The influences of isotacticity on the mechanical properties in four different sizes and piled up of spherulites of polypropylene "were studied under uniaxial stretching. The mechanism of stretching deformation for different spherulite were examined by polarizing microscope.In general

one can find some influences of isotacticity on the mechanical properties of polypropylene

but the influences of size and piled up of spherulltes are even more important. The differences in the mechanical properties of polyproylene with different spherulites are closely related with theri differences in the stretching deformation me-chanism.