Effect of the chemical structure of phenolic curing agents on the network structure and mechanical properties of cured epoxy resins containing a mesogenic group

An epoxy resin containing a typical mesogenic group such as biphenol was cured with a variety of catechol novolaks. In the epoxy resin cured with catechol novolaks which have a small substituent such as methyl group, a glass-rubber transition almost disappeared and a characteristic pattern like a schlieren texture was clearly observed with a crossed polarized optical microscope. On the other hand, the epoxy resin cured with catechol novolaks which contain a large substituent such as phenyl group showed a well-defined glass-rubber transition. These results show that the motion of the network chains is highly suppressed in the former system, because of the orientation of mesogenic groups in the cured resins. In the latter system, however, the orientation of the mesogenic groups seems to be prevented by the large substituents.