Permanently stabilized polyurethanes

Permanently stabilized polyurethanes containing polymer segments represented by the following formula:

• ##STR13## wherein Y represents the group derived from a diisocyanate or from an diisocyanat prepolymer,
• R represents hydrogen, a straight chain or branched chain alkyl group having 1 to 20 C atoms, an alkenyl group having 3 to 5 C atoms, an aralkyl group having 7 to 12 C atoms, the group --CH.sub.2 --CHR.sub.5 --OH wherein R.sub.6 denotes hydrogen, methyl or phenyl;
• the group --CH.sub.2 --CH.sub.2 --CN, the group --CH.sub.2 --CH.sub.2 -COOalkyl or the group ##STR14## R.sub.1 and R.sub.2 may be identical or different and may each represent a straight chain or branched chain alkyl group having 1 to 6 C atoms or, together with the ring carbon atom to which they are attached, they may represent a cycloalkyl ring having 5 to 7 C atoms.
• A may represent a direct bond, an .omega.-hydroxyalkyl, an .omega.-aminoalkyl, an .omega.-carboxylic acid hydrazido-, an .omega.-semicarbazido or an .omega.-carbazic ester group, in each case without the hydrogen atom in the end position.
• B represents an .omega.-hydroxyalkyl-, an .omega.-aminoalkyl-, an .omega.-carboxylic acid hydrazido- or an .omega.-semicarbazido group, in each case without the hydrogen atom in the end position,
• the quantity of these segments in the polyurethanes being selected so that the proportion of the stabilizers represented by the following formula ##STR15## is from 0.05 to 5% by weight in the polyurethane.