Lifetime of living polymers in cationic polymerization. III. Living polymerization of isobutyl vinyl ether initiated by a cationogen/etalcl2 system in the presence of 1,4‐dioxane as an added base

Abstract

AbstractThe concentration ([P*]) and lifetime (half‐life) of the propagating species were measured in the living cationic polymerization of isobutyl vinyl either initiated by the 1‐(isobutoxy) ethyl acetate [CH3COOCH (OiBu) CH3]/ethylaluminum dichloride (EtAlCl2) system in the presence of excess 1,4‐dioxane in n‐hexane at 0 to +70°C; the acetate serves as a cationogen that forms an initiating vinyl ether‐type carbocation. The measurements were based on the end‐capping reaction with sodiomalonic ester [Na⊕⊖CH (COOEt)2], which was shown to react rapidly and quantitatively with the living growing end. From the terminal malonate group of the quenched polymers, [P*] was determined by 1H‐NMR spectroscopy. In contrast to its constancy during the polymerization, [P*] progressively decreased with time after the complete consumption of monomer. The postpolymerization decay was first order in [P*], and the lifetime (half‐life) of the living end was determined from the decay rate constant. The lifetime increased on lowering polymerization temperature, decreasing EtAlCl2 concentration, and increasing dioxane concentration. In particular, the “base‐stabilized” living ends, generated by the CH3COOCH (OiBu) CH3/EtAlCl2/dioxane system, turned out extremely stable at 0°C (half‐life > 5 days in the absence of monomer).