The monomeric Nd-catalyst composed of Nd(neodecanoate)(3)(.)(neodecanoic acid)(NdV4)/AlEt2Cl/Al(iBu)(3) showed a high activity (2.0 x 10(6) gNd mol h), and the monomeric active-center was proposed through density functional calculations (B3LYP/CEP-31G). The microstructure of polybutadiene was controlled by chain-transfer with NdV4, catalyst composition and phosphine compounds. As with increase in Nd concentration, increase in branchness and decrease in cold-flow were observed. A series of phosphine compounds was employed to control the microstructure of polybutadiene, and ultra high cis polybutadiene with over 99% cis content was obtained in the presence of tri-p-fluorophenyl phosphine. The vulcanized properties of different microstructured polybutadienes were measured. Linear polymer, Nd-BR1, showed excellent tensile and dynamic properties such as low heat build-up and high abrasion resistance. However, poor processibility in view of high compound viscosity and hardness was obtained. Nd-BR2, designed to compromise both processibility and physical properties, exhibited improved processibility in terms of low compound viscosity with good tensile and dynamic properties. © 2005 Elsevier Ltd. All rights reserved.