We claim:
1. A composition comprising:
a) at least one hydrocarbon-containing cut of petroleum origin or obtained from biomass conversion, and
b) at least one copolymer resulting from the copolymerization of:

- at least one monomer selected from: acrylic acid and any salt thereof,
- optionally at least one monomer selected from: methacrylic acid and any salt thereof,
- at least one monomer selected from the monomers of formula (I):
R – X – R' (I) according to which:
- R represents a polymerizable unsaturated function,
- R' denotes hydrogen or an alkyl group having from 1 to 4 carbon atoms,
- X represents a structure comprising n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide PO,
- m and n are two integers in the range from 0 to 150, at least one of which is not zero.

2. The composition as claimed in claim 1 that comprises a content of hydrocarbon-containing cut (a) from 60 to 90 wt%, preferably from 65 to 85 wt% and more preferably from 70 to 80 wt% relative to the total weight of the composition.
3. The composition as claimed in claim 1 or 2, in which the hydrocarbon-containing cut (a) is a dearomatized hydrocarbon-containing cut.
4. The composition as claimed in any one of the preceding claims, in which the hydrocarbon-containing cut (a) has one or more of the following properties:

- a boiling point from 200 to 420°C, according to standard ASTM D86.
- a kinematic viscosity at 40°C from 2 to 20 mm2/s, according to standard ASTM D445.
- a flow point from -45 to +10°C, according to standard ASTM D97.
5. The composition as claimed in any one of the preceding claims, in which the hydrocarbon-containing cut (a) comprises a content by weight relative to the total weight of the hydrocarbon-containing cut (a):
- of paraffins from 60 to 99%,
- of naphthenes from 1 to 40%,
- of aromatic compounds less than or equal to 300 ppm.

6. The composition as claimed in any one of the preceding claims, which comprises a content of copolymer (b) from 10 to 40 wt%, preferably from 15 to 35% and more preferably from 20 to 30 wt% relative to the total weight of the composition.
7. The composition as claimed in any one of the preceding claims, in which m and n are two integers selected from the group from 1 to 150.
8. The composition as claimed in any one of the preceding claims, which comprises at least one copolymer (b) resulting from the copolymerization of a set of monomers consisting of, by weight relative to the total weight of monomers:

- at most 20% of at least one monomer selected from: acrylic acid and any salt thereof,
- from 0 to 10% of monomers selected from: methacrylic acid and any salt thereof, and
- at least 80% of monomers of formula (I).
9. The composition as claimed in any one of the preceding claims, which comprises
at least two copolymers (b) resulting from the copolymerization of a set of
monomers:
b1) at least one copolymer consisting of:
- monomers of acrylic acid and/or any salt thereof,
- monomers of formula (I):
R – X – R' (I) according to which:
- R represents a polymerizable unsaturated function,
- R' denotes hydrogen or an alkyl group having from 1 to 4 carbon atoms,
- X represents a structure comprising n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide PO,
- m and n are two integers in the range from 0 to 150, at least one of which is not zero
b2) at least one copolymer consisting of:
- monomers of acrylic acid and/or any salt thereof,
- monomers of methacrylic acid and/or any salt thereof,
- monomers of formula (I'):
R'' – X' – R''' (I') according to which:
- R'' represents a polymerizable unsaturated function,
- R''' denotes hydrogen or an alkyl group having from 1 to 4 carbon atoms,
- X' represents a structure comprising n' unit(s) of ethylene oxide EO and m' unit(s) of propylene oxide PO,

- m' and n' are two integers in the range from 0 to 150, at least one of which is not zero
10.The composition as claimed in the preceding claim, in which:
- copolymer b1) has a molecular weight Mw from 20 000 to 80 000 g/mol, and
- copolymer b2) has a molecular weight Mw greater than or equal to
500 000 g/mol.
11.The composition as claimed in any one of the preceding claims, which comprises a content of phthalates less than or equal to 1 wt% relative to the total weight of the composition.
12. A composition of acrylic mastic comprising a content by weight of the composition as claimed in any one of claims 1 to 11 from 1 to 20 wt% relative to the total weight of the mastic composition.
13.The composition of mastic as claimed in claim 12 comprising, by weight relative to the total weight of the composition:
- 0 to 60% of at least one filler,
- 10 to 88% of at least one acrylic polymer or copolymer in aqueous dispersion,
- 10 to 40% of water,
- 1 to 5% of at least one surfactant,
- 1 to 20% of at least one composition as claimed in any one of claims 1 to 12.
14.A composition of acrylic adhesive comprising a content by weight of the composition as claimed in any one of claims 1 to 11 from 1 to 20 wt% relative to the total weight of the adhesive composition.
15.The composition of adhesive as claimed in claim 14 comprising, by weight relative to the total weight of the composition:
- 0 to 60% of at least one filler and/or of at least one tackifying resin,
- 10 to 88% of at least one acrylic polymer or copolymer in aqueous dispersion,
- 10 to 40% of water,
- 1 to 5% of at least one surfactant,
- 1 to 20% of at least one composition as claimed in any one of claims 1 to 12.
16.The use of the composition as claimed in any one of claims 1 to 11 in acrylic mastics and adhesives, preferably as a plasticizer.