Olefin chains

Although most aromatic modified C-5 resins are typically higher softening point resins, certain appHcations, such as adhesives, require lower softening points. Copolymerization of a C-8—C-10 vinyl aromatic fraction with piperylenes in the presence of a C-4—C-8 mono-olefin chain-transfer stream yields resins with softening points ranging from 0—40°C (44). A particular advantage of these Hquid resins is the fact that they eliminate the need for plasticizers or oils in some pressure sensitive adhesive appHcations. 

PVP/alpha-olefins ISP/Ganex various (olefin chain length surface active film formers waterproofing... 

In their early studies, Schwartz and co-workers [5, 80] reported the zirconocene hydrido chloride [Cp2Zr(H)Cl] (1) as a reagent capable of reacting under mild conditions with a variey of non-functionalized alkenes to form isolable alkylzirconi-um(lV) complexes Cp2Zr(R)Cl in which the zirconium is attached to the least-hindered terminal primary carbon, irrespective of the original location of the double bond in the olefin chain. As an example, at room temperature in benzene, 1-octene, cis-4-octene and trows-4-octene all yield the n-octylzirconocene derivative (Scheme 8-6) [80]. 

For example, the decomposition of a hydroperoxide to generate an alkoxy free radical can result in the reaction of the alkoxy radical with an olefin. A carbon radical then forms. Olefin chain propagation and polymerization can follow to yield high-molecular-weight deposits. 

As the double bond is moved from 1 to the 2 position, there is a further increase in both the density and the refractive index, the increments becoming smaller as the double bond is buried more deeply in the normal olefin chain (normal octenes, Table II). 

The reaction has been applied to the synthesis of C-2, C-3 branched-chain uridine derivatives of either lyxo 67a or ribo configuration 67b. Interestingly, only one diastereo-isomer 68a is formed when the olefin chain is located on the (3-face of the furanose ring lyxo configuration), whereas a mixture of the two possible diastereoisomers 68b is obtained when the olefin is located on the a-face ribo configuration) [91] (see Scheme 26). 

A rather sophisticated application of Woessner s theory has been accomplished for all-frtws-retinal and its isomers [165], After determination of the components of the rotational diffusion tensor in retinal for various dihedral angles between the olefinic chain... 

Figure 14 shows the structures of the most stable transition states leading to the R products, for propene, 1-hexene and 1-decene. The authors claim that one can see how the elongation of the olefin chain from propene to 1-hexene increases the interactions between the olefin and the three most important parts of the catalysts, Quinoline A, PYDZ and Quinuclidine B. Moving from propene to 1-hexene, the carbon atoms added to the aliphatic chain are still close to these three parts of the catalyst, and can have strong interactions. In contrast, once the aliphatic n-alkene has six carbon atoms, all of the carbon atoms subsequently added to the chain are too far from the catalyst to interact strongly with it. These interactions between the aliphatic... 

If the successive vertical lines are located alternately on the opposite sides of the horizontal line, above and below it, in the adapted Fischer projection, or if the successive alkyl substituents appear alternately in front of and behind the plane of the extended polymer backbone in the flat zigzag projection (Figure 3.1), then a syndiotactic poly(a-olefin) structure occurs. These two representations show that the syndiotactic polymer contains neighbouring tertiary carbon atoms of opposite relative configurations. The syndiotactic poly (a-olefin) chain is characterised by the appearance of stereodiads of the opposed relative... 

The r diad has a twofold axis of symmetry, and consequently the two methylene protons are in equivalent environments in the poly(a-olefin) chain ... 

Let us recall that triad tacticity describes isotactic (mm), syndiotactic (rr) and heterotactic stereotriads (mr) in the poly (a-olefin) chain ... 

Let us consider typical steric defects in (mainly) isotactic poly(a-olefin) chains. One can imagine two ways in which a minor configurational error may be introduced into an isotactic polymer chain a steric propagation error, denoted as... 

Figure 3.45 Typical steric defects (pentad distribution of stereoerrors) in a (mainly) isotactic poly(a-olefin) chain (a) isolated r diad, characteristic of chain end stereocontrol (b) pair of r diads, characteristic of enantiomorphic site stereocontrol during the propagation...

The reaction conditions used were quite mild, e.g. 1 atm O2 ambient temperature. Reaction rate was studied both as a function of olefin chain length and as a function of solvent composition. It was found that In a mlcroemulslon the rate of reaction decreased with Increasing chain length. Catalyst turnover rates, after two hours, were Cj q=19.1, C, =15.7 and Ci8 12.4. 

