Trans-1,4-polyisoprene rubber

Kuraraj TP Technical Information No. 731, Kuraraj Trans Polyisoprene TP-301, Kuraray Isoprene Chemical Co., Ltd., Synthetic Rubber Dept., 3-8-2, Nihonbashi, Chuo-Ku, Tokyo, Japan, Oct. 1, 1982. 

Recently Fujiwara et al. reported on the in vitro polymerization of trans-polyisoprene using the enzymes isopentenyl diphosphate isomerase (IDI) and fra 3-isoprenyl diphosphate synthase (IDS) [271]. IDI catalyzes the interconversion of IPP and DMAPP. IDS can now catalyze the polymerization of IPP from DMAPP as outlined above for the synthesis of natural rubber, and as outlined in Fig. 13a. However, the condensation process is inhibited due to hydrophobic interaction between IDS and hydrocarbon of the longer products. The hydrophobic chain of the elongating product does not readily protrude into the aqueous phase and it tends to interact with the enzyme. To achieve an efficient in vitro synthesis, the authors used an organic-aqueous two-liquid phase system to successfully synthesize (low molecular weight) fran.y-polyisoprene (see Fig. 13b). 

IIR - ASTM designation for isoprene rubber, cis- or trans-polyisoprene are examples. 

Fig. 49. Standard 13C NMR spectrum (top) and DEPT spectra of sulfur cured natural rubber (6h at 138 °C). The label T indicates peaks from trans-polyisoprene units, X marks residual peaks from other subspectra and arrows indicate peaks due to crosslink sites (adapted from Ref. 194>)...

In 1954, 1,4-cA-polyisoprene, the synthetic equivalent of natural rubber, was obtained in the laboratories of Goodrich-Gulf [22] by isoprene polymerisation with new catalysts developed by Natta, and later on 1,4-trans-polyisoprene, a synthetic analogue of gutta percha, was obtained by Natta et al. [23]. 

Recall that we introduced the idea of stereoisomers in Chapter 3 in the section on natural rubber. The stereochemistry in polyisoprene arises because of the rigid nature of the carbon-carbon double bond. Natural rubber is cis-polyisoprene while gutta percha is trans-polyisoprene, the two polymers having drastically different properties... 

IP-PP and DMA-PP can yield volatile C3 hemiterpenes. At the other extreme, extensive polymerization of the C3-pyrophosphates (with release of pyrophosphate, PP ) yields the formation of the plant latex polymers such as eis-polyisoprenes (rubber) and trans-polyisoprenes (gutta-percha). In between these extremes, a variety of monoterpenes, sesquiterpenes, triterpenes and C3() carotenes derive from these C3-pyrophosphate precursors. 

Polyisoprene (R = CH3) with a c/s-1,4 configuration is common in nature in different species of piants and is known as natural rubber. Trans-polyisoprene is found in two naturai resins known as gutta-percha and balata. Natural or synthetic polyisoprenes, as well as polybutadiene, are among the most common elastomers with many practical uses. Other elastomers with extensive practical applications are copolymers, many of them using butadiene or isoprene in the starting monomer mixture. 

The polymer of isoprene is called polyisoprene. It exists in two forms, cis- and frons-polyisoprene. The two forms are called geometric isomers. They have the same kind and number of atoms, but the atoms are arranged differently in the two forms. Natural rubber consists of trans-polyisoprene, while another product found in rubber plants, gutta percha, is made of c/s-polyisoprene. 

Halogenation reactions of unsaturated polymers follow two simultaneous paths, ionic and free radical. Ionic mechanisms give soluble products from chlorination reactions of polybutadiene." The free-radical mechanisms, on the other hand, cause crosslinking, isomerization, and addition products. If the free-radical reactions are suppressed, soluble materials form. Natural rubber can be chlorinated in benzene with addition of as much as 30% by weight of chlorine without cycliza-tion. " Also, chlorination of polyalkenamers, both cis and trans, yields soluble polymers. X-rays show that the products are partly crystalline. The crystalline segments obtained from 1,4-trans-polyisoprene are diisotactic poly( 0 /rw-dichlorobutamer)s while those obtained from the 1,4-cis isomer are diisotactic polyOAfieo-l,2-dichlorobutamer)s. ... 

The first patent on PAB was granted to Parkes in 1846 for two natural polymers co-vulcanized during blending in the presence of CS2, i.e., a natural rubber (NR = amorphous c/s-polyisoprene, IR) with gutta-percha (GP = semicrystalline trans-polyisoprene, IR). Thus, mbber PAB predates that of synthetic polymers by ca. 80 years (PMA/PVAc 1929). Notably, while the early plastics were bio-based, their usage fell to <5 wt% nowadays slowly recovering from the absolute dominance of synthetic, petroleum-based plastics. 

Polyisoprene rubber products are illustrated by Natsyn . which is used to make tires and tire tread (cis isomer). Tires are the major cis-polyisoprene product. Trans-polyisoprene can be used to make golf ball covers, hot-melt adhesives, and automotive and industrial products. 

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. 

Polyethylene Polyvinyl alcohol Butyl rubber CIS -Poly butadiene ds-Polyisoprene trans -Polyisoprene Silicone rubber... 

Some examples of the analysis of the apparent activation energy Ea of blends can be found in the literature. When evolution of the Ea of liquid cis-polyisoprene/ trans-polyisoprene (CPI/TPI) blends was analyzed using the VFTH model [41], the Ea for pure TPI was observed to be higher than that of TPI/CPI blends. Moreover, as the concentration of TPI decreased, then the Ea also decreased this was ascribed to the fact that in glass-rubber relaxation the motion of molecules is governed by the crosslink density. As the decrease in TPI content caused a decrease in crosslink density, this in turn enhanced the motion of chains, and consequently less Ea was required to promote segmental cooperative movements. 

Addition of butadiene to ethene polymerizations gives cross-linked material, but dienes are themselves important substrates for polymerization reactions. Natural rubber is an all-ds polymer of isoprene (Figure 21.10), which we encountered in Chapter 11, as an important precursor of the terpenes. Synthetic rubber made by radical polymerization is a mixture of cis- and trans-polyisoprene, (21.10). The material produced by metal-catalyzed polymerization is, however, all-ds and essentially identical to natural rubber. 

Figure 1.3 shows several repeat units of cis-l,4-polyisoprene and trans-1,4-polyisoprene. Natural rubber is the cis isomer of 1,4-polyisoprene, and gutta-percha is the trans isomer. 

Figure 1.3 1,4-polyisoprene with R=CH3 (a) cis isomer natural rubber (b) trans... 

Related to stereoregularity is the possibility of cis, trans isomerism. The molecule of natural rubber is a c/s-1,4-polyisoprene whilst that of gutta percha is the trans isomer. 

The latex of the Sapota achras yields a thermoplastic material, chicle, consisting of about 17.4% hydrocarbon, 40% acetone soluble resin and 35% occluded water. The hydrocarbon appears to contain both trans- and c/s-polyisoprene. Although originally introduced as gutta pereha and natural rubber substitutes, deresinated chicle has become important as the base for chewing gum. Like other polyisoprenes, it is meeting competition from synthetic polymers. 

The infrared spectra of hevea (natural rubber), balata (or guttapercha), the latter both in the crystalline (a) and the amorphous forms, and of synthetic polyisoprene are compared in Fig. 32. The hevea and balata (amorphous) spectra offer calibrations for cfs-1,4 and irans-1,4 structures, respectively, in the synthetic polymer. Owing to the presence of the methyl substituent, however, the spectral difference between the as and trans forms is slight both absorb at about 840... 

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