Direct detection of free radicals by EPR method during the polymerization of compounds of the acetylenic series

Abstract

When the thermal bulk polymerizat ion of phenylacetylene, diphenylacetylene, p-iodophenylacetylene, phenoxyacetylene and diphenylbutadiyne (DPBD) is ca r r i edou t directly in an EPR spec t romete r at 150 o an intense EPR signal is observed immediately. In all cases , with the exception of DPBD, the EPR signal represen ts a single absorption line with a g factor that is close to the g factor of a free electron. In the polymerizat ion of DPBD the EPR signal has a hyperfine s t ruc ture (HFS) that consists of at least four lines, with a splitting of 35 Oe between the ext reme components. The two middle HFS lines are masked by an intense central signal, which has the same nature as the single absorption line in polyphenylacetylene, polydiphenylbutadiyne, and other polymers containing a conjugation system. Since the EPR signal disappears when the mater ia l is cooled to a t empera ture where the polymerizat ion of the corresponding monomer fails to occur , and the process is inhibited by N,N-diphenylpicrylhydrazyl , it may be assumed that we were the f i rs t to use the EPR method to direct ly detect the free radicals that take part in the polymerizat ion of c o m pounds of the acetylenic se r i es .