ABSTRACT
Most materials when stressed exhibit a limited elastic region where the material regains its original dimensions if the stress is removed. As the resulting strain is related to the extent of movement of atoms from their equilibrium conditions, substances such as metals and glass have elastic limits rarely exceeding 1% because atomic adjustments are localized. For long-chain polymers, under certain conditions, the situation is different; the extensive covalent bonding between the atoms to form chains allows considerable deformation, which is accompanied by long-and shortrange cooperative molecular rearrangement arising from the rotation about chain bonds.
