Gutta

All the double bonds in rubber have the Z (or cis) con figuration A different polymer of isoprene called gutta-percha has shorter polymer chains and E (or trans) double bonds Gutta percha is a tough horn like substance once used as a material for golf ball covers ... 

Gutta percha is a natural polymer of isoprene (3-methyl-l,3-butadiene) in which the configuration around each double bond is trans. It is hard and horny and has the following formula ... 

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. 

Although the conditions of the polymerization reaction may be chosen to optimize the formation of one specific isomer, it is typical in these systems to have at least some contribution of all possible isomers in the polymeric product, except in the case of polymers of biological origin, like natural rubber and gutta-percha. 

Alginates, alkaloids, glycerides, gutta, phenols, rosins, rubber, saponins sterols, tall oils, tannins, terpenes, waxes... 

Natural mbber (Hevea) is 100% i7j -l,4-polyisoprene, whereas another natural product, gutta-percha, a plastic, consists of the trans-1,4 isomer. Up until the mid-1900s, all attempts to polymerize isoprene led to polymers of mixed-chain stmcture. 

Bakelite, bleached 20-60 0.22 Gutta percha 20 1.983 zontal axis 0-100 0.0832... 

Prior to the eastern adventures of Linschoeten and Tradescant, the sailors of Columbus had discovered the natives of Central America playing with lumps of natural mbber. These were obtained, like gutta percha, by coagulation from a latex the first recorded reference to natural mbber was in Valdes La historia natural y general de las Indies, published in Seville (1535-1557). In 1731 la Condamine, leading an expedition on behalf of the French government to study the shape of the earth, sent back from the Amazon basin mbber-coated cloth prepared by native tribes and used in the manufacture of waterproof shoes and flexible bottles. 

By 1900 the only plastics materials available were shellac, gutta percha, ebonite and celluloid (and the bitumens and amber if they are considered as plastics). Early experiments leading to other materials had, however, been carried out. The... 

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. 

These different forms Figure 4.7) take up different crystalline structures and consequently the bulk properties of the polymer differ. At room temperature gutta percha is a stiff leathery material. 

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. 

As with c -polyisoprene, the gutta molecule may be hydrogenated, hydro-chlorinated and vulcanised with sulphur. Ozone will cause rapid degradation. It is also seriously affected by both air (oxygen) and light and is therefore stored under water. Antioxidants such as those used in natural rubber retard oxidative deterioration. If the material is subjected to heat and mechanical working when dry, there is additional deterioration so that it is important to maintain a minimum moisture content of 1%. (It is not usual to vulcanise the polymer.)... 

Gutta pereha has a lower water absorption than natural rubber and is a good dielectric. It is dissolved by carbon disulphide, chloroform and benzene but alkaline solutions and dilute acids do not affect it. It is destroyed by nitric acid and charred by warm concentrated sulphuric acid but resists hydrofluric acid. 

At one time gutta pereha had an important outlet in undersea cable insulation and a lesser use in chemical plant, in particular for storage of hydrofluoric acid. It is now virtually obsolete. 

The coagulated material consists of about 50% polyisoprene and the remainder is primarily composed of resins. Deresinated balata has been used as an alternative to gutta pereha, which it resembles in properties and also in belting applications. It is still used for making high-quality golf ball covers but for the cheaper balls it has now been replaced almost entirely by the ionomers (see Chapter 11). 

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. 

Chemical nature Isolation of casein from milk Production of casein plastics Properties of casein Applications Miscellaneous Protein Plastics Derivatives of Natural Rubber Gutta Percha and Related Materials Shellac... 

Condensation of isoprene (2-methyl-1,3-butadiene) either leads to a polymer in which all double bonds are trans ( natural rubber ) or in which they are cis (gutta-percha). 

Natural rubber is known to be more elastic (deformable) than gutta-percha. Is there any obvious difference in the structures in the two strands which might lead to a difference in the properties of the real polymers ... 

Rubber used in practical applications is crosslinked through disulfide (-S-S-) bonds, and is known as vulcanized rubber. Can you name another important class of polymers which are crosslinked through disulfide bonds Examine vulcanized rubber. How many individual strands does it comprise Are these strands of natural rubber or of gutta-percha What is the percentage (by weight) of sulfur incorporated into the polymer (The molecular weight of the sample is 1701 amu.) Does this classify as a low-sulfur polymer (<3%), a high-sulfur polymer (>10%) or in between ... 

Percha,/., -gummi, m. n. gutta-percha. Perchlor-athan, n. perchloroethane, hexaehloro-ethane. -athylen, n. perchloroethylene, tetrachloroethylene. -methan, n. perehloro-methane (carbon tetrachloride). 

Since 1960, gutta-percha or synthetic balata has been replaced by ionomer for use as a cover material in golf balls. It is based on a combination of ethylene and a carboxylic acid. It can be processed at a reasonable temperature to produce good, tough ball covers. Because of higher processing temperature of the ionomer... 

As noted in the Chapter 7 Focus On, rubber is a naturally occurring polymer of isoprene, or 2-methyl-l,3-butadiene. The double bonds of rubber have Z stereochemistry, but gutta-percha, the E isomer of rubber, also occurs naturally. Harder and more brittle than rubber, gutta-percha has a variety of minor applications, including occasional use as the covering on golf balls. 

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