SYNTHESES AND MAGNETIC CHARACTERIZATION OF POLY(1,3-PHENYLENEETHYNYLENE) WITH PENDANT NITRONYL NITROXIDE RADICALS

The (PPh3)2PdCl2-CuI-catalyzed polycondensation of 4,4,5,5-tetramethyl-3-oxido-2-(3,5-diethynylphenyl)-2-imidazolin-1-yloxyl with 5-tert-butyl- or 5-hexyl-1,3-diiodobenzene in triethylamine-pyridine at room temperature afforded nitronyl nitroxide pendant poly(1,3-phenyleneethynylene) polyradicals in almost quantitative yields. The polyradicals obtained as a blue powder are soluble in CH2Cl2 and CHCl3, partially soluble in THF and DMF, and insoluble in methanol, ether, and common hydrocarbons such as hexane and benzene. The number-average molecular weights (M(n)BAR) determined by GPC are 4300-4800, and the spin concentrations determined by electron spin resonance (ESR) are 1.12 x 10(21)-1.33 x 10(21) spins/g (82-91% spin/repeating unit). Both the solution (CH2Cl2) and powder ESR spectra of the polyradicals consist of a hyperfine-smeared single line, suggesting that spin-exchange narrowing takes place. The magnetic susceptibility (chi) measurements of the polyradicals have been carried out by a SQUID magnetometer in the temperature range 1.8-300 K. The chi-1 vs T and chiT vs T plots show that the polyradicals are paramagnetic species with a very weak antiferromagnetic coupling (THETA = -0.6 K) and that there are no significant ferromagnetic interactions among the spins. The magnetic susceptibility results are discussed in conjunction with the structure of the polyradicals.