Butadiene-isoprene copolymers (BIC) synthesized with rare-earth catalysts are characterized by high cis-1

4-butadiene and isoprene units in microstructures

and their vulcanizates have good low-temperature properties under proper B/I ratios. This work was undertaken to study the properties of compounded rubber and vulcanizate of BIC (sample Jin-20) by using two different vulcanization systems

(CZ-S) and TMTD. By comparing with that of IB and BR similarly polymerized with rare-earth catalysts

it has been found that Jin-20 has some notable features.