High-resolution solid-state NMR study of the domain structure and molecular motion in drawn films of a vinylidene fluoride and trifluoroethylene copolymer with 73 mol % vinylidene fluoride

摘要

The heterogeneous higher order structure and molecular motion in a single crystalline film of a vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer with 73 mol % VDF was investigated with the H-1-C-13 cross-polarization/magic-angle spinning NMR technique, A transient oscillation was observed in plots of the C-13 peak intensity versus the contact time for the CH2, CHF, and CF2 groups. On the basis of the extended cross-relaxation theory of spin diffusion, we determined that the oscillation behavior was caused by the TrFE-rich segments in the chain and that the crystal consisted of VDF-rich and TrFE-rich domains. The former had TrFE-rich segments in VDF and TrFE fractions of 0.24 and 0.27, respectively, and the latter had VDF-rich segments in a VDF fraction of 0.49. The spin-lattice relaxation time T-1rhoH in the rotating frame for each group was minimal in the three temperature regions of beta, alpha(b), and alpha(c) (up arrow) on heating and in the two temperature regions of alpha(1D) and alpha(c) (down arrow) on cooling. The alpha(c) (up arrow) and alpha(c) (up arrow) processes depended on the first-order ferroelectric phase-transition regions on heating and cooling, respectively. The motional modes for the other processes were confirmed by the T-1rhoH minimum behavior of the VDF and TrFE groups in the TrFE-rich domain and the VDF-rich segments in the VDF-rich domain. The beta and alpha(b) processes were attributed to the flip-flop motion of the TrFE-rich segments and the competitive motion of the TrFE- and VDF-rich segments in the ferroelectric phase, respectively. The alpha(1D) process was due to the one-dimensional diffusion motion of the conformational defects along the chain in the paraelectric phase, accompanied by the trans and gauche transformation of the VDF conformers of ttg(+)tg(-) and g(+)tg(-)tt. The effect of the competitive motion of the TrFE-rich segment on the thermal stability of the VDF-rich segment in the chain near the Curie temperature was examined. (C) 2002 Wiley Periodicals, Inc. [References: 19]