岸 肇

ABSTRACT The effect of polyethersulfone (PES) blends on the flame retardancy of dicyanate ester of bisphenol E (DCBE) cured resin was investigated. The DCBE/15 wt% PES cured blends formed co‐continuous phase structures by polymerization‐induced phase separation. When heating up to 200°C for curing, varying the temperature ramp rate was found to affect the size and glass‐transition temperature of domains of the two phases in the blends. The self‐extinguishing time was influenced by the phase domain size, with the highest flame retardancy being obtained when the width of the PES‐rich domains was around 3 μm. DCBE/15wt%PES/graphite filler composites with a co‐continuous phase structure and selectively localized graphite filler exhibited a higher thermal conductivity than DCBE/graphite filler composites without phase separation. The small amount of graphite filler was selectively localized in the cyanate‐rich continuous phases so that the graphite particles had more opportunities to contact each other within the micrometer‐sized templates. Due to their high flame retardancy and thermal conductivity, cured DCBE/PES polymer blends with a small amount of graphite filler offer great potential for applications in the aerospace industry.

Abstract Amorphous polymer/crystalline polymer blends can be prepared via the simultaneous polymerization of polymethacrylate/polyurethane combinations. The relationship between higher order structures and fracture mechanisms in these blends must be uncovered to elucidate the source of the increased fracture toughness of such materials. The present work involves the production of blended polymethacrylate/polyurethane and assess the internal structures of these specimens using optical and electron microscopy. These observations reveal the presence of both spherulites and elastomeric phases. The spherulites consisting of the polyurethane and are several micrometers in diameter whereas the phase‐separated polyurethane elastomeric domains are approximately 100 nm in size. Multiple cracks, crack bridging and plastic deformation around the precrack tips of loaded specimens are evidently responsible for the increased toughness of these blends. The former two phenomena are attributed to the presence of spherulites while the plastic deformation of the methacrylate matrix is ascribed to cavitation of the polyurethane elastomeric phases in response to loading.

This work studied the effects of tackifiers on the impact energy absorption properties of block copolymers (BCPs) comprising poly(styrene)-b-poly(isoprene)-b-poly(styrene) (SIS) and poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) (MAM). A rosin ester resin (RE) and an aliphatic petroleum resin (C5PR) were compared as the tackifiers. Analyses of Hansen solubility parameters and observations using electron microscopy indicated that both tackifiers were highly compatible with the poly(isoprene) component of the SIS, while the RE also showed good compatibility with the poly(n-butyl acrylate) phase of the MAM. The impact energy absorption characteristics of laminates made by applying layers of BCP/tackifier blends to cured epoxy substrates were evaluated using a pendulum impactor. The extent of energy absorption by these laminates was found to increase within specific tackifier concentration ranges. However, the C5PR showed poor compatibility with the MAM and had almost no effect on the energy absorption of the laminates. The energy absorption of the laminates could be described based on the calculated loss factor, eta, determined using the RUK equation including the viscoelastic parameters (both tan delta and storage modulus) for the BCP/tackifier blends, considering the time-temperature superposition principle, and for the laminate structures.

Room temperature ionic liquids (ILs) are the appealing research target as electrolytes for lithium batteries. The cation and anion structure of ILs influences their physical and chemical properties. In this study, an electron-donating branched substituent was introduced into imidazolium cations to promote charge delocalization and to improve the reduction stability of ILs. The ILs with branched substituent group at the third position of imidazolium cation, 1-allyl-3-isobutylimidazolium bis(fluorosulfonyl)amide ([AB(iso)Im][FSA]) and 1-allyl-3-tert-butylimidazolium bis(fluorosulfonyl)amide ([AB(tert)Im][FSA]), exhibited lower cathodic potential (-2.54 and -2.79 V vs. Fc/Fc(+), respectively). [AB(iso)Im][FSA] and [AB(tert)Im][FSA] showed sufficiently high ionic conductivity (4.85 and 3.66 mS/cm at 298 K, respectively), although the viscosity increased with the introduction of bulky branched substituent. Lithium secondary batteries composed of electrolytes using [AB(iso)Im][FSA] and [AB(tert)Im][FSA] showed stable charge-discharge behavior. (C) The Author(s) 2022. Published by ECSJ.

