Microgel compositions

1. A composition, comprising a plurality of microgel particles wherein adjacent microgel particles are covalently bound together as a result of a free-radical coupling reaction of vinyl-containing moieties of formula -L-B grafted onto the surfaces of unreacted microgel particles, and wherein the free-radical coupling occurs while the microgel particles are in a swollen state and in the absence of bridging aggregation, wherein:

B is a group comprising a vinyl functional group; and

L is a linking group between B and the unreacted microgel particles to which L-B is grafted;

wherein the microgel particles comprises a co-polymerized polymer particle defined by formula I:

Poly(Y-co-P-co-X)  (I)

wherein:

P is a pH-responsive co-monomer;

X is a functional cross-linking co-monomer;

Y is a hydrophobic co-monomer; and

wherein X constitutes 0.1 to 2 wt % of all of co-monomers P, X, and Y, and wherein the microgel particles are pH responsive in that prior to the free-radical coupling reaction, the microgel particles underwent a pH dependent transition from a collapsed state to a swollen state, and wherein the microgel particles in the composition are in the form of a hydrated gel, and further wherein the average diameter of the microgel particles in the swollen state is at least 100% greater than the average diameter of microgel particles in the collapsed state;

wherein: the microgel particles comprise carboxylic acid groups and each vinyl-containing moiety of formula L-B is formed by reaction of one of said carboxylic acid groups with an epoxide group of glycidyl methacrylate to form an ester of the carboxylic acid group; and

wherein:

the vinyl-containing moieties of formula -L-B are present at a concentration of between 1.8 and 60 mol. % with respect to all of the co-monomers of the microgel particles; and wherein the composition is buffered at pH 6.5-8.

2. The composition according to claim 1 , wherein the microgel particles comprise a polymer combination selected from the group consisting of: poly(ethylacrylate/methacrylic acid/ethyleneglycol dimethacrylate), poly(methylmethacrylate/methacrylic acid/ethyleneglycol dimethacrylate), poly(ethylacrylate/methacrylic acid/1,4-butanediol diacrylate) and poly(methylmethacrylate/methacrylic acid/1,4-butanediol diacrylate).

3. The composition according to claim 1 , wherein the elastic modulus (G′) of the composition of claim 1 is higher than a composition of the corresponding non-covalently bound microgel particles.

4. The composition according to claim 1 , wherein the elastic modulus (G′), as measured by dynamic rheology, is greater than 10 Pa.

5. The composition according to claim 4 , wherein the composition has a critical strain value (γ*) of 2 to 500%, wherein the critical strain value (γ*) is the value for the strain, measured by a rheometer, at which the elastic modulus (G′) first reaches a value of 95% of that measured when γ=1.0%.

6. The composition according to claim 1 , wherein the composition is non-porous.

7. The composition according to claim 1 , wherein the adjacent microgel particles of the compositions are in contact with each other.

8. The composition according to claim 1 , wherein the pH-responsive co-monomer (P) of the microgel particles comprises a substituted acrylic acid.

9. The composition according to claim 1 , wherein the functional cross-linking co-monomer contains two or more double bonds that are susceptible to chain addition through free-radical polymerization.

10. The composition according to claim 1 , wherein the composition further comprises sodium hydroxide or potassium hydroxide.

11. The composition according to claim 10 , wherein the composition further comprises ammonium persulfate.

12. The composition according to claim 1 , wherein the composition further comprises ammonium persulfate.

13. The composition according to claim 12 , further comprising ascorbic acid.

14. The composition according to claim 1 , wherein the vinyl-containing moieties of formula -L-B are present at a concentration of between 3.0 and 30 mol. % with respect to all of the co-monomers of the microgel particles.

15. The composition according to claim 1 , wherein the vinyl-containing moieties of formula -L-B are present at a concentration of between 5.8 and 30 mol. % with respect to all of the co-monomers of the microgel particles.

16. The composition according to claim 1 , wherein the composition is buffered at pH 6.6-7.5.

17. The composition according to claim 1 , wherein the microgel particles comprise poly(methylmethacrylate/methacrylic acid/ethyleneglycol dimethacrylate).

18. The composition according to claim 1 , wherein the composition further comprises sodium hydroxide and ammonium persulfate.

19. The composition according to claim 1 , wherein the composition further comprises potassium hydroxide and ammonium persulfate.