In the context of addition polymerization, what happens during the propagation stage?

During the propagation stage of addition polymerization, additional monomers are added to the growing chain. This process involves the sequential addition of these monomer units to the reactive site of a growing polymer chain. Once a reactive species, such as a free radical, initiates the reaction, it will react with a monomer, forming a larger reactive intermediate. This newly formed intermediate can then react with another monomer, continuing the chain growth.

The significance of this stage lies in its ability to rapidly increase the length of the polymer chain, which ultimately contributes to the physical properties of the final polymer product. As each monomer is added, the chain becomes more complex and exhibits characteristics specific to the polymer being formed. Thus, this continuous addition of monomers to the growing chain is the defining feature of the propagation stage, making the correct answer the addition of additional monomers to the growing chain.