Low Temperature Polymerization in p-Diethynylbenzene Crystal: Localization of Unpaired Electron in Poly-Conjugated System

Abstract

Optical and ESR spectroscopy study has revealed that the stereo-regular polymer is formed under UV- or γ-irradiation of para-diethynylbenzene (DEB) crystals over a wide temperature range (77–300 K). It has been shown that the unpaired electron of the macro-radical of the propagating linear polymer chain (77–230 K) is localized on the terminal monomer link to give a doublet splitting in the ESR spectrum. Delocalization of unpaired electron in the poly-conjugated system takes place at 230–300 K by addition of the linear macro-radical to the double bond of the polymer. In this case, a normal polyene-type radical, observed during the polymerization of acetylenic monomers at elevated temperatures, is formed and shows singlet splitting with the width of ΔH = 1 mT in the ESR spectrum. The encounter of the macro-radical with the double bond probably occurs via polymer chain propagation.