Natural rubber is an addition polymer of isoprene. Gutta percha is a similar rubber-like material, although its properties are rather different. (It is a hard material at room temperature but softens when heated.) Its structure has the trans form of polyisoprene instead of the cis form present in natural rubber.
a. Draw the structure of gutta percha.
b. If a sample of gutta percha has an average molecular mass of 250,000 amu, what is the average number of isoprene units in the polymer?
c. When you stretch a rubber band, it evolves heat. If the stretched rubber band is then spontaneously allowed to contract to its equilibrium shape, it cools. Does the entropy of rubber increase or decrease when it is stretched?