Novel neodymium (III) isopropoxide‐methylaluminoxane catalyst for isoprene polymerization

A novel catalyst composed of neodymium (III) isopropoxide [Nd(OiPr)3] and methylaluminoxane (MAO) was examined in isoprene polymerization. The Nd(OiPr)3‐MAO catalyst proved to be highly effective in heptane even at low [Al]/[Nd] ratios (ca. 30) to give polyisoprene that possessed high cis‐1,4 stereoregularity (> ca. 90%), a high number‐average molecular weight (Mn ∼105), and relatively narrow molecular weight distributions (Mw/Mn = 1.9–2.8). The catalyst activity increased with an increasing [Al]/[Nd] ratio from 10 to 80 as well as temperature of aging and polymerization from 0 to 60 °C. The polymerization proceeded in the first order with respect to the monomer concentration. Aliphatic solvents (heptane and cyclohexane) achieved a higher yield and Mn of polymer than toluene as a solvent. The Mw/Mn ratio remained around 2.0, and the gel permeation chromatographic curve was always unimodal, indicating that this system is homogeneous and involves a single active site. The microstructure of polyisoprene was determined by IR, 1H NMR, and 13C NMR. The cis‐1,4 contents of the final polymers stayed in the range of 90–92%, regardless of reaction conditions, indicating the high stability of stereospecificity of the catalyst.