Curable compositions

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof

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528170, 528172, 528173, 528174, 528176, 528185, 528188, 528220, 528229, 528322, 528342, 528350, 528352, 528353, 524600, 524606, 524879, 4284111, C08G 7312, C08J 504, B32B 0000

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059524537

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BRIEF SUMMARY
This invention relates to curable compositions.
High continuous use temperature ("CUT") composite materials of cross-linked polyimide matrices reinforced with fibres, especially continuous fibres, are known. Such composite materials have been used for many applications, especially in the aerospace industry in which strength-to-weight ratios and high CUT are particularly important, eg in jet engine components.
A particularly useful polyimide matrix material for use in such composites has been developed by NASA. This family of polyimide materials is known by the designation PMR (ie polymerisable monomer reactants). The PMR materials are the subject of inter alia U.S. Pat. Nos. 3,528,950, 3,745,149 and 7,603,055 and have been widely reviewed in the literature, for example T T Serafini and P Devigs, Applied Polymer Symposium No 22, 89-100, 1973; Ruth H Pater, SAMPE Journal, November/December 1981; T T Serafini, Proceedings of 5th International Conference on Composite Materials, 1007-1023, Metal Soc 1985, AIME; D Wilson, British Polymer Journal, 20(5), 405-416, 1988; and D A Scola and J H Vontell, Chemtech 112-121, February 1989.
The PMR curable compositions initially comprise an aromatic diamine, an end cap monomer and an aromatic tetracarboxylic acid, its dianhydride or alkyl diester. In accordance with U.S. Pat. No. 3,745,149, a useful combination of reactants is: ##STR1## wherein R' is a tetravalent aryl radical and R.sup.2 is alkyl or hydrogen and at least two R.sup.2 are alkyl; ##STR2## wherein R.sup.2 is as defined in a) and at least one R.sup.2 is alkyl and R.sup.4 is a divalent radical of the formula: ##STR3## wherein R.sup.5 is hydrogen or lower alkyl; the molar ratio of a:b:c being n:(n+1):2, wherein n has a value from 1 to 20.
A commercially-available PMR resin, derived from the monomers dimethyl ester of 3,3',4,4'-benzophenonetetracarboxylic acid (BTDE)/4,4'-methylenedianiline (MDA)/methyl ester of 5-norbornene-2,3-dicarboxylic acid (NE) has a CUT of up to 316.degree. C. in atmospheric air and is known by the designation PMR-15. The "15" in the designation is derived from the formulated molecular weight (FMW) of the composition. The FMW, as described in the 1985 Serafini paper, is considered to be the average molecular weight of imidized prepolymer that could have been formed if an amide-acid prepolymer had been synthesised and it is derived from the formula: +MW.sub.(methanol) ! the stoichiormetry of a PMR curable composition by dividing the FMW by 100.
A primary drawback of PRM-15, as reported in section 9.4 of the 1988 Wilson paper, is the suspected carcinogenic character of MDA. Although said section 9.4 indicates MDA has been substituted by other, less toxic, diamines (eg 4,4'-oxydianiline and 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane as reported by W B Alston, Proc. Conf. High Temperature Polymer Matrix Composites, NASA Lewis Research Centre, 187-205, March 1983, the combination of properties provided by MDA could not be matched.
Other variants are disclosed in the references, for example PMR-II derived from the monomers dimethyl ester of 4,4'-(hexa-fluoroispropylidene)bis(phthalic acid) (HFDE)/para-phenylene-diamine (p-PDA)/NE, and substitution of NE with aminostyrene, optionally with the addition of N-phenylnorbornene to improve processability, ie melt flow.
The reduced processibility of the curable composition resulting from substitution of MDA by p-PDA in PMR-II, thus enabling the enhanced thermal stability of p-PDA compared with MDA to be exploited, is offset by the increase in processibility afforded by the use of HFDE However, a primary drawback of PMR-II is the cost of HFDE.
It is an object of the invention to provide useful PMR curable compositions in which MDA is absent.
The object of the invention is achieved by the provision of a PMR curable composition in which the aromatic diamine comprises m-phenylenediamine or a mixture of p-phenylenediamine and m-phenylenediamine.
In particular, in accordance with the invention, a curable composition comprises: diester; m-phenylen

REFERENCES:
patent: 4455418 (1984-06-01), Lauver
patent: 4514447 (1985-04-01), Lauver
patent: 5091505 (1992-02-01), Serafini et al.
patent: 5149772 (1992-09-01), Serafini et al.
British Polymer Journal, vol. 20, No. 1, (1988) "PMR-15 Processing, Properties and Problem--A Review", Douglas Wilson, pp. 405-416.

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