Molecular design, synthesis, and magnetic characterization of poly(phenylacetylene) with pi‐toporegulated pendant nitronyl nitroxide radicals as models for organic superpara‐ and ferromagnets

The present article describes the synthesis and magnetic properties of poly(phenylacetylene) (3) with pi‐toporegulated pendant stable 4,4,5,5‐tetramethylimidazolin‐3‐oxide‐1‐yloxyl radicals topologically participating in the pi‐conjugated system of poly(phenylacetylene). Polyradical 3 was prepared by the condensation reaction of poly(p‐ethynylbenzaldehyde) with 2,3‐bis(hydroxylamino)‐2,3‐dimethylbutane followed by oxidation with lead dioxide. The spin concentration of 3 determined by the ESR spectroscopic method was 1.1 × 1021 spins/g. This value approximately corresponds to 0.5 unpaired electron spin per the repeating unit. A powder ESR spectrum of 3 gave a 100% Lorentzian single line showing spin‐exchange narrowing. The vibrating sample magnetometer (VSM) measurement of 3 afforded a straight line with a positive slope, suggesting that 3 has predominant paramagnetic properties within an experimental error.