a new class of copolymers obtained via the copolymerization of diethynylbenzene with an ethynyl - substituted polyimide oligomer has been used to prepare composite materials exhibiting zero void content . the copolymers are thermosetting in character and are particularly useful for the fabrication of composite structures such as glass fiber reinforced laminates and molding compounds and graphite fiber reinforced laminates and molding compounds .