Bonding and intermolecular forces in polymers

The single covalent bond consists of an electron shared between two atoms. There are three main ways of covalent bonding, of molecules such as methane (Fig. 2.2)  

Carbon has four electrons in its outer shell (quantum number n = 2) the shell would be full if it contained eight electrons. The outer shell (quantum number = 1) of hydrogen contains one electron it would be full if it contained two electrons. In methane, CH4, the carbon atom forms covalent 

Many monomers, and some polymers, contain covalent double bonds, written as C=C to indicate that two electrons are shared between the atoms. The first electron forms a o (single) bond but the second forms the less stable tt bond. The double bond prevents the rotation of the C atoms (or other atom pairs such as —C=0) relative to each other. 

If a covalent bond is broken, each atom has an unpaired electron known as a free radical, shown as a dot as in C.. Free radicals are extremely reactive and consequently their lifetimes are measured in milliseconds. 

Van der Waals forces are easier to quantify in molecular solids, such as solid methane, where they are the sole intermolecular force. The potential energy E of two methane molecules, with their centres a distance R apart, is given by 

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The primary valence bonds and intermolecular forces in polymer samples are exactly the same as those in any other chemical species, but polymers form strong... 

The energies of chemical bonds and intermolecular forces in polymers are thus typical of organic molecules. They are in the range that allows both chemical reactions and molecular motions to take place at the temperatures at which we use polymers. Thus polymer properties are typically more sensitive to both temperature and time than are those of other structural materials, such as metals and ceramics. 

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