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 .