A compound of following formula: in which: - R 1 is a straight-chain or branched alkyl group comprising 1 to 20 carbon atoms, optionally substituted by one or more OR a substituents, R a representing a hydrogen atom or an alkyl group comprising 1 to 20 carbon atoms, the said group R 1 optionally containing one or more unsaturations; or R 1 represents a mono-, bi- or tri- cyclic hydrocarbon radical, saturated or partly unsaturated, non-aromatic, comprising from 3 to 20 carbon atoms; - a represents a single or double bond; - R 2 is a hydrogen atom, an OR a group, R a representing a hydrogen atom or an alkyl group comprising 1 to 20 carbon atoms, or a straight-chain or branched alkyl group comprising 1 to 20 carbon atoms substituted by an OH group, or R 2 is a radical of formula -(OCH 2 CH 2) n -OH or -CH 2 -(CH 2 OCH 2) n -CH 3, n representing an integer of 1 to 100, preferably 6 to 50, preferably it is 6, 13 or 45; - R 3, when a is single bond, represents a hydrogen atom or, when a is a double bond, R 3 is absent; - R 4 is a hydrogen atom or an OR b group, R b representing a hydrogen atom or an alkyl group comprising 1 to 20 carbon atoms, or a straight-chain or branched alkyl group comprising 1 to 20 carbon atoms substituted by an OH group, or R 4 is a radical of formula -(OCH 2 CH 2) n -OH or -CH 2 -(CH 2 OCH 2) n -CH 3, n representing an integer of 1 to 100, preferably 6 to 50, and preferably it is 6, 13 or 45; - R 5, when a is a single bond, represents a hydrogen atom, or when a is a double bond R 5 is absent; and - A 1 is a divalent alkylene radical, straight-chain or branched, comprising 1 to 20 carbon atoms, the said alkylene radical optionally containing one or more unsaturations, and wherein at least one of the groups R 1, R 2 and R 4 comprises an OH or alkoxy group. - R 1 is a straight-chain or branched alkyl group comprising 1 to 20 carbon atoms, optionally substituted by one or more OR a substituents, R a representing a hydrogen atom or an alkyl group comprising 1 to 20 carbon atoms, the said group R 1 optionally containing one or more unsaturations; or R 1 represents a mono-, bi- or tri- cyclic hydrocarbon radical, saturated or partly unsaturated, non-aromatic, comprising from 3 to 20 carbon atoms; - a represents a single or double bond; - R 2 is a hydrogen atom, an OR a group, R a representing a hydrogen atom or an alkyl group comprising 1 to 20 carbon atoms, or a straight-chain or branched alkyl group comprising 1 to 20 carbon atoms substituted by an OH group, or R 2 is a radical of formula -(OCH 2 CH 2) n -OH or -CH 2 -(CH 2 OCH 2) n -CH 3, n representing an integer of 1 to 100, preferably 6 to 50, preferably it is 6, 13 or 45; - R 3, when a is single bond, represents a hydrogen atom or, when a is a double bond, R 3 is absent; - R 4 is a hydrogen atom or an OR b group, R b representing a hydrogen atom or an alkyl group comprising 1 to 20 carbon atoms, or a straight-chain or branched alkyl group comprising 1 to 20 carbon atoms substituted by an OH group, or R 4 is a radical of formula -(OCH 2 CH 2) n -OH or -CH 2 -(CH 2 OCH 2) n -CH 3, n representing an integer of 1 to 100, preferably 6 to 50, and preferably it is 6, 13 or 45; - R 5, when a is a single bond, represents a hydrogen atom, or when a is a double bond R 5 is absent; and - A 1 is a divalent alkylene radical, straight-chain or branched, comprising 1 to 20 carbon atoms, the said alkylene radical optionally containing one or more unsaturations, and wherein at least one of the groups R 1, R 2 and R 4 comprises an OH or alkoxy group.