POLYMER CHEMISTRY

Polymer chemistry is a multidisciplinary science that deals with the chemical synthesis and chemical properties of polymers which were considered by Hermann Staudinger as macromolecules. According to IUPAC recommendations, macromolecules refer to the individual molecular chains and are the domain of chemistry. Polymers describe the bulk properties of polymer materials and belong to the field of polymer physics as a subfield of physics.

Polymers and their Properties

Polymers are high molecular mass compounds formed by polymerization of monomers. The simple reactive molecule from which the repeating structural units of a polymer are derived are called monomer. A polymer is chemically described by its degree of polymerisation, molar mass distribution , tacticity, copolymer distribution, the degree of branching, by its end-groups, crosslinks, crystallinity and thermal properties such as its glass transition temperature and melting temperature. Polymers in solution have special characteristics with respect to solubility, viscosity and gelation.

Schematically polymers are subdivided into biopolymers and synthetic polymers according to their origin. Each one of these classes of compounds can be subdivided into more specific categories in relationship to their use, properties and physicochemical characteristics.

The biochemistry and industrial chemistry are disciplines that are interested in the study of the chemistry of polymers.

• Biopolymers : Polymers produced by living organisms:
  • Structural proteins : collagen, keratin,  elastin.
  • Functional proteins : enzymes, hormones.
  • Structural polysaccharides : cellulose, chitin.
  • Reserve polysaccharides :  starch, glycogen.
  • Nucleic acids : DNA, RNA.
• Synthetic polymers : these polymers are used for plastics, synthetic fibers, paints, building materials, furniture, mechanical parts and adhesives. These are divided into:
  • Thermoplastic polymers such as polyethylene,  teflon, polystyrene, polypropylene, polyester, polyurethane, Poly(methyl methacrylate), vinyl chloride, nylon, rayon, cellulose, silicon, glass fiber, , among others.
  • Thermoset plastics : vulcanized rubber, bakelite, Kevlar, polyepoxide.

History

The work of Henri Braconnotin 1777 and the work of Christian Schönbein in 1846 led to the discovery of nitrocellulose, which, when treated with camphor produced celluloid. Dissolved in ether or acetone, it is collodion, used as a wound dressing since the U.S. Civil War. Cellulose acetate was first prepared in 1865. In 1834, Friedrich Ludersdorf and Nathaniel Hayward independently discovered that adding sulfur to raw natural rubber (polyisoprene) helped prevent the material from becoming sticky. In 1844 Charles Goodyear received a U.S. patent for vulcanizing rubber with sulfur and heat. Thomas Hancock had received a patent for the same process in the UK the year before.

In 1884 Hilaire de Chardonnet started the first artificial fiber plant based on regenerated cellulose or viscose rayon, as a substitute for silk, but it was very flammable. In 1907 Leo Baekeland inented the first synthetic polymer, a thermosetting phenol-formaldehyde resin called Bakelite. Around the same time, Hermann Leuchs reported the synthesis of N-carboxyanhydrides and their high molecular weight products upon reaction with nucleophiles, but stopped short of referring to these as polymers, possibly due to the strong views espoused by Emil Fischer, his direct supervisor, denying the possibility of any covalent molecule exceeding 6,000 daltons. Cellophane was invented in 1908 by Jocques Brandenberger who squirted sheets of viscose rayon into an acid bath.

In 1922 Hermann Staudinger (of Worms, Germany 1881-1965) was the first to propose that polymers consisted of long chains of atoms held together by covalent bonds. He also proposed to name these compounds macromolecules. Before that, scientists believed that polymers were clusters of small molecules (called colloids), without definite molecular weights, held together by an unknown force. Staudinger received the Nobel Prize in Chemistry in 1953. Wallace Carothers invented the first synthetic rubber called neoprene in 1931, the first polyester, and went on to invent nylon a true silk replacement, in 1935. Paul Flory was awarded the Nobel Prize in Chemistry in 1974 for his work on polymer random coil configurations in solution in the 1950s. Stephanie Kwolek developed an aramid, or aromatic nylon named Kevlar, patented in 1966.

There are now a large number of commercial polymers, including composite materials such as carbon fiber-epoxy,  polystyrene-polybutadiene (HIPS), acrylonitrile butadiene-styrene (ABS), and other such materials that combine the best properties of their various components, including polymers designed to work at high temperatures in automobile engines.

In spite of the great importance of the polymer industry, it took a long time before universities introduced teaching and research programs in polymer chemistry. An "Institut fur Makromolekulare Chemie was founded in 1940 in Freiburg, Germany under the direction of Hermann Staudinger. In America a "Polymer Research Institute" (PRI) was established in 1941 by Herman Mark at the Polytechnic Institute of Brooklyn (now Polytechnic Institute of NYU). Several hundred graduates of PRI played an important role in the US polymer industry and academia. Other PRI's were founded in 1961 by Richard S. Stein at the University of Massachusetts, Amherst, in 1967 by Eric Baerat Case Western Reserve University, in 1982 at The University of Southern Mississippi, and in 1988 at the University of Akron.

Theories

Association theory is a discredited theory which tried to explain molecular structures of macromolecules.
Some other theories related to polymers include

• Scheutjens–Fleer theory.
• Flory–Huggins solution theory.
• Cossee-Arlman mechanism.
• Polymer field theory.
• Hoffman Nucleation Theory.

Biopolymers

They are produced by living organisms:

• structural proteins: collagen, keratin, elastin.
• chemically functional proteins: enzymes, hormones, transport proteins.
• structural polysaccharides: cellulose, chitin.
• storage polysaccharides: starch, glycogen.
• nucleic acids: DNA, RNA.

Synthetic Polymers

Examples of Synthetic polymers are plastics,  fibers,  paints,  building materials, furniture, mechanical parts, adhesives.

• thermoplastics, polyethylene,  Teflon, polystyrene,  polypropylene, polyester, polyurethane, polymethyl methacrylate, polyvinyl chloride, nylon, rayon, celluloid, silicone.
• thermosetting plastics: vulcanized rubber,  Bakelite, Kevlar, epoxy.

References

1. ^ Ravve, Abe (2000). Principles of Polymer Chemistry (Second ed.). Plenum Publishing. ISBN 978-0-306-46368-6.
2. ^ "Macromolecule. IUPAC. Retrieved 2011-09-05.
3. ^ "Polymer".  IUPAC. Retrieved 2011-09-05.
4. ^ "The Early Years of Artificial Fibres". The Plastics Historical Society. Retrieved 2011-09-05.
5. ^ Kricheldorf, Hans, R. (2006), "Polypeptides and 100 Years of Chemistry of α-Amino Acid N-Carboxyanhydrides", Angewandte Chemie International Edition 45 (35): 5752–5784, doi:10.1002/anie.200600693.
6. ^ "History of Cellophane", about.com. Retrieved 2011-09-05.

- Wikipedia