The cyclization of cis 1

4 polybutadiene in various solvents (mesitylene

xylene

toluene

benzene and cyclohexane) with the catalyst composed of CH2 CHCH2Cl-AlEt2Cl was studied.The infrared spectra of the cyclized products were investigated.It was shown that the products produced in cyclohexane and mesitylene have infrared spectra identical with those of the original cis-1

4 polybutadiene and the products obtained in other aromatics have infrared spectra different from each other and distinguishing with those of the pqrent cis-1

4 polybutadiene.The analyses of cis-1

4 polybutadiene at the given condition.Apossible reaction scheme involving and electrophilic substitution of carbonium ions for Ar—H of aromatic solvents was proposed.Some experimental facts wereexplained with great satisfaction on the basis of the above mechanism.