Cis- and Trans-1,4-Poly-1,3-Dienes

Stereoisomerism in 1,4-poly-1,3-dienes results in significant differences in the properties of the cis and trans polymers. The trans isomer crystallizes to a greater extent as a result of higher molecular symmetry and has higher Tm and Tg values (Table 8-1). These trends are 

TABLE 8-1 Glass Transition and Crystalline Melting Temperatures11 

4- polyisoprene used commerically is the natural Hevea rubber.) a r-l,4-Polyisoprene is also found in the guayule bush. Other trees, mostly in Central America and Malaysia, yield gutta percha or balata rubber, which is predominantly the trans isomer. 

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