Ethyl branch

Hydrogenation of polybutadiene converts both cis and trans isomers to the same linear structure and vinyl groups to ethyl branches. A polybutadiene sample of molecular weight 168,000 was found by infrared spectroscopy to contain double bonds consisting of 47.2% cis, 44.9% trans, and 7.9% vinyl. After hydrogenation, what is the average number of backbone carbon atoms between ethyl side chains ... 

The process is favored by low monomer concentrations as occurs at high conversions and in starved feed polymerizations.307 Theoretical calculations suggest that the incidence of backbiting should be strongly dependent on the tacticity of the penultimate dyad. 08 Double backbiting in VC or VAc polymerization will lead to 2-chloroethyl or 2-acetoxy ethyl branches respectively (as for E in Scheme 4.41 ).302... 

There are no proven examples of 1,2-hydrogen atom shifts this can be understood in terms of the stereoelectronie requirements on the process. The same limitations are not imposed on heavier atoms (e.g. chlorine). The postulate309 that ethyl branches in reduced PVC are all derived from cbloroethyl branches formed by sequential 1,5-intramolecular hydrogen atom transfers as described for PE (Section 4,4.3.1) has been questioned.,6,6 It has been shown that many of these ethyl branches are derived from dichloroethyl groups. The latter are formed by sequential 1,2-chlorine atom shifts which follow a head addition (Section 4.3.1.2). 

In 1990, Baumeister et al. [127] described the crystal and molecular structure of 4-ethoxy-3 -(4-ethoxyphenyliminomethyl)-4 -(4-methoxy-benzoy-loxy)azobenzene. The molecules have a bifurcated shape. The phenyliminom-ethyl branch is bent markedly from the nearly linear three ring fragment, but is almost coplanar with the azobenzene moiety. They found that the molecular conformation is affected by an intramolecular interaction of the carboxylic and azomethine groups. The crystal packing was described in terms of a sheet structure with interdigitating rows of molecules. 

With respect to the intensity resolution relationship of NSE, PEB-2 [essentially PE with one ethyl branch every 50 main chain bonds the sample is obtained by saturating 1-4 polybutadiene, the residual 1-2 groups (7%) cause the ethyl branches Mw = 73200 g/mol Mw/Mn = 1.02] has two advantages compared to PEP (1) the Rouse rate W/4 of PEB-2 is more than two times faster than that of PEP at a given temperature [W/pEP (500 K) = 3.3 x 1013 A4s 1 W/pEB (509 K) = 7 x 1013A4s-1] (2) at the same time, the topological constraints are stronger. 

On all the catalysts, n-hexadecane transformed into isomerization products (monobranched isomers M and multibranched isomers B) and into cracking products C. Monobranched isomers M were mainly methylpentadecanes ethyl-branched tetradecanes were formed in very small amounts, propyl-branched tridecanes were not observed. Multibranched isomers were bi- and tri-branched products, not formally identified. 

Attractive Compounds. The male-produced pheromones of sap beetles, known so far, show the rather stereotypic structures 125-147 (Scheme 15) methyl- and ethyl-branched hydrocarbons with three or four (T)-configured conjugated double bonds [4]. Up to now, 23 compounds could be identified, forming species specific mixtures. Major components in the bouquets are (2E,4E,6E)-5-ethyl-3-methyl-2,4,6-nonatriene, 128, in Carpophilus davidsoni [268] as well as in C.freemani [269], (2 ,4 ,6 )-4,6-dimethyl-2,4,6-nonatriene, 129,in C. truncatus [270], (3 ,5 ,7 )-5-ethyl-methyl-3,5,7-undecatetraene, 132, in C. mutillatus [271],(2 ,4 ,6 ,8 )-3,5,7-trimethyl-2,4,6,8-decatetraene, 134,in C. hemipterus [272] as well as C. brachypterus [273], (2 ,4 ,6 ,8 )-3,5,7-tri-... 

The biosyntheses of the sap beetle pheromones has been carefully investigated by Bartelt and his co-workers [47,48]. The typical methyl-branching of the compounds originates from propanoate (or methylmalonate) units that form the principal structures (see Fig. 2). Replacement of propanoate by butyrate during chain elongation yields ethyl-branching. In about half of the compounds (125-128,133-136,138-140, and 144) the structures suggest acetate to act as a starter while in 133 and 147 the starter should be butyrate. The chains... 

