Structure and stress-strain behavior of propylene copolymers with low content of ethylene units

Propylene copolymers containing 2.2 - 12.5 mol % of ethylene units were prepared using a modified titanium-magnesium catalyst. The structure and stress-strain behavior of the copolymers were studied. It was shown that the content of the α-crystalline modification decreases and the fraction of the γ-crystalline modification of polypropylene (PP) increases with an increase in the content of ethylene units and a decrease in the average length of crystallizable PP blocks in copolymers. The modulus of elasticity and yield stress at room temperature linearly decrease with the decreasing content of α-modification of PP. When the content of ethylene units increases, the values of ultimate elongation at break and the impact strength of copolymers rise. The value of tensile strength is maximum for the copolymer containing 2.2 mol % of ethylene units. Necking occurs both in the homopolymer and copolymers with low content of ethylene units. In the case of copolymers containing more than 6 mol % of ethylene units, the increasing content of the γ-crystalline phase of PP makes the plastic flow more homogeneous.