Time-dependent deformation of polymers

Duromers and elastomers also exhibit a glass transition temperature with melting of the non-covalent intermolecular bonds, with localised sliding of the molecules being consequently easier. However, due to the covalent bonds between the molecules, it is not possible to pull single molecules out of the molecular network. Thus, these materials never become viscous liquids, but always remain solid. It is not possible to heat them to temperatures where the covalent intermolecular bonds are molten because they will decompose before. 

Both the elastic and the plastic behaviour of polymers are time-dependent even at room temperature polymers are thus viscoelastic and viscoplastic. In this section, we discuss the time-dependent deformation behaviour phenomenologically and explain how thermal activation of relaxation processes causes the time-dependence of deformation. 

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