Anionic surfactants

1. An anionic surfactant of the formula (1):

R 2 —Y—(O)C—(HR)C—C(HR 1 )—C(O)—(OA) n —X  (I)*

wherein one of R and R 1 is a C 6 to C 22 linear or branched alkyl or alkenyl, and the other is hydrogen;

Y is O, or NH, or —NH—CH 2 —C(═CH 2 )—, or —N(CH 2 —CR 3 (═CH 2 ))—CH 2 —C(═CH 2 )— where R 3 is hydrogen or methyl;

when Y is O, R 2 is hydrogen, or a salt, or a C 1 to C 6 linear or branched alkyl, or an optionally substituted C 3 to C 10 linear or branched alkenyl;

when Y is NH, or —NH—CH 2 —C(═CH 2 )—, or —N(CH 2 —CR 3 (═CH 2 ))—CH 2 —C(═CH 2 )— where R 3 is hydrogen or methyl, R 2 is hydrogen or methyl;

OA is an oxyalkylene group;

n is 2 to 100; and

X is a group comprising at least one acidic H atom, or a salt thereof.

2. An anionic surfactant according to claim 1 wherein one of R and R 1 is a C 12 to C 20 alkenyl group.

3. An anionic surfactant according to claim 1 where n is in the range from 5 to 30.

4. An anionic surfactant according to claim 1 wherein X comprises at least one sulphur atom.

5. An anionic surfactant according to claim 1 wherein R 2 is an group of formula —CH2—C(═CH2)—R 4 where R 4 is hydrogen or methyl; or a group of formula —R 5 —O—C(O)—C(═CH 2 )—R 6 where R 5 is hydrogen or methyl, and R 6 is a C 2 to C 6 linear or branched alkyl.

6. A method of free radical initiated addition polymerisation of at least one ethylenically unsaturated monomer in the presence of a surfactant comprising adding at least one anionic surfactant of the formula (I):

R 2 —Y—(O)C—(HR)C—C(HR 1 )—C(O)—(OA) n —X  (1)

wherein one of R and R 1 is a C 6 to C 22 linear or branched alkyl or alkenyl, and the other is hydrogen;

Y is O, or NH, or —NH—CH 2 —C(═CH 2 )—, or —N(CH 2 —CR 3 (═CH 2 ))—CH 2 —C(═CH 2 )— where R 3 is hydrogen or methyl;

when Y is O, R 2 is hydrogen, or a salt, or a C 1 to C 6 linear or branched alkyl, or an optionally substituted C 3 to C 10 linear or branched alkenyl;

when Y is NH, or —NH—CH 2 —C(═CH 2 )—, or —N(CH 2 —CR 3 (═CH 2 ))—CH 2 —C(═CH 2 )— where R 3 is hydrogen or methyl, R 2 is hydrogen or methyl;

OA is an oxyalkylene group;

n is 2 to 100; and

X is a group comprising at least one acidic H atom, or a salt thereof, to a polymerization medium.

7. A method according to claim 6 wherein the ethylenically unsaturated monomer(s) is or comprises at least one vinyl monomer.

8. A method according to claim 7 wherein the vinyl monomer(s) represent at least 60% by weight of the ethylenically unsaturated monomer(s).

9. A method according to claim 6 wherein the at least one anionic surfactant of the formula (I) is used for a seed stage, and at least one non-ionic surfactant of the formula (II) below is used for a particle growth stage in emulsion polymerisation:

R 2 —Y—(O)C—(HR)C—C(HR 1 )—C(O)—(OA) n —Z—R 9   (II)

wherein R, R 1 , R 2 , Y, OA and n are as defined for the anionic surfactant of formula (I), and Z is O, or NH, or —NH—CH 2 —C(═CH 2 )—, or —N(CH 2 —CR 10 (═CH 2 ))—CH 2 —C(═CH 2 )— where R 10 is hydrogen or methyl;

when Z is O, R 9 is hydrogen, or a C 1 to C 6 linear or branched alkyl, or an optionally substituted C 3 to C 10 linear or branched alkenyl;

when Z is NH, or —NH—CH 2 —C(═CH 2 )—, or —N(CH 2 —CR 10 (═CH 2 ))—CH 2 —C(═CH 2 )— where R 10 is hydrogen or methyl, R 9 is hydrogen or methyl.

10. A process for emulsion polymerization comprising adding at least one anionic surfactant of the formula (I):

R 2 —Y—(O)C—(HR)C—C(HR 1 )—C(O)—(OA) n —X  (I)

wherein one of R and R 1 is a C 6 to C 22 linear or branched alkyl or alkenyl, and the other is hydrogen;

Y is O, or NH, or —NH—CH 2 —C(═CH 2 )—, or —N(CH 2 —CR 3 (═CH 2 ))—CH 2 —C(—CH 2 )— where R 3 is hydrogen or methyl;

when Y is O, R 2 is hydrogen, or a salt, or a C 1 to C 6 linear or branched alkyl, or an optionally substituted C 3 to C 10 linear or branched alkenyl;

when Y is NH, or —NH—CH 2 —C(═CH 2 )—, or —N(CH 2 —CR 3 (═CH 2 ))—CH 2 —C(═CH 2 )— where R 3 is hydrogen or methyl, R 2 is hydrogen or methyl;

OA is an oxyalkylene group;

n is 2 to 100; and

X is a group comprising at least ones acidic H atom, or a salt thereof, to a polymerization medium.

11. An anionic surfactant according to claim 2 where n is in the range from 5 to 30.