Sulfonium salt-initiated cationic copolymerizations of bisphenol-A diglycidyl ether (BADGE) with a soluble oligo(spiroorthocarbonate) bearing methyl group in the side chain (Me-OSOC) were employed, and the relationship between the resulting volume change degree upon the curing reaction and the lap-shear adhesive strength were evaluated. As a result, it might be suggested that the degree of volume change decreased along with increasing the addition amount of Me-OSOC, and the resulting tensile lap-shear adhesive strength was improved.

Curing behavior of the bisphenol A type epoxy resin and properties of the cured product were investigated using an acid anhydride having phenylethynyl carbonyl group as a curing agent. As a result, it was found that the reaction of the acid anhydride group and the epoxy group proceeded first at around 100 to 120 ℃, and then was follwed by the reaction of the phenylethynyl carbonyl groups at around 250－300 ℃. As a result of examining the properties of the cured product, it was found that the epoxy resin cured with an acid anhydride having phenylethynyl carbonyl group showed extremely excellent heat resistance and thermal decomposition resistance. These excellent thermal properties are attributable to strong intermolecular interaction (molecular packing) and suppression of movement of molecular chains by alkenes and polycyclic aromatic structures formed by polymerization of phenylethynylcarbonyl groups.

High thermal shock resistance during reflow soldering is required for the high thermal conductivity insulating materials, which have been so far produced with high T_g multifunctional epoxy compounds. We found that the selfalignable mesogenic epoxy during curing process showed better thermal shock resistance compared with conventional epoxy compounds although the T_g of mesogenic epoxy was relatively lower T_g. We clarified that composite materials with mesogenic epoxy showed higher peel strength at reflow soldering temperature compared with multifunctional high T_g epoxy because of the decrease in thermal stress at the interface between the composite materials and Cu substrates. We also found that the coefficient of linear thermal expansion of mesogenic epoxy was much lower than that of high T_g epoxy at reflow soldering temperature and showed lower difference of thermal expansion coefficient between the composite and Cu substrate. It is inferred that the molecular vibration of mesogenic epoxy is suppressed due to the formation of high order structure at reflow soldering temperature.

We performed atomistic molecular dynamics (MD) simulation for fracture analysis of cross-linked phenolic resins under tensile deformation with ReaxFF reactive force field. The MD results showed that material properties in the equilibrium state and linear elastic region are well consistent with experimental values and MD results using classical force field. Stress－strain relationships and changes in chemical bonding information in the large deformation region suggested that selective cleavage of covalent bond between phenolic ring and methylene causes macroscopic fracture of cross-linked structure. The change in three-dimensional structure showed fracture mechanisms that lead to macroscopic destruction by aggregation and inhomogeneous growth of voids due to elongation of molecular chains and breaking of chemical bonds at the void－resin interface. The MD results also indicated that the origin of fracture is not necessarily due to stress concentration in the region of low crosslink density, but is derived from the increase in crosslink density fluctuation induced by tensile deformation.

We have been developing reactive hot melt adhesives (PUR) for fine parts such as displays in smartphones and tablets. The cure time of PUR is important because it needs to be adjusted for each product. In this report, the influences of the type and amount of curing catalyst on the curing time and properties of PUR were investigated. As a result, the elastic modulus of PUR became higher as the amount of catalyst increased. And, it was found that the size of dispersed-phase droplets in the continuous phase was different, depending on the amount of catalyst. PUR tended to be compatibilized as the amount of catalyst increased. We revealed that the difference in microscopic properties between the dispersed phase and the continuous phase made the difference in the macroscopic properties of PUR with different morphology.

Bacterial cellulose (BC) gels have unique nano-fibrous, porous, and layered structures which can have applications in many fields. We report the preparation of three types of functional composites such as hydrophobic aerogels, thermoresponsive hydrogels with high mechanical strength, and sea cucumber-mimicking hydrogels from BC pellicles and other functional materials. Physical properties of the composites were enhanced by hierarchical structures of BC gels. We hope that these innovative material design strategies will open a door to an exploration of these materials as novel smart materials for practical applications.