The effect of a-methyl styrene dimer (AMSD), which is used as a scorch retarder, on the reaction mechanisms of the chemical crosslinking of polyethylene (PE) with dicumyl peroxide (DCP) at high temperatures was investigated using electron spin resonance. When AMSD was added to PE containing DCP, the AMSD radical was observed; however, the PE alkyl radical or allyl radical presence was not detected. At 145 degreesC, crosslinking was obstructed as a result of the reaction between AMSD and alkyl radicals. As the temperature increased, AMSD fragmented to form 2-phenyl-2-propyl and double bonds in PE. This generation of double bonds, however, accelerated crosslinking at 180 degreesC and was more effective than when AMSD was not present.