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 |
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Authors: | Won Ok Choi Mitsuo Sawamoto Toshinobu Higashimura |
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Abstract: | The 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). |
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