Our molecular design of the polymer solid electrolyte based on rubbery state of polymer is presented. Biocompatible segmented polyurethane elastomers with poly (oxyethylene)-poly(oxytetramethylene)-poly(oxyethylene) segments were used at first for the matrix of solid electrolyte. Next, oligomeric poly(oxyethylene) (PEO) chains were grafted to polysiloxane main chain to afford rubbery matrix for ion conduction when doped with lithium perchlorate. The latter showed higher conductivities than the former. However, the mechanical properties of the latter were poor, and its crosslinking resulted in the lower conductivity. Copolymer polymerized from ethylene oxide and epichlorohydrin was evaluated as a solid electrolyte. The epichlorohydrin units did not contribute to the ion conduction resulting in relatively low conductivities, though it was good in term of mechanical properties. Our final molecular design of the ion conductive matrix was the high molecular weight comb-shaped PEO with oxyethylene segments as side chains. Both main and side chains are oxyethylene units and the molecular weight was in the order of 106. The side oxyethylene units discouraged crystallization of PEO. Excellent conductivities were observed on doping with lithium salts.
High-resolution electron microscopic (HREM) observation with a transmission electron microscope (TEM) is a powerful experimental method to clarify complicated fine structures, if specimens can endure electron irradiation. Though polymer crystals are very sensitive to electron irradiation, it has turned out possible to observe them by high-resolution electron microscopy at molecular dimensions. If we perform our experiment carefully enough, the resolution limit predicted from the durability against radiation damage can be achieved even for the polymer crystals. One should recognize that HREM images are composed of lattice fringes which are formed by the interference between unscattered and scattered electron waves. Several factors determining performance of the TEM itself should be known. Then the optical systems of the TEM must be aligned carefully and they must be stabilized before taking HREM images. Photographic films are still the best medium to record HREM images. In HREM observation of polymer crystals, reducing the total amount of electron dose given to the specimen before taking an HREM photograph is the most important. A low-dose function which can focus the specimen at a position remote from the region to be photographed in the specimen is useful to reduce the radiation damage during focusing. The condition to record an HREM image is determined by the durability of each specimen against radiation damage. The method to increase the durability of a specimen to electron irradiation by cooling can improve the resolution limit of the specimen. HREM observation of the β-form single crystals of syndiotactic polystyrene is an example. Arrangement of molecular stems both in the solution-grown single crystal and in the melt-grown one was revealed by the HREM observation.
The critical shear rate for flow-induced homogenization of a polystyrene/poly(vinyl methyl ether) blend with nearly critical composition in the phase-separated region near the phase separation temperature was studied by rheological and light scattering measurements under steady shear flows. The critical shear rate by rheometry was determined from the change in shear rate dependence of first normal stress difference as in a previous study. This critical shear rate was almost consistent with the critical shear rate by flow-light scattering at which the intensity deviates from the value in the phase-separated region.
We report the effects of morphologies on mechanical properties of polystyrene-block-polyethylenebutylene-block-polystyrene (SEBS) triblock copolymers using SEBS samples with various compositions. The morphologies and the mechanical properties were examined by the small-angle X-ray scattering (SAXS) technique and the tensile stress-strain measurements, respectively. It is well known that the morphology of microphase-separated structures can be controlled by composition. We found that a border composition dividing spherical and cylindrical phases and that dividing cylindrical and lamellar phases shifted towards smaller values of φPS (in the case of φPS≤0.5) upon hydrogenation (from SEBS to SBS), where φPS denotes the volume fraction of polystyrene and SBS stands for polystyrene-block-polybutadiene-block-polystyrene. Namely, for example, an SEBS sample forms lamellar morphology even at a composition where an SBS sample forms cylinders. It is also confirmed that the mechanical properties were well correlated with change of the morphologies with composition or upon thermal annealing.
Experimental studies about the effect of block copolymerized structures on the uniaxial elongational viscosity were performed. Two poly (styrene-block-butadiene-block-styrene) (SBS, S/B weight ratio=4/6) samples with linear and star (4 arms) structures were used for the elongational viscosity measurement at constant strain rates. The block copolymer samples exhibited the strain-softening elongational viscosity. This property was in contrast to the strain-hardening elongational viscosity which is observed for homopolymer melts. The cause of the strain-softening property was analyzed from the structural change by small angle X-ray (SAX) and transmission electron microscope (TEM). The lamellar structures were more oriented and became longer along the elongational direction by the elongation, while the lamellar thickness remained almost constant. The obsrvation indicates that the lamellar structures, instead of the SBS molecules, were oriented and stretched. The rheological discussion on the strain-softening elongational viscosity was also carried out by the BKZ model. The damping functions of the block copolymers from step-shear relaxation experiments showed larger decrease than that of the Doi-Edwards prediction. The structural change observation and the BKZ analysis suggested that the largely decreased damping functions are due to the lamellar orientation and cause the strain-softening elongational property.
