Abstract: In our published works, it has been proved that the impact copolymer polypropylene(ICPP) has characteristic chain structure and phase structure which make CPPexhibit excellent low-temperature impact strength. The tensile stress-strain behavior at low-temperature of impact copolymer polypropylene strongly discloses the structure nature why impact copolymer polypropylene has so excellent low-temperature impact strength and comprehensive mechanical properties. The dependence of Young′s modulus, stress yield and the elongation at break on the variation of the temperature can be explained by the characteristic chain structure and characteristic phase structure of the impact copolymer polypropylene. The difference of the elongation at break between the homopolymer and copolymer indicates that ethylene-propylene rubber acts as the toughening phase in the impact copolymer polypropylene. The difference of stress yield between the two-copolymer polypropylenes comes from the difference of the adhesion between the rubber particles and the matrix PP. The Young′s modulus is closely related to the crystallinity of the matrix PP, the size of the spherulite and the size distribution, and the glass transition temperature of both ethylene-propylene rubber and PPmatrix can also give important influence on it.

Key words: Copolymer polypropylene, Stress-strain behavior, Low-temperature impact-resistance