Dual core golf ball having positive-hardness-gradient thermoplastic inner core and positive-hardness-gradient thermoset outer core layer

A golf ball comprising:

• a core comprising a thermoplastic inner core and a thermoset outer core layer, the inner core having a surface hardness of about 40 to 80 Shore C and a center hardness of about 30 to 75 Shore C and is less than the surface hardness to define a first positive hardness gradient;
• and
• a cover comprising an inner cover layer and an outer cover layer;
• wherein the thermoplastic inner core comprises a highly-neutralized ionomer comprising:
• an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer comprising alkyl acrylate or methacrylate;
• a plasticizer;
• an organic acid or salt thereof;
• and
• a cation source present in an amount sufficient to neutralize from about 70 to about 100% of all acid groups present in the material;
• and
• the outer core layer comprises a polybutadiene rubber and has a surface hardness greater than an interior hardness to define a positive hardness gradient of less than 25 Shore C.