1. Field of the Invention
The present invention relates to novel heat resistant polymers, and, more especially, to novel imido copolymers comprising the copolymerizate of at least one bis(imide) and at least one hindered diprimary diamine.
2. Description of the Prior Art
Polymers produced by reaction between an N,N'-bis(imide) of an unsaturated dicarboxylic acid such as, for example, an N,N'-bis(maleimide), with a diprimary diamine have been described to this art, e.g., in French Patent No. 1,555,564. The amounts of N,N'-bis(imide) and diamine are selected such that the ratio: ##EQU1## is at least equal to 1; moreover, it is generally preferable that it should be less than 50. Heat resistant resins are thus produced, which withstand severe thermal stresses exceptionally well.
It is also disclosed in the aforesaid French patent that the preparation of these resins can be carried out in bulk by heating the reactants, after intimate mixing thereof, or, alternatively, in an inert polar diluent such as dimethylformamide, N-methyl-pyrrolidone or dimethylacetamide. The latter process is applicable, for example, when the polymer is to be used in the form of a solution.
Finally, it is noted that, for many uses, it is advantageous to carry out the preparation in two stages; in a first stage, a prepolymer is prepared by heating the intimate mixture of the two reactants to a temperature on the order of 100.degree. to 250.degree. C. The prepolymer obtained may be used in the state of a solution, suspension or powder, or may, alternatively, be further shaped by simple hot casting. In a second stage, the curing of the prepolymer is effected by heating to temperatures on the order of 300.degree. C., optionally under pressure.
These polymers may be converted into films or into multicellular materials. They are of very special value for the production of molded shaped articles, optionally in combination with fibrous or pulverulent fillers, or of laminates based on inorganic fibers (simple fibers, fabric or bonded fibrous web) such as, for example, carbon, boron or glass fibers. However, the preparation and use of these polymers require precautions to be taken from the standpoint of health and hygiene, when the diprimary diamine employed is aromatic in nature, on account of the toxicity of certain of these.