While crystalline solids are only able to display elasticity at a strain limit of one percent, polymers can often withstand strains of up to several hundred percent and restore themselves to their original shape as a result of entropic elasticity. Shape memory polymers, on the other hand, return to their permanent shape after being stimulated by heat. These materials possess the ability to recover from extremely large strains imposed by mechanical loading, which allows bulky synthesized objects to be deformed into much smaller, pliable states for a temporary period of time and then be returned to their original shapes.
Researchers have invented a class of shape memory polymers that can be structurally tailored to fit many applications because the rate of strain relaxation is influenced by the number and type of covalent cross-links, non-covalent hydrogen bonds, and temperature, and thus the shape recovery rate is adjustable. These elastomers are produced using linear polymers that contain reversibly associating and crosslinkable side- or end-groups.
Utilizing photo-crosslinking methods to create shape memory elastomers by beginning with linear precursors allows for greater polymer characterization and complexity of shapes as the polymerization is conducted in solution. Additionally, since removing solvent does not induce stress on the material, these polymer networks are at stress-free states and can thus display more pronounced shape memory effects.