Novel block copolymers were synthesised by a two-step chemical modification of polystyrene-polybutadiene block copolymer (PS-b-PB). Such a modification includes hydrobromination or hydrosilylation of initial block copolymer and subsequent interaction of precursor with bidentate phosphine or phosphine oxide compounds. For interaction with the polymers, corresponding bidentate compounds were synthesised, which contained different amounts of carbon and silicon atoms between the phosphorus atoms. As both hydrobromination and hydrosilylation do not touch aromatic rings of polystyrene block, modification occurs solely in polybutadiene block.