Ternary catalyst systems

A ternary Rh catalyst system, [(nbd)RhCl]2-LiCPh=CPh2-PPh3, " induces the living polymerization of phenylacetylenes. In the latter case, the initiating species is a vinylrhodium 10, which was isolated and well characterized by X-ray analysis.The details for the living polymerization are described in Section 11.16.4.1. 

A molybdenum oxychloride-based catalyst system, MoOCl4- -Bu4Sn-EtOH, is more active than Mods ones. " In the polymerization of 1-chloro-l-octyne by the oxychloride-based catalyst, propagation rate is improved to be faster and MWD of the formed polymer is smaller. This ternary catalyst also induces living polymerization of... 

Last, but not least, the development of ternary catalyst systems consisting of a metallocene, an organoborate, and an aluminium compound will reduce the manufacturing costs of mPE and will improve its ability to compete with other polymers. 

Imai, Saegusa, Furukawa et al. (48,66) carried out kinetic studies of THF polymerization in bulk and in cyclohexane solution at 0° C. They used a ternary catalyst system consisting of AlEt3-H20(2 l)-epichloro-hydrin (ECH). They obtained high molecular weight polymer and noticed no evidence for either termination or transfer. Their polymerizations were preceded by an induction period as shown in Fig. 13 but after that their data could be fitted to an equation of the same form as equation 42. This time [f0] was defined as the concentration of propagating species ([P ]) determined from the amount and the molecular weight of product polymer. 

To increase the number of catalysts, the binary catalyst system zirconium/ platinum was extended to a ternary system by adding a third component such as molybdenum. The expected quality of such a composition is given in Figure 3.8. First results of such a ternary layer are presented in Figure 3.9 (left). The layer was deposited on a silicon monocrystalline wafer and the layer composition again examined with SNMS. 

From the early 1960s onwards, the use of lanthanide (Ln) based catalysts for the polymerization of conjugated dienes came to be the focus of fundamental studies [31]. The first patent on the use of lanthanides for diene polymerization originates from 1964 and was submitted by Union Carbide Corporation (UCC) [32,33]. In this patent the use of binary lanthanum and cerium catalysts is claimed. Soon after this discovery by UCC, Throckmorton (Goodyear) revealed the superiority of ternary lanthanide catalyst systems over binary catalyst systems. The ternary systems introduced by Throckmorton comprise a lanthanide compound, an aluminum alkyl cocatalyst and a halide donor [34], Out of the whole series of lanthanides Throckmorton... 

The high activity of Nd-based catalysts was reported by Shen et al. in 1980 [92], In this publication, the polymerization activity of the whole lanthanide series was studied. Ln halogen-based binary catalyst systems (LnCb/EtOH/AlEts or LnCl3 (TBPU/Al Bua), as well as Ln-carboxylate-based ternary catalyst systems (Ln(naphthenate)3/AlIBu3/EASC) were used. The activity profile for the entire series of lanthanides is depicted in Fig. 2. Two years later, Monakov et al. confirmed in a similar study that Nd is the most active Ln element [93,94]. 

It is speculated that the use of heterogeneous or partially heterogeneous Nd catalyst systems results in gel formation. Due to this reason, Nd-systems which are soluble in hydrocarbon solvents are preferred today, especially in large-scale operations. The soluble catalysts are usually based on ternary systems which consist of Nd salts with anions bearing long-chain aliphatic groups, an alkyl aluminum cocatalyst and a halide donor. 

Standard Nd-based catalysts comprise binary and ternary systems. Binary systems consist of Nd chloride and an aluminum alkyl or a magnesium alkyl compound. In ternary catalyst systems a halide free Nd-precursor such as a Nd-carboxylate is combined with an Al- or Mg-alkyl plus a halide donor. By the addition of halide donors to halide-free catalyst systems catalyst activities and cis- 1,4-contents are significantly increased. In quaternary catalyst systems a solubilizing agent for either the Nd-salt or for the halide donor is used in addition to the components used in ternary systems. There are even more complex catalyst systems which are described in the patent literature. These systems comprise up to eight different catalyst components. 