The structure formation and electrical conductivity of poly[diglycidyl ethers of bisphenol-F (DGEBF)]/poly [dicyclopentenyloxyethyl methacrylate (DPOMA)]/silver (Ag) filler composites were investigated. DGEBF/40 wt % DPOMA blends showed low viscosity and formed co-continuous phase structures at the micrometer scale via in situ radical polymerization of DPOMA followed by anionic polymerization of DGEBF. Scanning electron microscopy and nano-infrared spectroscopy revealed that the Ag fillers, surface-treated with myristic acid, were selectively localized in the methacrylate polymer-rich phases. Consequently, the Ag fillers were present in the self-assembled narrow area, which formed a conductive channel. The DGEBF/DPOMA/Ag composites thus achieved electrical conductivity with a reduction of the 30% Ag fillers, compared to the DGEBF/Ag composites. The mechanism for the selective placement of the Ag fillers was clarified in terms of the affinity among the epoxy-rich phase, the DPOMA polymer-rich phase, and the surface-treated Ag fillers by measurement of their Hansen solubility parameters (HSPs).

In a blend of acrylic block copolymer consisting of poly(methyl methacrylate) and poly(n-butyl acrylate) blocks and a special rosin ester resin (RE) tackifier as a model pressure-sensitive adhesive (PSA), RE exists in two states: as nm-sized agglomerated particles (A) and as dissolved molecules (B). The effect of A and B ratio on the PSA properties were investigated using REs with four different weight-average molecular weights (M(w)s) in the range from 680 to 1700. The formation of A increased with increasing of M-w because of lowering of miscibility. The glass transition temperature increased with increasing of M-w. The tack at lower temperatures and the fracture energy were improved by B, whereas the tack at higher temperatures was improved by A. A and B enhanced the cohesive strength and the wettability of PSA, respectively. However, the improvement of cohesive strength by the RE with highest M-w was remarkably low. This seems to be caused by the larger size of agglomerated particles. H-1 pulse nuclear magnetic resonance analysis was useful for estimating the degree of A formation. The model PSA investigated in this study was nanocomposite-like.

© 2020 Elsevier Ltd The fracture toughness and fracture process of second generation acrylic (SGA) adhesive joints were investigated in detail using tapered double cantilever beam (TDCB) tests. The distribution of granular elastomer with a size of ca. 150 nm in the bulk specimen by transmission electron microscopy (TEM) observation was similar to the distribution of cavitation determined by scanning electron microscopy (SEM) observation of the fracture surface. A mechanism was proposed for the role of the elastomer and acrylic phase in the cohesive failure process of SGA. A dimple, which is evidence of ductile fracture, was observed on the fracture surface. The relationships between the size of dimples, their number and energy release rate were clarified. An understanding of the proposed failure mechanisms is useful for constructing a numerical model for stress analysis and explaining the fracture phenomenon.

In this work a cycloaliphatic amine-cured epoxy (EP) resin was modified by micron-scale rubber particles (RP). Nominal RP, in sizes of 200 and 600 µm respectively, were produced using worn truck tires and ultra-high-pressure water jet cutting. The RP were dispersed into the EP resin using different mixing techniques (mechanical, magnetic, and ultrasonic stirring) prior to the introduction of the amine hardener. The dispersion of the RP was studied using optical light microscopy. A longer mixing time reduced the mean size of the particles in the EP compounds. Static (tensile and flexural), dynamic (unnotched Charpy impact), and fracture mechanical (fracture toughness and strain-energy release rate) properties were determined. The incorporation of the RP decreased the stiffness and strength values of the modified EPs. In contrast, the irregular and rough surface of the RP resulted in improved toughness. The fracture toughness and strain-energy release rate were enhanced up to 18% owing to the incorporation of 1% by weight (wt%) RP. This was traced to the effects of crack pinning and crack deflection. Considerably higher improvement (i.e., up to 130%) was found for the unnotched Charpy impact energy. This was attributed to multiple cracking associated with RP-bridging prior to final fracture.

Etherification of cellulose was performed using a mixture of ionic liquids (ILs) playing roles in both cellulose dissolution and catalysis. We investigated the effects of the reaction time and the ratio of these ILs in the mixture. Cellulose etherification was performed in these IL mixtures. The proportion of propoxy cellulose exceeded 2.5 after 24 h.

