Bimodal neodymium-catalyzed polybutadiene

A process for producing bimodal neodymium-catalysed polybutadiene having greater than 95% of cis-1,4 units and less than 1% of 1,2-vinyl content, wherein the bimodal neodymium-catalysed polybutadiene has a linear polymeric main fraction and a long chain branched polymeric fraction, wherein the slope in the RGM relationship is greater than 0.5 for the polymeric main fraction and less than 0.3 for the long chain branched polymeric fraction, comprising the steps of:

• a) performing a modified catalyst system comprising:
• component A:
• an alkoxide, a phosphonate, phosphinate and/or phosphate, a carboxylate, a complexed compound of rare earth metals with diketones and/or an addition compound of the halides of the rare earth metals with an oxygen or nitrogen donor compound,
• component B:
• a dialkylaluminium hydride,
• component C:
• a diene, and
• component D:
• at least one organometallic halide,
• by mixing the components A, B and C are at a temperature of −20° C. to 80° C., for a period of 5 minutes to 10 hours to produce a mixture, cooling the mixture to a temperature below −10° C. to produce a cooled mixture, and adding component D to the cooled mixture to produce the modified catalyst system;
• b) optionally performing the modified catalyst system at a temperature of −30° C. to 80° C., for a period of 10 minutes to 250 hours;
• c) polymerizing butadiene monomers in the presence of the modified catalyst system at a temperature between −20 and 100° C. to produce a polymerization solution, and
• d) after obtaining a conversion of butadiene of greater than or equal to 85% by weight in the step c, maintaining the polymerization solution at a temperature of greater than or equal to 100° C. for a delay time of 10 to 120 min.