Preparation of mixtures of linear three-block copolymers, and moldings produced therefrom

Claim 1

A composition from a process for the preparation of a mixture of block copolymers which essentially contain from 70 to 80% by weight of a monovinyl-aromatic monomer and from 20 to 30% by weight of a conjugated diene, the mixture essentially containing the two linear three-block copolymers A 1 -A 2 -B→A 3 and A 2 -B→A 3 where A 1 , A 2 and A 3 are non-elastomeric polymer segments of different molecular weight or different structure, and are based on a monovinyl-aromatic compound, and B is an elastomeric polymer segment based on a conjugated diene of 4 to 8 carbon atoms, and the transitions between the polymer segments B and A 3 are gradual and the other transitions are all sharp, by effecting the following process stages in an inert solvent: (a) in a first process stage, polymerizing 40 to 80% by weight of the total monovinyl-aromatic monomer(s) in the presence of an initial amount of a monolithium-hydrocarbon as the initiator, (Ia), until the monomer(s) has been substantially completely converted to A 1 -Li, thereafter (b) in a second process stage, adding the remaining amount of initiator, (Ib), the molar ratio of Ia:Ib being from 1:2 to 1:7, adding further a proportion of 15 to 30% by weight of the total monovinyl-aromatic monomer(s) to the solution, and continuing the polymerization until the monomer(s) has been substantially completely converted to a mixture of A 1 -A 2 -Li and A 2 -Li, and finally (c) in a third process stage, adding to the reaction solution a mixture of from 10 to 30% by weight of the total amount of monovinyl-aromatic monomer(s) to be employed, and from 20 to 30% by weight of conjugated diene monomer, based on the total amount of all monomers to be employed, and after complete conversion of the monomers the mixture of the lithium-terminated block copolymers A 1 -A 2 -B→A 3 -Li and A 2 -B→A 3 -Li is treated with protonactive compounds and the resulting mixture of block copolymers A 1 -A 2 -B→A 3 and A 2 -B-A 3 is isolated by removing the solvent.