Vulcanization and the Properties of Rubber

Rubber is composed of long stringlike polymer molecules, which are pinned together at random points by crosslinks. As the density of crosslinks is increased, the molecules get localized and the system undergoes a phase transition from a liquid to an amorphous solid state. The elastic properties of the resulting solid are very different from those of metals, and are primarily due to changes in the entropy of the chains upon stretching. This paper discusses why rubber solidifies, and why the solid has the properties it does.