AN APPROACH TO ORGANIC FERROMAGNETS - SYNTHESIS AND CHARACTERIZATION OF 1-PHENYL-1,3-BUTADIYNE POLYMERS HAVING A PERSISTENT NITROXIDE GROUP ON THE PHENYL RING

1-[3-(N-tert-Butylhydroxyamino)-4-chlorophenyl]-1,3-butadiyne (3) was obtained as colorless needles (mp ca. 140-degrees-C from diethyl ether) that Polymerized 100% in 24 h at 120-degrees-C to give a black, ethanol-insoluble microcrystalline product. Crystals of 3 are triclinic, space group P1BAR (No. 2), with a = 8.496 (3) angstrom, b = 10.755 (5) angstrom, c = 8.004 (3) angstrom, alpha = 92.77 (4)-degrees, beta = 106.51 (3)-degrees, gamma = 74.85 (3)-degrees, V = 676.6 (5) angstrom 3, and d = 1.22 g/cm3 for Z = 2 (C14H14ClON, MW = 247.72). The observed solid-state polymerization is estimated to have taken place along the a/c diagonal. Treatment of 3 with Fremy's salt in THF/H2O at room temperature gave the corresponding nitroxide radical 4 as red crystals (mp 81.0-82.0-degrees-C, a(N) = 13.8 G, g = 2.0066 in hexane). Whereas the planned solid-state polymerization of 4 proceeded neither by heat nor UV and gamma-irradiation, mixed crystals of 3 and 4 (70:30 to 50:50) did undergo polymerization in 20 h at 140-degrees-C to give a black, ethanol-insoluble solid. A broad X-band ESR signal that showed geometrical anisotropy was observed at ca. 3000 G in addition to resonances at g = 2 due to the isolated (S = 1/2) and exchange-narrowed nitroxide spins. The magnetic susceptibility of the polymer samples measured on a Faraday balance showed that ca. 90% of the nitroxide radical centers were lost during the polymerization. Most of the remaining spins are S = 1/2, and the rest are in a segment where S > 1/2. The latter spins were found to be quenched by an anomalous phase transition at ca. 250 K when the samples were warmed up from cryogenic temperatures.