LIVING CATIONIC POLYMERIZATION OF VINYL ETHERS BY ELECTOPHILE LEWIS ACID INITIATING SYSTEMS .6. LIVING CATIONIC POLYMERIZATION OF ISOBUTYL VINYL ETHER BY RCOOH/LEWIS ACID INITIATING SYSTEMS - EFFECTS OF CARBOXYLATE IONS AND LEWIS ACID ACTIVATORS

A series of acetic acid derivatives (RCOOH; R = CF3, CCl3, CHCl2, CH2Cl, CH3), coupled with zinc chloride (ZnCl2), induced living cationic polymerization of isobutyl vinyl ether (IBVE) in toluene at 0-degrees-C. Except for R = CH3, the number-average molecular weights (MBARn) of the polymers were directly proportional to monomer conversion and in excellent agreement with the calculated values, assuming that one polymer chain forms per unit IBVE-RCOOH adduct [CH3CH(OiBu)OCOR (1)]. The molecular weight distribution of the polymers was very narrow (MBARw/MBARn less-than-or-equal-to 1.1) for R = CF3 and CCl3; it gradually broadened (MBARw/MBARw = 1.1 --> 1.3) as the electron-withdrawing power of the substituent R decreased. The stronger RCOOH, the faster the reaction was. When a stronger Lewis acid activator, ethylaluminum dichloride (EtAlCl2), was employed in place of ZnCl2 in the 1/ZnCl2 system, a fast, conventional, nonliving polymerization occurred. However, this system indeed led to living polymerization of IBVE in the presence of an excess of 1,4-dioxane. Thus, the living nature was clearly affected by the nucleophilicity of acetate ions and the acidity of Lewis acid activators. The effects of RCOOH (initiator) and Lewis acid (MX(n);activator) demonstrated the importance of the nucleophilic interaction between the growing carbocation and the counteranion (-OCOR...MX(n)), and thereby the relation between "stabilization of a carbocation by a counteranion" and "stabilization of a carbocation by an externally added base", both of which are principles for living cationic polymerization proposed by us, was clarified.