ABSTRACTSuperior polyimide prepolymers particularly suitablefor fabrication of multi-layer printed boards areproduced by reacting unsaturated bisimides with diaminesto consist essentially of 41 - 55% of unreactedreactants, 39 - 54% of components having a molecularweight of between 400 and 15000, and 3.0 - 6.8% ofcomponents having a molecular weight of more than 15000.The resulting prepolymers enable the preparation of theirsolution having enough working life for successfullyimpregnating a given substrate therewith in thepreparation of prepregs. The prepregs, prepared from theabove prepolymers in such a way as to contain within theresin content thereof 29 - 35% of of unreacted reactants,51 - 65% of the components having a molecular weight ofbetween 400 and 15000, and 5 - 14% of the componentshaving a molecular weight of more than 15000, allow thefabrication of laminate products with remarkabledimension stability under a low molding pressure toeliminate the presence of voids in the products, inaddition to that the prepregs ensure a high bond strengthas well as elongated working life which is responsiblefor prevention of a blister in the finished laminate andfor easy control of the laminate forming process.
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