Polyimide can be divided into polycondensation and polyaddition type two.
(1)Condensation type polyimide,Condensed aromatic polyimide is composed of aromatic amines and aromatic two yuan two anhydride, aromatic carboxylic acid or aromatic carboxylic acid four four two alkyl esters produced. The synthesis reaction of condensation type polyimide is conducted in such two dimethyl formamide, N- methyl pyrrolidone high boiling aprotic solvents, and polyimide composite material is usually the prepreg molding process, material preparation process for these high boiling aprotic solvent in the prepreg is difficult to evaporate, at the same time in the polyamic acid cyclization (imide) period also volatile release, which is easy to produce porous composite products, it is difficult to get high quality, no porosity of composite materials. Therefore condensation type polyimide has less used as matrix resin composite materials, mainly used in the manufacture of polyimide thin films and coatings.
(2)Polyaddition type polyimide,Because the condensation type polyimide having the shortcomings, in order to overcome these shortcomings, has developed the polyaddition type polyimide. The current widely used mainly poly bismaleimide and norbornene terminated polyimides. Usually these resins are low relative molecular mass of polyimide with unsaturated groups end, again through the unsaturated end groups of polymer applications.
①POLYBISMALEIMIDE,Poly bismaleimide by maleic anhydride and two aromatic amines two and polycondensation. It compared performance of polyimide, equally matched, but the synthetic process is simple, easy processing, low cost, can be easily made into various composite products. But cured more brittle.
②Norbornene based terminated polyimide resin, of which the most important is a class PMR NASA Lewis research center of development (for insitu polymerization of monomer reactants, monomeric reactant in-situ polymerization) polyimide resin. RMR type polyimide resin is two alkyl esters of aromatic carboxylic acid, four aromatic amines and two yuan 5- norbornene -2, 3- two carboxylic acid monoalkyl ester monomers dissolved in a taste based alcohol (such as methanol or ethanol), as a solution can be directly used for the impregnation of fibers.