The first step of initiation by benzoyl peroxide, $\mathrm{C}{}_6\mathrm{H}{}_5\mathrm{COO}-\mathrm{OOCC}{}_6\mathrm{H}{}_5$, in an addition polymerisation is

1. Aheterolysis of the O-O bond to give $\mathrm{C}{}_6\mathrm{H}{}_5\mathrm{COO}{}^{-}$ and $\mathrm{C}{}_6\mathrm{H}{}_5\mathrm{COO}{}^{+}$
2. Bloss of $\mathrm{N}{}_2$ to give two alkyl radicals
3. Cprotonation of the peroxide to give a carbocation
4. Dhomolysis of the O-O bond to give two benzoyloxy radicals $\mathrm{C}{}_6\mathrm{H}{}_5\mathrm{COO}\cdot$