Functionalized, crosslinked, rubber nanoparticles for use in golf ball cores

1. A golf ball comprising:

a core comprising a polymer blend comprising a microgel having a T g of −100° C. to 20° C. formed from a first monomer, a first co-monomer, and a first initiator; and a thermoset rubber material; and

a castable polyurea or polyurethane outer cover layer having a thickness of 0.015 inches to 0.06 inches and comprising a polymer blend comprising a second microgel having a T g of 20° C. to 100° C. formed from a second monomer, a second co-monomer, and a second initiator;

wherein the second microgel is present in an amount sufficient to lower a water vapor transmission rate of the outer cover layer by 30% or greater.

2. The golf ball of claim 1 , wherein the first or second microgel is functionalized with a reactive group.

3. The golf ball of claim 2 , wherein the reactive groups comprise hydroxyl, anhydrides, epoxies, isocyanates, amines, acids, amides, or nitriles.

4. The golf ball of claim 3 , wherein the reactive groups comprise anhydrides, hydroxyl, amines, isocyanates, or epoxies.

5. The golf ball of claim 1 , wherein the outer cover layer has material hardness of 60 Shore D or less.

6. The golf ball of claim 1 , wherein the first or second monomer comprises butadiene, styrene, esters of acrylic or methacrylic acid, acrylic or methacrylic acid, hydroxyethyl acrylate or hydroxyethyl methacrylate, or hydroxybutyl acrylate or hydroxybutyl methacrylate.

7. The golf ball of claim 1 , wherein the first or second co-monomer comprises neopentyl glycol, trimethylol propane, pentaerythritol, triallyl trimellitate, divinyl benzene, di and triacrylates including urethane or urea diacrylate or methacrylate and triacrylate or methacrylate, or hydroxyl terminated polybutadiene.

8. The golf ball of claim 1 , wherein the first or second initiator comprises dicumyl peroxide; t-butylcumyl peroxide; bis-(t-butylperoxyisopropyl)benzene; di-t-butyl peroxide; 2,5-dimethylhexane-2,5-dihydroperoxide; 2,5-dimethylhexyne-3,2,5-dihydroperoxide; dibenzoyl peroxide; bis-(2,4-dichlorobenzoyl) peroxide; t-butyl perbenzoate; organic azo compounds; di- and polymercapto compounds; or mercapto-terminated polysulfide rubbers.

9. The golf ball of claim 8 , wherein the first or second initiator comprises dicumyl peroxide; t-butylcumyl peroxide; bis-(t-butylperoxyisopropyl)benzene; or di-t-butyl peroxide.

10. The golf ball of claim 1 , wherein the T g is from −80° C. to 0° C.

11. The golf ball of claim 1 , wherein the first or second microgel has a swelling index in toluene at 23° C. of 40 or less.

12. The golf ball of claim 1 , wherein the first or second microgel has an average particle diameter of 5 nm to 500 mm.

13. The golf ball of claim 12 , wherein the first or second microgel has an average particle diameter of 40 nm to 100 nm.

14. The golf ball of claim 1 , golf ball comprises an inner cover layer disposed between the outer cover layer and the core.

15. The golf ball of claim 14 , wherein the inner cover layer has a thickness of 0.020 inches to 0.045 inches.