Ethynyl-terminated polyimide

The idea of synthesizing imide oligomers which carry acetylenic terminations appeared attractive because homopolymerization through acetylenic endgroups occurs without any volatile evolution and provides materials with good properties. Landis et. al (8,9) published the synthesis of such acetylene terminated imide oligomers from benzophenone tetracarboxylic anhydride, aromatic diamine and 3-ethynylaniline via the classical route. As usual, the amide acid is formed as an intermediate which, after chemical cyclodehydration, provides the polymide. Since ethynyl-terminated polyimide is used as a matrix resin for fiber composites, processing is possible via the amide acid, which is soluble in acetone, or via the fully imidized prepolymer, which is soluble in NMP. The chemical structure of the fully imidized ethynyl-terminated polyimide is provided in Fig. 44. 

The cyclotrimerization of ethynylbenzene leads to 1,3,5-triphenylbenzene, and consequently polycyclotri-merization of bisethynylbenzene yields a high temperature stable polyphenylene resin.3° This chemical concept has been extended to develop the first ethynyl-terminated polyimide in the literature. " The following figure [7] outlines the synthetic route characterized by simply replacing some of the aromatic diamine with an ethynyl-substituted aromatic monoamine to provide a ethynyl-terminated polyimidf resin. 

From a practical viewpoint, the compounds most commonly used in the fabrication of addition polyimides are bismaleimides, bisnadimides and ethynyl terminated oligoimides [275]. Poly (bismaleimides) have actually achieved special importance as technical polymer materials [276]. Due to the aliphatic-type linkages, which appear as a consequence of polyaddition, polymers of this type are not as thermally stable as aromatic polyimides are. However, their good processability, the polymerization without volatiles release and the relative low cost of raw materials have helped them to become a real alternative for long term uses up to 200-250 °C. 

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