AQUEOUS DISPERSION OF POLYMER PARTICLES AND USES THEREOF AS AN ADHESIVE COMPOSITION

1 . An adhesive composition comprising an aqueous dispersion of polymer particles obtained by emulsion polymerization of a monomeric composition comprising:

a) ethylenically unsaturated monomers;

b) at most 0.2% by weight of chain transfer agent based on the total weight of the ethylenically unsaturated monomers;

c) a surfactant; and

d) an initiator;

wherein the polymer particles have been subjected to a post-polymerization treatment with a peroxide in an amount of at least 0.008 meq effective peroxide/g of polymer.

2 . The adhesive composition according to claim 1 , wherein the peroxide is selected from a persulfate, hydrogen peroxide, an organic hydroperoxide, a peracid, or a mixture thereof.

3 . The adhesive composition according to claim 1 , wherein the amount of peroxide used in the post-polymerization treatment is at least 0.010, at least 0.015, at least 0.020, at least 0.025, at least 0.030, or at least 0.035, meq effective peroxide/g of polymer.

4 . The adhesive composition according to claim 1 , wherein the post-polymerization treatment is carried out either:

in the absence of a reducing agent; or

in the presence of a reducing agent and the equivalent ratio between the peroxide and the reducing agent is at least 2.0.

5 . The adhesive composition according to claim 1 , wherein the post-polymerization treatment is carried out at a temperature of at least 60° C.

6 . The adhesive composition according to claim 1 , wherein the post-polymerization treatment is carried out until 80% of the peroxide is decomposed.

7 . The adhesive composition according to claim 1 , wherein the monomeric composition comprises a monomer a) which a C1-C12 alkyl (meth)acrylate or a mixture of C1-C12 alkyl (meth)acrylates.

8 . The adhesive composition according to claim 1 , wherein the total amount of monomer a) in the monomeric composition is at least 60%, at least 65%, at least 70%, at least 75% or at least 80%, by weight based on the total weight of the ethylenically unsaturated monomers.

9 . The adhesive composition according to claim 1 , wherein the monomeric composition further comprises one or more monomers selected from:

monomer b) which is a vinyl aromatic monomer;

monomer c) which is an ethylenically unsaturated monomer comprising an acidic group or a salt thereof;

monomer d) which is a vinyl ester of a carboxylic acid;

monomer e) which is a monomer bearing a functional group selected from hydroxy, epoxy, carbonyl and a nitrogen-containing functional group;

monomer f) which is a vinyl ether;

monomer g) which is a conjugated diene;

monomer h) which is an alpha-olefin;

monomer i) which is a vinyl halide;

monomer j) which is an alkoxysilane monomer;

and mixtures thereof.

10 . The adhesive composition according to claim 1 , wherein the chain transfer agent is a thiol.

11 . The adhesive composition according to claim 1 , wherein the monomeric composition is free of chain transfer agent.

12 . The adhesive composition according to claim 1 , wherein the total amount of chain transfer agent in the monomeric composition is from 0.005 to 0.2% by weight based on the total weight of the ethylenically unsaturated monomers.

13 . The adhesive composition according to claim 1 , wherein the polymer particles have a Tg of −65 to −10° C.

14 . The adhesive composition according to claim 1 , wherein the aqueous dispersion has a gel content of 50 to 90%.

15 . The adhesive composition according to claim 1 , wherein the adhesive composition further comprises a tackifier resin.

16 . The adhesive composition according to claim 1 , wherein the adhesive composition is a pressure-sensitive adhesive composition.

17 . A process for the preparation of an adhesive composition comprising the following steps:

i) preparation of an aqueous dispersion of polymer particles by emulsion polymerization of a monomeric composition as defined in claim 1 ;

ii) adding a peroxide to the aqueous dispersion of polymer particles obtained in step a) in an amount of at least 0.008 meq effective peroxide/g of polymer present in the aqueous dispersion of polymer particles.

18 . A process for increasing the adhesion of an adhesive composition wherein the process comprises a post-polymerization treatment of an aqueous dispersion of polymer particles with a peroxide in an amount of at least 0.008 meq effective peroxide/g of polymer present in the aqueous dispersion of polymer particles.

19 . A process for producing an adhesive article, the process comprising coating a substrate with the adhesive composition of claim 1 .

20 . An adhesive article comprising a substrate coated with the adhesive composition of claim 1 .