Gutta percha physical properties

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. 

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. 

C.E. Friedman, J.L. Sandrick, M.A. Heuer, G.W. Rapp, Composition and physical properties of gutta-percha endodontic filhng materials, J. Endod. 3 (1977) 304-308. 

In principle the value of a, the equivalent random link, may readily be compared with the length of a single bond or a monomer repeat unit. Values of the equivalent random link have been estimated by a number of methods (see Treloar, 1975) of which the optical anisotropy method is an example (Morgan and Treloar, 1972). This method gives a value for a of 1 73 isoprene units in the case of natural rubber (c/5-l,4-polyisoprene) and 3 39 for gutta percha (trafis-l,4-poly-isoprene) a result particularly interesting in view of the known differences in physical properties between the two polymers (see Chapter 4). 

The upshot is that their physical properties are quite different, for gutta percha is inelastic and hard, becoming rubbery only... 

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