In addition to the polymerization of dienes the versatility of NdP-based catalysts is exceptional regarding the number of different non-diene monomers which can be polymerized with these catalysts. Acetylene is polymerized by the binary catalyst system NdP/AlEt3 [253,254]. Lactides are polymerized by the ternary system NdP/AlEt3/H20 [255,256]. NdP/TIBA systems are applied in the copolymerization of carbon dioxide and epichlorhy-drine [257] as well as for the block copolymerization of IP and epichloro-hydrin [258]. The ternary catalyst system NdP/MgBu2/TMEDA allows for the homopolymerization of polar monomers such as acrylonitrile [259] and methylmethacrylate [260]. The quaternary system NdP/MgBu2/AlEt3/HMPTA is used for the polymerization of styrene [261]. 

In addition to these two studies the polymerization kinetics of three different Nd-compounds which were activated by DIBAH and EASC were comparatively studied. In this investigation a Nd alcoholate [NdA = neodymium(III) neopentanolate], a Nd phosphate [NdP = neodymium(III) 2-ethyl-hexyl-phosphate] and a Nd carboxylate (NdV) were compared with a special focus on the variation of the molar ratios of zzdibah/hncI and ci/ Nd [272]. For each of these ternary catalyst systems the polymerization activities depend... 

In the polymerization of dienes with Ziegler/Natta catalyst systems it is a well-established fact that the presence of halide donors is essential in order to achieve high catalytic activities and high cis-1,4-contents [360,361]. The halide free catalyst system NdO/TIBA is a good example for a catalyst with a poor performance and a high trans- 1,4-specificity [362,363]. For various binary and ternary catalyst systems the qualitative impact of chlorides on the stereochemistry of BR is demonstrated in a series of fundamental experiments the results of which are summarized in (Table 5) [364],... 

For ternary catalyst systems a vast number of halide donors was investigated which renders a complete quotation impossible. It is important to note, however, that for a given halide, the actual halide source neither has a strong influence on catalyst activity nor on cis- 1,4-contents. As halogen sources which are found in the literature cover the whole range from ionic halides to covalently bound halogen atoms the strength by which the halide is bound to the donor is not a critical factor. 

Variations of the amount of cocatalyst which are usually expressed by the molar ratio W Nd have a significant influence on polymerization rates, molar masses, MMDs and on the microstructures of the resulting polymers. These aspects are addressed in the following sections with a special emphasis on ternary catalyst systems. For ternary systems it has to be emphasized, however, that in many reports the ratio Ai/ Nd only accounts for the amount of aluminum alkyl cocatalyst and not for other Al-sources such as alkyl aluminum halides. Variations of the Ai/ Nd-ratios are also used for defined control of molar mass. This aspect is addressed in separate sections (Sects. 2.2.8 and 4.5). 

In the context of ternary catalyst systems Throckmorton s pioneering work is worth mentioning although in this study Ce rather than Nd-based catalyst systems were used. For the two catalyst systems Ce octanoate/TIBA/DEAC and Ce octanoate/TIBA/EADC catalyst activities increased up to TiBA/ Ce = 20. Further increases in the TiBA/ Ce-ratios from 20-60 did not result in further activity improvements [34]. For a ternary didymium (Di)-based oc-tanoate catalyst system Witte described a similar dependence. Within the wAl/ Di-range 20-40 significant increases of polymerization rates were reported. Further increases of the nAi//iDi-ratios did not have an additional effect [49]. 

Ternary Nd-carboxylate-based catalyst systems also show increasing catalyst activities with increasing Ai/ Nd-ratios. For NdV/TIBA/EASC the activity increase was described by a linear dependence in a double logarithmic... 

For the ternary neodymium phosphate-based catalyst systems (NdP/ DIBAH/EASC) a totally different dependence of polymerization rates on Ai/ Nd-rahos was reported [264-269,272]. According to these studies the catalyst system is highly active even at low Ai/MNd-ratios < 5 and polymerization rates decrease with increasing Ai/ Nd-ratios within the Ai/ Nd-range = 5-50 (Sect. 2.1.1.10) [272]. 

