Main Chemical Types of Synthetic POLYMERS

Similarly to small molecules, polymers can be classified based on their chemical nature, i.e. based on the functional groups present in their molecule. However, different from small molecules, one important element in polymer classification is the chemical structure of the polymeric backbone. The attached side atoms or groups of atoms to the polymer backbone play a different role compared to that of the presence of various atom types or groups of atoms in the backbone. For example, it is a significant difference between poly(oxy-1,4-phenylene-oxy-ethylene) that contains phenyl groups and oxygen atoms in the polymer backbone and poly(phenyl vinyl ether) that is a vinyl type polymer with a carbon chain as backbone, although both polymers are ethers. The two polymers are synthesized differently and have quite different properties. Their structures are shown below  

The classification of polymers from the point of view of their chemical nature considers first the chemical structure of the molecular backbone. The chemical nature of the side groups is used only as a second criterion of classification. In some cases, the position of the side groups is well known. In other cases, polymers for practical use may be 

Since the molecular backbone can be linear, branched, or network type, this aspect is also important for polymer structure. It is known that most polymers with a linear backbone are thermoplastics, while those with network backbone are thermosetting polymers. However, for classification from a chemical point of view, this differentiation is less significant. Many polymers with linear backbone are obtained from bifunctional monomers (e.g. terephthalic acid and glycol). If the polymer is obtained from similar monomers but with more than two functionalities (e g. terephthalic acid and ethylene glycerin), the polymer will have thermosetting characteristics. For this reason, this feature is not necessarily used for a classification from the chemical point of view. 

Based on the chemical structure of the backbone, a number of classes of polymers can be distinguished, as discussed below. 

If the sulfur atoms are not part of the polymeric backbone, the polymers are not included in this class. For example, in the vulcanization process of the polymers with unsaturated carbon chain backbone, -S-S- bonds are introduced in the polymer, but the resulting product is not classified as polymer with C-S bonds in the backbone, although in hard rubber (ebonite), for example, the content of sulfur can be as high as 32%. 

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