Early Polyolefin Catalysts

The most widely used transition metal salts have been the relatively cheap titanium or vanadium halides, reduced with aluminum alkyls. In Ziegler s work, titanium tetrachloride was reduced to brown yS-titanium trichloride, which was able to polymerize ethylene. However, when yS-titanium trichloride catalyst was used in the polymerization of propylene, the product contained a high proportion of the gum like atactic polymer, which was not viable for commercial use. In contrast, Natta, in his work on the polymerization of propylene and other a-olefins, showed that violet a-titanium trichloride could polymerize propylene to the useful, crystalline, isotactic polymer. Nevertheless, a relatively large quantity of atactic polypropylene still had to be separated from the commercial isotactic product. 

Most of the early catalyst development was related to the need for a more active catalyst to improve productivity. With low-activity catalysts, the polymer must be de-ashed to remove solid catalyst residues so as to meet product speci- 

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The addition of reagents containing X-H bonds in which X is more electronegative than H typically lead to addition across the M-C bond in the direction opposite to the addition of silane or borane to the early metal catalysts. Polymerization of etiiylene with lanthanide catalysts in the presence of phosphines generates phosphine-terminated polymers (Scheme 22.12) - by a mechanism in which the alkyl chain is protonated, and a metal-phosphido complex is generated. This phosphido complex then inserts olefin to start the growth of a phosphine-functionalized polyolefin. Marks subsequently showed that a similar process can be conducted witii amines. In this case, the bulky dicyclohexylamine was needed to sufficiently retard the rate of protonation to allow chain growth. The steric bulk also makes the olefin insertion more favorable thermodynamically. 

In order to achieve higher-performing engineering thermoplastic properties, significant modification of the polymer backbone is required. The use of carbon monoxide as a comonomer has been of interest based on its abundance and its ability to confer functionahty. However, conventional early transition metal polyolefin catalysts are ineffective at copolymerizing olefins with carbon monoxide. 

Based on an early process discovered by Natta in the 1950s, soluble transition metal catalysts like metallocenes were developed mainly in the 1950s as initiators for polyolefin syntheses. Others are still now under investigation, like the so-called LTM (for "late transition metal") catalysts. Metallocenes seem... 

In this contribution, we describe the discovery and application of phenoxy-imine ligated early transition metal complexes (FI catalysts) for olefin polymerization, including the concept behind our catalyst design, the discovery and the polymerization behavior of FI catalysts, and their applications to new polyolefinic materials. 

The annual production of various polymers can be measured only in billion tons of which polyolefins alone figure around 100 million tons per year. In addition to radical and ionic polymerization, a large part of this huge amount is manufactured by coordination polymerization technology. The most important Ziegler-Natta, chromium- and metallocene-based catalysts, however, contain early transition metals which are too oxophiUc to be used in aqueous media. Nevertheless, with the late transition metals there is some room for coordination polymerization in aqueous systems [1,2] and the number of studies published on this topic is steadily growing. 

Nature has long used reactions such as these to produce interesting solids such as cotton (seed pod), hemp (grass), and silk (cocoons for worms while they develop into moths) as fibers that we can strand into rope or weave into cloth. Chemists discovered in the early twentieth century that cellulose could be hydrolyzed with acetic acid to form cellulose acetate and then repolymerized into Rayon, which has properties similar to cotton. They then searched for manmade monomers with which to tailor properties as replacements for rope and sdk. In the 1930s chemists at DuPont and at ICl found that polyamides and polyesters had properties that could replace each of these. [Linear polyolefins do not seem to form in nature as do condensation polymers. This is probably because the organometaUic catalysts are extremely sensitive to traces of H2O, CO, and other contaminants. This is an example where we can create materials in the laboratory that are not found in nature.]... 

Let us first consider the catalyst/polyolefin particle in the early stage of its evolution. The particle consists of the solid catalyst carrier with catalyst sites immobilized on its surface, polymer phase, and pores. The first-principle-based meso-scopic model of particle evolution has to be capable of describing the formation of polymer at catalyst sites, transport of monomer(s) and other re-actants/diluents through the polymer and pore space, and deformation of the polymer and catalyst carrier (including its fragmentation). Similar discrete element modeling techniques have been applied previously to different problems (Heyes et al., 2004 Mikami et al., 1998 Tsuji et al., 1993). 

Metallocene Not a process, but a range of organometallic catalysts for making polyolefins. First commercialized in the early 1990s and now widely used. 

Titanium-based solid-state catalysts for the industrial production of polyolefin materials were discovered in the early 1950 s and have been continually improved since then (see Section 7.3). Due to the high degree to which they have been perfected for the production of large-volume polyolefin commodities, they continue to dominate the processes presently used for polyolefin production. Despite (or because of) this product-oriented perfection, only limited degrees of variability with regard to some relevant polymer properties appear to be inherent in these solid-state catalysts. 

If the metal cation is too electrophilic, CO coordination will be too strong, possibly by coordination via its oxygen atom, and CO will act as a poison rather than participating in the polymerization [40], The moderate electrophilicity of Pd" catalysts makes them tolerant also to a variety of heteroatom functionalities in the olefin substrate. In this respect, polyketone catalysis can have a wider applicability than early transition metal catalysis of polyolefins, which is highly intolerant of functional groups. 

Since the early 1990s there has been considerable interest in metallocene-based polyolefines using catalysts incorporating anilines, in which the nitrogen is a preferred heteroatom for ligand attachment139. 

Early work at Mitsui Petrochemicals concentrated on copolymerization of the multicyclic olefin dimethano-octahydronaphthalene (DMON, structure II (Ri = R2=H) in Fig. 4.1), using soluble vanadium catalysts [4] that eventually led to the commercialization of Apcl polyolefins [5]. Later, the utility of metallocene catalysts for cyclic olefin copolymerization was recognized by both Mitsui and Hoechst [6]. This led to the joint development of the Topas line of polyolefins [7], now being marketed by Ticona. 

The discoveries of several new types of catalysts for (non-aqueous) efhylene and 1-olefin polymerization based on late transition metals over fhe last decade have initiated great interest in fhis field [16, 53-55]. By comparison to early transition metal-based Ziegler or Phillips catalysts used for industrial polyolefin synfhesis [13—... 

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