Fiber length changes and their relation to fiber structure

Deformation processes in polymers are reviewed within the framework of rubber elasticity theory. The effect of hindered rotation on imposed and spontaneous length changes of polymeric fibers is discussed, leading to a new definition of crystallinity as a localized region of hindered rotation. This concept, together with a fringed‐micelle model, is used to relate length changes to molecular fine structure of polymers. The details of this model are described and compared with lamellar and paracrystalline models.