The novel phenolic resins with phosphaphenanthrene unit were synthesized by the reaction of a phenolic resin and benzyl alcohol derivative formed by the addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide with alkoxy benzaldehyde. The epoxy cured resin with phosphaphenanthrene modified phenolic resin was found to provide excellent flame retardancy and high heat resistance, which were required for the advanced printed circuit board applications. In this paper, we report the synthesis, properties, and effect of phosphaphenanthrene-content.

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Epoxy resins are generally two-component thermosetting resins composed of a hardener and a curing accelerator which are mixed at the time of use. However, it is inconvenient to weigh and mix the two-component resins just before use. Therefore, one-component resins which contain epoxides and hardeners are required. Acid hydrazide and dicyandiamide are typical hardeners that are used for the one-component epoxy resins. Both of them are solid dispersion type latent hardener based on their insolubility in the epoxy resin. In these systems, solid dispersion technique is needed, and they can not be used in the sealing and adhesion of the gap smaller than the particle size of the hardener. Hence, a hardener which can exhibit the latency in homogeneous system is required. We found that a phosphate synthesized from a phosphoric acid ester with an organic base can be used as a thermal latent hardener for epoxy resins. Because the reaction of the phosphate with epoxy resins was initiated by heating, the phosphate gave long pot life even in the homogeneous composition. It was suggested that the curing proceeded with an anionic polymerization mechanism initiated by a phenoxide anion generated by the reaction of the phosphate with an epoxy group.

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We synthesized various cross-linkable prepolymers from castor oil, isocyanates and alkoxysilanes, and evaluated their adhesive property. Influence of the alkoxysilyl group (methoxy or ethoxy) on the adhesion strength was small. On the other hand, adhesion strength of cross-linkable prepolymers synthesized from urethane prepolymer was stronger than those synthesized from isocyanate-silane. It was suggested that the amount of polar groups (urethane group) per castor oil unit had strong influence on the adhesion. Moreover, as compared cross-linkable prepolymers synthesized by usual urethane prepolymer method with those synthesized by via thin film evaporation method, adhesion intensity of cross-linkable prepolymer synthesized by via thin film evaporation method of urethane prepolymer exhibited much higher adhesion strength. Thus, it was suggested that adhesion strength of the prepolymer which had regular distances between cross-linking points was stronger than those with irregular distances.

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It is known that the glass transition temperature (T_g) of the resin cured by alkylboranes as a living radical initiator is higher than T_g of the resin cured by typical radical initiators such as peroxides or azo compounds. We infer that higher T_g of the resin cured by living radical initiator originates in the difference of cross-linking structure of the cured resin. In this study, we tried to evaluate the cross-linking structures by solid state NMR. ¹³C-NMR spectra and spin-lattice relaxation times (T₁ and T_1ρ) were obtained. In the ¹³C-NMR spectra of the resin cured by peroxide, the signals of allylic carbons produced through disproportionation were observed. T_1ρ value of the resin cured by alkylborane was shorter than those of resins cured by typical initiators. This implies that the resin cured by alkylborane had more ordered structure compared with resins cured by typical initiators. These results suggest the solid state NMR is effective for the analysis of cross-linking structure of thermoset resins.

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The precise estimation of glass transition temperature and relaxation time is great importance for the development of functional network-polymers. The general law of relaxation time proposed in this paper is effective to estimate the glass transition temperature measured by different frequency. With the low, we estimated Tg in the heating and cooling process. We also compared the dispersion maps obtained with the general law of relaxation time and WLF equation. As a results, relaxation time over wider temperature range was predicted by the general law of relaxation time, compared with the WLF equation.

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Polymer foams are widely used as thermal insulators, packing materials, acoustic materials, etc. Microcellular plastics are the foams with micro scale bubbles, which has higher mechanical properties and more excellent light reflecting properties than the foams with large bubbles. Microcellular plastics are generally made from thermoplastic resins, however, few studies have been published on that of thermosets. Microcellular plastics made from thermosets (network polymers) can provide high mechanical properties and improve some properties, such as the electrical properties (lower dielectric loss). In this paper, the resent studies about controlling the cell morphologies of network polymer foams are reviewed.

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