Homogeneous polyaUcene catalysis has progressed to the point where metals not generally associated with coordination polymerization can now be made to promote olefin chain growth and metals long ago associated with polyalkene catalysis have been given new life. 

The metal catalyst cracks paraffinic chains longer than C25 and reforms chains shorter than Ce. This is especially important to convert the a-olefin chains (1-alkenes) to saturated alkanes. The catalyst ensures that the final fuel has a carbon chain distribution in the range C8-C25 peaking at Cie (cetane) (Figure 15.8). The catalytic tower uses technology borrowed from the petrochemical industry for the hydrogenated of C=C double bonds, e.g. Raney Nickel or so-called Adams catalyst. 

D-Limonene and ot-pinene have been used as renewable solvents and chain transfer agents in metallocene-methylaluminoxane (MAO) catalysed polymerization of ot-olefins. Chain transfer from the catalyst to the solvent reduces the achieved in limonene compared with toluene and also reduces the overall catalyst activity. This was confirmed, as in the ROMP studies, by performing identical reactions in hydrogenated limonene. However, an increase in stereospecificity was seen when D-limonene was used as the solvent. This is measured as the mole fraction of [mmmm] pentads seen in NMR spectra of the polymer. 100% isotactic polypropylene would give a value of 1.0. On performing the same propylene polymerization reactions in toluene and then in limonene, the mole fraction of [mmmm] pentads increased from 0.86 to 0.94, indicating that using a chiral solvent influences the outcome of stereospecific polymerizations. Unfortunately, when a-pinene was used, some poly(a-pinene) was found to form and this contaminates the main polymer product. 

Chain termination probabilities are readily separated into the individual contributions from each type of chain termination [Eq. (4)]. The net termination to olefins becomes the difference between jSo, the probability of forming an a-olefin, and j8r, the probability that it will readsorb before leaving the catalyst bed. On both Co and Ru catalysts, the net olefin chain termination probability (j8 - j8r) decreases rapidly with increasing carbon number (Figs. 9a and 10a). This termination probability becomes zero for hydrocarbon chains larger than about C25 because olefins disappear from the reactor effluent, even at very short bed residence times. Bed residence times shorter than 2 s (and CO conversions less than about 10%) do not affect chain termination probabilities even for short hydrocarbon chains, because fast convective transport removes a-olefins from the catalyst bed before readsorption occurs. Yet, readsorption within pellets occurs even at short bed residence times, because intrapellet residence times do not depend on space velocity consequently, chain termination to olefins and the olefin content in products still decrease strongly with increasing hydrocarbon size. 

Fro. 13. Site density effects on selectivity and chain termination probability Co/TiOa (catalyst A 11.7 wt% Co, 1.5% Co dispersion, 79 h site-time yield, site density I.O /ig-atom surface Co m catalyst B 12.1 wt% Co, 5.8% Co dispersion, 82 h site-time yield, site density 3.3 /cg-atom surface Co m" 473 K, 2000 kPa, H2/CO = 2.1, <10% CO conversion). (a) C5+ selectivity (b) olefin chain termination probability (c) paraffin chain termination probability. 

Carbon number distribution plots also become linear when olefins readsorb very rapidly (large /3r) or when severe intrapellet transport restrictions (large ) prevent their removal from catalysts pellets before they convert to paraffins during chain termination (Fig. 24, jSr = 100). In this case, chain termination to olefins is totally reversed by fast readsorption, even for light olefins. Chain termination occurs only by hydrogen addition to form paraffins, a step that is not affected by secondary reactions and for which intrinsic kinetics depend only on the nature of the catalytic surface. The product distribution again obeys Flory kinetics, but the constant chain termination probability is given by )8h, instead of po + pH- Clearly, bed and pellet residence times above those required to convert all olefins cannot affect the extent of readsorption or the net chain termination rates and lead to Flory distributions that become independent of bed residence time. 

The process is based on the previous observation that in the absence of ethylene, olefins alkylate TEA in proportion to the concentration of each individual olefin present in the alkylation mixture. Thus, the distribution of alkyl groups of the alkylated TEA will be equal to the olefin chain length distribution fed to the alkylator. 

The attempted synthesis of O-bridged compounds from mixed allyl esters of diazomalonic acid of the type 723, in which the olefinic chain is located at the diazo side of the molecule, has failed (93JOC4646). However, tethering the olefin moiety to the chain that links the carbonyl and diazocarbonyl functionalities provides a great variety of tricyclic-nonfused compounds (82T1477 92JA1874 94TL7159). The most representative examples are shown in Schemes 41 and 42. 

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