Classification - natural and synthetic
Polymers are large molecules composed of repeated chemical units. The smallest repeating unit is called a mer. The term polymer is derived from the Greek words poly and mers meaning "many parts." Linear polymers are like ropes. For a polymer chain of 10,000 units (a typical length), a standard half-inch-thick rope would be about 128 meters (140 yards) long to represent the length-to-thickness ratio. Polymers are synthesized naturally and artificially to perform a wide variety of specialized tasks.
There are two types of polymers: synthetic and natural. Synthetic polymers are derived from petroleum oil, and made by scientists and engineers. Examples of synthetic polymers include nylon, polyethylene, polyester, Teflon, and epoxy.
1. Natural polymers
The polymers which are obtained naturally are called natural polymers. A natural polymer has its origin in plants and animals. Starch, cellulose, proteins, natural rubber etc. are the examples of a natural polymers. Let us briefly discuss these natural polymers:
It is polymer which forms the food reserve for all the plants. The monomer of starch is – D – glucose. When a polymer of starch is formed hundreds of – D – glucose molecules are joined through a linkage known as glycosidic linkage.
They are the building blocks for animals. Proteins are simply polypeptides and are formed when amino acids undergo polymerization. The structure of proteins can either be long chains or cross-linked. Hundreds of amino acids link together to form a protein molecule, the arrangement is highly organized.
2. Synthetic polymers:
The man-made polymers or the polymers which are synthesized in the laboratory are called synthetic polymers. Synthetic polymers find a huge application in our daily life. Most of the things that we use are made up of synthetic polymers. Some of the common examples of synthetic polymers are polyethylene, polyvinyl chloride, bakelite, nylon, synthetic rubbers.
As we know that natural rubber is a polymer of 2- methylbuta-1, 3-diene but synthetic rubbers are either homopolymers of 1, 3- butadiene derivatives or copolymers of 1, 3- butadiene or its derivatives with another unsaturated monomer. In general, synthetic polymer is any polymer which can be stretched to at least twice its length and regains its original shape after being stretched.
It is derived from unsaturated hydrocarbons. This synthetic polymer is used in making a large number of household articles. We have two types of synthetic plastic, that is low density plastic which is chemically inert, tough and extremely poor in conducting electricity. Hence it is widely used in making toys, insulation wires and pipes. On the other hand we have high density polythene which is also chemically inert. It is highly crystalline in nature. It is stiffer, harder and has greater tensile strength. It is used in the making of containers, pipes and bottles.
Methods of polymerization
Polymerization is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many forms of polymerization and different systems exist to categorize them.
In chemical compounds, polymerization occurs via a variety of reaction mechanisms that vary in complexity due to functional groups present in reacting compounds and their inherent steric effects.
In more straightforward polymerization, alkenes, which are relatively stable due to bonding between carbon atoms, form polymers through relatively simple radical reactions; in contrast, more complex reactions such as those that involve substitution at the carbonyl group require more complex synthesis due to the way in which reacting molecules polymerize . Polymerization that is not sufficiently moderated and proceeds at a fast rate can be very hazardous. This phenomenon is known as hazardous polymerization and can cause fires and explosions.
Emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating water,monomer, and surfactant. The most common type of emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer (the oil) are emulsified (with surfactants) in a continuous phase of water. Water-soluble polymers, such as certainpolyvinyl alcohols or hydroxyethyl celluloses, can also be used to act as emulsifiers/stabilizers. The name “emulsion polymerization” is a misnomer that arises from a historical misconception. Rather than occurring in emulsion droplets, polymerization takes place in the latex particles that form spontaneously in the first few minutes of the process. These latex particles are typically 100 nm in size, and are made of many individual polymer chains.