Curable (meth)acrylic resin compositions having enhanced viscosity

1 . A process for the preparation of polymeric particles, having an average diameter from 300 nm to 1200 nm and comprising at least a first inner layer and an outer layer, the process comprising:

(a) forming the first inner layer comprising a cross-linked polymer B; and

(b) forming the outer layer of the polymeric particles comprising a cross-linked polymer A distinct from the cross-linked polymer B,

wherein (b) is carried out by emulsion polymerization of a reaction mixture comprising at least one (meth)acrvlic monomer, a cross-linking monomer A, a polymerization initiator and a chain transfer agent, and

wherein the polymeric particles are obtained in (b) in form of an aqueous dispersion.

2 . The process for the preparation of polymeric particles according to claim 1 , wherein the process further comprises:

(c) processing, by a method selected from the group consisting of freeze coagulation, spray drying, lyophilization, or salting out, the aqueous dispersion obtained in (b) to give the polymeric particles in form of a powder.

3 . A process for the preparation of a (meth)acrylic resin concentrate or of a curable (meth)acrylic resin composition, comprising:

polymeric particles dispersed in a (meth)acrylic resin, wherein the polymeric particles have an average diameter from 300 nm to 1200 nm and comprise at least a first inner layer and an outer layer, the process comprising:

(a) forming the first inner layer comprising a cross-linked polymer B;

(b) forming the outer layer comprising a cross-linked polymer A distinct front the cross-linked polymer B, wherein (b) is carried out by emulsion polymerization of a reaction mixture comprising at least one (meth)acrylic monomer, a cross-linking monomer A, a polymerization initiator and a chain transfer agent,

wherein the polymeric particles are obtained in form of an aqueous dispersion;

(c) freeze coagulation, spray drying, lyophilisation, or salting out of the aqueous dispersion obtained in (b), wherein the polymeric particles are isolated in form of a powder; and

(d) dispersing the powder obtained in (c) in the (meth)acrylic resin.

4 . A process for the preparation of a cured (meth)acrylic resin composition comprising polymeric particles, wherein the polymeric particles have an average diameter from 300 nm to 1200 nm and comprise at least a first inner layer and an outer layer, the process comprising:

(a) forming the first inner layer comprising a cross-linked polymer B;

(b) forming the outer layer comprising a cross-linked polymer A distinct from the cross-linked polymer B, wherein (b) is carried out by emulsion polymerization of a reaction mixture comprising at least one (meth)acrylic monomer, a cross-linking monomer A, a polymerization initiator and a chain transfer agent,

wherein the polymeric particles are obtained in form of an aqueous dispersion;

(c) freeze coagulation, spray drying, lyophilisation or salting out of the aqueous dispersion obtained in (b), wherein the polymeric particles are isolated in form of a powder;

(d) dispersing the powder obtained in (c) in a first (meth)acrylic resin, wherein a (meth)acrylic resin concentrate or a first curable (meth)acrylic resin composition is obtained;

(e) optionally, mixing the (meth)acrylic resin concentrate from (d) with a second (meth)acrylic resin, wherein a second curable (meth)acrylic resin composition is obtained; and

(f) curing the first curable (meth)acrylic resin composition from (d) or the second curable (meth)acrylic resin composition from (e), wherein the cured (meth)acrylic resin composition is obtained.

5 . The process according to claim 1 , wherein the polymeric particles comprise:

from 50.0 wt.-% to 90.0 wt.-% of the cross-linked polymer B; and

from 50.0 wt.-% to 10.0 wt.% of the cross-linked polymer A, based on the weight of the polymeric particles.

6 . The process according to claim 1 , wherein the cross-linked polymer B comprises repeating units derived from

at least 60.0 wt.-% of a C 1-8 -alkyl acrylate; and

0.1 wt.-% to 10.0 wt.-% of a first crosslinking monomer, based on the weight of the cross-linked polymer B and/or

the cross-linked polymer A comprises repeating units derived from

from 65.0 wt.-% to 90.0 wt.-% of a C 1-8 -alkyl methacrylate;

from 34.0 wt.-% to 5.0 wt.-% of a C 1-8 -alkyl acrylate; and

from 0.1 wt.-% to 5.0 wt.-% of a second crosslinking monomer, based on the weight of the cross-linked polymer A.

7 . The process according to claim 1 , wherein

the cross-linked polymer B has a glass transition temperature Tg from −80° C. to −20° C., and

the cross-linked polymer A has a glass transition temperature Tg from 50° C. to 120° C. or a glass transition temperature Tg from −10° C. to 50° C.

8 . The process according to claim 1 , wherein the polymeric particles have an acetone-soluble fraction less than 15.0 wt based on the weight of the polymeric particles.

9 . The process according to claim 1 , wherein the chain transfer agent in (b) is a compound having at least one thiol group.

10 . The process according to claim 1 , wherein the reaction mixture in (b) comprises from 0.1 wt.-% to 0.5 wt. of the chain transfer agent, based on the total weight of the cross-linked polymer A in the polymeric particles.

11 . The process according to claim 1 , wherein the cross-linked polymer B and the cross-linked polymer A both comprise repeating units derived from allyl methacrylate.

12 . The process according to claim 3 , wherein the (meth)acrylic resin comprises from 50 wt.-% to 100 wt.-% of at least one monomeric (meth)acrylate, based on the weight of the (meth)acrylic resin.

13 . The polymeric particles obtainable by the process according to claim 1 .

14 . The curable (meth)acrylic resin composition obtainable by the process according to claim 3 .

15 . The cured (meth)acrylic resin composition obtainable by the process according to claim 4 .

16 . The process according to claim 9 , wherein the chain transfer agent is at least one compound selected from the group consisting of thioglycolic acid, pentaerythritol tetrathioglycolate, 2-mercaptoethanol, 2-ethylhexylthioglycolate and a C 1-20 -alkyl thiol.

17 . The process according to claim 16 , wherein the chain transfer agent is at least one C 1-20 -alkyl thiol selected from the group consisting of n-dodecylthiol or tert-dodecylthiol.

18 . A method for producing a material, the method comprising:

providing the curable (meth)acrylic resin composition according to claim 14 , wherein the material is selected from the group consisting of a pressure-sensitive adhesive, a material for dental application and a structural adhesive.

19 . A method for producing a material, the method comprising

providing the cured (meth)acrylic resin composition according to claim 15 , wherein the material is selected from the group consisting of an advanced composite, a material used for electronics, a coating material, a pressure-sensitive adhesive, a material for dental application and a structural adhesive.