The mechanisms of radiation damage are different for polymers and metals, since dislocations and grain boundaries do not have real significance in a polymer. Instead, polymers deform via the movement and rearrangement of chains, which interact through Van der Waals forces and hydrogen bonding. In the presence of high energy, such as ionizing radiation, the covalent bonds that connect the polymer chains themselves can overcome their forces of attraction to form a pair of free radicals. These radicals then participate in a number of polymerization reactions that fall under the classification of radiation chemistry. Crosslinking describes the process through which carbon-centered radicals on different chains combine to form a network of crosslinks. In contrast, chain scission occurs when a carbon-centered radical on the polymer backbone reacts with another free radical, typically from oxygen in the atmosphere, causing a break in the main chain. Free radicals can also undergo reactions that graft new functional groups onto the backbone, or laminate two polymer sheets without an adhesive.
