The understanding of crystallization in bulk polymers and morphological changes on a microscopic level during tensile deformation are essential to controlling the mechanical properties of semicrystalline polymeric materials and thus to possible improvement.When the fundamental of the structure of semicrystalline polymers (stacks of layer-like crystalline lamellae with thickness in the nanometer-range embedded in an amorphous matrix [1]) was revealed in the 1950s,considerations about the mechanism of formation of this structure started immediately.