Polyisoprene model compound

Figure 6. Competitive sulfonation of polyisoprene model compound vs. cis-l,4-polybutadiene model compound using acetyl sulfate. PIP c-PBD acetyl sulfate = 1 10 2 (mole). Temperature = 2rC. Solvent = decalin.

The polyisoprene model compound work has indicated that the structures in elemental sulfur vulcanization are alkylalkenyl and alkyl-alkyl in nature. These... 

From Table III, one can see that a common feature in both sets of shift parameters (that for 1,4-polyisoprene derivatives and that for 2-methylbutane derivatives) is a higher g effect for a methyl carbon (denoted g in Table III) than for a methylene carbon (denoted g in Table III). The difference between g and g effects is close to 4 ppm for the polymers whereas it is close to 3 ppm for the model compounds. On the other hand, one can see that there is no significant difference in the y effects whether the carbon under consideration is a methyl or methylene carbon. 

The sulfonation of low molecular weight model olefins was undertaken to determine the feasibility of this approach. Competitive sulfonations using acetyl sulfate were carried out on the model compounds below, representing the repeat structures of cis-l,4-polyisoprene (PIP), cw-l,4-polybutadiene (c-PBD), and trans-l,4-polybutadiene (Z-PBD), respectively. It was necessary to model both the cis and trans isomeric forms of 1,4-polybutadiene, since ttey have a nearly equal probability of occurrence when the anionic polymerization (Ii counterion) is conducted in a nonpolar hydrocarbon medium... 

The chemical structure of naturally occurring ais polyisoprenes was determined by 13C NMR spectroscopy using acyclic terpenes and polyprenols as model compounds. The arrangement of the isoprene units along the polymer chain was estimated to be in the order dimethylallyl terminal unit, three trans units, a long block of ais units, and ais isoprenyl terminal unit. This result demonstrates that the biosynthesis of cis-polyisoprenes in higher plants starts from trans,trans,trarcs-geranylgeranyl pyrophosphate. ... 

This paper describes the structural analysis of naturally occurring ois-1,4 polyisoprenes using 13C NMR spectroscopy. First, the structural characterization of polyprenols, which are linear isoprenoid compounds containing 30 to 100 carbons, was carried out on the basis of information obtained from acyclic terpenes having various ois and trans isoprene units as model compounds. This method was also applied to the structural analysis of polyisoprenes. The elucidation of the structure of the end groups and the arrangement of isoprene units provides information on the mechanism of the biosynthesis of polyprenyl compounds in nature. 

Following Ashby s first observation (7) of chemiluminescence from the oxidative degradation of polymers, a number of papers have appeared dealing with oxidative chemiluminescence from a variety of polymers (8-16). In this chapter we continue the 1,4-polyisoprene work with a study of the low-temperature chemiluminescence emitted in the autoxidation of three additional elastomers, cis-1,4-polybutadiene, amorphous 1,2-polybutadiene, and fmns-polypentenamer. We also report the chemiluminescence obtained from singlet-oxygenated samples of cis-1,4-polybutadiene and trans-polypentenamer, as well as rate data for singlet oxygen reactions with the 1,4-polyisoprene, 1,4-polybutadiene, and model compounds in solution. 

Values for Polymer and Model Compounds. 1,4-Polyisoprene and 1,4-polybutadiene are so sufficiently reactive toward singlet oxygen that we can conveniently obtain / -values by three methods (a) from oxygen-uptake rates by photosensitized oxidation at different polymer concentrations (b) by the initial disappearance rate of rubrene on photooxygenation of solutions with and without polymer (or model olefin) and (c) for 1,4-polyisoprene, by the amount of rubrene consumed upon addition of aliquots of triphenyl phosphite ozonide in the presence and absence of olefin or polymer. The treatment of data from methods (b) and (c) was modified to give /3-values directly from the following equations ... 

Photo-oxidation of cis-polybutadiene was also shown to involve singlet oxygen [570]. Attacks by singlet oxygen on double bonds with formation of allylic hydroperoxides and shifts of these double bonds according to the ene reaction were confirmed by several other studies [571]. On the other hand, a study of model compounds for photo-oxidation of polyisoprene failed to show formation of endo peroxides by 1,4-cycloaddition [572]. 

The trans-1,4-polyisoprene chain has infrared bands in the region 650 to 400 cm These bands is due to the backbone vibrations and the spectrum of the a-form is different from that of the j -form. The normal vibrations of these chains were calculated and the spectral differences were explained from the conformational change [55]. The spectra in this region were studies for the model compounds of cis- and trans-polyisoprene [54] and cis- and trans-polybutadiene [24]. The results were also correlated with the conformations. 

The results are reported of a study of accelerated sulphur vulcanisation using the above compounds. 2,3-Dimethyl-2-butene, was utilised as a model compound for polyisoprene and residual curatives, intermediates and products produced by heating the mixes for various times at 150C in sealed tubes were analysed using high-performance liquid chromatography. A synergistic effect was observed between bis(2-mercaptobenzothiazole) zinc(II) and 2-bisbenzothiazole-2,2 -disulphide. 23 refs. SOUTH AFRICA... 

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