POLYMERS
Polymers consist of very large molecules that are made up of many repeating smaller molecules.
Proteins, nucleic acids, starch, cellulose, silk and natural rubber are the most widely encountered natural polymers. These natural polymers can be imitated in laboratories and synthetic polymers produced.
80% of organic chemistry is related to polymer chemistry. One of the simplest polymers is polyethylene which is made from many ethylene molecules. Trash bags, sandwich wraps, teflon, automobile tyres, varnishes and paints are all examples of polymers that we use in our daily life.
POLYETHYLENE
Ethylene polymerizes by a radical mechanism when it is heated at a pressure of 1000-3000 atm at 250°C with a small amount of an organic peroxide. The properties of polyethylene may change according to the reaction conditions.
Polyethylene is the most widely used of all plastics because it is inexpensive, flexible, extremely tough, and chemically resistant.
High density polyethylene, HDPE, is used for grocery bags, car fuel tanks, packaging and piping.
Low density polyethylene, LDPE, is softer and more flexible than HDPE. LDPE is used for bottles, garment tags, frozen food packs, film and plastic toys.
Polyvinyl chloride IPVC)
If one hydrogen is replaced with chlorine in the ethylene molecule, vinyl chloride is formed. If vinyl chloride polymerizes polyvinyl chloride, known as PVC, is formed. PVC is lightweight, long lasting, and waterproof. In its rigid form, PVC is water-resistant and can be drawn out into pipes, house siding and drainpipes. It is also used in compact discs and computer casings.
Polystyrene
If one hydrogen in ethylene is replaced by a phenyl group, the compound styrene
is produced. Styrene is polymerized to polystyrene.
Polystyrene is an amorphous, white and brittle plastic. Polystyrene has many applications due to its rigidity. Polystyrene is used for making products such as toys, display boxes, packaging material, egg cartons and Styrofoam
Polytetrafluoro ethylene (Teflon)
If all the hydrogen atoms in ethylene are replaced by fluorine atoms, tetrafluoro ethylene results. Tetrafluoroethylene is polymerized to form polytetrafluoro ethylene. Polytetrafluoroethylene, known as teflon, is used in the production of nonstick cooking ware.
Polypropylene
The second member of alkenes, propylene, can also be polymerized under suitable conditions. Polypropylene is used in the production of bottles, electric battery cases and rugs.