Method for the production of branched polymerizates

A thermoplastic elastomer comprising a branched polymerizate made by radical polymerization of monomers in two stages comprising

• in a first stage, adding 10 to 500 parts by weight of at least one monomer M.sub.1 and 0.1 to 20 parts by weight of a mercaptan with an olefinic, radically polymerizable double bond RM and polymerizing said at least one monomer M.sub.1 and mercaptan RM to form a copolymer MM.sub.1, containing mercapto groups, in the presence of at least one polymerization initiator and 0 to 100 parts by weight of an inert, non-aqueous solvent, which completely dissolves the monomer M.sub.1 the mercaptan RM and the copolymer MM.sub.1, wherein the polymerizable double bonds of M.sub.1, and RM have a reactivity, expressed by a copolymerization parameter r, between 0.1 and 10, and
• in a second stage, adding 10 to 2000 parts by weight of a monomer M.sub.2 and 0.01 to 10 parts by weight of a saturated molecular weight regulator, and optionally, an inert, non-aqueous solvent, to the reaction mixture formed in the first stage, and polymerizing in the presence of at least one polymerization initiator to form a branched polymerizate, wherein polymer branches are polymerized via the SH groups.

A viscosity index improver comprising a branched polymerizate made by radical polymerization of monomers in two stages comprising

• in a first stage, adding 10 to 500 parts by weight of at least one monomer M.sub.1 and 0.1 to 20 parts by weight of a mercaptan with an olefinic, radically polymerizable double bond RM and polymerizing said at least one monomer M.sub.1 and mercaptan RM to form a copolymer MM.sub.1, containing mercapto groups, in the presence of at least one polymerization initiator and 0 to 100 parts by weight of an inert, non-aqueous solvent, which completely dissolves the monomer M.sub.1, the mercaptan RM and the copolymer MM.sub.1, wherein the polymerizable double bonds of M.sub.1 and RM have a reactivity, expressed by a copolymerization parameter r, between 0.1 and 10, and
• in a second stage, adding 10 to 2000 parts by weight of a monomer M.sub.2 and 0.01 to 10 parts by weight of a saturated molecular weight regulator, and optionally, an inert, non-aqueous solvent, to the reaction mixture formed in the first stage, and polymerizing in the presence of at least one polymerization initiator to form a branched polymerizate, wherein polymer branches are polymerized via the SH groups.