Syntheses follow a kind of bio-mimetic approach [283, 284] in building up the chain during a sequence of Wittig-type reactions or Horner-Wadsworth-Emmons olefination, adding two carbons to the chain at a time with either methyl- or ethyl-branches. As the final products need to be highly pure (E)-stereoisomers, reaction steps and purification need to be carefully controlled. 

An extract of secretion from the sebaceous glands on head and neck of sexually active feral billygoats increases the number of does ovulating. The extract was placed on cotton wool and worn in facemasks. 4-Ethyloctanoic acid and 4-methyloctanoic acid, responsible for the goaty odor, were not active but both the free fatty acid and lipid-free non-acid fractions were. The 4-ethyl branched fatty acids are present in the active fraction (Birch etal., 1989). 

Short branches, specifically ethyl branches up to about 2 mol%, are formed in the polymerization of ethylene by meso-ansa zirconocenes containing unsubstituted cyclo-pentadienyl and indenyl ligands [Melillo et al., 2002]. Ethyl branches form by an isomerization process in which the usual P-hydride transfer to monomer is immediately followed by reinsertion of the vinyl-terminated polymer into the formed ethyl-zirconium bond. 

The relative sensitivity of short-chain alkyl branches of different sizes to elimination on irradiation with formation of the corresponding alkane has been variously reported as being constant or varying (13,14). Figure 9 compares G values for formation of the alkane corresponding to the short-chain branch from samples of these three polymers with branch frequencies from 0.5 to 6 per 1,000 C atoms. There is a notably higher scission efficiency for ethyl branches. 

This technique has been used to investigate the distribution of short-chain branches in LDPE and the relatively higher scission efficiency of ethyl branches would rationalize the yields with 13C NMR measurements of branch frequencies (2). 

Infrared Spectroscopy. Spectra were obtained on a Perkin-Elmer model 521 grating infrared spectrophotometer. The amount of branching in these materials is very small and appears to be of the methyl type, which is indicated by the small absorption near 1140 cm"1. Ethyl branching was also sought but not detected at 770 cm 1. The results are summarized in Table II. 

HDPE is alinear polymer with the chemical composition ofpolymethylene, (CII2V Depending on application, HDPE molecules either have no branches at all. as in certain injection molding and blow molding grades, or contain a small number of branches which are introduced by copolymerizing ethylene with o-olefins, e g., ethyl branches in the case of 1-butene and -butyl branches in the case of 1-hexene. The number of branches in HDPE resins is low, at most 5 to 10 branches per 1000 carbon atoms in the chain. 

Oil soluble twin-tailed QAS V-butyl diethanolamine and methyl or ethyl branch added to ethylene spacer groups between ester groups and quaternary N atom Shell (Klomp, 1999)... 

Linear Polyethylene with Randomly Distributed Ethyl Branches (Hydrogenated Polybutadiene)... 

Examined are two samples that contain 2.2 mol % of ethyl side groups with molecular weights of 16,000 and 400,000 (samples PI6 and P420, respectively). The concentration of ethyl branches was determined by standard high-resolution 13C NMR methods [80-82]. These samples were crystallized from the melt by quenching at -78 °C. 

The half-widths of 37-39 and 78-88 Hz, respectively, for the crystalline and amorphous phases are significantly larger than 18 and 38 Hz for those of the bulk-crystallized linear polyethylene (cf. Table 1). This is caused by incorporation of minor ethyl branches. The molecular alignment in the crystalline phase is slightly disordered, and the molecular mobility in the amorphous phase will therefore be promoted. With broadening of the crystalline and amorphous resonances, the resonance of the interphase also widens in comparison to that of bulk-crystallized linear polyethylene samples. This shows that the molecular conformation is more widely distributed from partially ordered trans-rich, conformation to complete random conformation, characteristic as the transition phase from the crystalline to amorphous regions. 

One isomer has two methyl branches. None is possible with an ethyl branch. 

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