Isoprene oligomers

Vol. 4, p. 10) isoprene oligomers (e.g. 2,6-dimethylocta- 1,7-diene) into the corresponding alcohols [e.g. (52)] via epoxide rearrangement, and the synthesis140 of the alcohol (53) (Vol. 3, p. 15) are straightforward. The isopropenylation of alkenes via the reaction of iodine with lithium trialkylisopropenylborates has been used to... 

Pyrolysis of polyisoprene takes place by a free radical mechanism and generates mainly isoprene (MW=68), a dimer of isoprene (DL-limonene, MW=138), and several other unsaturated hydrocarbons (see Sections 2.6 and 6.1). The mass spectra fragmentation (generating fragments with specific mass/charge (m/z) ratios) of a model molecule simulating polyisoprene (isoprene oligomer) occurs by the mechanisms as indicated below ... 

The fragments from the pyrolysis and the mass spectra generated from a model isoprene oligomer are therefore very similar. This result is expected, due to the high number of it electrons in the polyisoprene molecule [22],... 

In order to assess the reliability of NMR data, Research Group on NMR, the Society of Polymer Science, Japan (SPSJ), collected H and 13C NMR spectra of two identical samples, a radically prepared PMMA and solanesol (a naturally occurring isoprene oligomer) from a number of NMR spectrometers by round robin method.10... 

The second TIC maximum occurs at higher temperatures (400-750°C) and represents the evolution of rubber thermal decomposition products (pyro-lyzates). The major FI-MS peaks in this region are isoprene oligomers (MW = 68n, Figure 6.17). Note that the two envelopes in Figure 6.15 are well-separated in time (or temperature) thus one can obtain separate mass spectra for the organic additives and the rubber pyrolyzates. 

Polypentadiene Isoprene oligomers Butadiene, isoprene and chloro-prene polymers... 

Oligomers of 1,3-Butadiene Oligomers of Isoprene Oligomers of 1,3-Butadiene... 

Other high molecular weight hydrocarbon polymers are not biodegradable, but oligomers of <7j -l,4-isoprene (83), butadiene (84), and styrene (85), are degradable. And there has been further confirmation of biodegradation of oligomeric ethylene (86). 

Butadiene and isoprene give rise to mixtures of what are usually called telom-ers, namely 1 1 telomers between the amine and the 1,3-diene (trae hydroamination products), 1 2 telomers and even higher homologs together with oligomers of the diene as exemplified in Eq. (4.41). 

Reactions of conjugated 1,3-dienes, mainly butadiene and isoprene, catalyzed by transition metal complexes to form a number of linear and cyclic oligomers and telomers, are one of the most fascinating fields of research in the last 20 years. Extensive studies from academic and in-... 

From their carbon skeletons terpenes can be seen as isoprene (C5) oligomers. Terpenes are classified according to their number of isoprene units as monoterpenes (C10), sesquiterpenes (Q5), diterpenes (C2o), etc. /1-Carotene (1) is a tetrater-pene. 

Formally, isoprenoids are derived from a single common building block, isoprene (2-methyl-l,3-butadiene), a methyl-branched compound with five C atoms. Activated isoprene, isopentenyl diphosphate, is used by plants and animals to biosynthesize linear and cyclic oligomers and polymers. For the isoprenoids listed here—which only represent a small selection—the number of isoprene units (1) is shown. 

Of the conjugated dienes, 1,3-butadiene undergoes base-initiated polymerization but does not yield oligomers since there is no proton transfer reaction. Isoprene and 1,3-pentadiene, in contrast, give linear and cyclic dimers. 

The first results of anionic polymerization (the polymerization of 1,3-butadiene and isoprene induced by sodium and potassium) appeared in the literature in the early twentieth century.168,169 It was not until the pioneering work of Ziegler170 and Szwarc,171 however, that the real nature of the reaction was understood. Styrene derivatives and conjugated dienes are the most suitable unsaturated hydrocarbons for anionic polymerization. They are sufficiently electrophilic toward carbanionic centers and able to form stable carbanions on initiation. Simple alkenes (ethylene, propylene) do not undergo anionic polymerization and form only oligomers. Initiation is achieved by nucleophilic addition of organometallic compounds or via electron transfer reactions. Hydrocarbons (cylohexane, benzene) and ethers (diethyl ether, THF) are usually applied as the solvent in anionic polymerizations. 

It seems that (PhCH=CHPh)2, 2Na+ is also capable of existing in the polymeric form in a THF solution. This salt is a typical initiator in the polymerization of unsaturated compounds such as isoprene and methylstyrene. In THF such polymerization can include the detachment or fixation (chemisorption) of a framing (terminal) link from the polymeric aggregate [(PhCH=CHPh)2, 2Na+] . Methylstyrene captures the come-off link, starting the polymerization process. The link and, probably, [(PhCH=CHPh)2, 2Na+] i oligomer are included in a polymeric globule. The situation resembles a snake in a cage. In experiments (Podol sky and others 1982), a-methylstyrene was polymerized in THF upon the action of [(PhCH=CHPh)2, 2Na+] labeled with 3H, 14C in the presence of nonla-beled PhCH=CHPh. The authors obtained a polymer that contains the whole amount of the label. In the case of the mixture of nonlabeled [(PhCH=CHPh)2, 2Na+] with labeled PhCH=CHPh in THF, the polymer obtained did not contain any label. 

Methods have been developed for the analysis of hydrocarbon polymers (e.g. styrene, butadiene and isoprene) by MALDI-TOF-MS, through the attachment of Ag(acac) to matrices of tran5-3-indoleacrylic acid or l,4-bis(2-(5-phenyloxazolyl))benzene . SUver-cationized molecular ions were produced for polymers of styrene, butadiene and isoprene up to mass 125,000 Da. For lower-mass styrene polymers, the resolved oligomer molecular ions provide information concerning the end group. This technique permits the analysis of many commercially important materials such as acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile, styrene-methyl methacrylate and styrene-isoprene copolymers. The use of the salts of transition metals other than Ag, Cu or Pd as the cationizing agents fails to cationize polystyrenes in MALDI. The ability of MALDI to reduce metals to the oxidation state 4-1 is critically important to polystyrene cationization, as without this reduction MALDI tends to fail to form polystyrene-metal cations. Cu(acac)2 was used for the verification of the above . 

Figure 12.6 Py-GC/MS chromatogram of natural rubber at 500°C. ix denotes oligomers of X isoprene units...

The fractions of isoprene and butadiene oligomers and polymers increase in the same way 96 97). After 4 hours of reaction, only the oligomeric fraction grows. 

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