NOVELTY - Polymer of benzodithiophene, is new.    USE - The polymer, monomer, polymer blend, or formulation is useful as charge transport, semiconducting, electrically conducting, photoconducting or light emitting material in optical, electrooptical, electronic, electroluminescent or photoluminescent components or devices, where component or device is selected from organic field effect transistors (OFET), thin film transistors (TFT), integrated circuits (IC), logic circuits, capacitors, radio frequency identification (RFID) tags, devices or components, organic light emitting diodes (OLED), organic light emitting transistors (OLET), flat panel displays, backlights of displays, organic photovoltaic devices (OPV), solar cells, laser diodes, photoconductors, photodetectors, electrophotographic devices, electrophotographic recording devices, organic memory devices, sensor devices, charge injection layers, charge transport layers or interlayers in polymer light emitting diodes (PLEDs), Schottky diodes, planarizing layers, antistatic films, polymer electrolyte membranes (PEM), conducting substrates, conducting patterns, electrode materials in batteries, alignment layers, biosensors, biochips, security markings, security devices, and components or devices for detecting and discriminating DNA sequences. Preferably, component or device is a bulk heterojunction OPV device (all claimed).    ADVANTAGE - The invention provides improved polymers for use as OSC materials especially in bulk heterojunction OPV devices, but also in OFET devices.    DETAILED DESCRIPTION - Polymer of benzodithiophene of formula I, is new.    A=on each occurrence identically or differently a group selected from formulae IIa, IIb, IIc, IId, IIe, and IIf;    B=on each occurrence identically or differently a group selected from formulae IIg, IIh, IIi, IIk, IIm, and IIn;    X1 and X2=on each occurrence identically or differently, and independently of each other, O, S or Se;    R1 and R2=on each occurrence identically or differently, and independently of each other, halogen, a straight-chain, branched or cyclic alkyl with 1 to 35C atoms, in which one or more non-adjacent C atoms are optionally replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-O-, -CR0=CR00- or -C-triple bond-C- and in which one or more H atoms are optionally replaced by F, Cl, Br, I or CN, or an aryl, heteroaryl, aryloxy or heteroaryloxy group having 2 to 40 ring atoms that is unsubstituted or substituted by one or more non-aromatic groups R5;    R3 and R4=on each occurrence identically or differently, and independently of each other, denote H or have one of the meanings given for R1;    R0 and R00=independently of each other H or an optionally substituted carbyl or hydrocarbyl group optionally comprising one or more hetero atoms;    Ar=on each occurrence identically or differently an aryl or heteroaryl group that is optionally substituted by one or more groups R1, is on each occurrence identically or differently H, halogen, -CN, -NC, -NCO, -NCS, -OCN, -SCN, -C(=O)NR0R00, -C(=O)X0, -C(=O)R0, -NH2, -NR0R00, -SH, -SR0, -SO3H, -SO2R0, -OH, -NO2, -CF3, -SF5, optionally substituted silyl, carbyl or hydrocarbyl with 1 to 40C atoms that is optionally substituted and optionally comprises one or more hetero atoms, or P-Sp-;    P=a polymerizable group;    Sp=a spacer group or a single bond;    X0=halogen;    m=on each occurrence identically or differently 0 or 1, where in at least one repeating unit m is 1;    o=on each occurrence identically or differently 0 or 1, where in at least one repeating unit o is 1;    i and k=on each occurrence identically or differently, and independently of each other, 0 or 1, where in at least one repeating unit at least one of i and k is 1; and    n=an integer of more than 1.    INDEPENDENT CLAIMS are:    (1) a monomer of benzodithiophene of formula IIIa;    (2) a polymer blend comprising one or more polymers, preferably selected from polymers having semiconducting, charge transport, hole/electron transport, hole/electron blocking, electrically conducting, photoconducting or light emitting properties;    (3) formulation comprising one or more polymers or polymer blends and one or more solvents, preferably selected from organic solvents;    (4) optical, electrooptical or electronic component or device comprising one or more polymers, polymer blends or formulations; and    (5) a process of preparing polymer.    i, k, m, and o=independently of each other 0 or 1, with at least one of i, k and o being 1;    R8 and R9=identical or different groups having one of the meanings of R6 different from H or being selected from Cl, Br, I, O-tosylate, O-triflate, O-mesylate, O-nonaflate, -SiMe2F, -SiMeF2, -O-SO2Z1, -B(OZ2)2, -CZ3=C(Z3)2, -C-triple bond-CH and -Sn(Z4)3; and    Z1-Z4=selected from alkyl and aryl, each being optionally substituted, and two groups Z2 may also form a cyclic group.