Abstract: The present invention relates to a fibre assembly comprising high-performance polymeric fibres and bonding fibres, the fibre assembly comprising at least 70% by weight of high-performance polymeric fibres and at most 30% by weight of bonding fibres, the fibre assembly having a layered arrangement of the fibres and at least some of the fibres being bonded together by points of contact obtainable by softening of the bonding fibres. The present invention further describes an insulation system comprising a fibre assembly of the invention.

Abstract: There are disclosed flame-retardant, high temperature resistant polyimide fibers of the general formula ##STR1## wherein n is an integer larger than 1, A is a tetravalent aromatic group and R is at least one divalent aromatic group. These polyimide fibers have been heat-treated in the unstretched state and have a maximum shrinkage of 14% when heated to a temperature of 400.degree. C. These polyimide fibers are produced by initially spinning crude fibers from a solution of the appropriate polyimide in an aprotic organic solvent, preferably according to the dry-spinning method, which solution optionally contains additives. The crude fibers obtained are washed with water to remove the solvent. The washed crude fibers are dried to a moisture content of less than 5% by mass, are subjected to a heat treatment at a temperature of between 315.degree. C and 450.degree. C, are cooled and, if desired, are crimped and cut to staple fibers.

Abstract: To produce flame-retardant thermostable new homopolyimides having structural units of the general formula ##STR1## by reacting 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride with an overall equimolar amount of 2,4- and/or 2,6-toluene diisocyanate, the reaction is carried out in the presence of a polymerization accelerator. The new homopolyimides have a glass transition point of at least 320.degree. C. and are processible to moulded articles exhibiting a similarly good structural strength as could hitherto be observed in mixed polyimides only. Furthermore, the new homopolyimides can be spun to fibres.