Method for preparing a superplasticizer
The invention chiefly concerns a method for preparing polyalkoxylated polycarboxylates in which the following are caused to react in the presence of water and a catalyst at a temperature of between 120 and 250° C.: at least one polycarboxylic acid obtained by polymerization of at least one unsaturated carboxylic acid; and at least one polyether carrying a free hydroxyl group capable of reacting with a carboxylic function of the said polycarboxylic acid, characterized in that the catalyst is an alkaline or alkaline-earth salt of a strong protic acid.
1. A method for preparing polyalkoxylated polycarboxylates wherein the following are caused to react in the presence of water and a catalyst at a temperature of between 120 20 C. and 250° C.:
at least one polycarboxylic acid obtained by polymerization of at least one unsaturated carboxylic acid; and
at least one polyether carrying a free hydroxyl group capable of reacting with a carboxylic function of the said polycarboxylic acid,
the method being characterized in that the catalyst is an alkaline or alkaline-earth salt of a strong protic acid, and wherein the reaction does not lead to cleavage of the polyether chains.
2. The method according to claim 1 , wherein the catalyst is chosen from the group comprising the salts of alkyl-, alkylaryl, aryl, or arylalkylsulfonic acids, alkyl-, alkylaryl-, aryl- or arylalkylphosphoric acids, alkyl-, alkylaryl-, aryl- or arylalkylphosphonic acids, and acid alkyl-, alkylaryl-, aryl- or arylalkylsulfates, the said acids possibly being substituted by halogen or by oxyalkylene groups, in particular alkyl-polyoxyalkylene, alkylaryl polyoxyalkylene and aryl polyoxyalkylene.
3. The method according to claim 2 , wherein the catalyst is chosen from among the salts of alkylsulfonic, arylsulfonic, alkylarylsulfonic or arylalkylsulfonic acids.
4. The method according to claim 3 , wherein the catalyst is a salt of p-toluenesulfonic acid.
5. The method according to claim 4 , wherein the catalyst is chosen from among the sodium, potassium, lithium, calcium and magnesium salts of p-toluenesulfonic acid.
6. The method according to claim 1 , wherein the catalyst is added in a quantity of 0.04% to 10 mole % relative to the number of carboxylic functions of the polycarboxylic acid.
7. The method according to claim 1 , wherein the polycarboxylic acid is chosen from among the homopolymers and copolymers of methacrylic acid and the copolymers of methacrylic acid and maleic acid or maleic anhydride.
8. The method according to claim 1 , wherein the polyether is an alkylether of polyalkylene glycol of formula:
HO-Q-R 3
where:
R 3 is H or an alkyl, aryl, alkylaryl, arylalkyl group with 1 to 20 carbon atoms, and Q is of formula (II):
where:
Y 1 is an alkylene group with 2 carbon atoms;
Y 2 is an alkylene group with 3 carbon atoms;
Y 3 is an alkylene group with 4 carbon atoms;
n is an integer varying from 3 to 500;
m is an integer varying from 0 to 150; and
q is a integer varying from 0 to 150.
9. The method according to claim 8 , wherein the polyether is of formula HO-Q-R 3 in which R 3 is a methyl or ethyl group.
10. The method according to claim 1 , wherein the polyether is of formula HO-Q-R 3 in which Q is of above-mentioned formula (II), in which:
n is an integer varying from 5 to 50;
m is an integer varying from 1 to 25; and
q is 0.
11. The method according to claim 8 , wherein the polyether is of formula HO-Q-R 3 in which Q is of the above-mentioned formula (II) and in which the mean ratio (n/n+m+q) is between 0.2 and 1.
12. The method according to claim 1 , wherein 5 to 80 mole % of polyether are added relative to the number of available carboxylic functions of the polycarboxylic acid.