The polycondensation type aromatic polyimide is prepared by reacting an aromatic diamine with an aromatic dianhydride, an aromatic tetracarboxylic acid, or an aromatic tetracarboxylic acid dialkyl ester. Because the synthesis reaction of polycondensation type polyimide is carried out in aprotic polar solvents such as dimethylformamide, N-methylpyrrolidone, etc., and polyimide composite materials usually use prepreg Molding process, these high-boiling aprotic polar solvents have been prepared in prepreg
It is difficult to volatilize cleanly during the process, and volatiles are also released during the cyclization (imidization) of polyamic acid, which easily creates pores in composite products and makes it difficult to obtain high-quality, non-voided composite materials. Therefore, polycondensation polyimide has been less used as the matrix resin of composite materials, mainly used for the production of polyimide films and coatings.
Since the polycondensation type polyimide has the above-mentioned disadvantages, in order to overcome these shortcomings, polyaddition type polyimides have been developed one after another. Polybismaleimide and norbornenyl-terminated polyimide are widely used. Usually these resins are low-molecular-weight polyimides with unsaturated groups at the ends, which are polymerized by unsaturated end groups when applied.
Polybismaleimide is composed of maleic anhydride and aromatic
Aromatic polyamine polycondensation. Compared with polyimide, its performance is not worse, but the synthesis process is simple, the post-processing is easy, the cost is low, and various composite materials can be conveniently made. But the cured product is brittle.
(2) Norbornene-terminated polyimide resin
The most important one is a type of PMR (for insitu polymerization of monomer reactants) type polyimide resin developed by NASA Lewis Research Center. PMR type polyimide resin dissolves monomers such as dialkyl ester of aromatic tetracarboxylic acid, aromatic diamine and monoalkyl ester of 5-norbornene-2,3-dicarboxylic acid in one This kind of alcohol (such as methanol or ethanol) can be used directly to impregnate fibers.
Polyimide is an aromatic heterocyclic polymer compound whose molecular structure contains imide groups. The English name is Polyimide (referred to as PI), which can be divided into homobenzene type PI, soluble PI, and polyamide-imide (PAI). And polyetherimine (PEI) four categories.