Syozo Murakami

Structural development of natural rubber during uniaxial stretching by in situ wide angle X-ray diffraction using a synchrotron radiation

Structural development of natural rubber during uniaxial stretching was examined by an in situ wide angle X-ray diffraction measurement using a synchrotron. During stretching, the amorphous part showed little change, i.e. an amorphous halo remained clear even at 500% strain. The fraction of induced crystals was very small, though a clear crystalline pattern was observed at 400% strain. Some polymer chains were oriented and crystallized, but most of the chains were not oriented at all in spite of large deformations of the specimen. Only a small amount of polymer chains contributes to the stress and hysteresis loss during elongation.

Characterization of comb-shaped high molecular weight poly(oxyethylene) with tri(oxyethylene) side chains for a polymer solid electrolyte

Structure and properties of high molecular weight comb-shaped poly(oxyethylene)s with tri(oxyethylene) segments as side chains (TECs) were evaluated as a polymer solid electrolyte. The weight-average molecular weights of the TECs were in the order of 10 6 , and the contents of the side chain were 5, 11 and 18 mol%. The presence of tri(oxyethylene) side chains decreased the crystallinity of oxyethylene segments, i.e., TECs with higher side chain content showed lower crystallinity. The crystallite size of oxyethylene units in TEC films did not change, but the amorphous phase content became higher by the introduction of tri(oxyethylene) side chains. The crystalline structure in TECs was found to be Form I monoclinic system and a 7:2 helical structure. When LiClO4 was doped in the TECs at the concentration of [Li]:[O]0.05, TECs with 11 and 18 mol% tri(oxyethylene) segments showed the ionic conductivities in the order of 10 4 Sc m 1 at 30°C and 10 3 Sc m 1 at 80°C, respectively, which were a class of the highest ionic conductivity reported. TECs doped with the salt formed very elastic self-standing film without crosslinking. Salt-doping at the concentration of [Li]:[O] 0.05 decreased the crystallinity of polymers, but the crystallite sizes were almost equal with those of the non-doped films.

A study on the structural changes during uniaxial drawing and/or heating of poly(ethylene naphthalene-2,6-dicarboxylate) films

The structural changes in the uniaxial drawing process of an unoriented amorphous film of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) and in the heating process of an oriented amorphous film of PEN were studied using X-ray diffraction apparatus equipped with imaging plates. This apparatus allows us to record a time-resolved series of two-dimensional patterns of wide-angle X-ray diffraction in rapid succession, and, therefore, we can follow the structural changes during uniaxial deformation and/or thermal treatment processes. The results are as follows: (1) When an unoriented amorphous PEN film was stretched below Tg (= 117 °C), it could be elongated up to a draw ratio (DR) of 4–5 via neck formation and became an oriented amorphous film. (2) In the heating process of the oriented amorphous film (DR = 3.6, 65 °C), crystalline reflections started to appear near 120 °C, accompanied by streaks on the off-equatorial layer lines. The existence of these streaks on such layer lines indicates a lattice distortion due to the axial shift of neighbouring chains along the chain axis with respect to one another. Finally the film exhibited a fibre structure (transverse isotropy). (3) When an unoriented amorphous PEN film was drawn at 150 °C, the film exhibited a fibre structure accompanied by a lattice distortion that is similar to that mentioned above, and thereafter frequently showed so-called double orientation (uniplanar axial orientation: (10)[001]) in which naphthalene rings in the main chain are preferentially aligned parallel to the film surface despite the fact that the film was deformed in the mode of uniaxial free-width drawing.

Effect of network-chain length on strain-induced crystallization of NR and IR vulcanizates

Abstract Strain-induced crystallization of natural rubber (NR) and synthetic isoprene rubber (IR) with various crosslinking densities was investigated by wide angle X-ray diffraction using a synchrotron radiation and simultaneous tensile measurements. The elongation ratio at the onset of crystallization (αc) was almost independent of crosslinking density. IR samples showed larger αc values than NR because of the lower stereoregularity of IR. These results suggest that the onset of crystallization is determined by increased melting temperature by strain due to an entropic reason. The amount of oriented amorphous component changed approximately linearly with strain, and was a little larger in IR than in NR when compared at the same elongation ratio. At small strain (and stress), crystallinity in IR was lower than in NR. These results indicate that, at small strain region, the more stress is assigned to oriented amorphous in IR than in NR.

Strain-induced molecular orientation and crystallization in natural and synthetic rubbers under uniaxial deformation by in-situ synchrotron X-ray study

Abstract In-situ synchrotron wide-angle X-ray diffraction (WAXD) studies and simultaneous measurements of stress and strain during uniaxial stretching of various vulcanized rubbers were carried out (at room temperature and 0°C) to reveal the strain-induced molecular orientation and crystallization relationships. Rubbers evaluated included natural rubber (NR), synthetic poly-isoprene rubber (IR), poly-cis-1,4-butadiene rubber (BR) and butyl rubber (IIR). Some universal features were observed in these systems: (i) At high strains (> 5.0), the majority of the chains (up to 50 ≈ 75%) in natural and synthetic rubbers remained in the un-oriented amorphous state with only a small amount of crystalline fraction formed (10–20%). The rest of the chains were in the oriented amorphous state. (ii) During deformation, the oriented amorphous chains acted as precursors to strain-induced crystallization. A network of micro-fibrillar crystallites is formed within the closely populated vulcanization points, leading to the e...

