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Divinyl ethers 1, 2, 3 and 4 caused ring-expansion cationic cyclopolymerization with a hemiacetal ester-incorporated cyclic initiator in conjunction with SnBr₄ to yield cyclic Poly(1), Poly(2), Poly(3) and Poly(4), respectively. High degree of cyclization of cyclopolymerization (>~98%) was necessary to obtain these macrocyclic cyclopolymers of well-defined structure quantitatively. The Tgs of these macrocyclic cyclopoly(divinyl ether)s were higher than those of the corresponding linear cyclopoly(divinyl ether)s.

The effect of different types of maleic anhydride-modified polypropylene on interfacial shear strength for carbon fiber-reinforced polypropylene composites: The effect of three types of maleic anhydride-modified polypropylenes (MAPP) on the interfacial shear strength (IFSS) of PP and carbon fiber (CF) were investigated. The localization of MAPP at the interface enabled sufficient chemical interaction regardless of MA content of MAPP, and the differences of MA content had little IFSS dependences. When the chemical interaction is sufficient at the interface, the IFSS values were attributed to the crystallinity at the interphase, which depends on the natures such as crystallinity of MAPP added.

The interfacial adhesion between olefinic double bond- or hydroxyl-terminated telechelic polypropylenes (PPs) and carbon fibers was studied to determine the potential of the telechelic PPs as a candidate for PP matrix resin-coupling agents for carbon fiber-reinforced PP composites. The hydroxyl-terminated PP showed higher interfacial shear strength than that of commercial PP and olefinic double bond-terminated PP. The hydroxyl-terminated PP could be used as a novel coupling agent of the PP matrix.

The new epoxy resins containing degradable acetal linkages were synthesized and used as sizing agents for carbon fibers. Using the degradable sizing agent-applied carbon fibers, the carbon fiber-reinforced plastics (CFRPs) were prepared via laminating prepreg sheets and heating them under pressure. The mechanical properties of the obtained CFRPs were comparable with those of the conventional CFRPs. With the treatment of acidic conditions, the CFRPs with the degradable sizing agents on carbon fiber surface were decomposed and the carbon fibers could be recovered.

Recyclable carbon fiber-reinforced plastics (CFRPs) with controlled degradability and stability were developed by using acid-degradable acetal linkage-containing epoxy resin (BA-CHDMVG). The obtained BA-CHDMVG-based CFRPs exhibited almost the same tensile and thermal properties as those of the conventional BA-based CFRPs and underwent smooth degradation through hydrolysis with the treatment of hydrochloric acid in a tetrahydrofuran (THF)/water (9/1) mixed solvent. On the other hand, in the absence of organic solvents, the BA-CHDMVG-based CFRPs have sufficient stability toward acid in the normal living environment.

Novel alcohol-derived degradable acetal-linkage-containing epoxy resins HBA–CHDMVG and HOBA–CHDMVG were synthesized. The thermal decomposition temperature of HOBA–CHDMVG was higher than 300 °C; moreover, HOBA–CHDMVG exhibited excellent Charpy impact strength. The cured HOBA–CHDMVG was completely decomposed during the hydrolysis reaction under acidic conditions, and the reaction products were soluble in a tetrahydrofuran/H₂O mixed solvent. Furthermore, the carbon fibers in the carbon-fiber-reinforced plastic with a HOBA–CHDMVG matrix were recovered via the complete decomposition of HOBA–CHDMVG.

Controlled cationic cyclopolymerizations of divinyl ethers with cyclohexene, norbornene, norbornane, cyclic acetal, or adamantane moiety were carried out. High-molecular-weight star-shaped cyclopolymers were synthesized by the reaction of the formed living cyclopolymers with a small amount of divinyl ether crosslinking agent. Glass transition temperatures (T_g’s) of both the cyclopolymers and star-shaped cyclopolymers were as high as 145−229 ^oC. Methacrylate-terminated end-functionalized star-shaped cyclopolymers were synthesized by the functionalized initiator-based living cationic cyclopolymerization of divinyl ethers followed by the chain linking reactions among the formed living cyclopolymers with divinyl ether crosslinker. The obtained end-functionalized star-shaped cyclopolymers were subjected to thermal crosslinking reaction to give star-shaped cyclopolymer networks with film-forming ability.