Methods for cross-linking thermoplastic polyurethane covers for golf balls

1. A golf ball comprising a core, an outer cover layer, and an intermediate layer disposed between the core and the outer cover layer, wherein the outer cover layer is formed from a composition comprising:

a thermoplastic polyurethane;

a multi-functional hydroxyl compound; and

a multi-functional compound selected from the group consisting of multi-functional amines, multi-functional imines, multi-functional isocyanates, and combinations of two or more thereof.

2. The golf ball of claim 1 , wherein the multi-functional hydroxyl compound is selected from the group consisting of polyvinyl alcohol, hydroxyl-functional acrylics, polyethylene glycol, polypropylene glycol, starch-based polymers, cellulosic polymers, polyether polyols, polyester polyols, polylactic acid, and combinations of two or more thereof.

3. The golf ball of claim 1 , wherein the multi-functional compound includes an isocyanate selected from the group consisting of 4,4′-methylene diphenyl diisocyanate; 2,4′-methylene diphenyl diisocyanate; toluene 2,4-diisocyanate; toluene 2,6-diisocyanate; 4,4′-dicyclohexylmethane diisocyanate; p-phenylene diisocyanate; and isophorone diisocyanate; and homopolymers and copolymers and blends thereof.

4. The golf ball of claim 1 , wherein the multi-functional compound includes polyaziridine.

5. The golf ball of claim 1 , wherein the multi-functional compound includes an amine selected from the group consisting of diethylene toluene diamine, mono or di-isopropanolamine, methy diethanol amine, methylene-bis-chloro diethylaniline, and combinations of two or more thereof.

6. The golf ball of claim 1 , wherein the core comprises an inner core layer formed from a first rubber composition and an outer core layer formed from a second rubber composition.

7. The golf ball of claim 6 , wherein the intermediate layer is formed from an ionomer composition selected from the group consisting of salts of O/X- and O/X/Y-type acid copolymers and mixtures thereof, wherein O is an α-olefin, X is a C 3 -C 8 α,β-ethylenically unsaturated carboxylic acid, and Y is a softening monomer.

8. The golf ball of claim 1 , wherein the golf ball consists of the core, the intermediate layer, and the outer cover layer, and wherein the core consists of a single layer formed from a rubber composition.

9. The golf ball of claim 8 , wherein the intermediate layer is formed from an ionomer composition selected from the group consisting of salts of O/X- and O/X/Y-type acid copolymers and mixtures thereof, wherein O is an α-olefin, X is a C 3 -C 8 α,β-ethylenically unsaturated carboxylic acid, and Y is a softening monomer.