AbstractThe strains on uniaxial extension of preoriented isotactic polypropylene are separated over the whole range of deformation into three processes: crystallite boundary slip (A1process), uniform shear deformation of crystallites (A2process), and restoration of molecular orientation from the sheardeformed state (Ā2process). They are separately evaluated by the use of the parameters of superstructure varying in deformation. Both the A1and A2processes predominate before the A2→ Ā2transition takes place. Wide‐ and small‐angle x‐ray goniometries detect this transition. After the A2→ Ā2transition takes place, the specimen cannot be deformed by the A1or A2process, but by a molecular process such as pulling out the isolated extending chains from the folded chain crystals followed by their refolding. From the quantitative evaluations of the strains associated with the A1and A2processes it is deduced that the initial shear compliance for the A1process is smaller than that for t
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