Friedel‐Crafts polymerizations. III. Medium effects in the Friedel‐Crafts polymerization of styrene

Abstract

In polymerizing styrene at room temperature in the presence of tin tetrachloride, it is found that the rate of polymerization is greatly affected by the dielectric constant of the medium. It increases by a factor of approximately 1400 when the dielectric constant changes from 6.5 to 18.4. At the same time the degree of polymerization increases only slightly. The results are interpreted as supporting evidence for the mechanism of Friedel‐Crafts polymerizations as suggested by Polanyi and co‐workers. A unimolecular termination by proton‐splitting cannot be reconciled with these results.Quantitative equations are derived relating the rate and degree of polymerization to the dielectric constant. Traces of liquid water have no visible effect on the polymerization while larger amounts cause retardation. The degree of polymerization, which is of the order of 20, does not change with conversion and is unaffected by the catalyst present.