| abstract |
Epoxy resin compositions having improved storage stability before curing and improved thermal and mechanical performance after curing comprise a mixture of a polyepoxide and a curing agent that is reactive with the polyepoxide. The epoxy resin composition is characterized by a glass transition temperature of less than 20°C, measured under standard conditions, after subjecting the epoxy resin composition to a specified thermal cycle. For attaining this, the curing agent should possess a melting point and a heat of fusion lying in area A of fig.1. The preferred curing agents are aromatic diamines, for example, 3,7-diaminodibenzothiophene-5,5-dioxide; 3,7-diaminophenothiazine sulfone, 3,7-diamino-N-methylphenothiazine sulfone; 2,7-diamino-9-fluorenone and 2,4,6,8-tetramethyl-3,7-diaminothioxanthene sulfone. Also claimed are prepregs and composites made therefrom containing the epoxy compositions in combination with reinforcing agents. |