The substituted aryl vinyl sulfoxides p-[RC(6)H(4)S(O)CH=CH2] (8a-c, R = F, Cl, OMe) were prepared and polymerized in the presence of(3-methyl-1,1-diphenylpentyl)lithium (MDPPLi, 1) as anionic initiator to give the corresponding poly(aryl vinyl sulfoxides) 9a-c. Upon thermolysis of compounds 9 between 70 and 120 degrees C, the arenesulfenic acids (10) were eliminated via an Ei mechanism generating all-trans-polyacetylene (PA, 11). The formation of all-trans-PA was monitored on-line by means of near-infrared-excited Fourier-transform (FT)-Raman spectroscopy. The kinetics of the reaction were found to be first-order at conversions above approximately 10%. On the basis of the rate constants determined for the thermolysis of 9a-c at 70, 80, 90, 100, and 120 degrees C, the relative reactivities of 9a-c, and thus the influence of the substituents R on the rate of the PA formation, could be quantitatively estimated, and the following ratios were found : 9a (R = F):9b (R = Cl):9c (R = OMe) = 1.0 +/- 0.1:2.2 +/- 0.3:0.8 +/- 0.1.