Cationic polymerizations of p-chlorostyrene (pClSt), p-(chloromethyl)styrene (pCMS), and p-(acetoxymethyl)styrene (pAcOMS) were examined with HCl-vinyl monomer adduct (1; CH3CH(R)Cl; 1a : R = Ph, 1b : R = OCH2CH2Cl)/SnX(4) initiating systems in the presence or absence of an ammonium salt. Living polymers were obtained from pClSt using the 1-phenylethyl chloride (1a)/SnCl4/nBu(4)NCl initiating system in CH2Cl2 at 0 degrees C. Thus, without the ammonium salt, the 1a/SnCl4 system led to a conventional cationic polymerization to give polymers with bimodal molecular weight distributions (MWDs), but in the presence of nBu(4)NCl, polymers with unimodal and very narrow MWDs ((M) over bar(w)/(M) over bar(n), approximate to 1.1) were obtained. The number-average molecular weight ((M) over bar(n); by H-1 NMR) of the polymers increased in direct proportion to conversion, agreed with the calculated value assuming that one polymer chain forms per molecule of 1a, and further increased on addition of a fresh pClSt feed into a completely polymerized solution. More important, living poly(pClSt) with narrow MWDs were also obtained even at +25 degrees C, where the corresponding polymerization of styrene is not living. This is the first example of living polymerization of pClSt at room temperature. Living polymers were also obtained by initiating the polymerization with the vinyl ether adduct (1b), and end-functionalized polymers of pClSt could be prepared by a functionalized vinyl ether adduct in a similar way. In contrast to pClSt, neither pCMS nor pAcOMS was polymerized in a living fashion.