Polymers

Polymers are substances consisting of large molecules that are made of many small, repeating units. The small molecules which combine to form a polymer are called monomers. The number of repeating units in one large molecule is called the degree of polymerization. Materials with a very high degree of polymerization are called high polymers. Polymers consisting of only one kind of repeating unit are called homo-polymers. Co-polymers are formed from several different repeating units. Most of the organic substances found in the living matter, such as protein, wood, rubber and resins, are polymers. Many synthetic materials, such as plastics, fibres, adhesives, glass, and porcelain, are also largely polymeric substances. 

Polymers can also classified as 

• fibres
• plastics and resins
• elastomers

a) Fibres are polymers which can be drawn out as threads and woven into fabrics. Examples are nylon, Terylene and rayon.

b) Plastics are synthetic polymers that can flow when heated. Plastics can be classified as

• thermoplastics - plastics which can be softened repeatedly by heating and hardened by cooling. Examples are poly(ethene), poly(propene), poly(chloroethene).
• thermosetting resins - plastics which do not soften on heating and can only be moulded at the manufacturing stage but cannot be remoulded. Examples are Bakelite(phenol-methanal resin)epoxy resins, urea-methanal resins.

c) Elastomers are polymers that  undergo deformation when a force is applied and regained the original form once the force is removed. Example are natural and synthetic rubber.

Uses of Polymers 

1. Polystrenes

• suitable for radio-frequency insulation
• accessories used in low temperatures, as in refrigeration installations and in aeroplanes desihned for high- altitude flight
• Styrofoam used for packaging, disposable cups, lunch boxes

2. PTFE ( polytetrafluoroethene)

• the coating used on non-stick cooking utensils
• electrical insulators

3. Rayon

• used in the garment and texttile industries (some saree and shirt materials are made from rayon)
• used in the tyre industry for making cords used in tyres
• mixed with wool and other fibres and used in carpet industry
• used in medical and pharmaceutical industry for making bandages, bottles, bags

4. Polyvinyl Chloride (PVC)

• used for insulation on domestic electrical wiring
• used in plastics pipe, vinyl coatings, and wire insulation

5. Nylon

• used in the manufacture of fabrics for such articles as hosiery, sleepwear, underwear, blouses, shirts, and raincoats
• used for parachutes, insect screening, medical sutures, strings for tennis rackets, brush bristles, rope, and fishing nets and line

6. Kevlar

• a synthetic polyamide
• used to make bullet-proof vests and fireproof garments

7. Terylene (Darcon)

• a synthetic polyester which is shrink-proof and crease-proof
• used for making clothing and sleeping bag

8. Bakelite (phenol-methanal resin)

• used for making switches, sockets, plugs, and insulators in electrical equipment

9. Poly (methyl methacrylate) / Perspex

• has excellent optical properties
• suitable for spectacles and camera lenses
• for streer and advertising illumination