Photoprotective/cosmetic compositions comprising cinnamonitrile-substituted polyorganosiloxanes/polyorganosilanes

A cinnamonitrile-substituted polyorgano-siloxane/polyorganosilane compound having the formula (3):

• ##STR23## in which the radicals R', which may be identical or different, are each a C.sub.1 -C.sub.8 alkyl radical or a phenyl radical;
• and the radical A is a monovalent radical bonded directly to a silicon atom and which has the following formula (4):
• ##STR24## wherein X.sup.1 is a cyano radical or an alkoxycarbonyl radical COOR.sup.1 in which the radical R.sup.1 is (i) a C.sub.1 -C.sub.20 alkyl radical, (ii) a C.sub.2 -C.sub.20 hydroxyalkyl radical, or (iii) a divalent radical --Y-- having the following formula (5):
• ##STR25## in which R.sup.2 is a hydrogen atom or a C.sub.1 -C.sub.4 alkyl radical, p is an integer ranging from 0 to 10, inclusive;
• m is 0 or 1;
• the --CH.sub.2 -- endgroup is directly bonded to a silicon atom;
• X.sup.2 is a hydrogen atom or an optionally substituted phenyl or C.sub.6 -C.sub.10 aryl radical;
• n is an integer ranging from 0 to 2, inclusive;
• the radicals X.sup.3, which may be identical or different, are each a C.sub.1 -C.sub.8 alkyl radical or a C.sub.1 -C.sub.4 alkoxy radical, with the proviso that, when the radicals X.sup.3 are alkoxy radicals, two adjacent radicals X.sup.3 (n=2) may together form an alkylidenedioxy group in which the alkylidene moiety contains 1 or 2 carbon atoms;
• and X.sup.4 is a hydrogen atom or a divalent radical --Y--, with the proviso that, if X.sup.4 is a hydrogen atom, then X.sup.1 is necessarily a radical COOY in which m is zero.