EFFECT OF THE NETWORK STRUCTURE ON THERMAL AND MECHANICAL-PROPERTIES OF MESOGENIC EPOXY-RESIN CURED WITH AROMATIC AMINE

The epoxy resin containing a typical mesogenic group such as biphenol was cured with catechol novolak and aromatic diamines which have neigh boring active hydrogens. In the biphenol-type epoxy resin cured with c atechol novolak, 4,4'-diaminodiphenylmethane, and p-phenylenediamine ( PPD), the glass-rubber transition almost disappeared, and thus a very high elastic modulus was obtained in the high temperature region. It i s clear that the thermal motion of the network chains is significantly suppressed in these cured systems. In addition, in the PPD-cured syst em, a characteristic pattern like a schlieren texture was clearly obse rved under the crossed polarized optical microscope. Thus we conclude that the mesogenic group contained in the epoxy molecule is oriented i n the networks when the mesogenic epoxy resin is cured with phenols an d diamines which have neighboring active hydrogens. On the other hand, the biphenol-type resin cured with 3,3',5,5'-tetraethyl-4,4'-diamino diphenylmethane (TEDDM) showed a well-defined glass-rubber transition and, thus, a low rubbery modulus. In this cured system, no characteris tic pattern was observed under the crossed polarized light. These resu lts show that the large branches, such as ethyl groups on the network chains, prevent the orientation of network chains which contain the me sogenic group. (C) 1997 John Wiley & Sons, Inc.