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Fiber-reinforced thermosetting polyester composites containing in excess of 30 wt %, based on the weight of the composite, reinforcing fiber, are made by a vacuum-assisted transfer molding technique from a 1-phase composite matrix precursor comprising a polyester, a reactive monomer, and a low-profi

Fiber-reinforced thermosetting polyester composites containing in excess of 30 wt %, based on the weight of the composite, reinforcing fiber, are made by a vacuum-assisted transfer molding technique from a 1-phase composite matrix precursor comprising a polyester, a reactive monomer, and a low-profile additive. The polyester has a molecular weight/double bond factor of between about 150 and 190, styrene is a preferred reactive monomer, and a preferred low-profile additive is a thermoplastic polymer with a weight average molecular weight in excess of 3,000 and which is miscible in the polyester and reactive monomer. The polyester composite is formed by coating the surface of a mold with a gel coat; applying a skin laminate over the partially cured gel coat; applying a fiber reinforcement to the skin laminate; closing the mold; and injecting the 1-phase matrix precursor while the mold is under vacuum. The hallmark of these composites is their combination of physical strength as measured by one or more standard strength tests for composites and smooth surface profile as compared to the thermosetting polyester composites made from a typical hand lay-up or spray up process, or a conventional vacuum-assisted transfer molding process.

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[ What is claimed is:] [1.] A vacuum-assisted transfer molding process for preparing a molded article comprising a fiber-reinforced thermosetting polyester composite, the composite comprising reinforcing fiber in excess of 30 wt %, based upon the weight of the composite, in a thermoset polyester mat

[ What is claimed is:] [1.] A vacuum-assisted transfer molding process for preparing a molded article comprising a fiber-reinforced thermosetting polyester composite, the composite comprising reinforcing fiber in excess of 30 wt %, based upon the weight of the composite, in a thermoset polyester matrix, wherein the process comprises:(a) coating the surface of a mold with a gel coat;(b) allowing the gel coat of step (a) to at least partially cure;(c) applying a skin laminate over the at least partially cured gel coat of step (b);(d) applying fiber reinforcement to the skin laminate of step (c);(e) closing the mold; and(f) while the mold is under vacuum, injecting a one-phase matrix precursor comprising, in weight percent based upon the weight of the matrix precursor, from about 20 to about 60% of an unsaturated polyester resin with a molecular weight/double bond factor between about 150 and about 190; 30 to about 70% of a reactive monomer; 1 to about 25% of a thermoplastic polymer which is miscible in a bend of the polyester resin and the reactive monomer; and an initiating amount of a free radical initiator.