Polymers

From ArticleWorld

Polymers are long chain molecules that are made up of many covalently bonded repeating units. These units are referred to as monomers and are small molecules linked together to form polymers in the process of polymerization. Monomers need not be identical but can have different chemical substituents. These differences can cause modifications in properties such as solubility, flexibility and strength. Most polymers tend to be organic molecules however there are some inorganic polymers.

Nomenclature

The classification of polymers is mainly into four groups. These are the linear or branch chains or thermoplastics, the cross-linked chains or thermosets, the elastomers and the coordination polymers. Polymers include a large and very different group of molecules and so they are often named from the monomer that makes them. The polymers of amino acid, proteins, are made up of mainly 20 amino acid monomers. This sequence determines the shape and function of the resulting polymer. These polymers are usually exact sequences with exact lengths unlike those in synthetic polymers which can vary significantly.

Physical properties

Some physical properties of polymers include degree of polymerization, molar mass distribution, crystallinity and thermal properties such as melting point. Branching can also occur in polymers. This can happen when the polymer curls back on itself and bonds to another area in the chain. When this breaks the result is small chains sprout from the polymer backbone. These branched chains cannot interact as well as those that are unbranched as fewer dipoles are able to occur. This results in the lowering of melting points, weaker intermolecular bonding and lowered tensile strengths. Stereoregularity is another property that describes the arrangement of the functional groups on the backbone isotactically. This type of alignment allows the ability to line up closer to one another in one direction and thus creates stronger more rigid polymers with crystalline areas. Atactic chains have randomly aligned substituent groups and these have low strength but great flexibility.