What are polymers?

Polymers are substances composed of macromolecules, very large molecules with molecular weights ranging from a few thousand to as high as millions of grams/mole. The IUPAC Gold Book definition of a macromolecule is: “A molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass.” Natural polymers include protein, starch, cellulose, DNA and make up most of the structures of living tissue. Synthetic polymers now constitute one of the most successful and useful classes of materials and possess a broad range of physical properties.

Today, synthetic polymers are being used to emit light, act as semiconductors in low cost printable devices, as light weight materials for bullet proof vests (where the fibers are stronger than steel), in medicine to deliver drugs, as artificial skin and for many other applications that were not imagined just a few years ago. Rapid advances in polymers are enabling the nanotechnology revolution. For example in microelectronics polymers make possible circuits of a few 10s of nanometers, that is, less than 1/1000th the size of a human hair.

Natural polymers have been used by man since prehistory and have been modified and processed empirically over many centuries for various applications, for example, textiles for clothing and papyrus. Most of the early modifications still in use today stem from developments in the 19th century or the beginning of the 20th century and relate to cellulose and natural rubber, for example, the mercerisation of cotton by Mercer (1844), the production of cellullose nitrate (1845), cuprammonium rayon (1859), cellulose acetate (1869) and cellophane (1908), the production of a waterproof fabric using natural rubber by Macintosh (1823) and the crosslinking of natural rubber by Goodyear (1839).

The first, wholly synthetic polymer material, phenol-formaldehyde resin (Bakelite), was developed by Baekeland from 1905 to 1909. It was followed by urea-formaldehyde resins in the 1920s and polyester (alkyd) resins in the 1930s. Linear vinyl polymers were discovered early, poly(vinyl chloride) in 1872 and poly(methyl acrylate) in 1880, but were not produced commercially until much later, for example, poly(vinyl acetate) in 1920, poly(methyl acrylate) in 1927 and poly(vinyl chloride) in 1930. Many of the other conventional linear polymers of today formed by chain polymerisation were developed in the 1930s to 1950s with something of a hiatus during the Second World War. The researches of Ziegler and Natta in 1953–1955 developing coordination catalysts for the polymerization of ethylene and propylene resulted in the award of a Nobel Prize (1963). (see a video about Natta) The important advance was one of closer control of chain structure in terms of the minimization of branching and the control of tacticity. Significantly, the close control of chain structure is still important for the development of polymer materials of the future.

The initial developments of synthetic polycondensation and polyaddition polymers occurred from about 1928 to 1947. The work of Carothers from 1928 to 1932 at the E.I. duPont and de Nemours company led to the controlled preparation of polyesters and polyamides. This was followed by the development of poly(ethylene terephthalate) (PET) by ICI in 1943 and that of polyurethanes from 1939 to 1947 by Bayer at Farbenfabriken Bayer. In subsequent years, another DuPont scientist (Stephanie Kwoleck) invented a fiber sold as Kevlar that is stronger than steel.

Notwithstanding the preceding advances spanning the last two hundred years or so, the macromolecular structure of polymers was not recognised until the landmark paper published by Staudinger in 1920 and was not fully accepted until several years later (see a video about Staudinger). Prior to Staudinger’s paper, macromolecular properties were thought to be achieved through the association of small-molecule entities and cyclic structures were often proposed. In this respect, the pioneering work of Carothers on the formation of polyesters and polyamides was important in establishing the covalent nature of macromolecules. Staudinger was eventually awarded a Nobel Prize in 1953.

Paul Flory was a Nobel laureate was a leading pioneer in understanding the behavior of polymers in solution, and won the Nobel Prize in Chemistry in 1974“for his fundamental achievements, both theoretical and experimental, in the physical chemistry of macromolecules.” Pierre-Gilles de Gennes was a French physicist and the Nobel Prize laureate in Physics in 1991. He was awarded a Nobel Prize for discovering “methods developed for studying order phenomena, …… in particular [relate] to liquid crystals and polymers.”

The 2000 Nobel Prize in Chemistry was awarded to Heeger, MacDiarmid and Shirakawa for research in conducting polymers. This work has enabled the creation of polymers that conduct electricity like a metal, polymers that emit light and plastic transistors. More recently, the 2005 Nobel Prize in Chemistry was awarded to Chauvin, Grubbs and Schrock (see interview of Grubbs and Schrock) for their work in developing new methods of making polymers more simply and cheaply. With uses ranging from fabrics to food packaging, polymers are among the most widely used and important type of materials today.

 

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