The effect of tetrabutylammonium chloride on the kinetics and the mole
cular weight distribution in the cationic polymerization of styrene in
itiated by I-phenylethyl chloride/SnCl4 was investigated. This ''livin
g'' system resembles classic cationic systems but proceeds with a lowe
r instantaneous concentration of active carbocations. The carbenium io
ns form covalent species reversibly. The fraction of unpaired carbocat
ions can be suppressed by addition of salts with common anions. When m
olecular weights are low enough, the transfer reactions cannot be easi
ly detected and polymers with low polydispersities are formed. For thi
s system, the upper limit of the molecular weight control is in the ra
nge of M(n) almost-equal-to 5000 at 20-degrees-C. Polymerization rates
decrease approximately 5 times in the presence of a small amount of s
alt ([salt]/[SnCl4] < 0.1), remain fairly constant until [salt]/[SnCl4
] almost-equal-to 1, and then rapidly decrease at ratios [salt]/[SnCl4
] > 1. The changes in the structure of Lewis acid and anions were moni
tored by Sn-119 NMR. One average signal was observed at low salt conce
ntrations due to a rapid exchange between SnCl4 and SnCl5-. At ratios
[salt]/[SnCl4] > 1 very broad signals were found which were converted
to a sharp signal of the SnCl62- anion at ratios [salt]/[SnCl4] greate
r-than-or-equal-to 2. The unusual kinetics and Sn-119-NMR data were ex
plained by nearly equal ionization ability of SnCl4 and the SnCl5- ani
on and by the formation of inactive oligomeric anions (Cl-[SnCl5-]n) a
t ratios [salt]/[SnCl4] > 1.