In the context of free radical polymerization, which of the following substances is primarily responsible for generating free radicals that initiate the polymerization process?

In free radical polymerization the initiator is the key substance that produces the first radicals, and common initiators include benzoyl peroxide or azobisisobutyronitrile. These molecules undergo homolytic cleavage, often triggered by heat, to form two radical species. Those radicals then attack a monomer’s double bond, starting the chain reaction. For example, heating benzoyl peroxide splits into two benzoyloxy radicals, which immediately add to a styrene monomer and begin the polymer chain.