NOVELTY - Polymer comprising at least one triarylamine structural unit (I), is new.    USE - The polymer is useful in an active layer of electronic or optoelectronic devices comprising organic electroluminescent devices, organic light-emitting electrochemical cells, organic field-effect transistors, organic integrated circuits, organic thin-film transistors, organic solar cells, organic laser diodes, organic photovoltaic elements or devices, and organic photoreceptors, preferably organic electroluminescent devices (all claimed).    ADVANTAGE - The polymer increases service life of the organic electroluminescent devices.    DETAILED DESCRIPTION - Polymer comprising at least one triarylamine structural unit of formula (-Ar1-N(Ar3)-Ar2-) (I), is new.    Ar1, Ar2 = mono- or polycyclic (hetero)aromatic ring with 5-60 aromatic ring atoms (optionally substituted by at least one group R);    Ar3 = mono- or polycyclic (hetero)aromatic ring with 5-60 aromatic ring atoms (optionally substituted by at least one group R), where Ar3 is substituted in at least one, preferably one of two ortho-positions by Ar4;    Ar4 = mono- or polycyclic and (hetero)aromatic ring with 5-60 aromatic ring atoms (optionally substituted by at least one group R); either    R = 1-40C alkyl or 1-40C (thio)alkoxy (both linear) or 3-40C alkyl or 3-40C (thio)alkoxy (both branched or cyclic) (where in all groups at least one non-adjacent CH2 group is optionally replaced by R1C=CR1, CC, Si(R1)2, C=O, C=S, C=NR1, P(=O)(R1), SO, SO2, NR1, O, S or CONR1, and at least one H is optionally replaced by D, F, Cl, Br, I or CN), mono- or polycyclic (hetero)aromatic ring with 5-60 aromatic ring atoms, (hetero)aryloxy with 5-60 aromatic ring atoms, (hetero)aralkyl with 5-60 aromatic ring atoms, diarylamino with 10-40 aromatic ring atoms, diheteroarylamino with 10-40 aromatic ring atoms or aryl-heteroaryl-amino with 10-40 aromatic ring atoms (all optionally substituted by at least one group R1), Q, H, D, F, Cl, Br, I, N(R1)2, CN, NO2, Si(R1)3, B(OR1)2, C(=O)R1, P(=O)(R1)2, S(=O)R1, S(=O)2R1 or OSO2R1; or    at least 2 R = mono- or polycyclic and aliphatic, aromatic and/or benzo-fused ring; either    R1 = aliphatic 1-20C hydrocarbyl or 5-20C (hetero)aromatic hydrocarbyl (in both groups at least one H is optionally replaced by F), H, D or F; or    at least 2 R1 = mono- or polycyclic and aliphatic or aromatic ring; and    Q = crosslinkable group.    INDEPENDENT CLAIMS are also included for:    (1) preparing the polymer;    (2) a polymer blend comprising at least one above polymer, and at least one further polymeric-, oligomeric-, dendritic- and/or low molecular weight substance; and    (3) a solution or formulation comprising the polymer or the polymer blend in at least one solvent.