Why is traditional free radical polymerization uncontrollable?

The high concentration of free radicals in traditional free radical polymerization results in uncontrollability. In traditional free radical polymerization systems, the concentration of free radicals is high, and termination reactions of free radicals are prone to occur, resulting in uncontrollable reactions. Adding a special chain transfer agent with a high chain transfer constant to the polymerization system allows degradation and transfer between the growing free radicals and the chain transfer agent, which can reduce the concentration of free radicals.