A linear unsaturated co-dimer of styrene andp-chlorostyrene, 1 -phenyl-3-(4-chlorophenyl)-lbutene (2), was preferentially produced by reaction of 1-(4-~hlorophenyl)ethyl diphenyl phosphate (1) with styrene. The reaction was found to be extraordinarily accelerated by addition of trifluoromethanesulfonic acid. 1-(4-Chlorophenyl)ethyl acetate reacts readily with styrene in the presence of trifluoromethanesulfonic acid to afford 2 in good yields, whereas the acetate is inert toward styrene in the absence of a super acid. Cl 1 4 Makromol. Chem. 185, No.