Unsaturated polyesters UP

Unsaturated polyester (UP) resins are obtained by polycondensation of one or more diacids with one or more glycols, with at least one of the components containing an ethylenic double bond capable of subsequent reaction with a vinyl, acrylic or allylic compound.

The term polyester resin refers to the dissolution of unsaturated polyester prepolymer in a copolymerizable reactive diluent, the most widely used of which is styrene. It is in this liquid form that polyester resins are delivered to converters.

After the addition of various additives, fillers and reinforcements, various transformation processes, under the action of a suitable catalytic system, bring about the final copolymerization of the resin into a thermoset object.

Unsaturated polyesters have a relatively long history of use (1950s), mainly in the building industry (contact molding). They underwent a major revival from 1980 onwards, particularly in terms of formulations and process reliability, thanks to the development of industrial technologies for injection and compression molding in the automotive industry.