Polymers are molecules composed of repeating units. The simplest polymers are made up of only two types of atoms, carbon and hydrogen. These are called hydrocarbons. Other common polymers include those made from combinations of nitrogen, oxygen, and chlorine atoms. Polymers can be natural or synthetic (man-made).
The structure of a polymer is critical to its properties. The physical properties of a polymer depend on the type and arrangement of the atoms in its chain as well as on the way the chains interact with each other.
The simplest type of polymer is a straight chain, in which all the monomers (repeating units) are aligned in a row. This type of polymer is not very strong because the chains can slide past each other easily.
A more complex type of polymer is a cross-linked chain, in which some monomers are linked together by chemical bonds that form between their atoms. This type of polymer is stronger because the chains cannot slide past each other as easily.
The strength and flexibility of a polymer also depend on how its chains are held together. If the chains are held together by weak forces, such as Van der Waals interactions, then the polymer will be weaker and more flexible. If the chains are held together by strong covalent bonds, then the polymer will be stronger and less flexible