP. The polarization and dielectric behaviors imply that the terpolymer is a typical ferroelectric relaxor. The terpolymer also shows higher room temperature dielectric constant than that of copolymer due to the lower phase-transition temperature. (c) 2007 Elsevier Ltd. All rights reserved.