Polymers

In our everyday life, we often give credit to engineers for creating new gadgets to improve our standard of living. However, do u ever give a though of where did all the plastics and other materials that make productions these gadgets possible? It is the credits of chemist mostly those polymer scientist that have done extensive research that our life is so much easier today.

What are polymers? Polymers are large molecules that are produces from small molecules by polymerization via chemical reaction. These large molecules exist as chains of smaller molecules and these chains are held together by intermolecular forces such as van der waals forces or hydrogen bonds. The special thing about polymers is that they are partially crystalline and partially amorphous. They do not simply form large crystals but rather crystalline regions called crystallites within an amorphous base. These regions where segments of the chains lie close together and those that are regularly packed together would be crystalline and those where segments of the chains are not regularly packed would be amorphous.

There a lot of types of polymers. However, polymers can be classified into three category that is elastomers, thermoplastics (thermoplastic polymers) and thermosets (thermosetting polymers). Elastomers are polymers that can be stretched easily to several times their original length and return to their original state when the applied stress is released. Elastomers has this kind of property are due to their lightly cross-linked with covalent bonds. The scarce number of cross link causes the polymer to return to its original state when applied stress is released. These polymers are usually come from natural rubber or syntheric rubber.

The second type of polymer is thermoplastics which can be repeatedly softened by heating and solidified by cooling without decomposition. Hence, their shape can be manipulated by repeatedly heating and cooling. In thermoplastics, there are no covalent cross links between the polymers chains but is replaced by weak van der waals forces or hydrogen bonds instead. When heat is applied to it, these bonds can be easily broken and the polymer chains can slide over one another making it easy for shape manipulation. The ability to be remolded makes thermoplastics extremely useful in industry and the production of thermoplastics greatly exceeds than that of thermosets. Some of the thermosets are polyethene , poly propene or polyphenylethene which are usually the plastic that are found in our every life usage.

Thermosets on the other hand are polymers which its shape cannot be changed once it is solidified. Hence, they can be only be moulded once. This is because they are extensive covalent cross links between the polymer chains making the polymer structure rigid and strong. Some examples of thermosets are Bakelite, polyurethanes and epoxy resins.