Porphyrin-containing silicones having increased thermal stability

A method of increasing thermal stability of a silicone composition subject to thermal or thermal oxidative stress, consisting essentially of adding a porphyrin or mixture of porphyrins of the general formulae

• where ##STR2## R.sub.2 is an identical or different radical selected from the group consisting of --H, --OH, --OR.sup.3, --COR.sup.3, --OCOR.sup.3, --NO.sub.2, --CN, --F, --Cl, --Br, --I, --SCN, --OCN, --N.dbd.N--OH, --NR.sup.3.sub.2 and --SO.sub.3 A and a monovalent hydrocarbon radical having from 1 to 20 carbon atoms which is optionally substituted by --H, --OH, Or.sup.3, --COR.sup.3, --COOR.sup.3, OCOR.sup.3, --NO.sub.2, --CN, --F, --Cl. --Br, --I, --SCN, --OCN, --N.dbd.N--OH, --NR.sup.3.sub.2, --N.sup.3.sub.3 B or SO.sub.3 A, where, in the optionally substituted monovalent hydrocarbon radical, non-adjacent --CH.dbd. units are optionally replaced with --N.dbd. units and --CH.sub.2 -- units are optionally replaced with --O--, --S-- or --NH-- units,
• R.sup.3 is selected from the group consisting of --H and a monovalent hydrocarbon radical having from 1 to 20 carbon atoms,
• A is selected from the group consisting of --H, Na, and K,
• B is selected from the group consisting of Cl, F, Br and I,
• R.sup.1 is an identical or different R.sup.2 radical or two vicinal radicals R.sup.1 where together with the carbon atoms of the porphyrin ring to which they are bound from a cyclic hydrocarbon radical having from 5 to 10 carbon atoms in which non-adjacent --CH.dbd. units are optionally replaced with --N.dbd. units and --CH.sub.2 -- units are optionally replaced with --O--, --S-- or --NH-- units, where, in the cyclic hydrocarbon radical, --CH.dbd. and --CH.sub.2 -- units are optionally substituted with --H, --OH, OR.sup.3, --COR.sup.3, --COOR.sup.3, OCOR.sup.3, --NO.sub.2, --CN, --F, --Cl, --Br, --I, --SCN, --OCN, --N.dbd.N--OH, --NR.sup.3.sub.2, --NR.sup.3.sub.3 B or SO.sub.3 A,
• M is a metal selected from the group consisting of Li, Na, K, Rb and Cs, Be, Mg, Sr, Ba, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Ru, Hf, Os, Cd, Hg, Ag, Au, Pd, Pt, Si, Ge, Sn, In and Ce, where, if the oxidation state of M is higher than two, the free valences are satisfied by radicals R.sup.2 or radicals of organosilicon compounds;
• to a silicone composition of the general formula
• R.sup.4.sub.a SiO.sub.(4-a)/2 ( 3)
• and the following optional components
• i. a polyorganosiloxane of the formula
• --OSi(R.sup.4.sub.2)R.sup.5 Si(R.sup.4.sub.2)O-- (4)
• linked to the silicone composition (3), and
• ii. a crosslinking additive,
• where
• R.sup.4 is an identical or different, monovalent hydrocarbon radical having from 1 to 18 carbon atoms which are optionally fluoro-, chloro-, bromo-, or cyano-substituted,
• R.sup.5 is an identical or different, divalent hydrocarbon radical having from 1 to 18 carbon atoms which are optionally fluoro-, chloro-, bromo-, or cyano-substituted, or a polyoxy-C.sub.1 -C.sub.4 alkylene radical, and
• a is 0, 1, 2 or 3.