Disclosed are a polymer, and a mixture or a formulation and an organic electronic device containing same, and applications thereof, and further a monomer of which the polymer is made; the polymer comprises on its side chain a repeating structure unit E, characterizing in that its S1(E)−T1(E))≤0.35 eV or even less, which may allow the said polymer having thermally activated delayed fluorescence (TADF) property. Thus a TADF polymer suitable for printing processes is provided, thereby reducing OLED manufacturing costs.