Trans-l,4-Polyisoprene

Orthopedic devices -trans-l,4-polyisoprene m [ELASTOMERS SYNTHETIC - POLYISOPRENE] (Vol 9)... 

A number of high molecular weight polyisoprenes occur in nature which differ from natural rubber in that they are essentially non-elastic. As with natural rubber they are obtained from the latex of certain plants but they differ in that they are either trans-l,4-polyisoprenes and/or are associated with large quantities of resinous matter. 

A minor part of the spectra had a singlet contour which was assigned to polyenyl radicals, —(—CR CR2 ) CH—, where R2 and R2=H or CH3, and n is about 3, judging from the linewidth. Free radicals were found to be stable at —196° C but decayed sharply near the glass-transition temperature. Trans-l,4-polyisoprene irradiated with UV light gave a similar spectrum to that of the ds-form. 

Polymerization of isoprene can yield high-purity cis-l,4-polyisoprene and trans-l,4-polyisoprene. Isoprene is 2-methyl-1,3-butadiene, 2-methyldivinyl, or 2-methylerythrene. Isoprene is polymerized by 1,4 or vinyl addition, the former producing cis-1,4 or trans-1,4 isomer. ... 

Trans-l,4-polyisoprene rubber (i.e., PIR, sometimes called Gutta Percha in the past) is a synthetic rubber with properties similar to those of its natural counterpart It was first industrially prepared during World War 11 because of a lack of supply of natural rubber but despite containing fewer impurities than natural rubbers and having a simpler preparation process it is not widely used because it is also more expensive. Mechanical properties and chemical resistance is identical to that of natural rubber. As with many other rubbers its mechanical properties can be also improved by the vulcanization process. 

The bromination of trans-l,4-polyisoprene crystals in CCl suspension at 0 C has received some study.In that work the disappearance of bromine was monitored with a correction made for polymer solubility. Under the conditions used the total amount of bromine consumed becomes essentially constant after 1-3 hours. from surface bromination exceeds that from epoxidation ([MCPBA] =. 011 M) for all preparations used and therefore it appears that substitution as well as addition might be occurring during the... 

The quantitative estimation of cis-ltrans- isomerization is best made using NMR spectra (for example see Golub et al, 1962). Figure 7.1 shows parts of the spectra of natural (hevea) rubber, amorphous balata (a natural trans-l,4-polyisoprene similar to gutta percha) and an... 

Products of cyclization of trans-l,4-polyisoprene are virtually identical to those obtained from c/5-l,4-polyisoprene. 

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