Answer
H2C=CHC6H5 > H2C=CHCH3 > H2C=CHCI > H2C=CHC02CH3
Most reactive ----------------------------------->Least reactive
Work Step by Step
STEP-1:The alkenes most reactive to cationic polymerization contain electron-donating functional groups that can stabilize the carbocation intermediate.
STEP-2:The reactivity order of substituents in cationic polymerization is similar to the reactivity order of substituted benzenes in electrophilic aromatic substitution reactions