With a few exceptions, for binary as well as for ternary catalyst systems cis-1,4-contents decrease with increasing Ai/ Nd-ratios. This decrease of as-1,4-contents can be best explained on the basis of a model given in Scheme 30 in Sect. 4.3. According to this model aluminum alkyls act as ligands competing for vacant Nd sites. 

For ternary catalyst systems the decrease in cis- 1,4-contents with increasing Ai/ Nd-ratios is a common feature. The first report in which the decrease of ds-1,4-contents with increasing cocatalyst concentrations is addressed dates back to Throckmorton s study in which Ce-based catalyst systems were used [34]. The same dependence was confirmed in a subsequent study in which didymium octanoate-based catalysts were used [49]. In this study BD was polymerized and a decrease of the cis- 1,4-content from 95% at Al/ Di = 20 to 90% at Ai/ r)i = 60 is reported. 

Halide donors constitute an essential component of ternary catalyst systems (Sect. 2.1.3). In these systems variations of the molar ratios x/ Nd (X = halide) affect catalyst activities, molar masses, MMDs and the microstructures of the poly(diene)s. 

In ternary catalyst systems halides play an important role in the activation process of the Nd-precursor (Sect. 4.2). At low x/ Nd-ratios the contribution of the halide is small. Increasing Mx/ Nd-ralios, on one hand result in catalyst... 

For Nd-based ternary catalyst systems the dependence of polymerization rates on nx/ Nd ratios was in the focus of numerous studies. The results of these studies are summarized in Table 8. 

The literature referring to catalyst preformation of binary catalyst systems is not addressed in this work. In this review the available studies on ternary catalyst systems are summarized. The available literature is discussed in the following two subsections Preformation without Monomer and Preformation in the Presence of Diene Monomers . 

In two articles Dong et al. report on the variation of the addition order in ternary catalyst systems of the type Nd(0 Pr)3/Al-cocatalyst/tBuCl. In both studies two components of the ternary system are prereacted prior to the addition of the third component. In the first of these studies the Al-cocatalyst DIBAH was used [232], In the second study DIBAH was replaced by MAO [232], The results of these two investigations are summarized in the Tables 12 and 13. 

Literature describes a series of additives which are deliberately added to Nd catalyst systems. These additives aim at an increase of the solubility of catalyst components in organic solvents and at an increase of polymerization activity. In addition, additives are used to influence the width and the modality of MMDs. By the use of additives the number of catalyst components is increased from two (binary catalyst systems) or three (ternary catalyst systems) to multi-component systems which comprise up to seven or even eight different components. Additives reported in the literature and the influence of these additives is discussed in the following section. 

The first report on higher polymerization activities in hexane than in benzene dates back to Throckmorton s pioneering work on ternary Ce-based catalyst systems [34], To the present day there are several reports available in the literature in which the influence of solvents on polymerization activities, microstructure of the resulting polymers and molar masses are compared. The relevant results of these investigations are summarized in this section. 

For ternary catalyst systems polymerization activities are also higher in aliphatic and cycloaliphatic hydrocarbons than in aromatic solvents. These features were observed for various catalysts systems. Detailed studies are available for NdzO/TIBA/DEAC [161,165,166], NdV/DIBAH/EASC [205,422], Nd(N(SiMe3)2)3/TIBA/DEAC [318,320], NdV/DIBAH/fBuCl [423] and NdV/ MAO/fBuCl [175]. 

In the most recent study by Dong et al. the impact of solvents was determined for the ternary catalyst system Nd(() Pr)3/[ I INMe2Ph]+[B(C6F5)4] / TIBA (1/1/30) [233]. In heptane and cyclohexane polymer yields are particularly high. Polymerization in heptane provided a polymer with a relatively narrow MMD whereas the use of cyclohexane resulted in a bimodal MMD. Czs-1,4 contents are slightly higher in cyclohexane (91.3%) than in heptane (90.4%). Polymerization in dichloromethane results in a very low polymer yield and an increased cis- 1,4-content (93.4%). In toluene no polymer is obtained, at all. 

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