Alkylated 2,2'-biphenylene phosphites

A 1,1'-biphenyl-2,2'-diyl phosphite of the formula ##STR9## wherein R is an alkyl group of 1 to 18 carbon atoms,

• R.sup.1 is hydrogen or alkyl group of 1 to 18 carbon atoms, and
• R.sup.2 is an alkyl group of 1 to 20 carbon atoms, phenyl, phenyl substituted by 1 to 3 alkyl groups each having 1 to 8 carbon atoms, or by two alkyl groups each having 1 to 8 carbon atoms and by --COOR.sup.4 where R.sup.4 is alkyl of 1 to 18 carbon atoms,
• R.sup.3 is an n-valent radical selected from the group consisting of a straight- or branched-chain alkylene of 2 to 12 atoms, a straight- or branched chain alkane-triyl, -tetrayl, -pentayl or -hexayl of 3 to 6 carbon atoms, alkylene of 4 to 6 carbon atoms, cycloalkylene of 6 to 12 carbon atoms, 1,4-cyclohexanedimethylene, arylene or arylene or arenetriyl of 6 to 10 carbon atoms, p-xylylene, phenylene-E-phenylene where E is a direct bond, --O--, --S--, --NR.sup.5 --, where R.sup.5 is alkyl of 1 to 18 carbon atoms;
• a straight- or branched chain alkylene or alkylidene of 1 to 12 carbon atoms or cycloalkylidene of 5 to 6 carbon atoms, said arylene or said phenylene-E-phenylene substituted by 1 to 4 alkyl groups each having 1 to 8 carbon atoms, --(CH.sub.2).sub.x X(CH.sub.2).sub.x where x is 2 to 6, dipentaerythrityl, and ##STR10## where Y is hydrogen, methyl or ethyl and z is 1 to 10,
• X is oxygen or sulfur, and n is 2 to 6.