Synthesis and characterization of poly(1,3-phenylene)-based polyradicals carrying cyclic aminoxyls

The synthesis and magnetic properties of poly(2,2,4,4-tetramethyl-N-yloxy-1,4-dihydro-2H-3,1-benzoxazine-6,8-diyl-1,3-phenylene) (4) are described. Polyradical 4 was prepared by the Pd-catalyzed cross-coupling reaction of 6,8-dibromo-2,2,4,4-tetramethyl-1,4-dihydro-2H-3,1-benzoxazine and bis(trimethylene) 1,3-phenylenediboronate, followed by oxidation with m-chloroperoxybenzoic acid. The number average molecular weights of 4 determined by SEC (size exclusion chromatography) were similar to 4120 (15 repeating units), and the spin concentrations determined by EPR were up to 0.75 spin per repeating unit. The EPR spectrum of 4 in a toluene glass matrix showed the DeltaM(s) = 2 forbidden transition at g = 4.0. A Curie plot of the DeltaM(s) = 2 signal intensity vs. 1/T gave a straight line, suggesting that the polyradical is in a triplet ground state or a nearly degenerate singlet-triplet state.