The development of modern technology has brought tremendous changes to our life- styles in the last 30 years. One of the most significant changes has been the gradual replacement of natural materials, sut as wood, wool and cotton with man- made synthetic polymers.
For better or worse, we are becoming a 'plastic' society. In this chapter 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'.
The formation of polythene is an exact of this process
Frequency, the end- groups of polymers 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 the reaction mixture. In some cases, the end- groups can be controlled.
The properties of polymer are governed almost entirely by the bulk of the polymer molecule rather than the end- groups.
To emphasis the basis structure of the polymer, it is customary not to include the end- groups in the formula.
Polymers are said to be linear, if the repeating units are joined together like links in a chain.
The chains may be branched, or joined together by cross-links, or both. More exten- sive cross- linking may lead to the formation of a three dimensional cross- linked or net-work polymers.
There are two types of polymerisation processes:
Addition polymerisation and
Condensation polymers.
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.
