pThe invention relates to methods for increasing the mooney viscosity in a stepwise manner in the production of high molecular weight polybutadiene having a fraction of eis 1,4 units 95 wt% and a fraction of 1,2-vinyl 1 wt% characterized in that 1) at least one monomer selected from butadiene and/or isoprene is polymerized in the presence of at least one inert organic solvent and in the presence of at least one catalyst based on neodymium carboxylate at temperatures of -20°C to 150°C, 2) then the polymerization is stopped by adding protic compounds and 3) thereafter sulfur chlorides are added to the polymerizate the sulfur chlorides being treated with a carboxylic acid fatty acid and/or fatty acid ester before being added to the polymerizate./p
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