Highly-neutralized thermoplastic copolymer center for improved multi-layer core golf ball

1. A golf ball comprising:

a center having a diameter of from 0.80 inches to 1.40 inches, a compression of from 62 to 107, and formed from a composition comprising:

a copolymer of ethylene and an α, β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates and methacrylates;

an organic acid or salt thereof present in an amount of from 5 wt% to 50 wt %, based on the total weight of the copolymer and organic acid or salt thereof; and

a cation source present in an amount sufficient to neutralize greater than 80% of all acid groups present in the composition;

an outer core layer having a thickness of 0.090 inches or greater and formed from a composition having a Shore D hardness of from 40 to 70; and

a cover formed from a polyurethane;

wherein the golf ball has a first coefficient of restitution of 0.81 or greater when measured at an incoming velocity of 125 ft/s and a second coefficient of restitution of 0.76 or greater when measured at an incoming velocity of 160 ft/s; and

wherein a sphere resulting from a combination of the center and the outer core layer has a compression of 80 or greater; and

wherein the Shore D hardness of the center composition is less than the Shore D hardness of the outer core layer composition.

2. The golf ball of claim 1 , wherein the cation source is present in an amount sufficient to neutralize from 90% to 100% of the acid groups of the copolymer.

3. The golf ball of claim 1 , wherein the cation source is present in an amount sufficient to neutralize 100% of the acid groups of the copolymer.

4. The golf ball of claim 1 , wherein the polyurethane cover composition has a Shore D hardness of from 45 to 60.

5. The golf ball of claim 1 , wherein the cover has a thickness of from 0.02 inches to 0.04 inches.

6. The golf ball of claim 1 , wherein the center composition has a Shore D hardness of from 42 to 51.

7. The golf ball of claim 1 , wherein the cation source is selected from the group consisting of metal cations of lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, and combinations thereof.

8. The golf ball of claim 1 , wherein the cation source comprises magnesium.

9. The golf ball of claim 1 , wherein the compression of the center is 80 or greater.

10. The golf ball of claim 1 , wherein the salt of an organic acid comprises an organic acid selected from the group consisting of aliphatic organic acids, aromatic organic acids, saturated mono- or multi-functional organic acids, unsaturated mono- or multi-functional organic acids, and multi-unsaturated mono- or multi-functional organic acids.

11. The golf ball of claim 1 , wherein the salt of an organic acid comprises stearic acid, behenic acid, erucic acid, oleic acid, linoelic acid or dimerized derivatives thereof.

12. The golf ball of claim 1 , wherein the salt of an organic acid comprises oleic acid.

13. The golf ball of claim 1 , wherein the salt of an organic acid comprises a cation selected from the group consisting of barium, lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium, strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin, and calcium.

14. The golf ball of claim 1 , wherein the salt of an organic acid comprises magnesium.

15. The golf ball of claim 1 , wherein the golf ball additionally comprises an inner cover layer.

16. The golf ball of claim 15 , wherein the inner cover layer is formed from a thermoplastic composition comprising a polymer selected from the group consisting of ionomeric copolymers and terpolymers, ionomer precursors, grafted metallocene-catalyzed polymers, high-crystalline acid polymers and their ionomers, and cationic ionomers.

17. The golf ball of claim 1 , wherein the thickness of the outer core layer is from 0.090 inches to 0.180 inches.