A polymer is a large molecule or a macromolecule formed by joining many repeated subunits. They may be naturally found in plants and animals (known as the natural polymer) or may be man-made (called synthetic polymer).
Different polymers have a number of unique physical and chemical properties due to which they have become part and parcel of our life. In this article, we will discuss the preparation of some important additional polymers like polyethene(or polyethylene), Teflon, and polyacrylonitrile.
Table of Contents
- Preparation of Polythene
- Structure of Polythene
- Types Of Polythene
- Uses Of Polythene
- Polytetrafluoroethylene (Teflon)
- Recommended Videos
Preparation of Polythene
To prepare polythene, the monomer ethylene is first converted into a polymer. This is done by passing ethylene gas through a catalyst at a high temperature. The polymer chains then grow by linking together to form a long, repeating chain.
The chemical equation for the preparation of polythene is shown as:
Structure of Polythene
Types Of Polythene
Polythene is the most common plastic used broadly in the packaging industry. Based on the density, polythene can be classified into two types:
- Low-density polythene: It has a density range of 0.910–0.940 g/cm3 and is prepared by the free-radical polymerization of ethene. The reaction is carried out at a temperature of 350 K to 570 K under the pressure of 1000 to 2000 atmospheres in the presence of a catalyst, dioxygen (in traces) or a peroxide initiator. The highly branched structure of LDP gives it a unique flow property in the molten state. It is a poor conductor of electricity and is chemically inert. The LDPs are used for making plastic bags and film wrap.
- High-density polythene: It has a density greater than or equal to 0.941 g/cm3 and has a low degree of branching. It is obtained when the addition polymerization of ethene takes place in a hydrocarbon solvent. The reaction is carried out under a pressure of 6 to 7 atmospheres and at a temperature of 333 K to 343 K in the presence of Ziegler-Natta catalysts or metallocene catalysts. HDPs are chemically inert as well and are used in making bottles, butter tubs, milk jugs, water pipes and garbage containers.
Uses Of Polythene
- Polythene having lower density have the ability to deform without breaking and better gives superior elongation by stretching up to six times to its original length before breaking.
- It is a useful plastic for moulding and extruding in various shapes such as bottles, sheets and pipes etc.
- It is used for plastic bags, and stretch films because of its clear and crystalline nature.
- Polythene has greater chemical resistance which covers a wide ranges of chemicals.
Teflon is manufactured by free-radical polymerization of tetrafluoroethylene. The catalyst used is per sulphate at high pressure. The reaction is given as:
n F2C=CF2 → −(F2C−CF2)n−
It is manufactured by free radical polymerization of acrylonitrile in the presence of Peroxide(as a catalyst). The chemical equation for the same is shown below :
Synthetic Polymers – Uses and Applications
Natural Polymers: Characteristics and Examples
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