Question

8. Predict the order of reactivity (and briefly justify your prediction):
a) in cationic polymerization: styrene, p-nitrostyrene, p-dimethylaminostyrene, p-methylstyrene

b) in anionic polymerization: styrene, p-nitrostyrene, p-dimethylaminostyrene, p-methylstyrene

Answer 1

a) To find the order of reactivity, we need to see the nature of substituents attached to the ring. Nitro is electron withdrawing group and dimethyl amino and methyl are electron donating groups. The electron donating groups stabilise the cation formed in the cationic polymerisation and thus fastens the reaction. So, dimethyl amino and methyl groups will fasten the reaction and out of these two, methyl will be more electron donating than dimethyl amino because of the tertiary amines are moderately activating group. So, the order of reactivity is:

p-methylstyrene > p-dimethylamino styrene > styrene > p-nitrostyrene

b) The opposite is true for the anionic polymerisation. In here, the electron donating effect will destabilise the anion formed during anionic polymerisation. The nitro group will stabilise the anion most. So, the order is:

p-methylstyrene < p-dimethylamino styrene < styrene < p-nitrostyrene