Transparent, thermoplastic moulding composition, process for its preparation, and its use

The invention relates to a transparent, thermoplastic moulding composition containing, based on A + B, A from 5 to 95% by weight of polystyrene which has been produced in a manner known per se by free-radical polymerisation, B from 95 to 5% by weight of a non-elastomeric block copolymer which is branched in a star-shaped manner, built up from, based on B, b1 from 60 to 95% by weight of styrene and b2 from 5 to 40% by weight of at least one conjugated diene having 4 or 5 carbon atoms, which has been prepared by sequential anionic polymerisation using at least one organolithium compound as initiator and in the presence of a solvent, where firstly, in a first process step, an amount of styrene S1 of from 50 to 80% by weight of the styrene, based on the total amount of styrene, is polymerised in the presence of an amount of initiator I1 and then, in a second process step, a smaller amount of styrene S2 is polymerised with simultaneous addition of a further amount of initiator I2, and, in a third process step of the polymerisation, a mixture of a residual amount of styrene, S3, and the total amount of the diene are reacted, followed by coupling and work-up of the reaction product, characterised in that the amount of initiator I1 in the 1st process step is from 0.05 to 1.0 mmol/100 g of total monomer and that, in the 2nd process step, an amount of styrene S2 of from 12 to 47% by weight of styrene, based on the total amount of styrene, ... in the presence of from 0.5 to 10 mmol/100 g ... Original abstract incomplete.