Synthesis of propylene/ethylene copolymers and their characteristics
Polimery 2002, No 11-12, 808
Propylene/ethylene copolymers (KEP) containing 1.3-5.1 mole % of ethylene were prepared with using supported titanium-magnesium catalyst, TiCl4/MgCl2, activated with dibutyl phthalate as internal donor, AlEt3 as cocatalyst and dicyclopentylodimetoxysilane as external donor. The suspension copolymerization has been carried out in two steps. At first homopolymerization of propylene was conducted and then copolymerization of propylene with small amount of ethylene was carried out in the same reactor. The effects of propylene homopolymerization time (Table 1) and copolymerization time (Fig. 2) on the catalytic system activity were studied. KEP samples obtained have been characterized by determining the effect of ethylene mers content on melting temperature, isotacticity index (Fig. 3) as well as on the tensile strength and impact strength at low temperature (Table 2). The data obtained suggest that using of super active titanium catalyst let obtain copolymers containing up to about 5 mole % of ethylene with higher yield, in comparison with propylene homopolymer synthesized in the same conditions. Polypropylene modified this way shows improved mechanical properties, especially better impact strength at low temperature. The effect of KEP composition (in the range of 1.3-5.1 mole % of ethylene mers content) on the material properties changes, in comparison with PP, has been expressed quantitatively (Table 3).
Keywords: polypropylene modification, copolymerization with ethylene, titanium-magnesium catalyst, functional properties, impact strength.