Of Pvdf-based Graft Polymer Preparation And Research

In recent years, in order to obtain high performance and inexpensive electroactive polymers (EAPs), many efforts have been made to modify the crystal structure and morphology in the PVDF-based polymers, including studies of the effects of irradiation on PVDF-based copolymer and terpolymers, PVDF-based composites, and PVDF-based polymer blends with thermal treatment. In addition,as an important method of modifying polymers, graft copolymerization of comonomers from the backbone of these fluoropolymers have the potential to prepare satisfactory ferroelectric polymers.In this work, Poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) and Poly(vinylidene fluoride-chlorotrifluoroethylene-trifluoroethylene) (P(VDF-CTFE-TrFE)) were selected as macroinitiator to prepare graft copolymers. They were grafted with a mesogenic monomer, i.e.6-((4-cyano-4'-biphenyl)oxy) hexyl methacrylate (CBHM) using atom transfer radical polymerization (ATRP) from secondary chlorines on the main chain backbone. The resultant graft copolymers were characterized by 1H NMR, FT-IR spectroscopy, GPC and elemental analysis. Their crystalline structure and thermal property were investigated by employing XRD, DSC,POM and TGA. The thermo-mechanical behavior was examined by DMA. The electrical properties were also examined.The research results show that:1. The mesogenic monomer, i.e. CBHM was successfully grafted from the secondary chlorines of CTFE units using ATRP. ATRP can yield polymers with controlled molecular weight and low polydispersity. The synthetic approach used here offers a feasible way to modify other fluoropolymers containing CTFE units.2. The graft copolymer was turned from amorphous to semicrystalline after grafting from the P(VDF-CTFE). There are someαphase induced by PCBHM side chains in the the crystalline regions. The crystallinity of the polymer increased slightly after grafting from the P(VDF-CTFE-TrFE), and the crystalline regions in the graft copolymer contained moreβphase which has all-trans chain conformation. The curie temperature decreased by 4℃.3. Upon the introduction of PCBHM side chains, the thermal stability of the graft copolymers were lower than the pristine polymers, but the storage modulus was enhanced significantly, which is beneficial for breakdown field strength enhancement.4. The dielectric constant (at 1kHz) of the graft copolymers represent a decrease about 1～2. Over the observed frequency range, the dielectric loss of the P(VDF-CTFE-TrFE)-g-PCBHM is lower than that of the parent polymer. But the P(VDF-CTFE)-g-PCBHM is contrary to that. Noteworthy is that, at high frequencies (～MHz), both of them is much lower than that of the parent polymer. In comparision with the parent polymers, the breakdown field of the graft copolymers was enhanced significantly. Moreover, the remnant polarization (Pr) of the graft copolymers decreased and the saturation polarization (Pmax) increased.