Golf balls including rigid compositions and methods for making same

A golf ball comprising:

• a core formed from a composition comprising:
• a polymer component comprising about 60 percent to about 99 percent polybutadiene by weight of the polymer portion,
• a crosslinking agent, and
• a free-radical initiator;
• and
• a cover having at least one of a dimple coverage of greater than about 60 percent, a hardness from about 35 to 80 Shore D, or a flexural modulus of greater than about 500 psi,
• wherein the polybutadiene comprises at least about 80 percent trans-isomer and no more than about 15 percent vinyl-isomer, and wherein the polybutadiene has an absolute molecular weight of at least about 200,000 and a polydispersity of no more than about 4.

A method of forming a golf ball which comprises:

• mixing a resilient polymer component, a free-radical initiator, a crosslinking agent, and about 60 weight percent to about 99 weight percent controlled-isomer polybutadiene to form an uncrosslinked first mixture having a rigidity as determined by a flexural modulus greater than about 3.5 Mpa, wherein the controlled isomer polybutadiene comprises about 80 percent trans-isomer or greater and about 10 percent or less vinyl-isomer, and wherein the controlled-isomer polybutadiene has an absolute molecular weight of at least about 100,000;
• forming the first mixture into at least two shells in a desired shape, wherein the controlled-isomer polybutadiene imparts sufficient rigidity to the at least two shells to maintain a desired shape until the first mixture is crosslinked;
• providing a center;
• assembling the at least two shells concentrically about the center to form an intermediate layer, wherein the intermediate layer and center together form the golf ball core;
• applying sufficient heat and pressure to the core for a time sufficient to crosslink the first mixture in the shells, thereby curing at least a portion of the golf ball core;
• and
• forming a cover about the golf ball core, wherein the cover at least one of a dimple coverage of greater than about 60 percent, a hardness from about 35 to 80 Shore D, or a flexural modulus of greater than about 500 psi.