The present study focuses on the terpolymer of styrene (St), isoprene (Ip), and butadiene (Bd) synthesized together in cyclohexane at 70 degrees C with neodymium (Nd) compound, alkylaluminum, and chlorinating agent (Cl) rare earth cocatalyst system. The resultants possessed atactic St-St sequences and high cis-1,4 polyconjugated olefins in macromolecular chains besides controllable composition. The composition of the St-lp-Bd terpolymers and molecular weight (M,), molecular weight distribution (M-w/M-n) were controlled through the adjustment of Nd compound, alkylalumium, monomers feed ratio (St/Ip/Bd), and [Nd]/[monomers]. With the inventory rating of St raised from 15% to 55%, the content of St in the terpolymers got increased from 2% to 15%. And the content of the lp segments and Bd segments in the terpolymers increased from 33% to 56% and from 28% to 54%, respectively, with the proportion of Ip/Bd varied from 1/2 to 2/1. As the [Nd]/[monomers] varied from 1.0 x 10(-3) to 5.0 x 10(-4), the molecular weight increased from 1.3 x 10(4) to 2.7 x 10(4). According to the proton nuclear magnetic resonance (H-1-NMR) and C-13-NMR, it was proved that both microstructures of polybutadiene segments and polyisoprene segments were high cis-1,4-configuration. A single glasstransition temperature was observed in the differential scanning calorimetry curve. (C) 2013 Society of Plastics Engineers