SynopsisMechanisms for low-temperature relaxations of three spiro-ring-type epoxide resin systems with and without methoxy branches were investigated by comparison with those of a bisphenol A-type resin system. In the spiro-ring-type epoxi.de resin systems, two well-defined relaxation peaks, denoted as the 8 and 8' relaxations, and a shoulder peak were observed a t about -70, + 60, and OOC, respectively. The magnitude of the relaxation was decreased by the introduction of methoxy branches on the phenylene group. This phenomenon could be interpreted as a result of the formation of hydrogen bonds between the hydroxy-ether group and methoxy branch.Moreover, it was concluded that the 8' relaxation and the shoulder peak are due to the motion of the p-phenylene group adjacent to the spiro-ring and of the hydroxy-ether group blocked by the hydrogen bond, respectively. that the p' relaxation, which is observed from +50 to + 100°C, is due to the motion of the phenylene group in the n e t w~r k . '~*~ In this paper the effect of the epoxide resin structure on the low-temperature relaxation of cured resins is studied by comparing the relaxation behavior of a bisphenol A-type and three spiro-ring-type resins. The relaxation mechanisms for the cured spiro-ring-type epoxide resins are discussed in detail.
SynopsisBisphenol-A type and biphenyl type epoxide resins were cured with two types of aromatic diamines which have or do not have the carbon bridge between aromatic rings. Internal stress of these cured resins decreased with the introduction of a biphenyl structure into the networks. This reduction of the internal stress is attributed to the decrease of the elastic modulus in the glassy region caused by the low mobility of the biphenyl segment. On the other hand, the glass transition temperature increased with increasing the concentration of the biphenyl unit in the networks. These results revealed that the consistency of the decrease of the internal stress with the improvement of the heat resistance of the cured systems is possible by introducing the biphenyl structure to the epoxide resin networks.
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