Polyurethane synthesis by means of self-condensation

A compound of following formula (I):

• in which:
• R1 is a straight-chain or branched alkyl group comprising 1 to 20 carbon atoms, optionally substituted by one or more ORa substituents, Ra representing a hydrogen atom or an alkyl group comprising 1 to 20 carbon atoms, the said group R1 optionally containing one or more unsaturations;
• a represents a single or double bond;
• R2 is a hydrogen atom, an ORa group, Ra 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 R2 is a radical of formula —(OCH2CH2)n—OH or —CH2(CH2OCH2)n—CH3, n representing
• an integer of 1 to 100;
• R3, when a is single bond, represents a hydrogen atom or, when a is a double bond, R3 is absent;
• R4 is a hydrogen atom or an ORb group, Rb 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 R4 is a radical of formula —(OCH2CH2)n—OH or —CH2—(CH2OCH2)n—CH3, n representing an integer of 1 to 100;
• R5, when a is a single bond, represents a hydrogen atom, or when a is a double bond R5 is absent;
• and
• A1 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,
• wherein at least one of the groups R1, R2 and R4 comprises an OH group.