Inhibitors act by removing free radicals from the system. Depending on the relative reactivities of the inhibitor and the radical concerned, the free radicals may be removed either as fragments of initiator decomposition or as very short chain radicals.
Commonly encountered inhibitors include nitrobenzene
NO,
/WW СН,— CHX
and Ferric chloride
/WWCH2-CHX + FeCI3 ————— 1 /WWCH-CHXCI + FeCI2
ЛЛ/W CH2— CHXCI + FeCI2 ——- ► /sawCH2=CHX + HCI + FeCI3
Figure 1-16
The radical formed with benzoquinone is resonance stabilised and thus will not initiate polymerisation.
о
II
0 + CH2— CHX —————- ► СН,— CHX — о
II
о
p-benzoquinone
resonance stabilised radical
Figure 1-17