Brief account on polymers, composite materials with special emphasis on superconductors, semiconductors and introduction of plasma.
Any of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units, each a relatively light and simple molecule. Polymers may consist of long chains of unbranched or branched monomers or may be cross-linked networks of monomers in two or three dimensions. Their backbones may be flexible or rigid. Some natural inorganic materials (e.g., the minerals diamond, graphite, and feldspar) and certain man-made inorganic materials (e.g., glass) have polymer-like structures. Many important natural materials are organic polymers, including cellulose (from sugar monomers; see polysaccharide), lignin, rubber, proteins (from amino acids), and nucleic acids (from nucleotides). Synthetic organic polymers include many plastics, including polyethylene, the nylons, polyurethanes, polyesters, vinyls (e.g., PVC), and synthetic rubbers. The silicone polymers, with an inorganic backbone of silicon and oxygen atoms and organic side groups, are among the most important mixed organic-inorganic compounds.
Many polymers have both a common name and a structure-based name specified by the International Union of Pure and Applied Chemistry (IUPAC). Some polymers are commonly known by their acronyms. Some companies use trade names to identify the specific polymeric products they manufacture. For example, Fortrel® polyester is a poly (ethylene terephthalate) (PET) fiber. Polymers are often generically named, such as rayon, polyester, and nylon. See also Organic nomenclature; Polyamide resins; Polyester resins. Composition.
Polymer structures can be represented by similar or identical repeat units. These are derived from smaller molecules, called monomers, which react to form the polymer. Propylene monomer and the repeat unit it forms in polypropylene are shown below. 1 [pic]
With the exception of its end groups, polypropylene is composed entirely of this repeat unit. The number of units (n) in a polymer chain is called the degree of polymerization (DP). Other polymers, such as proteins, can be described in terms of the approximate repeat unit where the nature of R (a substituted atom or group of atoms) varies. See also Polyvinyl resins; Protein.
Types of Polymers
There are two main types of polymers:
Natural Polymers –Polymers are widely found in nature. The human body contains many natural polymers, such as proteins and nucleic acids. Cellulose, another natural polymer, is the main structural component of plants. Most natural polymers are condensation polymers, and in their formation from monomers water is a by-product.
There are two types:
Cellulose: – flexible, strong natural polymer; gives shape to plant cells ** made in plants when sugar molecules are joined into long strands. Cellulose nitrate Other names[hide]
Cellulose nitrate; Flash paper; Gun cotton; Collodion; Pyroxylin:
The very first synthetic polymer came about when a scientist reacted cellulose, in the form of cotton, with nitric acid. The result was cellulose nitrate
In general, cotton was used as the cellulose base, and is added to concentrated sulfuric acid and 70% nitric acid cooled to 0oC to give cellulose trinitrate (or guncotton). While guncotton is dangerous to store, its risks can be reduced by storing it wet.
Cellulose is treated with sulfuric acid and potassium nitrate to give cellulose mononitrate. This was used commercial as Celluloid, a highly flammable plastic used in the first half of the 20th Century for lacquers and photographic film Nitrocellulose (also: cellulose nitrate, flash paper) is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating...
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