Gutta-percha properties

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. 

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... 

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 ... 

Polymers containing each of these configurations are known, the most common being the cis- A and the 1,4-isomers. The first of these, poly(c/ -l,4-isoprene), is the macromolecular constituent of natural rubber the second is the material known as gutta percha. The latter, unlike natural rubber, has no elastomeric properties, but has a leathery texture. It has been used for diverse applications such as golf-ball covers and as an insulating material for the trans-Atlantic cables of the late nineteenth century. 

We might well expect this differing stereochemistry to have a marked effect on the properties of the polymer, and this is borne out by the two naturally occurring polyisoprenes, natural rubber and gutta percha. The former, which before vulcanisation is soft and tacky, has all cis junctions in its chains while the latter, which is hard and brittle, has all trans junctions. 

After the extraction, by means of ether, of the two resins contained in the thin, leaves of white or purified gutta-percha, leaving the last portion of ether with which they were impregnated to evaporate in the open air, these leaves, inclosed in a flask, experienced, alter remaining there for two months.at a temperature of from 68° to 82°, an alteration which appeared to depend on their porosity, the action of the air, end perhaps the ether retained in their pores. However it be, these leaves had then acquired new properties they were brittle exhaled a very distinct sharp odor brought Into contact with en excess of anhydrous ether, they ware partially dissolved the soluble portion obtained by tho evaporation of tho ether, and exsiccation at 194°, was glutinous end translucent it became opaque and hard by coding down to 14°. 

By mixing only two per cent, of chloride of sulphur, or ouly fifteen per cent, of the other substances, with the sirupy solution of gutta-percha, a compound is obtained which does not materially differ from guttapercha in Ite properties. 

When ten per oent. of chloride of sulphur Is added, the properties of the gutta-percha are quite changed, and the compound is unaltered by a temperature of 212°,... 

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. 

Gutta-percha, the trans 1,4-isomer of natural rubber, is hard and brittle at room temperature. The reason for the difference in properties between the cis and trans isomers readily can be seen by inspecting molecular models. The chains with trans double bonds are able to lie along side of each other, forming a semicrystalline array, as shown in Figure 13-2. This ordered arrangement cannot be deformed easily, hence the material is hard and brittle. However, when the double bonds are cis, steric hindrance prevents the chains from assuming a similar ordered structure and the bulk of the material exists in a... 

Some of the polybutadienes obtained with transition metal-based coordination catalysts have practical significance the most important is cA-1,4-polybutadiene, which exhibits excellent elastomeric properties. As regards isoprene polymers, two highly stereoregular polyisoprenes, a cA-1,4 polymer (very similar to natural rubber) and a trans- 1,4-polymer (of equal structure to that of gutta percha or balata) have been obtained with coordination catalysts. Various polymers of mixed 3,4 structure, amorphous by X-ray, were also obtained [7]. 

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... 

Vulcanization of soft or India rubber was discovered by Charles Goodyear in 1839. He was followed by Nelson Goodyear, who patented the vulcanization of hard rubber in 1851. These processes involve the treatment of natural rubber with heat, sulfur, and various metallic compounds. The resultant material is stronger and more stable than raw rubber, while still retaining the desirable properties of elasticity and flexibility. It is also resistant to heat and does not melt like raw rubber or gutta percha. 

Gutta percha objects were created from raw, untreated latex that was melted and molded, or from vulcanized gutta percha, which has most of the same properties as hard rubber. Molded gutta-percha was made into a staggering diversity of objects, including golf balls, jewelry, thread, tool and weapon handles, condoms, water pipes, buttons, and in dentistry as a base for dentures, as fillings, and as artificial teeth. The thread was woven into waterproof blankets, tents, and other fabrics, mosdy for use by the military. 

It is obtained from latex extracted from the Hevea brasiliensis tree. There exists another structural isomer called gutta-percha formed from po y trans-1,4-isoprene), whose elastic properties differ from those of natural rubber. 

Source.—The common substance which is known as rubber is the product obtained by the coagulation of the juice or latex which is present, usually in the bark, but sometimes in the woody tissue, of certain tropical or sub-tropical trees, shrubs and vines. Gutta-percha is a variety of rubber differing in physical properties. The chemical individual present in rubber is a terpene hydrocarbon known as caoutchouc. 

Paints, medicinal Liquid medicinal preparations possessing antiseptic, caustic, soothing, or stimulating properties, usually applied by means of a brush. Paints intended to remain in contact with a specified surface are usually prepared with collodion, glycerin, glycerin and water, egg albumin in alcohol, or gutta percha. Paints intended to be absorbed are prepared with oleic acid or fatty oils. Caustic substances are usually applied dissolved in distilled water, alcohol, or ethereal vehicles, whereas resinous substances, such as benzoin. 

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. 

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 percha, 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). 

With the notable exceptions of natural rubber and gutta-percha, almost all naturally occurring polymers are optically active. Historically, interest in optically active synthetic polymers has focused on modeling natural polymers, interpreting the conformational properties of macromolecules in solution, and investi-... 

WhUe the primary emphasis in this chapter will be directed toward manmade polymers, it is important to remember that many natural products are polymeric. One of the most important of these is rubber, a form of polyisoprene with distinctive elastic properties from which its practical importance is derived. Other important natural polymers are silk, wool, gutta-percha, cellulose, starch, and all the natural proteins. It is a curious and interesting fact that natural polymers have not been obtained synthetically (with the possible exception of a recently prepared polyisoprene which has a structure similar to the natural one), even though the experimental conditions which can be employed in the laboratory may be varied and controlled to a much greater d ree than the actual conditions under which these polymers are formed in nature. 

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