Polybenzimidazoles have been extensively in~estigatedl-~ since they were first described in 1959.4 The outstanding thermal and chemical stabilities of this class of polymers have suggested broad utility in high-temperature films, laminates, adhesives, fibers, and insulating foams.Traditionally, polybenzimidazoles have been obtained by the reaction of aromatic tetraamines with dicarboxylic acids or their derivatives at high tern~eratures.'-~ In a two stage process for the preparation of poly[2,2'-( rn-phenylene)-5,5'bibenzimidazole], the final stage involves solid state polymerization at 385°C: A useful solution polymerization method has been described by Marvel utilizing refluxing sulfolane or diphenylsulfone as solvent? More recently, polyphosphoric acid has been utilized as a solvent for the preparation of a variety of polybenzimidazoles, polybenzoxazoles, and polybenzothiazoles?We recently reported' that polyamides derived from the reaction of bis(2-oxazolin-5-one)s (bisazlactones) and diamines readily cyclodehydrate thermally to produce polymers containing 2-imidazolin-5-one units. Seeking to utilize bisazlactones in the synthesis of other heterocyclic polymer systems, we considered azlactones as reagents to convert o-phenylenediamines into benzimidazoles. We now report the facile preparation of benzimidazoles from the reaction of azlactones and o-phenylenediamines, and the extension of this reaction to the preparation of poly(amide-benzimidazo1e)s.
EXPERIMENTAL
Measurements'H-and 13C-NMR spectra were recorded using a Varian EM360L, Jeol FX100, Varian XL200, or Varian XL400 spectrometer, under the conditions noted in Tables I and 11, using tetramethylsilane or DMSO-d, as an internal reference. Infrared spectra were obtained on a Perkin-Elmer 283B spectrophotometer. Melting point determinations were made using a Bristoline hot-stage microscope and are uncorrected. A Cannon-Ubbelohde viscometer was used to determine the inherent viscosity of polymer solutions with concentrations of 0.5 g/100 mL in DMF at 30 0.1'C.
Materials2-Phenyl-2-oxazolin-5-one (9a),15 N-benzoyl-a-aminoisobutyric acid,',, l7 4,4-dimethyl-2-phenyl-2-oxazolin-5-one (9b)," N, N'-terephthaloylbis(glycine),'' N, N'-terephthaloylbis( a-aminoisobutyric acid)," 2,2-p-phenylenebis(2-oxazolin-5-one) (12a)," and 2,2'-p-phenylenebls(4,4-dimethyl-2-oxazolin-5-one) (12b)" were prepared according to literature procedures. 2,2'-rn-Phenylenebis(4,4-dimethyl-2-oxazolin-5-one) (12c), mp 125-127OC (lit." mp 129OC) was prepared by procedures analogous to those in the literature." 3,3',4,4'-Tetraaminobiphenyl was purified by sublimation (0.1 torr, 220°C) as yellow crystals, mp 181OC.
Model Compounds
N-Hippuryl-o-phenylenediamine (loa):A solution of o-phenylenediamine (3.36 g, 0.031 mol) in dry DMF (8 mL) was added to a vigorously stirred solution of 2-phenyl-2-oxazolin-5-one (5.0 g, 0.03 mol) in DMF (5 mL) at room temperature. After stirring overnight, the product was filtered, dried overnight in uacm, and crystallized from ethanol to give 1 O a in 95% yield: m...
