Process for the polymerization or copolymerization of butadiene

In a process for the preparation of 1,4-cis polybutadiene or butadiene copolymers with other related diolefins for the catalytic polymerization or copolymerization of butadiene monomer, in the absence or substantial absence of solvents or diluents, comprising preparing a catalytic mixture by placing in contact in an inert hydrocarbon vehicle the following:

• (a) at least one neodymium compound chosen from among neodymium oxide, alcoholates, phenates and carboxylates or mixtures thereof with other rare earth elements;
• (b) at least one organic compound containing hydroxyl groups derived from alcohols or phenols or carboxyl groups, with the possible addition of water;
• (c) at least one halogen compound, chosen from among secondary or tertiary alcohol halogenides, aryl or alkylaryl halogenides, halogenides or organic acids, metallic or organometallic halogenides, and halogens;
• and
• (d) at least one organometallic aluminum compound or relative hydride derivatives thereof;
• wherein
• the quantities of compounds (a) and (b) are such so as to obtain a ratio between hydroxyl groups (including those of water) and/or carboxyl groups and neodymium atoms of 2/1 to 80 and maintaining contact of said components to thereby obtain a catalytic mixture having an aluminum/neodymium ratio of 20/1 to 80/1 and a halogen/neodymium ratio of 0.2/1 to 3/1;
• feeding said catalytic mixture and liquid butadiene monomer, possibly premixed, in quantities of 10.sup.4 to 4.multidot.10.sup.5 g.mols of butadiene per g.atom, discontinuously in an agitated polymerization reactor, or continuously in two reactors in series the first of which is homogeneous, or at one end of an elongated reactor in which is carried out the polymerization of the mixture flowing by piston ("plug-flow"), controlling the temperature through the partial evaporation of butadiene monomer from the liquid phase of polymerization, until a mixture with a polymer content of approximately 25 to approximately 70% by weight is obtained, which is discharged from the other end of the reactor;
• and separating and recovering 1,4-cis polybutadiene from said mixture discharged from the reactor;
• the improvement comprising carrying out polymerization in two phases, the first phase is carried out at a temperature of between 0.degree. and 30.degree. C. and the second phase is carried out at a temperature of between 50.degree. and 90.degree. C.