A-Olefins s. Ethylene

C-2,7-Octadien-l-ylation 26, 827 Olefins s. Ethylene derivs. a-Olefins s. Ethylene derivs., terminal Oligomerization... 

Olefins s. Ethylene derivatives a-Olefins s. Ethylene derivatives, terminal Oligonucleotides, removal of 0-prolective groups 21, 25 —, solid-phase synthesis 19, 33 suppl. 21 Orgaiiometallic compounds (s. a. under individual metals. Metal complex compounds)... 

Olefins s. Ethylene derivatives a-Olefins s. Ethylene derivatives, terminal Oleic acid as reagent 16, 867 Oligopeptides... 

How can one explain the occurrence of steric defects in tactic poly(ot-olefin)s Explain why high-resolution nuclear magnetic resonance is the most convenient method for determining the chain micro structure in poly(a-olefin)s. Consider how 3H and 13C NMR spectroscopy can provide stereochemical information concerning a-olefin polymer chains on the diad level (m, r) and the triad level (mm, rr, mr). Explain why /1-olefins, which do not homopolymerise (without isomerisation) in the presence of Ziegler-Natta catalysts, undergo copolymerisation with ethylene in the presence of these catalysts. 

YOO Yoorr, J.S., Chrmg, C.Y., and Lee, I.H., Solrrbihty and diffusion coefficient of gaseous ethylene and a-olefin in ethylene/a-olefin random copolymers, Eur. Polym. J., 30, 1209, 1994. 

FIG. 5 The influence on the glass transition temperature of poIy(a-olefin)s of the atomic mass of the side-group radical attached directly to the a-C atom in the ethylenic main... 

In contrast, catalysts that can operate in high-temperature processes (> 100 ° C) can overcome the limitations and form OBCs through sequential monomer addition. Only catalyst systems 1-4 have demonstrated CCTP in ethylene polymerization at reactor temperatures in excess of 100 °C. The solubility of atactic PPs (aPPs) and other poly(a-olefin)s allows CCTP at lower temperatures with these monomers, as described for catalyst system 24. However, this catalyst system has not yet been used to synthesize BCPs using CCTP. To date, only catalyst system 4 has been used to make OBCs using single catalyst CCTP and sequential monomer addirion. ... 

Idemitsu Process. Idemitsu built a 50 t x 10 per year plant at Chiba, Japan, which was commissioned in Febmary of 1989. In the Idemitsu process, ethylene is oligomerised at 120°C and 3.3 MPa (33 atm) for about one hour in the presence of a large amount of cyclohexane and a three-component catalyst. The cyclohexane comprises about 120% of the product olefin. The catalyst includes sirconium tetrachloride, an aluminum alkyl such as a mixture of ethylalurninumsesquichloride and triethyl aluminum, and a Lewis base such as thiophene or an alcohol such as methanol (qv). This catalyst combination appears to produce more polymer (- 2%) than catalysts used in other a-olefin processes. The catalyst content of the cmde product is about 0.1 wt %. The catalyst is killed by using weak ammonium hydroxide followed by a water wash. Ethylene and cyclohexane are recycled. Idemitsu s basic a-olefin process patent (9) indicates that linear a-olefin levels are as high as 96% at C g and close to 100% at and Cg. This is somewhat higher than those produced by other processes. 

Functionalized polyethylene would be of great industrial importance, and if synthetic methods to control the microstructure of functionalized polymers using transition-metal-based catalysis are developed, it would significantly broaden the utility and range of properties of this class of polymers. Recent progress in the field of late transition metal chemistry, such as Brookliart s use of nickel-based diimine catalysts, has enabled the copolymerization of ethylene with functional a-olefins.29 However, these systems incorporate functionalized olefins randomly and with limited quantity (mol percent) into the polymer backbone. 

The amount of ethylene is limited because it is necessary to restrict the amount of unsaturated components so as to avoid the formation of deposits caused by the polymerization of the olefin(s). In addition, ethylene [boiling point —104°C (—155°F)] is more volatile than ethane [boiling point —88°C (—127°F)], and therefore a product with a substantial proportion of ethylene will have a higher vapor pressure and volatility than one that is predominantly ethane. Butadiene is also undesirable because it may also produce polymeric products that form deposits and cause blockage of lines. 

Metathesis activity. A quantitative comparison of metathesis activities was made in the gas phase homometathesis of propylene. The reaction kinetics are readily monitored since all olefins (propylene, ethylene, cis- and fra/3s-2-butylenes) are present in a single phase. Metathesis of 30 Torr propylene was monitored in a batch reactor thermostatted at 0 °C, in the presence of 10 mg catalyst. The disappearance of propylene over perrhenate/silica-alumina (0.83 wt% Re) activated with SnMe4 is shown in Figure 2a. The propylene-time profile is pseudo-first-order, with kob (1.11 + 0.04) X 10" slightly lower rate constant, (0.67 constants are linearly dependent on Re loading. Figure 3. The slope yields the second-order rate constant k = (13.2 + 0.2) s (g Re) at 0°C. 

Polyolefins with vinyl end groups can be readily transformed into end-functionalized polyolefins by post-polymerization functionalization to yield a wide variety of end-functionalized polyolefins, which include epoxy-, amine-, and hydroxy-terminated polyolefins. Brookhart, Gibson, and co-workers reported on diimine-pyridine-ligated Fe complexes incorporating sterically less hindered alkyl substituents such as a methyl group ortho to the imine-A s, F12-1, that selectively converted ethylene to oligomers, affording linear a-olefin mixtures (>99%) (see also Section... 

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