Polymerization of Diphenylbutadiyne Derivatives in Solution by Free Radical Initiator

In order to study free radical reactions of aromatic diacetylenes, the reaction of diphenyldiacetylene with di‐t‐butylperoxide was carried out in 1,2‐dichlorobenzene. The presence of t‐butoxy radicals considerably accelerated product formation, and oligomers with number average molecular weights of 700–2000 were obtained. There is no fragment of the t‐butyl group in the oligomers obtained according with the ¹H‐NMR spectrum. Furthermore, it is impossible that the t‐butoxy radicals would have initiated the oligomerization. The intense ESR spectra observed during the reaction at 130°C are due to the diradicals of oligomeric diphenylbutadiyne. It was concluded that the oligomerization proceeds via coupling of diradicals, and not the successive addition of radicals to monomers. The purified product oligomers did not contain carbonyl groups indicating there was no oxidation, and their ESR spectra have revealed that these oligomers contained a substantial amount of living free radicals stable in air at room temperature. The reason why high polymers are not obtained is the steric effect of oligomeric diradicals for coupling, as well as probable cyclization.