Polymers are very large molecules that occur in nature (proteins, polysaccharides, DNA, natural rubber, silk, cotton, wool) or may be synthesized in the laboratory (plastics, synthetic fibers, synthetic rubber).  Natural rubber samples were first brought back from South America by 16th century Spanish explorers.  When John Priestly discovered that this emulsion which oozed from trees could rub out lead pencil marks, it was called "rubber."  But rubber had limited commercial applications because it melted in summer and froze in winter. When Charles Goodyear accidentally mixed sulfur and rubber on a hot stove (1839), he was surprised to find the rubber did not melt. Goodyear patented the process, which he named "vulcanization," after Vulcan, the Roman god of fire.  This article highlights the achievements of the five polymer pioneers shown below:

Hermann Staudinger(1881-1965)
Although the polymer industry was given a boost by Goodyear's discovery, understanding large molecules begins with Staudinger, the German chemist who first defined a polymer.  By the early 1920's a debate raged as to whether polymers consisted of  long-chain molecules or many small molecules held together by "secondary" forces.  From his experiments with rubber colloids, Staudinger provided evidence for the existence of large molecules, which he called "macromolecules."  Staudinger also showed that smaller molecules (monomers) could be combined to form long chainlike structures (polymers) by chemical interaction and not simply by physical aggregation.

Staudinger won the 1953 Nobel Prize for Chemistry for demonstrating that polymers are long-chain molecules and his work provided the theoretical basis for polymer chemistry.  The first polymer journal,  Macromolecular Chemistry and Physics, was founded in 1943 by Staudinger.  It is interesting to note that in the 1930s Staudinger voiced his beliefs on the important role that macromolecules played in living systems, especially proteins.
 

Wallace Carothers (1896 -1937)
In 1928 DuPont initiated a basic research laboratory and hired Carothers to lead the program.  Carothers, who was teaching at Harvard, was promised a team of postdoctoral associates, an emphasis on theoretical research, and the most up-to-date equipment.  Three years later DuPont started to manufacture neoprene, a synthetic rubber created by Carothers' lab.  Following neoprene, the research group worked on developing a synthetic fiber that could replace silk.   Later the group developed nylon and the technology for its production.  In the nine years Carothers spent at DuPont the group was awarded over 50 patents and the Carothers approach to industrial research was emulated by scientists around the world.   But Carothers was a lonely, troubled man, and at age 41 committed suicide.
 

Paul Flory (1910-1985)
Flory was awarded Nobel Prize for Chemistry in 1974.  His scientific activities ranged from the introduction of commercially successful polymers to studies of polymer properties in solution. His research demonstrated the importance of understanding the sizes and shapes of these flexible molecules in establishing relationships between chemical structures and physical properties. From 1961 to 1976 he was a professor of chemistry at Stanford University, becoming emeritus in 1976.  Visit the Paul Flory Reading Room at The University of Akron.
 

Karl Ziegler (1898-1973)      Giulio Natta (1903-1979)
Chemists Ziegler (German) and Natta (Italian) will always be linked together. Ziegler's early research was devoted to the study of free radicals and the use of lithium in organic synthesis.  After the second world war he developed catalysts that revolutionized the production of addition polymers.  The catalyst, derived from triethyl aluminum and TiCl4, permitted synthesis of polyethylene to yield a linear polymer of high molecular weight and valuable plastic properties.  In 1953 Natta used Ziegler's catalysts to obtain polypropylenes of highly regular molecular structure (isotactic).  The high strength and high melting points soon proved very commercially  important.
In 1963 Ziegler shared the Nobel Prize in Chemistry with Natta for research that led to development of superior polymer products. Now known as Ziegler-Natta catalysts, highly ordered polymers are obtained.  The significance of highly ordered polymers is described in the next section.
 

Preparing Polymers
Polymers are prepared by two methods:

Condensation polymerization occurs when a small molecule such as H2O or HCl form for each extension of the polymer chain. Assume A can react with B to form A-B (A+B®A-B). To make a polymer, put A on both ends of a smaller molecule separated by C & H atoms (represented by X).  Do the same for B but separate with Y. The reaction can go on indefinitely to form a polymer.
  AXA  +  BYB ® AXA-BYB-AXA-BYB-AXA-BYB-AXA-BYB-AXA-BYB   and so on!
monomer   monomer                                              polymer

To show that the structure goes on indefinitely, we represent the repeat unit of the polymer as:  (AXA-BYB)n

To prepare nylon, the monomers are a diamine and a diacid chloride:

 

Addition polymerization occurs when monomers add together to produce the polymer and no other products are formed. Addition polymers are often formed using alkenes (C=C).  If vinyl chloride (VC) is the monomer, a free radical (R.) attaches to VC and the VC now becomes the free radical.  This free radical then attaches to another VC and the propagation continues to produce polyvinyl chloride (PVC).

Properties of PVC depend on the orientation (stereochemistry) of Cl atoms.  For example, if all Cl atoms point out as shown below, the polymer is said to be isotactic. In a normal polymerization, the orientation of the Cl atoms are random and the polymer is atactic.  The Ziegler-Natta catalyst generates isotactic polymers.  Highly ordered isotactic polymers exhibit high degree of crystallinity and high density.

For polymers such as polybutadiene, (CH2-CH=CH-CH2)n, the carbon-carbon double bonds offer the opportunity of connecting molecules by means of sulfur links.The process, known as crosslinking, adds strength while maintaining elasticity.

See Brief History of Polymers