Radiation-induced cationic polymerization of vinyl ethers in solution: 2. Polymerization of ethyl vinyl ether in methylene dichloride solution

The rates and degrees of polymerization of ethyl vinyl ether (EVE) polymerized by gamma radiation in methylene chloride (CH₂Cl₂) have been studied in detail. The addition of even a small amount of CH₂Cl₂ sharply reduced the rates and degrees of polymerization. After about 0.5 ml_?1 of CH₂Cl₂ the rates became roughly first order in monomer. It is postulated that CH₂Cl₂ strongly solvates the growing chain ends disrupting the solvation by the polymer chains themselves, leading to lower rates. The degrees of polymerization support this hypothesis. Isodielectric constant solutions of EVE in benzene-CH₂Cl₂ mixtures gave rates at the same monomer concentrations, which fitted perfectly those obtained in EVE-CH₂Cl₂ mixtures. These results indicate that the dielectric constant is not the predominating property as formerly thought but that solvation is a more important factor. The activation energies were lower in CH₂Cl₂ solution than in bulk monomer or in low dielectric constant solvents, again indicating perhaps a different state of solvation of the growing chain ends.