| abstract |
A modified conjugated diene copolymer obtained by polymerizing a conjugated diene compound in an organic solvent by the use of a catalyst containing a lanthanoid rare earth compound and modifying the obtained polymer having an active organometallic site with a modifying agent, which has a degree of modification of 15% or above and a cis-1,4 linkage content of the conjugated diene chain satisfying the relationship (I) as determined by Fourier transform infrared spectroscopy: cis-1,4 linkage content > 98.00 % ... (I) or which has a degree of modification of 75% or above and a cis-1,4 linkage content of the conjugated diene chain satisfying the relationship (II) as determined by Fourier transform infrared spectroscopy: 94.00 (%) < cis-1,4 linkage content < 98.00 (%) ... (II) rubber compositions which contain the copolymer and which can give tires having low heat build-up, excellent failure characteristics and abrasion resistance, and so on; and tires made by using the compositions and having the above properties. |