Heterophasic copolymers comprised of polypropylene (PP) matrix and ethylene-propylene copolymer (EPC) dispersed phase were investigated with respect to the dispersed phase composition, i.e., ethylene/propylene ratio. The rheological properties, morphology, as well as thermal and mechanical relaxation behavior were studied to describe the structure evolution and phase interactions between the components of the PP copolymers. Decrease of the ethylene content of the EPC leads to a higher matrix-dispersed phase compatibility, as evaluated by the shift of the glass transition temperatures of EPC and PP towards each other. At ethylene content of EPC of 17 wt %, the glass transition temperatures of the both phases merged into a joint relaxation. The effect of the EPC composition on the internal structure of the dispersed domains and on the morphology development of the heterophasic copolymers was demonstrated. Decreasing ethylene content was found to induce a refinement of the dispersed phase with several orders of magnitude down to 0.18 m for propylene-rich EPC. Optical microscopy observations showed that the dispersed propylene-rich phase is preferably rejected at the interlamellar regions of the spherulites and/or at the interspherulitic regions, while the ethylene-rich domains are engulfed within the PP spherulites. Both of these processes impose an additional energetic barrier and influence the spherulite growth rate of the heterophasic materials.

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ABSTRACT:The initial state polymerization of propylene with Ziegler-Natta catalysts has been investigated and discussed at very low polymerization yields under adiabatic industrial prepolymerization conditions in diluted slurry regarding the effects of significant process parameters like monomer pressure, aluminum alkyl, and donor kind and concentration including the morphology of the catalyst/polymer particles formed. A sharp temperature increase in the first minutes of the initial state polymerization is followed by a temperature maximum and a slow decrease. With cocatalyst triethyl aluminum (TEAL), high prepolymerization yields were already achieved at a molar ratio TEAL/Ti of 3.0, remaining about constant until ratios of at least 300. The external donor dicyclopentyl dimethoxy silane leads to higher polymerization yields than the donor cyclohexyl dimethoxymethyl silane in the initial state polymerization too; however, both show a remarkable decreasing effect on polymerization yield above a specific molar ratio donor/Ti obviously correlated with the bulkiness of the alkyl groups. The particle size of the catalyst and the catalyst/prepolymer particles is increasing with polymerization yield until about 22 g PP/g Cat with particles almost perfectly spherical. The particle size distribution is rather broad at lower prepolymerization stages but unifying with lower polymerization rates at higher polymerization times.