Heike Windisch

Polymerization of 1,3-butadiene initiated by neodymium versatate/diisobutylaluminium hydride/ethylaluminium sesquichloride: Kinetics and conclusions about the reaction mechanism

The kinetics of the polymerization of 1,3-butadiene initiated by the ternary Ziegler-Natta catalyst system comprising neodymium versatate (NdV), diisobutylaluminium hydride (DIBAH) and ethylaluminium sesquichloride (EASC) have been studied in order to quantify the impact of the catalyst components EASC and DIBAH on the polymerization rate, the control of molar masses, the molar mass distributions as well as on the microstructure of the resulting polymer (cis-1,4, trans-1,4 and 1,2 content). A further focus of the work was on the elucidation of the living nature of the polymerization. It has been found that the catalyst component EASC influences the reaction rate and the microstructure of the obtained polybutadiene. The main effect of the variation of DIBAH is on the molar mass, but the polymerization rate and the microstructure are also influenced. Straight lines are obtained for the dependence of the molar masses on monomer for the dependence of the molar masses on monomer conversion revealing the living nature of the polymerization. The theoretically predicted molar masses are significantly higher than those experimentally found. This discrepancy is explained by the existence of dormant species resulting from the reversible transfer of living polymer chains from Nd onto Al. Only one third of the DIBAH which is not consumed by the processes of scavenging of impurities and activation of the Nd catalyst, is involved in this transfer reaction. This makes DIBAH an inefficient chain control agent for the experimental conditions applied (namely 60°C). A reaction scheme is put forward which accounts for the features observed.

Polymerization of 1,3‐Butadiene Initiated by Neodymium Versatate/Triisobutylaluminum/Ethylaluminum Sesquichloride: Impact of the Alkylaluminum Cocatalyst Component

Abstract The polymerization of 1,3‐butadiene (BD) by the ternary Ziegler/Natta (Z/N) catalyst system neodymium versatate (NdV)/ethylaluminum sesquichloride (EASC)/aluminum alkyl is investigated. Special attention is paid to the impact of the aluminum alkyl on the polymerization kinetics and on the control of molar masses. In this respect diisobutyl aluminumhydride (DIBAH) and triisobutylaluminum (TIBA) are compared. Within a broad range of n Al‐Alkyl/n NdV‐ratios for both aluminum compounds the features of a living polymerization with a reversible exchange of the living polybutadienyl chains between neodymium (Nd) and aluminum are observed. The equilibrium position of this reaction is different for TIBA and DIBAH. At the same molar loadings DIBAH results in polybutadienes with molar masses which are 1/8 of those obtained in the presence of the cocatalyst TIBA. This difference is explained by a significantly more facile substitution of a hydride moiety from DIBAH than an isobutyl group from either DIBAH or TIBA by a living polybutadienyl chain.

Komplexkatalyse LI. Komplexe des Tris(allyl)lanthans mit verschiedenen Donorliganden La(η3-C3H5)3 · L (L:DME, TMED, 2HMPT) und ihre katalytischen Eigenschaften in der stereospezifischen Butadienpolymerisation

Abstract The dimeric tris(allyl)lanthanum dioxane complex [La(η3-C3H5)3 · (C4H8O2)1.5]2 1 can be transformed by reaction with other donor ligands in monomeric complexes of the type [La(η3-C3H5)3 · L] (L:DME = dimethylethyleneglycolether (2), TMED = tetramethylethylenediamine (3) and 2HMPT = hexamethylphosphorictriamide (4)). The complexes were characterized by elemental analysis, 1H, 13C and 139La NMR spectroscopy. Single crystal X-ray structure analysis of 3 gave the formula [La(η3-C3H5)3 (η2-Me2NC2H4NMe2)] in the monoclinic space group P21/n with cell parameters a = 8.124(4) A, b = 14.458(6) A c = 15.233(7) A and β = 94.14(2)°. The complexes catalyze polymerization of butadiene in toluene at 50°C with high 1,4-trans selectivity. The catalytic activity decreases accordingly to 1 ≈ 2 > 3 ≫ 4 depending on the bond strength of the ligands. With addition of methylaluminoxane (MAO) the catalytic activity increases correspondingly and a 1,4-cis selectivity of 40–60% is obtained.