We report here the terpolymerization of butadiene (BD), isoprene (IP), and styrene (St) by a half-sandwich scandium catalyst bearing an unsubstituted cyclopentadienyl ligand, (C5H5) Sc(CH2C6H4NMe2-o)(2)[Ph3C][B(C6F5)(4)], which afforded for the first time the BD-IP-St terpolymers containing high cis-1,4-BD and high cis-1,4-IP units and atactic polystyrene blocks. The copolymerization of BD and IP by this catalyst took place in a quasi-living, cis-1,4-selective fashion, yielding the random BD -IP copolymers with high cis-1,4 content of both monomer units (selectivity > 94%), controllable molecular weight (M-n = 5.1 x 10(4) - 28.7 x 10(4)) and narrow molecular weight distribution (M-w/M-n = 1.18 -1.40). The incorporation of atactic polystyrene blocks into high cis-1,4 content BD-IP copolymers was realized in a wide range of St content (17-76 mol%) by carrying out the polymerization in the presence of the three monomers St, BD and IP with varying feed ratios. The NMR and DSC analyses suggest that the resulting copolymers are St-BD-IP terpolymers with atactic polystyrene blocks, high cis-1,4-IP (selectivity up to 98%) and high cis-1,4-BD (selectivity up to 96%) units. (C) 2015 Elsevier Ltd. All rights reserved.