| To develop high performance polypropylene products, propylene homo-polymer and multiphase multi-component polypropylene in-reactor alloys were produced in a wide range of polymerization temperature using MgCl2-supported Ziegler-Natta catalysts. The structure of polyolefin products were modified by changing the polymerization temperature. Polymerization kinetics characteristics for propylene homo-polymerization and copolymerization stages of in-reactor alloys were investigated by flow rate technique at different polymerization temperature. The flow rate technique is based on continuous compensation of monomer consumption such that the pressure in the system is kept constant. The relation between the structure of polymers and polymerization temperature also were studied.In the laboratory reactor system, the influences of the mole ratios of Al/Ti and Al/Si on activity of catalyst systems were studied at different polymerization temperature. Kinetics characteristics of liquid-propylene bulk polymerization were examined for both with and without pr-contacting and pre-polymerization process at different polymerization temperature. It was found that the activity of catalyst systems was improved after conducting pre-contacting and pre-polymerization of catalyst systems in range of polymerization temperature of test. When the polymerization temperature was elevated, the role of pre-contacting and pre-polymerization on improving activity of catalyst systems was obviously. The heat transfer resistance equation and the fragmentation step-by-step model of catalyst-particles were presented. The equation and model showed that the mechanisms of heat and mass transfer were dominant factor for the role of the pre-polymerization on improving activity of catalyst systems. At the same time, effects of pre-polymerization conditions on kinetics of propylene Supercritical polymerization and particle size distribution of polymer were investigated.The effect of polymerization temperatures on the microstructure of isotactic polypropylene were investigated with a number of different catalyst systems in the polymerization range from 70 to 100℃ for both in the presence and absence of hydrogen. In all series of experiments, when the polymerization temperature was at 85-90℃, the highest activities and narrowest of MWD were obtained. The polypropylene samples obtained at 85-90℃ contained the higher content of the polymer component with high isotacticity for the MgCl2/TiCl4/DNBP-TEA/external donor and MgCl2/TiCl4/DIBDMP-TEA catalyst systems in the absence or presence of hydrogen. The differences in the isotactic productivity of polymers obtained at different polymerization temperatures may be due to the different propagation rate shown by the different isospecific centers at different temperatures and to the different stability constants of the complex of catalyst/donor. For the MgCl2/TiCl4/DNBP-TEA catalyst system, the isotacticity of polypropylene remained approximately constant in the temperature range of experiments. This can be ascribed to elution of phthalate ester after the activation.An experimental setup for preparation of polypropylene/poly (ethylene-co-propylene) in-reactor alloys is used to study the kinetics of the second stage polymerization, i.e. ethylene/propylene gas phase co-polymerization, with constant gas phase composition. The time evolution of gas phase composition in reactor was examined when the constant gas phase composition was compensated into reactor such that the pressure in the system is kept constant. The effects of co-polymerization conditions, such as co-polymerization temperature, co-polymerization pressure and gas phase composition, on the kinetics characteristics of co-polymerization were discussed in detail. Based on propylene gas phase homo-polymerization model, a binary monomers co-polymerization kinetic model was developed to describe the kinetics of ethylene/propylene gas phase co-polymerization in the second stage. In the catalyst-polymer particle surface, a concentration of adsorbed monomers, Cm, was estimated by Flory-Huggins equation for the co-polymerization model. In different co-polymerization temperature condition, the reactivity ratios of monomers of equation of co-polymerization model were calculated by 13C NMR data and Fineman-Ross equation, respectively. When the co-polymerization temperature was 70-80 ℃, the decay order, n, and others parameters of equation of co-polymerization kinetics model were assessed by the experimental data of gas phase propylene homo-polymerization. It was found that the kinetics model of co-polymerization for ethylene/propylene gas phase co-polymerization in the second stage fitted the experiments well at 70-80 ℃.Multiphase multi-component polypropylene in-reactor alloys were prepared by a multistage polymerization process at different temperatures. The chain structure, components, compatibility and morphology of the above polypropylene in-reactor alloys were studied. It was found that those polypropylene in-reactor alloys composed of high isotactic propylene homo-polymer, low isotactic propylene home-polymer, polyethylene or long chain of polyethylene, completely amorphous ethylene-propylene random copolymers, and semicrystalline ethylene-propylene block copolymers. In the co-polymerization stage,85 ℃ of co-polymerization temperature was conducive to preparation of completely amorphous ethylene-propylene random copolymers, while 100℃ of co-polymerization temperature was easy produced semicrystalline ethylene-propylene block copolymers.The thermal behavior of those samples was studied by differential scanning calorimeter (DSC) and dynamic mechanical analysis (DMA). It was found that the glass transition temperature (Tg) of ethylene-propylene copolymers (EPC) of sample, which was produced by 85 ℃ of co-polymerization temperature, was the highest. However, the Tg both of EPC and matrix of sample, which was produced by 100℃ of co-polymerization temperature, were shifted to low temperature, and the different between the Tg of EPC and Tg of matrix was least, indicating the good compatibility between EPC and matrix of this sample. The morphology and dispersion state of the EPC phase of those samples were investigated by scanning electron microscopy (SEM). The dispersion of the EPC phase in sample, which was produced by 100℃ of co-polymerization temperature, was much more uniform than the others. |
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