Fumiaki Ishii

Thermal isomerization of cis-poly(phenylacetylene). Scission of polymer main-chain and formation of 1,3,5-triphenylbenzene as a pyrolysis product

Abstract After cis-poly(phenylacetylene)s (cis-PPAs) were heated at 180°C for 1 h, the Mns decreased from 5000–53000 to 2000–2600, 1,3,5-TPB corresponding to the cyclic trimer of phenylacetylene was formed, and the yields of the annealed PPA and 1,3,5-triphenylbenzene (1,3,5-TPB) did not significantly vary. A peak at 280 nm due to the phenyl ring and broad band up to 600 nm due to the π-π∗ transition of the main-chain were observed in the u.v./vis. spectrum of cis-PPA. On the other hand, the absorption due to the conjugated main-chain disappeared for annealed PPA, though the phenyl group absorption was detected. The disappearance of the main-chain absorption can be explained by deflection of the main-chain.

Critical Behaviors of the NMR Line Width in Vinylidene Fluoride and Trifluoroethylene Copolymers near Tc

NMR line widths in VDF/TrFE copolymers with VDF 65 and 52 mol.% were measured as a function of the alignment angle γ between the drawn axis and the magnetic field over a temperature range from 20 to 130degC and the results were compared with those for VDF 72 mol.% copolymer. In the cooling process, a slight increase was observed on the line width for each copolymer near the Curie temperature Tc, which depended on the angle γ. This finding was explained by applying the effective Ising model to the configuration fluctuation of the trans segments. The anomalous part of the line width, ΔHfluc with the form of T2(T-T0)-1/2 was derived. Using the experimental values of ΔHfluc for each copolymer, the effective nearest-neighbor distance, d, between fluctuating trans segments, and the correlation length, ξ, were calculated. Both the values of d and ξ became larger in the order of 72, 52 and 65 mol.%. The magnitude of ξ for each copolymer was very close to the average distance, r (=5.9 A), between the fluctuating order units. The contribution of ξ to the polarization fluctuation was discussed by comparing the results which had been obtained from the spin-lattice relaxation time measurement.

NMR study of chain orientation in drawn poly (vinylidene fluoride) films. I: The effects of poling on the double orientation distribution function

The double orientation distribution function (DODF) of the chains in the drawn film of PVDF was determined by the NMR second-moment dependence on the angle between the magnetic field H0 and the normal to the film surface. The Fourier coefficient a2 of DODF determined for the unpoled sample changed from -0.24 to 0.28 on poling, but a4=0.08 did not change. These values were obtained from the highly oriented noncrystalline and crystalline parts in the drawn film. By using the Fourier coefficients a2mc (m=1, 2) of the DODF of the b-axis for the crystalline part in the poled sample obtained by the X-ray diffraction method, the Fourier coefficients a2mor (m=1, 2) of the DODF in the highly oriented non-crystalline part were estimated to be a2or=0.3 and a4or=0.24 at 18degC. The invariant of a4 was explained in terms of the DODF of the noncrystalline chains which are aligned preferentially upon poling with the chain dipoles oriented normally to the film surface. This paper discusses the molecular motion in the highly oriented noncrystalline part due to the temperature dependence of these coefficients.

Cis-trans isomerization and 13C-NMR chemical shift of polyphenylacetylene

Before and after cis-trans isomerization, the observed 13C-NMR chemical shifts of poly(phenylacetylene) (PPA) in the solid state were investigated on the basis of 13C-NMR chemical shift calculations within AM1 for the cis-transoidal and deflected trans-transoidal forms. Two 13C-resonance peaks in the observed CP/MAS 13C-spectrum were assigned theoretically by the 13C chemical shifts of the main and side chains. After thermal isomerization, the 13C peak of the main chain for PPA shifted upfield by 3.5 ppm, in contrast to the downfield shift of the 13C peak for polyacetylene. This upfield shift of trans-PPA largely was attributed to the increases of the excitation energy from the ground state to the lowest φπ–π* state in the paramagnetic terms of 13C chemical shift on the main chain carbons with the increase in deflected angle τ of 0 to 80°. The ±80° deflected conformation of the trans-transoidal chain due to the cis-trans isomerization was confirmed.

Fixed crosslink formation and viscoelasticity of polystyrene networks

The crosslinking formation in the 8/92 mol % random copolymer of ethynylstyrene and styrene is clarified quantitatively from the IR spectrum analysis on the basis of the thermally homogeneous reaction of ethynylstyrenes between the chains. The viscoelastic properties of the crosslinked polystyrene, CL-P(ESt/St), are investigated based on the temperature and frequency dependencies of the dynamic Young modulus. The relaxation spectrum of CL-P(ESt/St) drops deeply like the Wedge type with a slope of -1 in the glass transition region, and became a plateau without a terminal zone in the rubbery elasticity region. The effects of the ethynyl crosslinked junctions for the micro-Brownian motions of the segments in the strand are discussed.

1H–13C Nuclear Cross-Relaxation and Molecular Motion in Single Crystalline Film of Vinylidene Fluoride and Trifluoroethylene Copolymer with 75 mol% Vinylidene Fluoride

1H–13C nuclear cross relaxation and molecular motion in a highly double-oriented film of vinylidene fluoride (VDF) and trifluoroethylene (TrFE ) copolymer with 75 mol% VDF were studied using the cross-polarization/magic angle spinning nuclear magnetic resonance technique. A transient oscillation was observed in the 13C peak intensity vs. contact time plots for the CH2, CHF and CF2 groups. Based on the cross relaxation theory of the spin diffusion process, it was clarified that the oscillation behavior was caused by the TrFE-rich domain and that the crystal consisted of VDF-rich and TrFE-rich domains. The spin-lattice relaxation time T1ρH in the rotating frame in both domains showed the two T1ρH minimum processes of β and αb in the ferroelectric phase, which are respectively due to the flip-flop motion of the TrFE segment and the oscillational motion of the VDF segment, and the T1ρH minimum process of α1D is due to the one-dimensional diffusion motion of the conformational defects along the chain, accompanied by the trans and gauche transformations of the VDF conformers in the paraelectric phase on cooling. The anomaly of the T1ρH minimum at the Curie temperature depended on the conformational stability of both segments. The deflected trans TrFE segment did not experience any conformational change in the transition region, in contrast to the trans-gauche conformational change in the VDF segment.