Kinetic effects of salts on vinyl polymerization in non‐aqueous systems

The polymerization of vinyl monomers in non‐aqueous solvents, such as N,N‐dimethylformamide, is influenced by a variety of inorganic salts, and both the cationic and anionic components of the salt may be active in this respect. Cations derived from metals possessing several valency states may terminate the kinetic chains by a one‐electron transfer process, e.g., with styrene equation image The kinetics of the polymerization of several monomers in the presence of ferric chloride have been worked out, and the absolute rate constants for the termination reactions calculated. Their magnitude is briefly discussed in terms of the structure of the radicals. It is pointed out that these reactions provide a very useful method of determining rates of initiation. Even cations such as lithium, which have only a single valency state, may have an effect on the kinetics of polymerization, for example in the case of acrylonitrile. This arises from association between the metal ions and the radicals which modifies the reactivity of the latter. The associated anions may also interact with radicals in a similar manner. This effect is particularly marked with chloride ions and acrylonitrile, and leads to an increase in the rate of propagation and chain transfer with electron accepting reagents such as carbon tetrabromide.