methods of foaming and fully curing polyimide resins entirely by the application of microwave energy . foamable polyimide resins may be prepared by esterifying a suitable dianhydride , reacting the product with a suitable diamine , drying the resulting product and heating to spontaneously form a foam . in the past , such materials could be foamed but could not be satisfactorily cured to a resilient foam entirely by microwave energy . post - foaming direct application of thermal energy was required to produce a satisfactory foam . we have found that adding a suitable oxoimine , such as caprolactam , to the reaction mixture results in a foam material which is fully and completely cured entirely by the application of microwave energy , considerably simplifying the process and reducing costs .