A prepolymerized resin prepared by subjecting a composition to a pre-reaction in the presence of a polymerization inhibitor. The composition at least includes bis(vinylphenyl)ethane and polybutadiene. The polybutadiene has a 1,2-vinyl content of 85% or above and a number average molecular weight of less than 3000, wherein the pre-reaction has a conversion rate of between 30% and 90%. During the pre-reaction, components in the composition are partially crosslinked to leave residual vinyl groups. The composition further includes vinyl-containing polyphenylene ether and has a number average molecular weight of between 4,000 and 12,000.