Over-indexed thermoplastic polyurethane elastomer, method of making, and articles comprising the elastomer

1. A method of making a golf ball, comprising the steps of:

forming a golf ball precursor, the precursor having at least one golf ball layer but not an outer cover layer and

forming an outer cover layer substantially surrounding the golf ball precursor,

wherein the outer cover layer comprises a composition of an over-indexed, crosslinked thermoplastic polyurethane elastomer including crosslinks formed from allyl groups and the thermoplastic polyurethane elastomer is a reaction product formed from reacting a mixture of a diisocyanate and:

(a) an unsaturated diol of the formula

 in which R 1 is a substituted or unsubstituted alkyl group, substituted or unsubstituted aryl group, or substituted or unsubstituted alkyl-aryl group, which may optionally include an ether or ester group or an unsaturated bond in any group, or is H; R 2 is a substituted or unsubstituted alkyl group, substituted or unsubstituted aryl group, or substituted or unsubstituted alkyl-aryl group, which may optionally include an ether or ester group, and R 2 includes an allyl group; and x and y are integers independently having any value from 1 to 10;

(b) a chain extender having at least two reaction sites with isocyanates and having a molecular weight of less than about 450;

(c) a long chain polyol having a molecular weight of between about 500 and about 4,000; and

(d) a sufficient amount of free radical initiator so as to be capable of generating free radicals that induce crosslinking structures in the hard segments by free radical initiation,

wherein the mixture has a stoichiometric excess of isocyanate moieties of at least about 1 mol percent;

wherein forming the outer cover layer further comprises applying the composition over the golf ball precursor and then moisture curing the composition; and

wherein the outer cover layer has a flexural modulus between 400 psi and 900 psi.

2. The method of making the golf ball according to claim 1 , wherein the organic isocyanate moieties to the hydroxyl moieties are in a molar ratio of from about 1.06:1.00 to about 1.18:1.00.

3. The method of making the golf ball according to claim 2 , wherein the molar ratio is from about 1.10:1.00 to about 1.15:1.00.

4. The method of making the golf ball according to claim 1 , wherein the free radical initiator is present in the mixture in a weight ratio of free radical initiator to unsaturated diols of from about 0.1:100 to about 100:100.

5. The method of making the golf ball according to claim 4 , wherein a weight ratio of the crosslinked thermoplastic polyurethane elastomer to the unsaturated diols is about 100:10.

6. The method of making the golf ball according to claim 1 , wherein the unsaturated diol is trimethylolpropane monoallyl ether.

7. The method of making the golf ball according to claim 1 , wherein the free radical initiator generates free radicals through at least one of thermal cleavage and UV radiation cleavage.

8. The method of making the golf ball according to claim 1 , wherein the free radical initiator is selected from the group consisting of peroxides.

9. The method of making the golf ball according to claim 1 , wherein the step of forming a golf ball precursor further comprises the steps of:

forming an inner core layer comprising a highly neutralized acid polymer;

forming an outer core layer substantially surrounding the inner core layer; and

forming an inner cover layer substantially surrounding the outer core layer.

10. The method of making the golf ball according to claim 1 , wherein the applied composition is allowed to partially-cure before the moisture-curing step.

11. A golf ball made according to the method of claim 1 .