PURPOSE: A highly heat-resistat resin composition improved in heat generation during curing, prepared by heat-curing a BT resin and a flexbile bisphenol A- derived epoxy resin having a butadiene component in the molecular skeleton.

CONSTITUTION: A thermosetting resin having a bismaleimide component and a triazine component in the molecule (BT resin) and a flexible bisphenol A-derived epoxy resin having a butadiene component in the molecular skeleton are heat cured. The BT resin is an addition-polymerizable thermosetting resin consisting mainly of two components, i.e., component B (bismaleimide) and component T (triazine resin) and are prepare from three materials, i.e., a bismaleimide of formulaI, a triazine resin of formula II and a triazine resin oligomer of formula III. By varying the proportion of the above three components, it is possible to produce BT resins, including normally liquid resins to resins having a m.p. ≥100°C, and these resins are porperly used according to use, performance requirement and methods of processing.