Polymerisation titanium catalyst

One variation in polyester intermediates that has roused some interest are those prepared by a ring-opening polymerisation of e-caprolactone and methyl-e-caprolactones with titanium catalysts and diol and triol initiators Figure 27.6). 

Alkoxides and imido are used as anionic ligands in zirconium and titanium catalysts for the polymerisation of alkenes, sometimes as the only anions, but often in combination with cyclopentadienyl ligands. Imides linked to cyclopentadienyl groups form part of the single-site catalyst developed by Dow (Chapter 10) (Figure 1.9, 1). In very different titanium catalysts, namely those used for epoxidation of alkenes, also alkoxide ligands are used (Chapter 14). 

Another application of an isomerisation reaction can be found in the production of the third monomer that is used in the production of EPDM rubber, an elastomeric polymerisation product of Ethene, Propene and a Diene using vanadium chloride catalysts. The starting diene is made from vinylnorbomene via an isomerisation reaction using a titanium catalyst. The titanium catalyst is made from tetravalent salts and main group hydride reagents, according to patent literature. 

The next major improvement in sample quality was the result of developments in direct synthesis. Oriented samples were obtained by the polymerisation of acetylene with the conventional titanium catalyst on a single crystal substrate and in nematic liquid crystals, see Tsukamoto (1992). Heat-treating the catalyst was found to produce polymer that could be stretched to give oriented samples. This resulted in a higher electrical conductivity along the orientation direction, up to 2xl05 fl-lm-1 being obtained. Naarman and co-workers heat treated the catalyst at 393 K and carried out the reaction in silicone oil at room temperature (Theophilou et al., 1986). Silicone oil was chosen as it has the same viscosity at room temperature as the usual solvents... 

In 1956 Natta discovered that propene can be polymerised with a titanium catalyst and that a highly regular polymer is formed. Ziegler and Natta shared the Nobel prize in 1963. 

As previously demonstrated for the ROP of rac-LA, titanium complexes supported by benzotriazole-phenolate 23-28/ a mixture of rac- and meso-amino bis(alkanolate) 40/41 and anatrane 66-69 ligands proved to be efficient catalysts for the ROP of rac-BBL to give poly(3-hydro g butyrate) (PHB). The most notable features of these catalysts are the high polymerisation activity and productivity in solvent-free reactions at 80 °C (rac-BBL Ti = 200, 95-99% conv. after 9-48 min), combined in some cases with high stereoselectivity (i.e. in syndiotactic PHB, up to Pr = 0.73) and narrow PDIs (1.19-1.36). Note that up to now there is no report of isospecific polymerisation of rac-BBL using titanium catalysts. 

Changing the isoprene polymerisation method, in the presence of a titanium catalyst, exerts a different influence on the width of the MWD. The hydrodynamic impact on the double Ti-Al catalytic system, in the turbulent mode, results in the formation of... 

Modern theoretical concepts of the polymerisation of dienes on Ziegler-Natta catalysts are based on the principle of their inherent polycentrism [49]. Substantial changes in the MW characteristics of polyisoprene and polybutadiene, due to the formation of a microheterogeneous titanium catalyst in the turbulent mode, make it reasonable to analyse the distribution of macromolecular growth centres on their kinetic activity. 

Changes in the kinetic activity distribution of the macromolecule growth centres can be observed in the butadiene polymerisation process when a titanium catalyst is prepared in situ. The function F(/w of the studied catalytic system has several maximums, indicating different types of AC in the butadiene polymerisation process and caxaXytk. complex prepared in situ, which is directly in the monomer solution. The number of maximums depends on the conversion (Figure 3.48). Five different types of AC have been identified for the studied system each of them is responsible for the synthesis of the polymer fraction with a specific MW Type -lnM = 7.1-7.8 Type II - / M = 9.4-9.9 Type III - / M = 11.0-12.0 Type IV - / M = 12.7-13.2 and Type V-lnM = 14.6-14.8. 

However, ring-opening polymerisation of the lactide, as practised by Cargill, appears more advantageous. The latter is polymerised in the presence of tin/zirconium or titanium catalysts (this technique is also used to polymerise lactones, e.g. caprolactone on the large scale). Lactide, rather like lactic acid, but now possessing two asymmetric carbon atoms within its structure can exist as three stereoisomers L-lactide, D-lactide, and the meso-lactide (see Figure 10.9). 

High density polyethylene (HDPE) is defined by ASTM D1248-84 as a product of ethylene polymerisation with a density of 0.940 g/cm or higher. This range includes both homopolymers of ethylene and its copolymers with small amounts of a-olefins. The first commercial processes for HDPE manufacture were developed in the early 1950s and utilised a variety of transition-metal polymerisation catalysts based on molybdenum (1), chromium (2,3), and titanium (4). Commercial production of HDPE was started in 1956 in the United States by Phillips Petroleum Company and in Europe by Hoechst (5). HDPE is one of the largest volume commodity plastics produced in the world, with a worldwide capacity in 1994 of over 14 x 10 t/yr and a 32% share of the total polyethylene production. 

Oiganometallic usage is shown in the piepaiation of titanium- oi vanadium-containing catalysts foi the polymerisation of styrene or butadiene by the reaction of dimethyl sulfate with the metal chloride (145). Free-radical activity is proposed for the quaternary product from dimethylaruline and dimethyl sulfate and for the product from l,l,4,4-tetramethyl-2-tetra2ene and dimethyl sulfate (146,147). 

Polyolefins. The most common polyolefin used to prepare composites is polypropylene [9003-07-0] a commodity polymer that has been in commercial production for almost 40 years following its controlled polymerisation by Natta in 1954 (5). Natta used a Ziegler catalyst (6) consisting of titanium tetrachloride and an aluminum alkyl to produce isotactic polypropylene directly from propylene ... 

As indicated by the title, these processes are largely due to the work of Ziegler and coworkers. The type of polymerisation involved is sometimes referred to as co-ordination polymerisation since the mechanism involves a catalyst-monomer co-ordination complex or some other directing force that controls the way in which the monomer approaches the growing chain. The co-ordination catalysts are generally formed by the interaction of the alkyls of Groups I-III metals with halides and other derivatives of transition metals in Groups IV-VIII of the Periodic Table. In a typical process the catalyst is prepared from titanium tetrachloride and aluminium triethyl or some related material. 

Mention has already been made in this chapter of metallocene-catalysed polyethylene (see also Chapter 2). Such metallocene catalysts are transition metal compounds, usually zirconium or titanium. Incorporated into a cyclopentadiene-based structure. During the late 1990s several systems were developed where the new catalysts could be employed in existing polymerisation processes for producing LLDPE-type polymers. These include high pressure autoclave and... 

Polystyrene produced by free-radical polymerisation techniques is part syndio-tactic and part atactic in structure and therefore amorphous. In 1955 Natta and his co-workers reported the preparation of substantially isotactic polystyrene using aluminium alkyl-titanium halide catalyst complexes. Similar systems were also patented by Ziegler at about the same time. The use of n-butyl-lithium as a catalyst has been described. Whereas at room temperature atactic polymers are produced, polymerisation at -30°C leads to isotactic polymer, with a narrow molecular weight distribution. 

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