a cyanoethyl group - containing graft polymer comprising a hydrocarbon polymer backbone comprising butadiene units , to which a cyanoethylated acrylate monomer of the formula : ch . sub . 2 ═ cr . sub . 1 -- coo -- r . sub . 2 --. sub . m in which r 1 is a hydrogen atom or a methyl group ; r 2 is a residue derived from a - valent polyhydroxyl compound by the removal of all the hydroxyl groups ; and m is an integer of at least 1 , which is useful as a binder resin for positive and negative electrodes of lithium ion secondary batteries and for organic dispersion type electroluminescent device .