Embodiments herein relate to a prepreg comprising a thermosetting resin, and reinforcing fibers in the thermosetting resin, wherein when the prepreg is cured in vacuum bag only conditions, and a method of making the same. The method also applies for autoclave processing. Embodiments also relate to a cured fiber reinforced composite material made by thermally curing the prepreg.

A method for crosslinking a copolymer of ethylene and at least one other monomer using an organic peroxide represented by Formula (1): wherein R1 is either a methyl or an ethyl group and wherein (i) R1 is a methyl group, R2 is an alkyl group having 1 to 8 carbon atoms optionally substituted with groups containing O, Si, P, S, SO or SO.sub.2 functionalities; (ii) if R1 is an ethyl group, R2 is an alkyl group having 2 to 8 carbon atoms optionally substituted with groups containing O, Si, P, S, SO or SO.sub.2 functionalities. ##STR00001##

The valve member according to one embodiment of the present disclosure is a resin formed product having a crosslinked ethylene-tetrafluoroethylene copolymer as a main component, and having a crosslinking density of 85.0 mol/m.sup.3 or more calculated from a storage modulus at 300 C.

Provided is a dip molding emulsion including, at least: an elastomer that contains a (meth)acrylonitrile-derived structural unit, an unsaturated carboxylic acid-derived structural unit, and a butadiene-derived structural unit in a polymer main chain; an epoxy crosslinking agent; water; and a pH modifier, in which dip molding composition the elastomer contains the (meth)acrylonitrile-derived structural unit in an amount of 20% by weight to 40% by weight, the unsaturated carboxylic acid-derived structural unit in an amount of 1% by weight to 10% by weight, and the butadiene-derived structural unit in an amount of 50% by weight to 75% by weight, and the epoxy crosslinking agent includes an epoxy crosslinking agent containing an epoxy compound having three or more epoxy groups in one molecule and has a dissolution rate in water of 10% to 70% as determined by a specific measurement method.