Hiromu Saito

Strain recovery mechanism of PBT/rubber thermoplastic elastomer

Abstract The thermoplastic elastomer (TPE) prepared by dynamic vulcanization is a two-phase material in which crosslinked rubber particles are densely dispersed in a ductile polymer matrix. The TPE shows an excellent strain recovery, even though the matrix consists of ductile plastics. This behavior was exemplified in a 50/50 poly(butylene terephthalate)(PBT)/ethylene rubber blend. Finite element method (FEM) analysis revealed that: (1) the low stress evolved in PBT matrix with bulk deformation, especially in the ligament matrix between rubber particles in stretching direction, is locally preserved within an elastic limit and it acts as an in situ formed adhesive for interconnecting the rubber particles, and (2) the volumeric strain of rubber particles with high Poissons ratio provides the contractile stress to heal the plastically deformed PBT phase outside the ligament matrix. Such strain mechanisms were supported by the polarized FT-Raman spectroscopy in terms of the peak shift caused by chain distortion, its anisotropy, and the gauche-to-trans transformation associated with plastic deformationm, in comparison with those in neat PBT.

Dielectric study of the crystal-amorphous interphase in poly(vinylidene fluoride)/poly(methyl methacrylate) blends

Abstract We investigated the dielectric properties of crystalline poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blends in a wide range of frequency f at various temperatures T . A large peak of the dielectric loss e ″( f ) due to the interfacial polarization was found in the blend below the frequency region of the α c process. Such a peak was not observed in neat PVDF. The difference may be ascribed to the existence of a large amount of PMMA at the crystal-amorphous interphase in the blend. We also demonstrated that a low T peak in e ″( T ), which was thought of as an interfacial peak, is not related to the α a process of PVDF in the interphase, but to the β process of PVDF.

Physical characterization of a polyolefinic thermoplastic elastomer

Physical characterization of a commercial polyolefinic thermoplastic elastomer (TPE), Santoprene®, was undertaken to understand the elastomeric nature of the two-phase material in which rubber particles are dispersed in a matrix of polypropylene (PP). Dynamic mechanical analysis showed that the PP matrix contains a small amount of rubber. PP crystal lamellae in rubber particles in a well-annealed sample were observed by transmission electron microscopy, suggesting that PP had been occluded in the rubber phase. Such partial phase-mixing may be caused by homogenization under high shear during dynamic vulcanization. Wide angle X-ray diffraction (WAXD) studies showed that PP crystallites in TPE are smaller than those in neat PP. That is, the occluded rubber in the PP matrix may play the role of impurity to render the smaller crystallites. By WAXD analysis on crystal orientation and its relaxation in stretching and releasing processes, it was shown that the smaller crystallites suffer less plastic deformation and, rather, play the role of tie points to provide the elastic properties of the PP matrix itself. About 40 wt% of process oil was found to be loaded on TPE; however, the oil seems to play a minor role in providing the elastomeric character.

Dielectric studies of specific interaction and molecular motion in single-phase mixture of poly(methyl methacrylate) and poly(vinylidene fluoride)

Abstract It is well known that the miscibility of dissimilar polymers with high molecular weights arises from specific interaction, such as hydrogen bonding. To discuss the influence of the interaction on a side group rotation and main chain motion of poly(methyl methacrylate) (PMMA) in PMMA/poly(vinylidene fluoride) (PVDF) blends, we investigated the dielectric loss e″ as a function of frequency f. e″(f) showed a peak at around 104 Hz, which is assigned to the β process characteristic of the side group rotation of PMMA below the glass transition temperature (Tg) and the αβ process characteristic of the side group rotation cooperative with the main chain motion above Tg. Above Tg, the peak frequency fmax increased and then decreased with increasing PVDF content (/gf); fmax(/gf) showed a peak at /gf ≈ 10 wt.%. The increase may be interpreted by the acceleration of main chain motion by lowering of Tg with increasing the content of the lower Tg component (PVDF). Increasing further the PVDF content, the specific interaction seems to restrict the main chain motion and prevails over the Tg effect so that the peak appears in the fmax(/gf) curve. fmax decreased with increasing annealing time ta, suggesting the increase in restriction with ta. This may imply that the association of dissimilar polymers by the specific interaction is a very slow rate process on a time scale of thousand minutes. Also observed after annealing were broadening of the relaxation time distribution and the appearance of interfacial polarization, suggesting a change in chain conformation from random coil to a locally stretched state to form a nematic domain.

Sustainable cycloolefin polymer from pine tree oil for optoelectronics material: living cationic polymerization of β-pinene and catalytic hydrogenation of high-molecular-weight hydrogenated poly(β-pinene)

(−)-β-Pinene, a major constituent of pine tree oil, was cationically polymerized to generate a high-molecular-weight polymer and then subsequently hydrogenated via metal catalysts to give a high-performance, bio-based cycloolefin polymer with an alicyclic backbone. To obtain the high-molecular-weight polymer, the controlled/living cationic polymerization of (−)-β-pinene was investigated by an initiating system, consisting of a protonic acid, a Lewis acid, and an added base, along with an incremental monomer addition technique. Among the various systems, the RCl/EtAlCl2/Et2O system gave a high-molecular-weight poly(β-pinene) (Mw > 100 000). The catalytic hydrogenation of the obtained high-molecular-weight poly(β-pinene) was examined using various metal catalysts, among which Pd/Al2O3 enabled the quantitative hydrogenation (>99.9%) of the unsaturated CC group in the repeating unit under mild reaction conditions (1.0 MPa pressure of H2). These reactions could be performed even at relatively large scales to produce several hundred grams of the polymer, which can be then processed through injection-molding. The synthesized bio-based cycloolefin polymers demonstrated promising potential properties as high performance optical plastics with good processability, low density, high optical transparency, low birefringence, non-hygroscopicity, high mechanical strength, and excellent thermal properties.

