Acetylene ethynyl terminated polyimides

Around 1970, the US Air Force funded a program on acetylene terminated imide oligomers and the first patent was filed by Hughes Aircraft [67] and has been described in the literature [68]. Benzophenone tetracarboxylic anhydride was condensed with an aromatic diamine and 3-ethynylaniline to give either an amide acid soluble in acetone, or a fully imidized structure, soluble in NMP. 

The first commercial product was introduced in 1975 as Thermid 600 by Gulf Oil Chemicals and is now sold by National Starch and Chemical Corporation. The fully imidized prepolymer has to be processed in NMP, with all its attendant problems. However, the molecular weight can be adjusted to provide a resin which melts at about 200° C and immediately starts to polymerize when molten and so, has a narrow processing window. 

3-ethynylanlllne 3.3, 4,4 -bezoph8non8telracarboxylk dianhydrid8 (BTDA) 1,3-bis(3 nlnoph8no4 btnzans 

A resin system, Thermid FA-700, based on hexafluoroisopropane-bisphthalic anhydride was introduced and can be easily processed into composites using THF, DMF or DMAc [29]. 

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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. 

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