A process for synthesizing formulations for polyimides suitable for use in high-temperature composites in which all reactions other than chain-extension have already taken place prior to making a composite is described, wherein the resulting oligomers comprise a backbone and at least one difunctional endcap. The resulting resin systems have only the single step of endcap-to-endcap reactions during composite processing. Prior to the initiation temperature of these endcap-to-endcap reactions, the resins are stable affording the composite manufacturer a very large processing window.