NOVELTY - Polymer comprising at least one phenyl derivative structural unit (I) is new.    USE - The polymer, the mixture or the solution is useful in at least one active layer of electronic devices, preferably polymer electroluminescent devices (polymer light-emitting diodes) (preferred), organic electroluminescent devices (organic light-emitting diodes), organic integrated circuits, organic field-effect transistors, organic thin film transistors, organic solar cells, organic laser diodes, organic photovoltaic elements or devices, or organic photoreceptors (all claimed).    ADVANTAGE - The electronic devices comprising the polymers exhibit increased efficiency and longer service life.    DETAILED DESCRIPTION - Polymer comprising at least one phenyl derivative structural unit of formula (I) is new.    X = C(R1)2, NR1, C(R1)2-C(R1)2, CR1=CR1 or substituted fluorene moiety of formula (II);    Y1, Y2 = C(R1)2, NR1, C(R1)2-C(R1)2, CR1=CR1 or single bond, where either Y1 or Y2 is a single bond;    m = 0 or 1; either    R1 = 1-40C alkyl or 1-40C (thio)alkoxy (all linear), 3-40C alkyl or 3-40C (thio)alkoxy (all branched or cyclic and optionally substituted by at least one group R2, where in all groups at least one non-adjacent CH2 groups may be replaced by R2C=CR2, CC, Si(R2)2, Ge(R2)2, Sn(R2)2, C=O, C=S, C=Se, C=NR2, P(=O)(R2), SO, SO2, NR2, O, S or CONR2 and at least one H may be replaced by F, Cl, Br, I, CN or NO2), 5-40C (hetero)aryl, 5-40C (hetero)aryloxy (both optionally substituted by at least one non-aromatic group R1), H, D, F, Cl, Br, I, N(A1)2, C(=O)A1, P(=O)(A1)2, S(=O)A1, S(=O)2A1, CR2=CR2A1, ON, NO2, Si(R2)3, B(OR2)2 or OSO2R2; or    at least 2 adjacent R1 = aliphatic or aromatic, mono- or polycyclic ring or an electron-transport moiety R3, where at least one of the group R1 is an electron transport moiety R3;    A1 = (hetero)aryl or (hetero)aromatic ring; either    R2 = H, 1-20C aliphatic hydrocarbon or 6-20C aromatic hydrocarbon; or    at least 2R2 = ring;    R3 = electron-transport moiety; and    n = 1-4.    INDEPENDENT CLAIMS are also included for:    (1) preparing the polymer comprising (I);    (2) a substituted phenyl derivative of formula (III);    (3) a mixture comprising at least one above polymer with a further polymeric, oligomeric, dendritic and/or low molecular weight substance; and    (4) a solution or a formulation comprising at least one above polymer or the above mixture in at least one solvent.    W1, W2 = halo, O-tosylate, O-triflate, O-SO2R4, B(OR4)2 or Sn(R4)3; either    R4 = H, 1-20C aliphatic hydrocarbon group or aromatic hydrocarbon group with 6-20 ring atoms; or    at least 2R4 = aliphatic ring.    DESCRIPTION OF DRAWING(S) - The drawing 1 shows a schematic representation of the polymer light-emitting diodes. The drawing 2 shows a schematic representation of indium-tin oxide structure deposited on a glass substrate and complete electronic structure with indium-tin oxide structure. The drawing includes non-English language text.