The development of modern has technology tremendous changes to our life-style in the last 30 years. One of most significant changes has been the gradual replacement of naturalaterial, such as wood, wool and cotton with man-made synthetic polymers.
For better or worse, We are becoming a 'plastic' society. In this article we will study how polymers are made and how they are used.
Polymers are high molecular weight compounds, whose structures are composed of a large number of simple repeating units. The repeating units are usually obtained from low molecular weight, simple compounds, referred to as monomers. The conversion process, monomers to polymers, is known as 'polymerisation'.
Frequency, the end-groups of polymer are unknown- they may arise from impurities in the reaction mixture. In some cases, the end-group can be controlled. The properties of a polymer are governed almost entirely by the bulk of the polymer molecules rather than the end- groups in the formula.
Polymers are said to be linear, if the repeating units are joined together likes in a chain.
The chains may be branched, or joined together by cross-links, or net-work polymers.
There are two main types of polymerisation processes: addition polymerisation and condensation polymerisation. In addition polymerisation, all atoms in the monomers are present in the polymer, but condensation polymerisation is characterised by the elimination of small molecules, such as water, methyl alcohol, carbon dioxide, etc.
ALTERNATING COPOLYMER
nA+nB⟶ -A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A
RANDOM COPOLYMER
nA+nB⟶ -A-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A
Sarnar is an important copolymer. It is obtained by training of choroide with vinylidene choroide in the presence of benzoyl or louroyl peroxide catalysts
Saran is used to make tough wraps that is very effective moisture barrier. Automobiles upholstery can also be fabricated from Saran.
CONDITIONS POlYMERS
Condensation polymers are formed by combination of monomers with the elemination with the elimination of simple molecules such as H2O or CH3OH. There are two main types of condensation polymers:
- Polyesters or
- Polyamides
(a). Terylene (Dacron or Teron) is the most important polyester. It is prepared by heating ethylene glycol with dimethyl terephthalate at 270-280° in the presence of matal oxide. The polymer melt can be spun into fibres and combined with such naturally occurring fibres as cotton.
The polymer melt can be into fibres and combined with such naturally occurring fibres as cotton. The combination of cotton and polyester yields a fabric (e.g., 60/40 cloth). that dries quickly without wrinkling, yet still retain the coolness and comfort of 100%cotton. Polymers have revolutionised the cloth industry.
Ethylene of glycol is manufactured by catalyts oxidation of ethylene oxide which is then trated with dilute acid.
Dimethyl terephthalate is obtained catalytic oxidation of p-x lene following by esterification of the resultant acid.
(b) Nylon-6,6 is the most important polyamides. It is obtained by heating adipic acid with hexamethlne under nitrogen at 180-220°C. Nylon- 6,6 derives its name from its starting materials, adipic acid hexamethylene, both of which have six/ carbons.
