In this study, thermally crosslinked polymers were synthesized by thiol‒ene reactions of the allyl groups included in the side chain of an N-allylmaleimide/2-ethylhexyl acrylate copolymer and polyfunctional thiol crosslinkers. The network structure and physical properties of the cured materials were evaluated. The maleimide copolymer was cured thermally using three kinds of the thiol crosslinkers containing an ether or ester linkage in the presence of triallylisocyanurate as the additional crosslinker. The conversion of the functional groups was determined based on the results of NMR and IR analyses. All of the thermosets prepared in this study exhibited excellent thermal stability. The network structure and mechanical properties of the products were almost independent of the structure of the crosslinkers. On the other hand, a remarkable difference was observed in the acid hydrolysis resistance of the cured polymer materials. It was found that the polymers obtained by using the ether-type crosslinker exhibited excellent acid resistance.

Thermosetting hyperbranched polymers were synthesized by radical copolymerization of dodecyl methacrylate and ethyleneglycol dimethacrylate in the presence of an addition-fragmentation chain transfer agent, methyl 2-(bromomethyl) acrylate. The resulting polymers had a branched structure containing multiple end groups per one polymer chain. By changing the comonomer compositions and the stoichiometric ratio of the total comonomer to the addition-fragmentation chain transfer agent, the glass transition temperatures of the resulting hyperbranched polymers can be controlled in a wide range from -80 ℃ to 13 ℃. The hyperbranched polymer contains multiple vinyl groups, i.e., side-chain vinyl groups (methacryloyl group) derived from ethyleneglycol dimethacrylate unit and ω-end vinyl groups (2-methoxycarbonyl-2- propenyl group) generated by addition-fragmentation chain transfer. Therefore, the hyperbranched polymers underwent spontaneous polymerization above ca. 100 ℃, and exhibited thermosetting properties even in the absence of a radical curing agent. The glass transition temperatures of the hyperbranched polymers were significantly increased to 130 ℃ or higher by thermal curing at 180 ℃for 1 h.

High performance epoxy resins are required by advancement of functional material fields. As a measure for this purpose, there are liquid crystalline epoxy resins having a mesogen unit, but they have a problem in solvent solubility due to their high melting points. As a result of studying epoxy resin having a diphenylene ether structure, it was found to give a crystalline cured product with a high melting point (185.6℃). The crystallinity of the cured product was estimated to be 52% from XRD measurement. Corresponding to this high crystallinity, CTE decreased in addition to the improvement in thermal conductivity. The moisture permeability was 0.48g/m²･day, which was an order of magnitude lower than that of the amorphous cured product. Furthermore, as a result of evaluation as a molding material, the heat distortion temperature increased significantly to 183℃.

The curing reaction of N-(3,4,5,6-tetrahydrophthalimide)ethyl acrylate (THPA), which is a bifunctional monomer having acryloyl and maleimide groups, under ultraviolet (UV) irradiation was analyzed by MALDI-MS. In the case of UVirradiation to THPA alone, the formation of THPA oligomers up to a heptamer was confirmed by the mass spectroscopy.This result indicates that not only the photodimerization of maleimides but also the intermolecular radical coupling between maleimide and acryloyl groups are caused by UV-irradiation to THPA without photoinitiator. A mixture of THPA and neopentyl glycol diacrylate (NPGDA) was then UV-irradiated in the presence of a photoinitiator, hydroxy-2-methylpropiophenone (HMPP), to form a cured sample, which was subjected to supercritical methanolysis. The two series of methyl acrylate oligomers having a THPA unit at a chain end were identified by the MALDI-MS of the methanolysis product. This observation suggests that the UV-curing of THPA-NPGDA in the presence of HMPP might proceed by the polymerization of acryloyl groups initiated not only with a radical formed by the dissociation of HMPP but also with that formed on maleimide moiety.