Werner Obrecht

Neodymium-based ziegler/natta catalysts and their application in diene polymerization

This article reviews the polymerization of dienes by neodymium (Nd) based Ziegler/Natta-catalyst systems. Special attention is paid to the monomer 1,3-butadiene (BD). The review covers scientific as well as patent literature which was published during the last decade to 2005. For a better understanding of the recent developments the early work on lanthanide-catalyzed diene polymerization is also addressed. The most important product obtained by Nd catalysis, butadiene rubber (Nd-BR) is introduced from an industrial as well as from a material scientists point of view. Strong attention is paid to the great variety of Ziegler/Natta type Nd-catalyst systems which are often referred to as binary, ternary and quaternary systems. Different Nd-precursors, cocatalysts, halide donors and other additives are reviewed in detail. Technological aspects such as solvents, catalyst addition order, catalyst preformation, polymerization temperature, molar mass control, post-polymerization modifications etc., are presented. A considerable part of this review discusses variations of the molar ratios of the catalyst components and their influence on the polymerization characteristics. Non-established polymerization technologies such as polymerization in bulk, slurry and gas phase as well as the homopolymerization in the presence of other monomers are addressed. Also the copolymerizations of butadiene with isoprene, styrene and alkenes are reviewed. Mechanistic aspects such as formation of the active catalyst species, the living character of the polymerization, mode of monomer insertion, and molar mass control reactions are also explained. In the summary Nd technology is evaluated in comparison with other established technologies for the production of high cis-1,4-BR. Unsolved and open questions about Nd-catalyzed diene polymerization are also presented.

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.

Molar Mass Control by Diethyl Zinc in the Polymerization of Butadiene Initiated by the Ternary Catalyst System Neodymium Versatate/Diisobutylaluminum Hydride/Ethylaluminum Sesquichloride

The polymerization of 1,3‐butadiene (BD) catalyzed by the ternary Ziegler/Natta catalyst system neodymium versatate (NdV)/diisobutylaluminum hydride (DIBAH)/ethylaluminum sesquichloride (EASC) is investigated in regard to molar mass control by diethyl zinc (ZnEt2). Within the investigated range of ratios of ZnEt2 to NdV, the features of a living polymerization with a reversible exchange of the living polybutadienyl chains between neodymium and zinc are observed. In summary, ZnEt2 can be considered as an efficient molar mass control agent, which has a negligible impact on polymerization rates. In addition to the reduction of molar masses, ZnEt2 also reduces the polydispersity (PDI) and leads to a decrease of the cis‐1,4‐content.

Comparison of the Solvents n‐Hexane, tert‐Butyl Benzene and Toluene in the Polymerization of 1,3‐Butadiene with the Ziegler Catalyst System Neodymium Versatate/Diisobutylaluminum Hydride/Ethylaluminum Sesquichloride

The influence of the solvents n‐hexane, tert‐butyl benzene (TBB) and toluene on the Nd‐catalyzed polymerization of butadiene was studied. Special emphasis was placed on polymerization kinetics and on the evolution of molar masses and molar mass distributions with monomer conversion. Distinct differences were found between the three solvents. From the polymerization kinetics there is evidence which supports Porris view on the competitive coordination between aromatic solvents and butadiene to active Nd‐sites. In addition, there are indications for the irreversible transfer of benzyl‐H‐atoms from toluene to active allyl‐anionic polymer chains. The evolution of molar mass distributions with monomer conversion provides evidence for the existence of two active catalyst species which are present in all three solvents. One of these two species is highly reactive (“hot”) and short‐lived. This species generates BR with high molar mass. The second species has a low reactivity and lives throughout the entire course of the polymerization. In n‐hexane the “hot”, short‐lived species is present only at the start of the polymerization, whereas in TBB and toluene, the short‐lived species becomes evident at monomer conversion>10% and is constantly (re)generated. Cis‐1,4‐contents determined at final monomer conversion are not in line with other available studies in this field.

A Comparison of Neodymium Versatate, Neodymium Neopentanolate and Neodymium Bis(2‐ethylhexyl)phosphate in Ternary Ziegler Type Catalyst Systems With Regard to their Impact on the Polymerization of 1,3‐Butadiene

In ternary Ziegler catalyst systems comprised of a Nd‐component, diisobutylaluminum hydride (DIBAH) and ethylaluminum sesquichloride (EASC), three Nd salts [neodymium versatate (NdV), neodymium neopentanolate (NdA) and neodymium bis(2‐ethylhexyl)phosphate (NdP)] are compared regarding their activities in the polymerization of 1,3‐butadiene (BD) and the various features of the poly(butadiene)s obtained. For these three systems, the impact of the molar ratios nCl/nNd and nDIBAH/nNd on catalyst activity and polymer properties (M¯n, PDI and microstructure) has been studied. The highest polymerization activity is found for the catalyst system NdV/DIBAH/EASC at nCl/nNdV=2 and nDIBAH/nNdV=30. The NdP based system is characterized by remarkably high activity, especially at low ratios of nDIBAH/nNdP (e.g. nDIBAH/nNdP=5). The NdA containing catalyst systems are less active compared to NdV and NdP systems. In all three catalyst systems, the cis‐1,4‐content decreases with increasing ratios of nDIBAH/nNd. The highest cis‐1,4 content (97.6%) is found for the NdP‐containing system at nDIBAH/nNdP=5 and nCl/nNdP=2.

New Branched Polyisobutenes and Butyl Rubbers by the Inimer Method

This paper reviews the synthesis of branched and hyperbranched polymers from an industrial point of view. The synthesis of branched polyisobutene and butyl rubber using the inimer method is presented. Branched copolymers were prepared in solution and bulk, using p-chloromethylstyrene (vinylbenzyl chloride) as inimer and MAO and diethylaluminum chloride as coinitiators. The polymers were characterized by SEC-viscometry.