Gutta-percha rubber

Latex is a term used to describe the milky white sap of various tropical plants that is the parent material of rubber and gutta-percha. Rubber is the... 

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 ... 

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. 

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. 

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. 

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 ... 

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. 

Natural rubber (Chapter 7 Focus On) is the most common example of an elastomer. Rubber has the long chains and occasional cross-links needed for elasticity, but its irregular geometry prevents close packing of the chains into crystallites. Gutta-percha, by contrast, is highly crystalline and is not an elastomer (Figure 31.5). 

Figure 31.5 (a) Natural rubber is elastic and noncrystalline because of its cis double-bond geometry, but b) gutta-percha is nonelastic and crystalline because its geometry allows for better packing together of chains. 

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. 

This discussion of the structures of diene polymers would be incomplete without reference to the important contributions which have accrued from applications of the ozone degradation method. An important feature of the structure which lies beyond the province of spectral measurements, namely, the orientation of successive units in the chain, is amenable to elucidation by identification of the products of ozone cleavage. The early experiments of Harries on the determination of the structures of natural rubber, gutta-percha, and synthetic diene polymers through the use of this method are classics in polymer structure determination. On hydrolysis of the ozonide of natural rubber, perferably in the presence of hydrogen peroxide, carbon atoms which were doubly bonded prior to formation of the ozonide... 

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. 

Figure 13 Chemical structures of trans and cis isomers of 1,4 polyisoprene (gutta-percha and natural rubber, respectively).

Polymerised isoprene. Naturally-occurring polyisoprenes are natural rubber (cA-form) and gutta percha (trans- form). The use of stereo specific catalysts has made possible the manufacture of synthetic cA-polyisoprene and fraws-polyisoprene both of which are now available commercially. 

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. 

Butadiene and isoprene have two double bonds, and they polymerize to polymers with one double bond per monomeric unit. Hence, these polymers have a high degree of unsaturation. Natural rubber is a linear cis-polyisoprene from 1,4-addition. The corresponding trans structure is that of gutta-percha. Synthetic polybutadienes and polyisoprenes and their copolymers usually contain numerous short-chain side branches, resulting from 1,2-additions during the polymerization. Polymers and copolymers of butadiene and isoprene as well as copolymers of butadiene with styrene (GR-S or Buna-S) and copolymers of butadiene with acrylonitrile (GR-N, Buna-N or Perbunan) have been found to cross-link under irradiation. 

Which is a trans isomer (a) gutta percha or (b) hevea rubber ... 

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