LIVING CATIONIC POLYMERIZATION OF STYRENE IN THE PRESENCE OF TETRABUTYLAMMONIUM SALTS

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.