Patent ID: 7169870

Claim:
A statistically random copolymer of butadiene and isoprene obtained by a process comprising copolymerizing butadiene and isoprene in the presence of a catalyst system comprising: (a) a conjugated diene monomer; (b) an organic phosphoric acid salt of at least one rare earth metal; (c) an alkylaluminum alkylating agent of the formulae AlR 3 or HAlR 2 where R is an alkyl group; and (d) an alkylaluminum halide halogen donor, said salt being in suspension in at least one inert, saturated, aliphatic or alicyclic hydrocarbon solvent which is included in said catalytic system, the alkylating agent:rare earth salt molar ratio having a value of from 1 to 8, and wherein the copolymerization reaction optionally is conducted in an inert hydrocarbon solvent, said statistically random copolymer comprising butadiene and isoprene units which succeed one another in a random manner in accordance with Bernoulli's law, such that the glass transition temperature T Gexp of said copolymer, measured by the differential enthalpy analysis method, satisfies the following relationship: −0.05≦( T Gexp −T Gth )/ T Gth ≦0.05 where T Gth is a theoretical glass transition temperature for said copolymer, calculated in accordance with the Fox equation: 1 /T Gth =α/T G(BR) +β/T G(IR) , where T G(BR) and T G(IR) are respectively the glass transition temperatures, measured by said differential enthalpy analysis method, of a polybutadiene and a polyisoprene synthesized by means of said catalyst system.