Silanes azocarbonilo functions

Silanes azocarbonilo functions of the general formula I: (R1) 3-a (R2) aSi-RI-NH-C (O) -N> = N-R4 (I) wherein R1 groups are independently C1 C18, C5-C18 cycloalkyl groups or C6-C18 aryl groups, unsubstituted, R2 is independently -OH, a C1-C18 group unsubstituted C5- C18 cycloalkoxy group or a polyether alkyl group O (CH2 -CH2-10 O) n-R3 or O (CH (CH3) -CH2-O) n-R3, where average n is 1 to 18 and R3 is each independently a C1-C32 hydrocarbon chain monovalent branched or unbranched, saturated or unsaturated, RI is a hydrocarbon C1-C30 divalent aliphatic, aromatic or aliphatic / aromatic mixed, branched or unbranched, saturated or unsaturated, a> = 1, 2 or 3, R4 is unsubstituted aryl, halophenyl, tolyl, alkoxyphenyl, o-, m- or p-nitrophenyl, unsubstituted alkyl, nitromethyl, nitroethyl, nitropropyl, nitrobutilo or nitro-iso-butyl.