Which stage of addition polymerization involves the initial attack of a radical on a monomer?

The stage of addition polymerization referred to in the question is initiation. During this phase, a radical species comes into contact with a monomer, resulting in the formation of a new radical that allows the polymerization process to begin. The initial radical can be generated through various means, such as heat, light, or chemical initiators, and it is this radical that attacks the monomer, resulting in the opening of a double bond.

This reaction marks the crucial start of the polymerization chain reaction, leading to subsequent steps. Following initiation, the process moves into propagation, where the growing polymer chain continues to react with more monomers, adding them one by one. Initiation is essential for creating the first reactive site that allows the chain growth process to proceed, thus making it a vital stage in the overall addition polymerization mechanism.