Kinetic studies of crystallization in mixtures of isotactic polystyrene and atactic polystyrene

We investigated the spherulite growth rate G in 60/40 isotactic polystyrene (i-PS)/atactic polystyrene (a-PS) mixtures under a polarized microscope with a TV video recording system. When the molecular weight M A of a-PS was higher than 1.91 × 10 4 , linear growth was observed, i.e. G was constant throughout the crystallization, and the chain diffusivity D T decreased monotonously with increasing M A . In contrast, when M A was less than 5.2 × 10 3 , the growth was non-linear, i.e. G decreased with time, and D T increased with increasing M A ( D T ∞ M 1/2 A ). Both M A dependences on D T were successfully interpreted using a modified Hoffman-Lauritzen theory involving the exclusion effect of a-PS. On the basis of this modified Hoffman-Lauritzen theory, the spherulite growth mode, i.e. linear or non-linear, was also interpreted in terms of a new kinetic parameter λ = D * A / D * a and D s being the tracer diffusion coefficient of a-PS and the self-diffusion coefficient of i-PS, respectively.

Thermal reversibility in crystalline morphology of LLDPE crystallites

We investigated the temperature dependence of the crystalline morphology in linear low density polyethylene by light scattering, small-angle X-ray scattering (SAXS) and oscillating-DSC. Optical anisotropy in the spherulite, defined by model calculation of the Vv scattering pattern, and the order parameter of crystal orientation within spherulite, estimated by sharpness of the Hv scattering profile, increased in the cooling process while they decreased in the heating process. That is, the morphology is thermally reversible. The morphological change with time after the temperature drop or jump was found to be very fast in several seconds. Oscillating-DSC and SAXS results suggest that the disordering in the heating process is caused by melting of thermally unstable thin lamellae existing between the thick lamellae, which are already developed at high crystallization temperature. Thus, the thermal reversibility is ascribed to the thermally unstable thin lamellae; i.e. the thin lamellae are developed fast at wide temperature range in the cooling process and they melt fast in the heating process at the temperature close to the temperature they are developed. Owing to the fast development of the thin lamellae, the crystalline morphology obtained at high temperature cannot be frozen by quenching.

Significant correlation between refractive index and activity of mitochondria: single mitochondrion study.

Measurements of refractive indices (RIs) of intracellular components can provide useful information on the structure and function of cells. The present study reports, for the first time, determination of the RI of an isolated mitochondrion in isotonic solution using retardation-modulated differential interference contrast microscopy. The value was 1.41 ± 0.01, indicating that mitochondria are densely packed with molecules having high RIs. Further, the RIs of each mitochondrion were significantly correlated with the mitochondrial membrane potential, an index of mitochondrial activity. These results will provide useful information on the structures and functions of cells based on the intracellular distribution of RIs.

Phase behaviour and morphology development in a blend of isotactic polypropylene and hydrogenated poly(styrene-co-butadiene)

Abstract A hydrogenated poly(styrene- co -butadiene) (hSBR) was found to be miscible with isotactic polypropylene (iPP) above the melting point of iPP. The mixture was phase-separated at lower temperatures, i.e. the iPP/hSBR blend exhibited upper critical solution temperature ( UCST ) type phase behaviour ( UCST ≈ 100°C). The UCST phase behaviour was determined by time-resolved light scattering analysis. In the quenched 50/50 blend, a microphase-separated structure of hSBR domains, having a diameter of 20 nm, dispersed quite regularly in an iPP-rich matrix (periodic distance /2~ 40 nm) was observed by transmission electron microscopy. The microphase-separated structure seems to originate from spinodal decomposition below the UCST during the quenching process. The formation of large and ordered lamella crystallites was suppressed to yield fine PP crystallites (of size ≈ 8 nm, as estimated by the Sherrer equation). This man be caused by the presence of the hSBR. Thus, the partially miscible impurity (hSBR) produces fine iPP crystallites which can act as crosslink points to provide thermoplastic elastomer-type character to the blend.

Aramid/poly(ether sulphone) blend : crystallization accelerated by the presence of amorphous polymer

Abstract An aramid, prepared by the polycondensation of bis(4-aminophenyl) ether with isophthaloyl chloride, was found to render a single-phase mixture with poly(ether sulphone) (PES) by solution casting. Crystallization of the blend was studied by wide-angle X-ray diffraction, Hv light scattering, differential scanning calorimetry, Fourier-transform infra-red spectroscopy and scanning electron microscopy. The crystallization of aramid was found to be accelerated dramatically by adding PES, e.g. the crystallization rate constant of a 50 50 blend was shown to be one decade higher than that of neat aramid at around 310°C. The accelerated crystallization was ascribed to the elevation of chain mobility of aramid by blending with PES. It may be caused by the decrease of Tg via blending of a low-Tg component (PES), but this contribution was estimated to be small. The major contribution seems to be due to the partial dissociation of aramid-aramid interactions and the ‘up-hill diffusion’ associated with the liquid-liquid phase separation.