1.4- Poly isoprene trans

Poly(isoprene), trans 104389-32-4 homopolymer Poly( 1-methyl-1 -buteiie-1,4-diyl). R ... 

Figure 2.16 reports the conformational energy maps as a function of the torsion angles 0i and 02 of the two single bonds adjacent to the double bonds for 03 = T = 180° for cis-1,4-poly (1,3-butadicnc) (cisPBD),69 tranx-l,4-poly(l,3-butadiene) (transPBD),70 ds-l,4-poly (isoprene) (cisPI),68 trans-1,4-poly(isoprene) (transPI),71 ds-l,4-poly(2,3-dimethyl-l,3-butadiene) (cisPMBD),68 and lrans-, 4-poly(2,3-dimethy 1-1,3-butadicnc) (transPMBD).68 These polymers are representative examples of polydienes with A = A = H... 

Figure 2.16 Maps of conformational energy of various cis and trans polydienes as function of torsion angles 9i and 0268 (a) cis-l,4-poly( 1,3-butadiene), (b) /ra .v-l,4-poly( J, 3-buladiene), (c) cis-l, 4-poly(isoprene), (d) trans-1,4-poiy(isoprenej, (e) cis-1,4-poly(2,3-dimethyl-1,3-butadiene), and (/) trans- 1,4-poly(2,3 -dimethyl-1,3-butadiene). Isoenergetic curves are reported every 2 kJ/mol of monomeric units with respect to absolute minimum of each map assumed as zero. (Reproduced with permission from Ref. 68. Copyright 1986 by the Societa Chimica Italiana.)...

Natural rubber is a polymer of isoprene- most often cis-l,4-polyiso-prene - with a molecular weight of 100,000 to 1,000,000. Typically, a few percent of other materials, such as proteins, fatty acids, resins and inorganic materials is found in natural rubber. Polyisoprene is also created synthetically, producing what is sometimes referred to as "synthetic natural rubber". Owing to the presence of a double bond in each and every repeat unit, natural rubber is sensitive to ozone cracking. Some natural rubber sources called gutta percha are composed of trans-1,4-poly isoprene, a structural isomer which has similar, but not identical properties. Natural rubber is an elastomer and a thermoplastic. However, it should be noted that as the rubber is vulcanized it will turn into a thermoset. Most rubber in everyday use is vulcanized to a point where it shares properties of both, i.e., if it is heated and cooled, it is degraded but not destroyed. 

The standard infra-red methods are clearly inadequate for poly-isoprene. The determination of relative amounts of cis and trans structures in particular is subject to large errors (113) as the infra-red bands are virtually coincident and differ only in band shape and intensity. The N. M. R. method of analysis (16) is more satisfactory, particularly for determination of the cis/trans ratio1. As can be seen from the table the results are often widely different from those obtained by infra-red analysis. 

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