Gutta Percha and Balata

In the tapping of wild trees, the gum was extracted from the stem by making cuts 45 ° to the axis of the stem, 5 to 10 inches long. At the lower end of this cut, a vertical cut would be made, with a small cup at its end, attached to the tree. Most of the latex coagulated in the cup and was removed therefrom, but some that ran into the cup coagulated later. 

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Non-elastomeric chemical derivatives of natural rubber are discussed in Chapter 30 in which chemically related naturally occurring materials such as gutta percha and balata are briefly considered. 

A class of hydrocarbons occurring in many essential oils of plants. They can be regarded as low-molecular weight polymers of isoprene (C5I I8)n. Dipentene is a terpene, while natural rubber, gutta percha and balata have been termed polyterpenes. 

By contrast, cis- 1,4-polyisoprene is produced in limited amounts, since it is not price competitive with natural rubber (owing to the relatively high costs of manufacturing the isoprene monomer). The same applies to trans- 1,4-polyisoprene, which is more expensive than its natural counterparts gutta percha and balata. 

The polymer in natural rubber (from the Hevea bmsiliensis tree) is pure cis polyisoprene gutta percha and balata are composed of the trans isomer. 

Polymers with unsaturated carbon chain backbone form another important class of macromolecules, many of the compounds from this class having properties of elastomers. The most common polymers from this class are obtained from 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene) and their derivatives. Natural rubber, which is poly(c/s-isoprene), as well as the natural polymers gutta-percha and balata also have an unsaturated carbon chain backbone. For many practical applications, the polymers from this class are subject to a process known as vulcanization, which consists of a reaction with sulfur or S2CI2, and leads to the formation of bridges between the molecular chains of the polymer. This process significantly improves certain physical properties of practical interest. A separate subclass of polymers with unsaturated carbon chain backbone is formed by polyacetylene. 

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. 

Deformation of frozen rubber, gutta percha and balata.631... 

Polymers related to natural rubber include ebonite, chlorinated rubber, oxidized rubber, cyclized rubber, and gutta-percha and balata. 

The natural products gutta-percha and balata consist of tra w-l,4-polyisoprene. With the aid of vanadium trichloride and triethylalumium, tra w-l,4-polyisoprene can be produced with 98% trans-, A enchainments [133,258]. The optimal Al/V ratio is the range of 5 to 7. The activity can be increased by the addition of small amounts of ether, heterogenerization on supports (kaolin, Ti02), or blending with titanium(III) chloride or titanium alcoholates [259-261]. Further catalysts featuring lower activity, however, are allylnickel iodide, trisallylchormium on silica, or complexes of neodymium [262 265]. 

Gutta-percha and balata are two types of natural trans-polyisoprenes, which comes from such tropical trees as the Palaquium Gutta of Malaysia and the Bolle tree of Brazil, respectively. Because the trans-polyisoprenes are crystalline at room temperature, they form tough thermoplastics. Applications have included golf ball covers and dental materials. 

Let us consider further the consequences of head-tail additions. If an additional molecule of IPP is added head-to-tail to farnesyl pyrophosphate geranylgeranyl pyrophosphate, a diterpene, is obtained. The series of events outlined above can now be repeated at a higher level of complexity geranylgeranyl pyrophosphate can either be converted to other diter-penes or two molecules of geranylgeranyl pyrophosphate can be joined tail-to-tail to give 40 C bodies. In this way tetraterpenes, i.e. carotenoids, are obtained. Further head-to-tail additions of IPP lead, finally, to the polyterpenes rubber, gutta-percha, and balata. 

Of the polyterpenes rubber, gutta-percha, and balata, our discussion will be restricted to the technically most important product, rubber. About 2,000 species of higher plants produce rubber but only a few of them, mainly from the families Apocynaceae, Asclepiadaceae, Compositae, Euphorbiaceae, and Moraceae, do so in sufficient quantity as to make its extraction technically worthwhile. A few of the more important species are listed in Table 5. The main source of rubber is the rubber tree Hevea brasiliensis. Achras sapota, the chicle of which provides the basic ingredient of chewing gum, is also included in the list. 

In the case of polymerization of substituted dienes such as 2-methyl-butadiene (isoprene), the structure of the resulting product may be more complicated because it is possible to create polymers with structure of type 1.2 and 3.4, as well as 1, 4 cis and 1, 4 trans. Moreover, structures head to tail and head to head t3 e may be formed. The results of the analysis of S5mthetic polyisoprene have shown that, in general dominating is the head to tail arrangement and the 1, 4 trans configuration. The natural rubber is 1,4 cz5-polyisoprene, whereas gutta-percha and balata have 1, 4 trans structure. 

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