To analyze the effect of strain rate upon the state of internal strain energy accumulated in largely stretched glassy polymethyl methacrylate (PMMA), we studied its strain recovery behavior at heating. Specimens were subjected to up- and down-jump schemes of strain rate and stretched to various amounts of strain at a temperature below the glass transition temperature Tg. As an ultimate case of the down-jump scheme, the stress relaxation experiment was also performed for various durations. Comparing transient stress responses due to the strain rate jump imposed on the specimens with their strain recovery behaviors at heating, we found that to increase time length of viscoelastic stress relaxation had an effect of shifting a temperature range of sub-Tg strain recovery to higher temperatures. Since the strain recovery at less than Tg has been found to be accompanied by a release of the internal strain energy, the present result allowed us to conclude that molecular kinetics of nonlinear viscoelastic relaxation occurring in the largely deformed polymer had an effect to enhance the thermal stability of the internal strain energy accumulated in the deformed polymer.
Tensile ductility of uniaxially thermoformed sheets of polymethyl methacrylate (PMMA) was analyzed in their longitudinal and transverse directions in connection with their residual birefringence and deformation recovery at reheating. The intensity of the residual birefringence increased almost linearly with the increase of extension ratio. The deformation recovery at the reheating of the thermoformed sheets indicated that molecular rearrangement induced by the uniaxial stretching in the rubbery state was accompanied by little storage of internal strain energy and thus of highly entropic elongation of polymer chains. As expected from these results, specimens cut from the thermoformed sheet in its transverse direction were less ductile than those from an unstretched sheet. Yet, specimens cut in the longitudinal direction were much more ductile in comparison with the unstretched sheet despite the development of tensile stress during the rapid cooling process in the thermoforming. Data of mechanical work consumed in the longitudinal and transverse specimens during their tensile test enabled us to propose a recommendable range of residual strain remaining in the thermoformed PMMA sheet with respect to their tensile ductility.
We have investigated mechanical properties of bimodal networks, which have a two-peak distribution of the length of the network chains between crosslinks, in equilibrium swollen state. The bimodal networks were prepared by end-linking mixtures of short and long poly (dimethylsiloxane) (PDMS) chains with tetra-functional crosslinker. The ratio of molecular mass of the short and long PDMS chains was ca. 11. The stress-strain relationships have been investigated as a function of molar fraction of short chains. The networks with more than 98mol% short chains are brittle and they have high elastic moduli. When the molar fractions of short chains fall below 95mol%, the networks become markedly extensible. The stress-strain relations of unimodal networks and bimodal network with small fraction of short chains obey the prediction of the classical theory of rubber elasticity, while those of other bimodal networks deviate from the theoretical prediction. The dependence of network structure on the composition of precursor chains has been estimated from the analysis of the stress-strain behavior. The structure model proposed in small angle X-ray scattering (SAXS) study on bimodal networks has been re-examined on the basis of the results of mechanical experiments in this study.
Morphology of thin films of natural rubber (NR), which had been crystallized under molecular orientation, was examined by transmission electron microscopy (TEM). Thin films of NR (RSS#1) were made by casting its solution (2.0wt%) in benzene onto the water surface, stretched by a strain of about 200%, and then mounted on carbon-coated grids for TEM. The specimens thus prepared were introduced into a TEM column by using a cryo-transfer specimen-holder and crystallized there isothermally at -25°C. Selected-area electron diffraction of the NR film gave a well oriented h0l-pattern, which illustrated that the chain axis (c-axis) of NR was oriented parallel to the prestretching direction and also the (010) lattice plane was parallel to the film surface: uniplanar axial orientation. The dark-field image of such a film taken using the 200 equatorial reflection showed that narrow bright striations were oriented perpendicular to the prestretching direction and some of them were stacked in that direction to make row structure or shish-kebab-like structure. Each of these striations, namely of “α-filaments” by Andrews, was concluded to be an edge-on lamella which had been grown plausibly in the  direction.
We measured biaxial and planar stress relaxation moduli of polystyrene (PS) and low-density-polyethylene (LDPE) melts. For both PS and LDPE, and for both biaxial and planar elongations, the relaxation moduli were factored into strain and time dependent factors. The strain dependent factor, i.e., the damping function was larger for LDPE than for PS. The damping function for the uniaxial elongation was estimated from the uniaxial elongational viscosity data. The damping functions for uniaxial (hE), biaxial (hB) and planar (hP) elongations were found to be in order of hB<hP<hE, if compared at the same strain. The damping function for shear deformation (hr) was also measured. It was found that hP was smaller than hr even if plotted against the strain invariant, although the critical strain, at which the damping functions started to decrease, was almost the same for hP and hr.
The sandwich-type heat insulating board with fiber assemblage as a core layer was molded by applying a compression molding method to the waste cord assemblage whose surface layer was melted partially beforehand by an infrared heating technique. The fairly small thermal conductivity could be achieved for the present molded plastic board. In the complex phenomena during the molding process, this paper focused on the melting behavior of thermoplastic waste cord of synthetic fabrics heated by the infrared heaters. The melting test was performed in the special closed furnace. The temperature response and distributions in the waste cord assemblage were measured by using thermocouples and the melting behavior was observed for various heating power of the infrared heaters. Moreover, the melting rate was measured for the waste cord assemblages with various void ratios. The simple compression molding method described in this paper shows promise as a contribution towards the recycling of wastes of thermoplastic fibrous material, and the experimental results obtained here may be contribute to the establishment of the optimum molding system.