Yoshio Hayakawa

Multi-scale instrumental analyses showed that the crosslinker changed the morphology to homogenous while the graft polymer increased molecular mobility.

The molecular mobility and compatibility of plasticized polyhydroxyalkanoates (PHA) were investigated, focusing on changes due to copolymerization using either flexible poly (butylene succinate) (PBS) or rigid poly(lactic acid) (PLA) units. For the case of a poly(3-hydroxybutyrate) (PHB) unit in plasticized PHA, copolymerization of either PBS or PLA decreased ¹H and ¹³C spin-lattice relaxation times in the laboratory frame (T₁H and T₁C) in the same manner, while PBS produced a lower ¹H spin-lattice relaxation time in the rotating frame (T_1ρH) than PLA. Both the signals of ¹H MAS (magic-angle spinning) and ¹³C PST (pulse saturation transfer) MAS nuclear magnetic resonance (NMR) spectra were sharpened and increased by copolymerization with PBS. A variable temperature relaxation time analysis showed that the decrease of T₁H values was dominated by the ¹H spin diffusion via the interface between PHB and the added polyester because of the good compatibility. Meanwhile, the decrease of T₁C values was dominated by increasingly rapid molecular motions of PHB because of the lowered crystallinity due to the plasticization. Slow molecular motions (kHz order) were enhanced more by the addition of PBS than PLA, although rapid molecular motions (MHz order) were enhanced by either polyester. Several NMR parameters were beneficial for analyzing the manufacturing process as the indexes of polymer compatibility and molecular motions.

Changes in the polymer properties of poly(lactic acid) (PLA) fibers during drawing and degradation processes were analyzed using solid-state NMR, with the goal of elucidating morphological changes that influence fiber tensile properties. Combination of X-ray diffraction (XRD) and differential scanning calorimeter (DSC) indicated that the drawn PLA fibers consisted of different proportions of α crystalline and amorphous forms. 13C CP-MAS NMR spectra showed amorphous-like broad singlet signals, of which the full width at half maximum (FWHM) decreased with increasing crystallinity and crystal orientation. The T1H value decreased by interaction with additives and increased with increasing crystal orientation. The interaction with additives also reduced T1C values, which increased with increasing crystallinity. Use of organic clay enhanced the crystallization of high draw-ratio PLA fibers due to nucleation, which increased tensile strength; this effect gradually decreased with time during accelerated weathering. In contrast, the plasticization due to the addition of flexible polymers increased fiber elongation, which rapidly dropped during the degradation. Changes of FWHM, T1H, and T1C values indicated that the degradation occurred at sites within the amorphous portions of the PLA fibers containing organic clay, while the flexible polymers were preferentially degraded if they were present in the PLA fibers.

The effects of phenol formaldehyde (PF) resin impregnation into Japanese cedar plates were studied by the integrated analysis of solid-state NMR spectra and relaxation times. ¹³C cross-polarization/magic angle spinning (CP-MAS) NMR spectra showed that PF resin permeated near carbohydrate polymers as well as lignin regions, providing hydrophobicity in a woody material. Additionally, ¹³C pulse saturation transfer/magic angle spinning (PST-MAS) NMR spectra revealed that the molecular mobility of cellulose endocyclic groups was suppressed by the PF resin impregnation. Spin-lattice relaxation times in the laboratory frame, T₁H and T₁C, for both untreated and impregnated woods decreased in humid conditions while they were increased by the PF resin impregnation. Meanwhile, spin-lattice relaxation in the rotation frame, T_1ρH, decreased in humid conditions as well as being a result of the PF resin impregnation. According to the tendencies of the T₁H, T₁C, and T_1ρH values associated with the PF resin impregnation, although faster molecular motions of lignin OCH₃ group were increased in the MHz frequency range, slower molecular motions of the cellulose ring were suppressed in the kHz frequency range, which confirmed the result from the ¹³C PST-MAS NMR spectra.

Hexafluoropropene trimers were reacted with C₆F₅Si(CH₃)₃ to provide not only pentafluorophenyl but also perfluorophenylene derivatives [F(C₆F₄)_nC₉F₁₇; n=2–9] by successive pentafluorophenylation of perfluoroaryl rings. Their structures, including rotational isomers, were determined by MS, ¹⁹F and ¹³C–{¹⁹F} NMR spectroscopy, and/or X‐ray crystallography, and were further confirmed by B3LYP‐GIAO calculation of NMR shieldings. Formation of a pair of gear‐meshed rotamers with clockwise and counterclockwise conformations was identified by NMR measurements for the structures having geminal (CF₃)₂CF groups at the C=C bond. That the predominantly formed counterclockwise rotamer was gradually converted to the clockwise rotamer over 50 days at room temperature through a synchronized movement of gears was also confirmed by NMR measurements. A comparison between the X‐ray structure and B3LYP calculations showed some structural differences that arise from the crystal packing.

Methacrylic monomers with biphenyl cores and those with fluorinated substituents were copolymerized to afford fluorinated composites having good mechanical properties and inertness. Adding a large amount of silica fillers to the polymer precursors followed by molding and complete thermal curing gives polymer composites that can be used as an artificial tooth material with improved durability and anti-fouling properties.