Abstract: The reaction of phosphonic acid or a phosphonic acid ester of the formula II ##STR1## with a phosphonic acid dichloride of the formula III ##STR2## wherein R, R.sup.1 and R.sup.2 are as defined in claim 1, gives a phosphonic anhydride of the formula IV ##STR3## which, with or without being isolated from the reaction solution, is reacted with pentaerythritol, in the temperature range from 60.degree. to 120.degree. C., to give a compound of the formula I ##STR4## the molar ratio of anhydride of the formula IV to pentaerythritol being about 2:1.

Abstract: Heat-curable mixtures which are stable on storage and consist of (a) poly-imides of specific unsaturated dicarboxylic acids of the general formula I ##STR1## in which A is a x-valent organic radical having at least 2 and not more than 30 carbon atoms, Z is a radical of the formulae ##STR2## and x is the number 2 or 3, and (b) poly-(.beta.-iminocrotononitriles) of the formula II, III and/or IV ##STR3## in which Y is a m-valent organic radical having at least 2 and at most 30 carbon atoms, R' is a hydrogen atom or an alkyl having 1 to 6 carbon atoms, cycloalkyl having 5 or 6 carbon atoms or aryl having 6 to 10 carbon atoms, R is an aliphatic or aromatic radical having not more than 30 carbon atoms, E, together with the two nitrogen atoms, is a five-membered or six-membered ring, m is 2 or 3 and n is 1 or 2, are suitable for the production of moulded materials, preferably by casting the resin mixture or by laminating or bonding substrates.

Abstract: In the production of maleimides of the general formula I ##STR1## in which n is one of the numbers 1, 2 or 3, R.sup.1 and R.sup.2 are each a hydrogen atom or methyl, and A is an n-valent aliphatic, cycloaliphatic, aliphatic-cycloaliphatic or aliphatic-aromatic radical having up to 30 C atoms, by means of cyclising dehydration of a maleamic acid of the formula II ##STR2## in which the acid amide group (s) is (are) attached to aliphatic or cycloaliphatic C atoms, in the presence of low-molecular dehydrating carboxylic anhydrides in an organic solvent and in the present of catalysts, there is advantageously used as solvent a polar aprotic solvent containing at least one N-lower-alkyl-substituted acid amide group in the molecule, or a solvent mixture containing an aprotic solvent of this type, and as catalyst a metal compound, and the cyclising dehydration is performed in the temperature range of 40.degree. to 100.degree. C.

Abstract: The invention relates to the improvement of the conventional processes for manufacturing monomaleimides and polymaleimides, in which it is known to cyclodehydrate corresponding monomaleamic or polymaleamic acids in the presence of acetic anhydride and tertiary amines. According to the invention, the tertiary amines are used only in very small amounts (0.1 to 0.5 mole per mole of maleamic acid group) and the dehydration is carried out at temperatures between 10.degree. and 50.degree. C. The end products are obtained in purer form and greater yield than in conventional processes.

Abstract: Mixtures which can be cured to give moulded materials having technically valuable mechanical and dielectric properties, characterized that they contain(a) polyimides of maleic acid or citraconic acid,(b) derivatives of .beta.-amino-crotonic acid, and optionally(c) polyamines.

Abstract: A mixture which can be converted to a heat-resistant foamed plastic and which contains a solid blowing agent, a thermoplastic prepolymer of a polyimide of an unsaturated acid, an azomethine and a polyamine. On warming, the mixture gives a foamed plastic of high heat resistance and good resistance to chemicals.