Science Explains Polymers

The rapid success of Bakelite, the first truly synthetic plastic, parked a flurry
of synthesis investigations and innovations in both America and Europe. As the financial stakes rose, the hit-or-miss garage inventors’ approach that had
dominated the industry gave way to more systematic efforts. As they were no
longer content simply to tinker with undefined raw materials and various
processing conditions, scientists began basic research designed to understand
the molecular structure of polymers.

In 1920, the German chemist Hermann Staudinger, fascinated by the seemingly unique properties of polymers, began investigating their behavior and chemical characteristics. Staudinger's research suggested that polymers are composed
of long chain molecules of many identical or closely related chemical units. Moreover, he suggested that their unusual tensile strength and elasticity are
a result of that great length or, in chemical terms, of their high molecular weight. Staudinger's ideas may not sound especially radical today, but at the time he
was ridiculed by his colleagues in organic chemistry, and his theories had little impact on the scientific community. Indeed, the existence of polymeric chain molecules was not accepted until 1928, when Kurt Meyer and Herman Mark,
working for the German chemical trust I. G. Farben in Ludwigshafen,
demonstrated their existence by examining the crystalline structure of polymers
with x-rays. Many years later Staudinger was recognized for his efforts and persistence, when in 1953 he became the first polymer chemist to receive a
Nobel Prize.

Staudinger's key insights – that polymers are long chains of many small chemical units and that chain length – plays a crucial role in determining physical
properties and behavior--pointed up the need for tools to assess molecular
weight and thus chain length. One of the first tools was the ultracentrifuge,
invented by the Swedish chemist Theodor Svedberg. The ultracentrifuge spins samples at very high speeds and can separate molecules according to their size.
It can be used to estimate both the size of the molecules and the distribution of
sizes in a given polymer sample.

By the end of the 1920s, armed with better tools and better theories, polymer scientists were making dramatic breakthroughs. In 1928, the DuPont Corporation hired chemist Wallace Hume Carothers to build new kinds of polymers in a new laboratory dedicated to basic research. To test Staudinger's still-controversial
theory, Carothers carefully joined small organic compounds into long chains and examined the properties of his products. He found that collections of very long
chain molecules produced stiffer, stronger, and denser materials. By 1930, Carothers's systematic synthetic approach was bearing fruit as he came up with
a new class of polymers called polyamides, or ”nylons“. These polymers could
be melted and drawn into a remarkably strong fiber.

19.01.2009

PET, a polyester, is a chemical feedstock in polymer industry. Its synthesis may follow either of two ways ...

-> More