A highly active neodymium chloride isopropanol complex/modified methylaluminoxane catalyst for preparing polyisoprene with high cis-1,4 stereospecificity and narrow molecular weight distribution

Neodymium chloride isopropanol complex (NdCl3 center dot 3 (i) PrOH) activated by modified methylaluminoxane (MMAO) was examined in isoprene polymerization in hexane, with regards to Nd compounds, aluminum (Al) compounds, [Al]/[Nd] ratio, polymerization temperature and time. NdCl3 center dot 3 (i) PrOH exhibited high activity producing polymers featuring high cis-1,4 stereospecificity (> 96%), very high molecular weight (Mn > 1.0 x 106) and fairly narrow molecular weight distribution (MWD, Mw/Mn < 2.0) simultaneously. In comparison, neodymium isopropoxide also showed high activity providing polymers with narrow MWD (Mw/Mn = 2.07), but somewhat low cis-1,4 content (ca. 92%), while neodymium chloride had no activity under present polymerization conditions. The Al compounds affected the polymer yield in the order of Al(i- Bu)(3) > MMAO > Al(i-Bu)(2)H. MMAO as cocatalyst afforded polyisoprene with high Mn over 1.0 x 106, whereas as stronger chain transfer agent than MMAO, Al(i-Bu)(3) and Al(i-Bu)(2)H yielded polymers with low Mn (1.0 x 10(5)-8.0 x 105). NdCl3 center dot 3 (i) PrOH/MMAO catalyst showed a fairly good catalytic activity even at relatively low [Al]/[Nd] ratio of 30, and the produced polymer remained high cis-1,4 content of 95.8% along with high Mn over 1.0 x 106 even at elevated temperatures up to 70A degrees C. The polymerization rate is of the first order with respect to the concentration of isoprene. The mechanism of active species formation was discussed preliminarily.