Viscosity-reducing super-plasticising copolymers

1. Process for lowering the viscosity of hydraulic cement compositions, comprising the addition to the hydraulic composition of a (co)polymer comprising a main chain, essentially consisting of (meth)acrylic units, and polyoxyalkylated side chains containing statistically-distributed hydrophobic units as an adjuvant, wherein the main chain has a degree of polymerisation of 15 to 45, and the mean molecular weight of the side chains is between 500 and 5000 g/mol.

2. The process according to claim 1 , wherein the weight average molecular weight of the (co)polymer is 10 000 to 50 000 g/mol.

3. The process of (co)polymers according to claim 1 , wherein the hydrophobic units are oxypropylene and oxybutylene groups.

4. The process according to claim 3 , wherein the hydrophobic units are oxypropylene groups.

5. The process according to claim 1 wherein the (co)polymer comprises (meth)acrylic units of following formula (I):

wherein:

R 1 is hydrogen or methyl;

Z is O or NH; and

R 2 is H or an alkyl, aryl, alkylaryl, arylalkyl group with 1 to 20 carbon atoms, or -Q-R 3 group in which R 3 is H or an alkyl, aryl, alkylaryl, arylalkyl group with 1 to 20 carbon atoms, and Q is of formula (II):

wherein:

Y 1 represents an alkylene group with 2 carbon atoms;

Y 2 represents an alkylene group with 3 carbon atoms;

Y 3 represents an alkylene group with 4 carbon atoms;

n is an integer of 1 to 100;

m is an integer of 0 to 150;

q is an integer of 0 to 150; and

(n+m+q) is an integer of 1 to 500,

bearing in mind that the (co)polymer of formula (I) comprises at group in which in or q>0.

6. The process according to claim 5 , wherein the (co)polymer is obtained by radical polymerisation of a (meth)acrylic monomer of following formula (Ia):

wherein the substituents R 1 , Z and R 2 have the same meaning as for formula (I) in claim 5 .

7. The process according to claim 6 wherein in the formula (Ia), Z is an oxygen.

8. The process according to claim 6 wherein in the formula (Ia), R 2 is a -Q-R group in which R 3 is a methyl or ethyl group.

9. The process according to claim 5 wherein in the formula (I), Z is an oxygen.

10. The process according to claim 5 wherein in the formula (I), R 2 is a -Q-R 3 group in which R 3 is a methyl or ethyl group.

11. The process according to claim 5 , wherein in formula (II) R 2 is a -Q-R 3 group in which n varies from 1 to 100 and m varies from 1 to 75 and q equals 0.

12. The process according to claim 1 , wherein the (co)polymer dosage is adjusted so that the content of hydrophobic groups in the composition of the hydraulic binder is between 0.02 and 0.5% by weight relative to the weight of binder.

13. The process according to claim 1 , wherein the (co)polymer is obtained using a method in which the following are caused to react in the presence of water and at a temperature of between 120 and 250° C.:

at least one polycarboxylic acid obtained by polymerising at least one unsaturated carboxylic acid; and

at least one polyether containing a free hydroxyl group capable of reacting with a carboxylic function of the said polycarboxylic acid,

the catalyst being an alkaline or alkaline-earth salt of a strong protic acid.