SYNTHESIS AND MAGNETIC-BEHAVIOR OF POLYRADICAL - POLY(1,3-PHENYLENEETHYNYLENE) WITH PI-TOPOREGULATED PENDANT STABLE AMINOXYL AND IMINE N-OXIDE-AMINOXYL RADICALS

The palladium-catalysed polycondensation of N-tert-butyl-N-(3,5-diethy nylphenyl)aminoxyl with ,5-tetramethyl-3-oxido-2-imidazolin-3-ium-1-yl oxyl in pyridine-triethylamine at room temperature afforded poly(1,3-p henyleneethynylene) with pendant aminoxyl and imine N-oxide-aminoxyl r adicals as a light blue powder in 78-83% yields. The number-average mo lecular weights (<(M)over bar (n)>) of the polyradical determined by G PC were 2670-3030 and the spin concentrations determined by EPR were 1 .91-2.02 x 10(21) spins g(-1). Both solution (CH2Cl2) and powder EPR m easurements of the polyradicals gave a hyperfine-smeared single line s pectrum, suggesting that spin-exchange narrowing took place due to the high spin concentrations of the polyradicals. The magnetic susceptibi lity (chi) measurements of the polyradicals were carried out on a supe rconducting quantum interference device (SQUID) magnetometer in the te mperature range of 1.8-300 K. The chi Tvs. T plots showed that the pol yradicals were a paramegnetic species yielding a weak antiferromagneti c coupling (theta = -1.5 K) below 30 K. The absence of the through-bon d ferromagnetic interaction is accounted for by masking of the interac tion by the stronger through-space antiferromagnetic interactions.