Rubber is an example of an elastomer type polymer, where the
polymer has the ability to return to its original shape after
being stretched or deformed. The rubber polymer is coiled when
in the resting state. The elastic properties arise from the its
ability to stretch the chains apart, but when the tension is
released the chains snap back to the original position.
Natural rubber is an addition polymer that is obtained as
a milky white fluid known as latex from a tropical rubber tree.
Natural rubber is from the monomer isoprene (2-methyl-1,3-butadiene).
Since isoprene has two double bonds, it still retains one of
them after the polymerization reaction. Natural rubber has the
cis configuration for the methyl groups.
Charles Goodyear accidentally discovered that by mixing sulfur
and rubber, the properties of the rubber improved in being tougher,
resistant to heat and cold, and increased in elasticity. This
process was later called vulcanization after the Roman god of
fire. Vulcanization causes shorter chains to cross link through
the sulfur to longer chains.
The development of vulcanized rubber for automobile tires
greatly aided this industry.
Link to Polyisoprene
- Natural Rubber - with Chime molecule - Macrogalleria at
U. Southern Mississippi