The first high molar mass polyaminoboranes with an organic substituent at boron, namely the B-arylated polyaminoboranes [NH2-BHPh]n (2a) and [NH2-BH(p-CF3C6H4)]n (2b), have been prepared via catalytic dehydropolymerisation. These materials can be considered as inorganic analogues of polystyrene with a B-N main chain. Their synthesis was achieved from B-aryl amine-borane precursors in solution using an [IrH2(POCOP)] precatalyst.