In order to better understand the effects of molecular weight on the performance and service life of polymeric matrix composites we designed a series of investigations on a polyimide system which was developed for possible use in the airframe industry. We wanted to determine if engineering properties depend on the molecular weight of the potential matrix material, assuming that the polymer is not cross-linked. For this study we prepared six batches of the polyimide LaRC-SI™, where each batch possessed a different molecular weight. Cross-linking was discouraged by the addition of “end caps” which attach to the ends of the molecules and renders them chemically inert.