Effect of network structure on thermal and mechanical properties of cured epoxide resins

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Dynamic mechanical properties and internal stress were investigated using several different kinds of epoxide resins with different chemical structures. Resin containing a tetramethyl biphenol structure showed a very high rubbery modulus, a low glassy modulus and a low internal stress, in addition to exhibiting a high glass transition temperature. Furthermore, the effect of the introduction of methyl branches into the biphenol skeleton on viscoelastic properties of cured epoxide resin was investigated by comparing with that of bisphenol-A type resin in detail. In the case of bisphenol-A type resin, the introduction of methyl branches slightly affected the modulus in the rubbery and the glassy regions and the glass transition temperature. These results show that the introduction of methyl branches into the resin does not significantly affect the mobility of network chains or the free volume of cured resins. In contrast, the introduction of methyl branches into biphenol type resin resulted in a decrease in modulus in the rubbery region and an increase in the peak height of tan δ. These results show that the introduction of methyl branches into biphenol type resin increases the mobility of network chains in the rubbery region. On the other hand, the modulus in the glassy region increased according to the introduction of methyl branches. This is due to the decrease in free volume in the glassy region with an increase in the mobility of network chains in the rubbery region.