Study Of Cis-1,4-isoprene Polymerization With Nd(i-octa)₃ -Al(i-Bu)₃-RCl_n Catalyst

Neodymium catalyst is commonly used for preparation of polyisoprene. Polyisoprene with high cis-1,4 content was obtained by Nd(i-octa)₃-Al(i-Bu)₃-RCln(RCln =AlCl₃,CCl₄)catalyst. The solution of polyisoprene is compounded in hydrogenated gasoline. The effect of monomer ratios, catalysts mole ratios and other conditions of polymerization were discussed in detail. Polyisoprene having the best properties was obtained under the following conditions: Nd(i-octa)₃-Al(i-Bu)₃-AlCl₃ catalyst n(Nd)/n(Al)/n(Cl)=1:40:3, n(Nd)/n(Ip)=2.72×10-4, aging mode (Cl+Al)+Nd+Al, sedimentation temperature 20℃, sedimentation time 30min, 50℃polymerized for 1hr; Nd(i-octa)₃-Al(i-Bu)₃-CCl₄ catalyst n(Nd)/n(Al)/n(Cl)=1:40:3, n(Nd)/n(Ip)=6.8×10-4, aging mode Cl+Al+Nd, sedimentation temperature 50℃, sedimentation time 15min, 50℃polymerized for 5hrs.Nd(i-octa)₃-Al(i-Bu)₃-AlCl₃ catalyst polymerized isoprene to afford products featuring high cis-1,4 stereospecificity(ca.96.9%), high molecular weight (ca.105) and relatively narrow molecular weight distributions (Mw/Mn=3.0³.5) simultaneously. The molecular weight distribution curves are unimodal, which indicates that only one kind of active sites are presented in the catalytic system. Moreover, some living polymerization characteristics were demonstrated: (a) absence of chain termination; (b) linear correlation between Mn and polymer yield; (c) increment of molecular weight in the'seeding'polymerization.The Nd(i-octa)₃-Al(i-Bu)₃-CCl₄ catalyst polymerized isoprene to afford products featuring high cis-1,4 stereospecificity (ca.95%), but relatively low molecular weight (ca.104) and rather wide molecular weight distributions (Mw/Mn=8.4). The catalyst produces polymer with unimodal molecular weight distribution indicating that only one kind of active sites are presented.The interaction of components of Nd(i-octa)₃-Al(i-Bu)₃-CCl₄ catalyst was studied from the aspect of conductivity. The results showing that mechanism of the catalyst system was that AlCl3 and Al(i-Bu)3 reacted firstly, then provided Cl to neodymium salt to form active site which had bi-metal complex structure.