Electron paramagnetic resonance and magnetic susceptibility studies of new substituted poly(acetylene) derivatives

Abstract

A series of triphenylmethyl-substituted poly(acetylenes) has been studied by electron paramagnetic resonance (EPR) spectroscopy, and compared to poly(phenylacetylene)(PPA) as a reference material. All the polymers were found to exhibit spin concentrations varying between 10¹⁶ and 10¹⁹ spins g^–1, and thus were only very weakly paramagnetic. The target polyradical, poly[(4-ethynylphenyl)diphenylmethyl], was shown to display a small reversible increase in spin concentration with increasing temperature between 220 and 370 K. Magnetic susceptibility measurements on this polymer confirmed an increase in the molar ratio of spins in the temperature range 200–340 K. This polymer did not display bulk ferromagnetic behaviour, and the spin concentrations observed together with the results of elemental analysis and IR spectroscopy, suggested that spin pairing may have taken place after generation of free-radical sites on the polymer, although no firm evidence for this could be obtained.