How rubbery state works
The glass transition temperature (Tg) of rubber is lower than room temperature, it is in a high elastic state at room temperature, and highly crosslinked and crystalline polymers can be in a high elastic state when the temperature is higher than Tg. Highly crosslinked and too small molecular weight polymers have no high elasticity. When the external force is removed, the molecular chain structure of the network will recover the number of chain conformations before stretching, forming a rubber retraction, and the deformation disappears. At this time, the entropy increases, so unlike Hook Elasticity, rubber elasticity is entropy elasticity. During the deformation process, the change of entropy is major, and the change of internal energy is minor.