In both types of processes, the corresponding reactive intermediates (radicals, ions) are permanently regenerated, and thus they proceed by a self-propagating chain mechanism.
ɪn bˈoʊθ tˈaɪps ʌv pɹˈɑːsɛsᵻz, ðə kˌɔːɹɪspˈɑːndɪŋ ɹɪˈæktɪv ˌɪntɚmˈiːdiəts ɹˈædɪkəlz, ˈaɪɑːnz ɑːɹ pˈɜːmənəntli ɹiːdʒˈɛnɚɹˌeɪɾᵻd, ænd ðˈʌs ðeɪ pɹəsˈiːd baɪ ɐ sˈɛlfpɹˈɑːpɐɡˌeɪɾɪŋ tʃˈeɪn mˈɛkənˌɪzəm.