Polymers are the long chain massive organic molecules assembled from numerous smaller molecules termed as monomers. Polymers comprise of many repeating monomer units in long chains. A polymer is analogous to a necklace made up from numerous small beads (that is, monomers).
Basics of Polymers:
Polymers are the high molecular weight compounds built up via the repetition of small chemical units termed as monomers. They are either natural or synthetic. The natural polymers comprise cellulose, rubber, wool, starch and proteins whereas the synthetic polymers comprise nylon, polyvinyl chloride, polyethylene and polyester. The word polymer comes from the two Greek terms: poly, meaning many and mer, meaning parts. A polymer is thus a high molecular weight compound made up of hundreds or thousands of many similar small fundamental units (that is, monomers) of carbon, hydrogen, oxygen or silicon atoms. The monomers are linked altogether covalently in a chemical procedure termed as polymerization.
Classification of Polymers:
I) Based on Nature of Monomers:
Polymers are categorized on the basis of nature of monomers linked altogether into homopolymers and copolymers.
They comprise of chains having similar bonding linkages to each and every monomer unit. This implies that the polymer is made up from all similar monomer molecules. Homopolymers might be symbolized as - [A-A-A-A-A-A]-
They comprise of chains having two or more linkages generally implying two or more different kinds of monomer units. The synthetic rubber employed to make shoe soles, for illustration, is a copolymer made up of the monomers butadiene and styrene. Copolymers might be symbolized as- [A-B-A-B-A-B]-
II) Based on Mode of Polymerization:
Polymers are further categorized by the reaction mode of polymerization into addition polymers and condensation polymers.
A) Addition Polymers:
Whenever monomers merely add on to form the polymer, the method is known as addition polymerization. The polymer is the only product example: Ethylene monomers add on to form the polyethylene. The monomer molecules bond to each and every other without the loss of any other atoms. The highest groups of polymers in this class are the alkene monomers.
B) Condensation Polymers:
Here, two different monomer molecules condense with the loss of a small molecule, generally water to make a polymer. The condensation occurs between two reactive functional groups, similar to the carboxyl group (of an acid) and the hydroxyl group (of an alcohol). Polyesters and polyamides (like nylon) are in this class of polymers.
III) Based on Physical property related to heating:
The classification of polymers can as well be based on the physical property associated to heating. This categorizes them to thermoplastics and thermosets.
These are the plastics which soften whenever heated and become firm again whenever cooled. They are more admired as the heating and cooling might be repeated. Thermoplasts can be shaped and melted over and over again. Illustrations of thermoplastics comprise acetal, cellulose acetate, acrylic, polystyrene, polyethylene, vinyl and nylon.
These are the plastics which soften whenever heated and can be molded, however harden permanently. Thermosets can be melted and shaped just once. If heated a second time, they tend to crack or break up. Illustrations of thermosets comprise epoxy, amino and phenolic and unsaturated polyesters.
Characteristics of Polymers:
The characteristics of polymers comprise:
a) Low Density
b) First-class corrosion resistance
c) Low coefficient of friction
d) Superb surface finish can be obtained
e) Good mould capability
f) Very bad tensile strength
g) Can be produced by means of close dimensional tolerances
h) Poor temperature resistance
j) Can be produced transparent or in various colours
k) Low mechanical properties
Applications of Polymers:
The Polymers have applications in Medicine, Agriculture, Consumer Science, Industry and Sports.
The polymeric materials are employed in and on soil to enhance the aeration, give mulch and promote the health and growth of plant. Polymers have revolutionized the agricultural and food industry by latest tools for the molecular treatment of diseases, rapid disease detection and improving the capability of plants to absorb nutrients. Functionalized polymers were employed to raise the effectiveness of herbicides and pesticides, allowing lower doses to be employed and to protect the atmosphere indirectly via filters or catalysts to decrease pollution and clean-up existing pollutants.
Most of the biomaterials, particularly heart valve replacements and blood vessels, are made up of polymers such as Teflon, Dacron and polyurethane. Illustrations of newer medical applications of polymeric materials comprise controlled drug delivery, polymeric drugs and artificial skin.
Plastic containers of all sizes and shapes are light weight and economically less costly as compare to the more traditional containers. Floor coverings, clothing, garbage disposal bags and packaging are other polymer applications.
The automobile parts, windshields for fighter planes, packing materials, pipes, tanks, insulation, wood substitutes, adhesives, matrix for composites and elastomers are all polymer applications utilized in the industrial market.
Playground tools, different balls, golf clubs, swimming pools and protective helmets are regularly prepared from polymers.
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