Polyaminoboranes, [RNH-BH2](n), are boron-nitrogen analogues of polyolefins: however, to date, few soluble, well-characterized examples have been described. Herein, we show that metal-catalyzed dehydrocoupling of N-alkylamine-boranes Ph(CH2)(x)NH2 center dot BH3 (x = 2-4) with pendant aryl groups yields soluble polyaminoboranes [Ph(CH2)(x)NH-BH2](n), using skeletal nickel, [Rh(mu-Cl)(1,5-COD)](2) (COD = cyclooctadiene), and [IrH2(POCOP)] (POCOP = kappa(3)-1,3-(OPtBu2)(2)C6H3) as precatalysts in THF. Application of the most efficient catalytic system (1 mol %, [IrH2(POCOP)], THF, -40 degrees C) enabled the isolation of high molar mass, soluble polyaminoborane [Ph(CH2)(4)NH-BH2](n) in moderate (ca. 40%) yield. Structural characterization was achieved by multinuclear nuclear magnetic resonance, infrared, and elemental analysis; and the molar mass was determined to be high (M-n > 10 000 g mol(-1)) by gel permeation chromatography, dynamic light scattering, and, for comparison, also H-1 diffusion-ordered spectroscopy methods. The optimized dehydropolymerization conditions for the Ir catalyst were also used to prepare copolymers from mixtures of Ph(CH2)(4)NH2 center dot BH3 with either MeNH2 center dot BH3, Ph(CH2)(2)NH2 center dot BH3, or NH3 center dot BH3. Significantly, soluble copolymers containing ca. 67% of [NH2-BH2] repeat units were prepared. The thermal stability of the polyaminoborane homopolymers and copolymers was studied by thermogravimetric analysis. The use of a cross-linker, H3B center dot NH2(CH2)(8)NH2 center dot BH3, in the dehydropolymerization reactions led to improved ceramic yields after pyrolysis indicating that, with appropriate structural design, polyaminoboranes may be of potential future interest as precursors of boron-based ceramics.