Structure development in the uniaxial-drawing process of poly(ethylene naphthalate)

Amorphous films of poly(ethylene naphthalene-2,6-dicarboxylate) were drawn isothermally up to desired draw ratios at 130, 140, 150 and 160°C mainly to study structure formation during uniaxial drawing by wide-angle X-ray diffraction (WAXD). The results were analysed in comparison with stress-strain curves in order to find the draw ratio associated with the onset of crystallization at the above-mentioned temperatures. To obtain further detailed information, birefringence and density were measured for the films drawn at 150°C to elucidate the relationship between the degree of chain orientation and the crystallinity. A series of results was discussed in relation to previously reported interesting phenomena of the time-resolved two-dimensional WAXD patterns recorded using the imaging plate system (Polymer 1995, 36, 291).

Thickening process of polyethylene single crystals at an early stage of annealing

By the use of a position sensitive proportional counter, changes in small and wide angle X-ray scattering during annealing of polyethylene single crystal mats were measured from the start in successive spans of very short measuring time. At high temperatures, the long period relating to stacking of lamellae rapidly increased at an early stage, passed through a plateau, and thereafter again increased gradually. With a decrease in annealing temperature, the amount of its first rapid increase was reduced and the plateau changed into an ascending slope. At much lower annealing temperatures, the long period increased following the logt law after an induction time. The integral breadth of a peak corresponding to the long period first increased rapidly, simultaneously with the rapid increase in the long period, and thereafter decreased. Wide angle X-ray measurement showed that the integrated intensity of 110 reflection first decreased and then increased during annealing at high temperatures. This fall and rise process was more marked, when the annealing temperature is higher and the initial thickness of lamellae is smaller. From these observations, it was inferred that in the thickening process, stacking order of lamellae at first decreased because of rapid reorganization due to partial melting or melt-recrystallization and subsequently increased through increasing evenness of lamellar thickness.

MORPHOLOGY OF MELT-CRYSTALLIZED POLY(ETHYLENE 2,6-NAPHTHALATE) THIN FILMS STUDIED BY TRANSMISSION ELECTRON MICROSCOPY

Thin films of poly(ethylene 2,6-naphthalate) (PEN) were isothermally crystallized at 190 °C after being melted at 300 °C. Morphological observation by transmission electron microscopy (TEM) showed the spherulitic texture in the films. Selected-area electron diffraction (SAED) indicated that the crystals in the films are the a form, as expected from our thermal condition for crystallization. The SAED pattern from the untilted specimen was characterized by the fairly intense reflection ring accompanied by other weak rings, and this intense ring was indexed as 010. A series of SAED patterns, which were obtained from the same specimen area tilted at various angles in the TEM column, suggested that the crystallites are oriented with their (001) planes being preferentially parallel to the film surface. Subsequently, a set of the dark-field images of the two-dimensional spherulite taken by using two different parts of the 010 reflection ring revealed that most of the crystallites in such a spherulite are oriented with their (010) planes being parallel in its radial direction. In addition, the spherulites in small pieces (0.05–0.08 mm thick) of PEN, which had been crystallized under the same thermal condition as above, were determined to be negatively birefringent by polarizing light microscopy.

Strain-induced birefringence and molecular structure of glassy polymers

Abstract The dynamic birefringence and viscoelasticity were measured for poly(ethylene naphthalene-2,6-dicarboxylate), and the contributions from the main chain orientation and the rotational orientation of repeating unit to the strain-induced birefringence were evaluated. The values, together with published ones for other glassy polymers, were compared with the anisotropy of polarizability tensor of the repeating units. The contribution from the main chain orientation for various polymers was in accord with that evaluated from the excess polarizability of the unit in the main chain direction assuming a quasi-affine orientation of the unit. The contribution from the rotation was well correlated with the anisotropy in the plane perpendicular to the chain axis. The degree of the rotational orientation was similar among the polymers. The rotational orientation was high for vinyl polymers with large side-groups.

Elastomeric Comb-Shaped High Molecular Mass Poly(Oxyethylene) for Polymer Electrolyte: Morphology and Ionic Conductivity

The morphology, dynamic mechanical properties and ionic conductivity of high molecular mass comb-shaped poly(oxyethylene)s with tri(oxyethylene) side chains (TECs) were investigated, when LiClO 4 was doped at the concentration of [Li]/[-O-] = 0.05 ∼ 0.15, The samples were TEC-11 and TEC-18, the contents of tri(oxyethylene) side chain of which were 11 and 18 mol %, respectively. With increasing salt concentration, the glass transition temperature increased and the melting temperature decreased followed by the disappearance of the melting point. By adding the salt at the concentration of [Li]/[-O-] = 0.10 or 0.15, an alternative structure was suggested to be formed although the poly(oxyethylene) matrix was completely amorphous. Due to the morphological characteristics of TECs and the concentration of the salt, both TEC-11 and TEC-18 exhibit the high ionic conductivities of 10 -4 S/cm at 30°C, when the salt was doped at the concentration of [Li]/[-O-] = 0.10. The high molecular mass, over 10 6 , of TECs gave rubbery electrolyte films without chemically crosslinked structure. The addition of the salt to TECs decreased the shear storage modulus at room temperature and expanded the temperature range of the rubbery plateau region within the range of salt concentrations studied here.