Flame-resistant polyamide, method for the production of said flame-resistant polyamide, and use of said flame-resistant polyamide

A process for producing a flame-retardant polyamide comprising polycondensation of one or more diamines in the form of a AH salt with one or more dicarboxylic acids under an initial pressure of between 16 and 25 bar at elevated temperature of between 230° C. to 280° C., in the presence of water, in order to build up the pressure in the reactor that is required at the selected reaction temperature, and with one or more diphosphinic acids of the formula (III)

• and/or with one or more carboxy-phosphinic acids of the formula (IV),
• the dicarboxylic acid being replaced in part, under the stoichiometric conditions on which the polycondensation is based, by the diphosphinic acid (III) and/or by the carboxy-phosphinic acid (IV), the pressure in the reaction space after the polycondensation being lowered to less than 250 mbar, and
• wherein the following definitions applying to the formulae (III) and (IV):
• R2 and R3, independently of one another, are a linear, cyclic or branched C1-C6 alkyl group or an aryl group, and
• R4 is a divalent organic group,
• said polycondensation yielding a flame-retardant polyamide FR containing in its main chain not only the amide structural units of the formula (I)
• —CO—NH— (I)
• but also phosphinamide structural units of the formula (II)
• —PO(R1)—NH— (II),
• R1 being hydrogen or an organic group, and in which individual phosphinamide structural units within the main chain may be different, and in that the polyamide FR attains a relative viscosity, measured as a 1% strength solution in 96% strength sulfuric acid at 25° C., of at least 2.0 and not more than 4.0 (according to DIN 51562), wherein the proportion of the reactants in the form of the diamines, dicarboxylic acids, diphosphinic acids, and the carboxy-phosphinic acids is adjusted such that the phosphorus content of the flame-retardant polyamide process product obtained, based on the polyamide FR, is between 0.01 wt % and 10.0 wt %.