LIVING CATIONIC POLYMERIZATION OF ISOBUTYL VINYL ETHER BY ME3SII LEWIS ACID SYSTEMS IN THE PRESENCE OF ACETONE - INITIATION VIA A SILYLOXYCARBOCATION

In the presence of acetone, the trimethylsilyl iodide/zinc iodide (Me3SiI/ZnI2) initiating system induced living cationic polymerization of isobutyl vinyl ether in toluene below 0 °C. The number-average molecular weight [inline formula omitted] of the polymers was directly proportional to monomer conversion and in excellent agreement with the calculated value, assuming that one polymer chain forms per Me3Sil molecule. Accordingly, the Ma values (at 100% conversion) were inversely proportional to the initial concentration of Me3Sil but were independent of the initial Znl2concentration; the molecular weight distribution of the polymers stayed very narrow [inline formula omitted] throughout the reaction. The rate of the living polymerization was in first order with respect to monomer, Me3Sil, and Znl2, respectively. When iodine (I2) was used instead of Znl2, living cationic polymerization also occurred in toluene at -40 °C. Thus, in the presence of acetone, the Me3Sil/Lewis acid (Znl2 or I2) system mediated a new type of living cationic polymerization where the initiation is via a silyloxycarbocation (Me3SiOC+Me2·l-) that is generated by a reaction of Me3Sil with acetone. The product polymers were shown to carry one silyloxyl terminal group per chain, the acidolysis of which gave a hydroxyl terminal group. © 1990, American Chemical Society. All rights reserved.