A co-polymer obtainable by a process comprising the co-polymerization of at least one monomer of formula wherein a is 0 or 1; a) P represents a radical susceptible of generating an odoriferous α,β-unsaturated ketone, aldehyde or carboxylic ester and is represented by formula in which the wavy line indicates the location of the bond between said P and X; R 1 represents a hydrogen atom, a C 1 to C 6 alkoxyl radical or a C 1 to C 15 linear, cyclic or branched alkyl, alkenyl or alkadienyl radical, possibly substituted by C 1 to C 4 alkyl groups; and R 2, R 3 and R 4 represent a hydrogen atom, an aromatic ring or a C 1 to C 15 linear, cyclic or branched alkyl, alkenyl or alkadienyl radical, possibly substituted by C 1 to C 4 alkyl groups; or two, or three, of the groups R 1 to R 4 are bound together to form a saturated or unsaturated ring having 6 to 20 carbon atoms and including the carbon atom to which said R 1, R 2, R 3 or R 4 groups are bound, this ring being possibly substituted by C 1 to C 8 linear, branched or cyclic alkyl or alkenyl groups; b) X represents an oxygen or a sulfur atom; c) R represents a hydrogen atom or a methyl or ethyl group; d) G represents a group selected from the group consisting of formulae 1) to 4): in which formulae the hatched lines indicate the location of the bond between said G and the CH 2 =CRCO moiety, the bold lines indicate the location of the bond between said G and X; R has the same meaning as above; m represents an integer varying from 1 to 5; each n is 0 or 1; Z represents an oxygen or sulfur atom or a NH or NR 5 group, R 5 representing a hydrogen atom, a C 1 -C 5 hydrocarbon group or a CH 2 -U-X-Q or CH 2 CH 2 - n -X-Q group; U is a group of formula - - or -O -, the bold line having the same meaning as indicated above; Q represent a hydrogen atom, an alkali metal or a group P as defined above; w represents an integer from 1 to 20; and at least a monomer of formula: wherein, R has the meaning given above for formula, n is 0 or 1; and A represents an oxygen or sulfur atom or a NH or NR 9 group, R 9 representing a hydrogen atom or a C 1 -C 5 hydrocarbon group; R 6 represents: - a hydrogen atom or an alkali metal atom, if n is 1; - a COR 7 group, R 7 being a hydrogen atom or C 1 -C 10 group, if n is 0; or a C 1 -C 20 hydrocarbon comprising up to four functional groups selected from the group consisting of amine, quaternized nitrogen, COOY and PO 3 Y, Y being a hydrogen or an alkali metal atom, and optionally comprising one or two functional groups selected from the group consisting of ether and ester. a) P represents a radical susceptible of generating an odoriferous α,β-unsaturated ketone, aldehyde or carboxylic ester and is represented by formula in which the wavy line indicates the location of the bond between said P and X; R 1 represents a hydrogen atom, a C 1 to C 6 alkoxyl radical or a C 1 to C 15 linear, cyclic or branched alkyl, alkenyl or alkadienyl radical, possibly substituted by C 1 to C 4 alkyl groups; and R 2, R 3 and R 4 represent a hydrogen atom, an aromatic ring or a C 1 to C 15 linear, cyclic or branched alkyl, alkenyl or alkadienyl radical, possibly substituted by C 1 to C 4 alkyl groups; or two, or three, of the groups R 1 to R 4 are bound together to form a saturated or unsaturated ring having 6 to 20 carbon atoms and including the carbon atom to which said R 1, R 2, R 3 or R 4 groups are bound, this ring being possibly substituted by C 1 to C 8 linear, branched or cyclic alkyl or alkenyl groups; b) X represents an oxygen or a sulfur atom; c) R represents a hydrogen atom or a methyl or ethyl group; d) G represents a group selected from the group consisting of formulae 1) to 4): in which formulae the hatched lines indicate the location of the bond between said G and the CH 2 =CRCO moiety, the bold lines indicate the location of the bond between said G and X; R has the same meaning as above; m represents an integer varying from 1 to 5; each n is 0 or 1; Z represents an oxygen or sulfur atom or a NH or NR 5 group, R 5 representing a hydrogen atom, a C 1 -C 5 hydrocarbon group or a CH 2 -U-X-Q or CH 2 CH 2 - n -X-Q group; U is a group of formula - - or -O -, the bold line having the same meaning as indicated above; Q represent a hydrogen atom, an alkali metal or a group P as defined above; w represents an integer from 1 to 20; - a hydrogen atom or an alkali metal atom, if n is 1; - a COR 7 group, R 7 being a hydrogen atom or C 1 -C 10 group, if n is 0; or a C 1 -C 20 hydrocarbon comprising up to four functional groups selected from the group consisting of amine, quaternized nitrogen, COOY and PO 3 Y, Y being a hydrogen or an alkali metal atom, and optionally comprising one or two functional groups selected from the group consisting of ether and ester.