ABSTRACT
MY-720 is the base resin for several state-of-the-art structural prepreg resin systems used in aircraft laminates. The popularity of polyester resins is accounted for by their ease of handling, good cured properties, and the fact that they are the lowest cost addition-curing thermoset available. After various additives have been blended in the resin is ready for packaging. Molecular weight of the backbone polymer is controlled by the manufacturer and varied to suit his particular formulation. Molecular weights are usually in the 1,000–4,000 range. A route to improving processability has been to change the backbone structure to make the fully imidized thermoplastic polyimide more tractable in order to allow melt processing. Since complete imidization must be achieved to obtain optimum properties, water is evolved even in the last stages of composite formation and is one cause of porosity in the finished parts when the matrix resin is a condensation polyimide.
