Compound of formula: in which: - R 1, R 2, R 3 and R 4 are each, independently of each other, chosen from the group consisting of: H; a linear or branched alkyl group comprising from 1 to 20 carbon atoms; and a group -C -X-R 9 in which: o X represents an oxygen atom or a radical NR 10; o R 9 is chosen from the group consisting of: a linear or branched, aliphatic or cyclic alkyl group comprising from 1 to 60 carbon atoms, preferably from 1 to 20 carbon atoms, preferentially from 1 to 12 carbon atoms, said alkyl group possibly being interrupted with one or more heteroatoms chosen from O and S, said alkyl group possibly comprising one or more unsaturations; an aryl group comprising from 6 to 24 carbon atoms, preferably from 6 to 12 carbon atoms; and an arylalkyl group in which the alkyl group comprises from 1 to 12 carbon atoms; o R 10 is chosen from the group consisting of: a hydrogen atom, a linear or branched, aliphatic or cyclic alkyl group comprising from 1 to 60 carbon atoms, preferably from 1 to 20 carbon atoms, preferentially from 1 to 12 carbon atoms, said alkyl group possibly being interrupted with one or more heteroatoms chosen from O and S, said alkyl group possibly comprising one or more unsaturations; an aryl group comprising from 6 to 24 carbon atoms, preferably from 6 to 12 carbon atoms; and an arylalkyl group in which the alkyl group comprises from 1 to 12 carbon atoms; - R 5 represents a hydrogen atom, a linear or branched, cyclic or aliphatic alkyl radical comprising from 1 to 20 carbon atoms, preferably from 1 to 12 carbon atoms, or a radical -R 6 -SiR 7 p (OR 8) 3-p; - R 6 represents a linear or branched, cyclic or aliphatic alkylene radical comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms; - R 7 represents a linear or branched, cyclic or aliphatic alkyl radical comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms; - each R 8 represents, independently of each other, a linear or branched, cyclic or aliphatic alkyl radical comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms; or two radicals R 8 may together form a ring comprising from 3 to 12 carbon atoms; and - p represents 0, 1 or 2; on condition that a radical from among the radicals R 1, R 2, R 3 or R 4 represents a group -C -X-R 9. - R 1, R 2, R 3 and R 4 are each, independently of each other, chosen from the group consisting of: H; a linear or branched alkyl group comprising from 1 to 20 carbon atoms; and a group -C -X-R 9 in which: o X represents an oxygen atom or a radical NR 10; o R 9 is chosen from the group consisting of: a linear or branched, aliphatic or cyclic alkyl group comprising from 1 to 60 carbon atoms, preferably from 1 to 20 carbon atoms, preferentially from 1 to 12 carbon atoms, said alkyl group possibly being interrupted with one or more heteroatoms chosen from O and S, said alkyl group possibly comprising one or more unsaturations; an aryl group comprising from 6 to 24 carbon atoms, preferably from 6 to 12 carbon atoms; and an arylalkyl group in which the alkyl group comprises from 1 to 12 carbon atoms; o R 10 is chosen from the group consisting of: a hydrogen atom, a linear or branched, aliphatic or cyclic alkyl group comprising from 1 to 60 carbon atoms, preferably from 1 to 20 carbon atoms, preferentially from 1 to 12 carbon atoms, said alkyl group possibly being interrupted with one or more heteroatoms chosen from O and S, said alkyl group possibly comprising one or more unsaturations; an aryl group comprising from 6 to 24 carbon atoms, preferably from 6 to 12 carbon atoms; and an arylalkyl group in which the alkyl group comprises from 1 to 12 carbon atoms; o X represents an oxygen atom or a radical NR 10; o R 9 is chosen from the group consisting of: a linear or branched, aliphatic or cyclic alkyl group comprising from 1 to 60 carbon atoms, preferably from 1 to 20 carbon atoms, preferentially from 1 to 12 carbon atoms, said alkyl group possibly being interrupted with one or more heteroatoms chosen from O and S, said alkyl group possibly comprising one or more unsaturations; an aryl group comprising from 6 to 24 carbon atoms, preferably from 6 to 12 carbon atoms; and an arylalkyl group in which the alkyl group comprises from 1 to 12 carbon atoms; o R 10 is chosen from the group consisting of: a hydrogen atom, a linear or branched, aliphatic or cyclic alkyl group comprising from 1 to 60 carbon atoms, preferably from 1 to 20 carbon atoms, preferentially from 1 to 12 carbon atoms, said alkyl group possibly being interrupted with one or more heteroatoms chosen from O and S, said alkyl group possibly comprising one or more unsaturations; an aryl group comprising from 6 to 24 carbon atoms, preferably from 6 to 12 carbon atoms; and an arylalkyl group in which the alkyl group comprises from 1 to 12 carbon atoms; - R 5 represents a hydrogen atom, a linear or branched, cyclic or aliphatic alkyl radical comprising from 1 to 20 carbon atoms, preferably from 1 to 12 carbon atoms, or a radical -R 6 -SiR 7 p (OR 8) 3-p; - R 6 represents a linear or branched, cyclic or aliphatic alkylene radical comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms; - R 7 represents a linear or branched, cyclic or aliphatic alkyl radical comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms; - each R 8 represents, independently of each other, a linear or branched, cyclic or aliphatic alkyl radical comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms; or two radicals R 8 may together form a ring comprising from 3 to 12 carbon atoms; and - p represents 0, 1 or 2;