Reaction between the NH groups in polybenzimidazole (PBI) and bisoxazoline compounds (1,3-phenylene bisoxazoline, 1,3-PBO) resulted in the successful preparation of novel network polymers. Adjusting the amount of the bisoxazoline compound, which is a cross-linking agent for the preparation of network polymers, and obtaining dynamic mechanical measurements, electrical resistivity measurements, thermomechanical measurements, and tensile tests allowed the determination of the heat resistance and mechanical strength of these novel network polymers. Examination of the elementary reaction of PBI and the1,3-PBO curing reaction by using model compounds revealed that the NH group in the PBI structure reacted with the oxazoline group of 1,3-PBO. Comparison of noncross-linked PBI with the PBI network polymers obtained through cross-linking reaction with bisoxazoline compounds demonstrated improvements in heat resistance and mechanical strength of the PBI-bisoxazoline network polymers.

Nanostructures of diglycidyl ether of bisphenol-A epoxy/poly(methyl methacrylate)-b-poly(n-butyl acrylate)-bpoly( methyl methacrylate) (PMMA-b-PnBA-b-PMMA) triblock copolymer (BCP) blends were studied in relation to their mechanical properties. Three types of self-assembled nanostructures, such as spheres, random cylinders, and curved lamella, were controlled in phenol novolac-cured epoxy blends with a wide range of BCP content. Three types of nanostructures were observed using two-dimensional and three-dimensional transmission electron microscopy (TEM). The 3D-TEM, dynamic viscoelastic analyses, and theoretical model on the elastic modulus clarified that the spheres and the random cylinders, consisted of epoxy-immiscible PnBA phases, were discontinuously dispersed in the epoxy matrix. In contrast, the curved lamella formed co-continuous nanostructure, in which both the PnBA and epoxy phases formed continuous channels. The fracture toughness (critical strain energy release rate, G(IC)) and the flexural moduli of elasticity (E) of the cured blends were evaluated for various amounts of BCP content. The highest G(IC) was obtained from the random cylindrical nanostructured blends in the three types of nanostructures with the same PnBA content. The lowest E was obtained for the curved lamella with co-continuous nanostructures. The details of deformation and fracture events were observed using optical and electron microscopy, and the mechanical properties are discussed in relation to the nanostructures.

The phase structures obtained from blends consisting of an epoxy resin, an aromatic amine and a PMMA-b-PnBA-b-PMMA triblock copolymer (BCP) were studied, in terms of the effect of the process used to blend the BCP into the epoxy/amine mixture. The thermal dissolution of the BCP in the amine was found to promote the in situ generation of carboxylic acids in the PMMA segments of the BCP. This enhanced the compatibility of the BCP with the cured epoxy/aromatic amine resin, allowing the self-assembly of the BCP to form nanophase structures in the polymeric matrix. This work also determined that modification of the heating conditions was an effective means of controlling the quantity of carboxyl groups generated (that is, the acid value). Such variations led to the formation of different types of micelle structures, such as curved lamellae, coexisting of worm-like micelles and vesicles and spheres, from epoxy/amine/BCP blends having the same composition.

Etherification of cellulose, in particular, its epoxidation in the presence of glycidol, was conducted using a binary ionic liquid mixture as the solvent and catalyst. The influence of reaction time and component ratio was studied. The degree of cellulose epoxidation exceeded 2.2 at 60 degrees C for 18 h.

Separation of microphase morphologies of epoxy resins with PMMA-b-PnBA-b-PMMA acrylic triblock copolymers during curing was confirmed by in situ small-angle X-ray scattering (SAXS)/differential scanning calorimetry (DSC). Cured blends contain a variety of nano-ordered structures via self-assembly of PMMA-b-PnBA-b-PMMA upon curing; however, the mechanism was unclear. As the curing reaction proceeded, size and interdomain spacing of the micelles increased. Late in curing, the morphologies rapidly re-organized until the miscible PMMA chains were pinned in the epoxy network, which was driven by strong repulsion between the PnBA domains and the polymerized epoxy. During this process, length of the PMMA chains played an important role in disordering of phase separation; the longer PMMA chains prevented the re-organization of the neighboring micelles and the disordering of the phase-separated domains. (C) 2016 Elsevier Ltd. All rights reserved.