Plastic Polymers
Plastics are polymers - long-chain carbon-based or "organic" molecules.  These chains are made up of repeating fundamental molecular elements, or "monomers."

The term plastics covers a range of mostly synthetic or semi-synthetic organic condensation or polymerization products that can be molded or extruded into objects or films or filaments.  The name is derived from the fact the properties are in a semi-liquid state that is malleable, or has the property of plasticity.  Plastics vary immensely in temperature tolerance, hardness, resiliency.  Combined with this adaptability, the general uniformity of composition and lightness of plastics ensures their use in almost all industrial applications today.

Natural Polymers
People have been using artificial organic polymers for centuries in the form of waxes and shellacs.  A plant polymer named "cellulose" provides the structural strength for natural fibers and ropes, and by the early 19th century natural rubber, tapped from rubber trees, was in widespread use.

Eventually, inventors learned to improve the properties of natural polymers.  Natural rubber was sensitive to temperature, becoming sticky and smelly in hot weather and brittle in cold weather.  In 1834, two inventors, Friedrich Ludersdorf of Germany and Nathaniel Hayward of the US, independently discovered that adding sulfur to raw rubber helped prevent the material from becoming sticky.

In 1839, the American inventor Charles Goodyear was experimenting with the sulfur treatment of natural rubber when, according to legend, he dropped a piece of sulfur-treated rubber on a stove.  The rubber seemed to have improved properties, and Goodyear followed up with further experiments, and developed a process known as "vulcanization" that involved cooking the rubber with sulfur.  Compared to untreated natural rubber, Goodyear's vulcanized rubber was stronger, more resistant to abrasion, more elastic, much less sensitive to temperature, impermeable to gases, and highly resistant to chemicals and electric current.

Vulcanization remains an important industrial process for the manufacture of rubber in both natural and artificial forms.  Natural rubber is composed of an organic polymer named "isoprene."  Vulcanization creates sulfur bonds that link separate isoprene polymers together, improving the material's structural integrity and its other properties.

Some interesting polymers sites: Plastics, Yahoo