Effects Of Polymerization Process And Catalyst On Preparation Of Polypropylene Reactor Alloy

Polypropylene reactor alloy prepared by multi-stage polymerization presents good mechanical property, overcoming the limitation of polypropylene on toughness. Both polymerization process and catalyst are important factors determining the property of polypropylene reactor alloy, which were investigated in this work.This study focused on the investigation and development of polypropylene reactor alloy. The effects of polymerization process and catalyst support on composition, structure, morphology and property of polypropylene reactor alloy were investigated. The microstructure of polypropylene reactor alloy was studied by fraction and characterization. The mechanical property of polypropylene reactor alloy was investigated. Spherical isotactic polypropylene porous particles containing a certain amount of hydroxyl groups were prepared with the copolymerization of propylene and triethyaluminum treated dihydromyrcene alcohol catalyzed by Z-N catalyst. These particles were efficient in supporting metallocene catalyst by chemical anchoring and were applied to ethylene and propylene slurry copolymerization to produce PP/m-EPR reactor alloys. PP/EPR reactor alloys were prepared with a metallocene/Ziegler-Natta hybrid catalyst system using a specially devised process composed of three stages.Propylene polymerizations catalyzed by Z-N catalyst were conducted with liquid bulk, slurry, and gas process respectively. The effect of homopolymerization process on the structure and morphology of polypropylene was investigated. The result showed that diffusion limitation was more severe in liquid process than in the other two processes, which resulted in the broad molecular weight distribution of PP prepared by liquid process. Polymerization processes evidently affected the macro-morphology of PP, but slightly affected the micro-morphology of PP. The morphology of PP particles prepared by liquid process was the most regular with slight fragmentation, however, that prepared by gas process showed the worst particle morphology with severe fragmentation.PP/EPR reactor alloys were prepared by Z-N catalyst with the same homopolymerization process but different copolymerization processes. The effects of copolymerization process on the structure and morphology of PP/EPR reactor alloy were investigated. It was found that the order according to ethylene content of EPR was slurry process, gas process and liquid process in sequence. The morphology of PP/EPR particles prepared by gas process were well scattered with little agglomeration, however, PP/EPR particles prepared by liquid process showed a certain extent of agglomeration, and that prepared by slurry process showed bad particle morphology with severe agglomeration. Therefore, gas copolymerization process is better than the other two processes in copolymerization stage of reactor alloy technology.Liquid bulk polymerizations of propylene were carried out catalyzed by TiCl4/MgCl2 (DQ) and TiCl4/MgCl2/SiO2 (MSQ) respectively. The influence of catalyst support on polypropylene (PP) particle morphology was investigated. It was found that the fragmentized degree of MSQ-PP particles was lower than that of DQ-PP at the same polymerization condition, which indicated that employing MgCl2/SiO2 as the support of Z-N catalyst could reduce excessive fragmentation of catalyst-polymer particle during reaction. MSQ-PP particles possessed narrower size distribution compared with DQ-PP particles owing to the uniform size distribution of MSQ catalyst particles, suggesting the effective control of polymer particle size with MSQ catalyst. Catalyst support evidently affected the macro-morphology of PP, but slightly affected the micro-morphology of PP. Moreover, MSQ-PP showed higher Mw and narrower PDI than DQ-PP due to the small diffusion resistance in MSQ-PP particles. In a word, MSQ catalyst is better than DQ catalyst in controlling the morphology of PP particles. Compared with DQ-PP, the porosity of MSQ-PP is higher, which is beneficial not only to the second process in sequential polymerization, copolymerization of ethylene and propylene with diffusion limitation, but also to the acceptance of more rubbery copolymer in PP/EPR reactor alloy.The microstructure of polypropylene reactor alloy was studied by fraction and characterization. The results showed that polypropylene reactor alloy was composed of ethylene-propylene random copolymer, short sequence copolymer, long sequence copolymer and isotactic polypropylene. The composition and microstructure of PP reactor alloy could be well controlled by copolymerization condition such as monomer composition, reaction temperature and pressure. Random copolymer was proved to be more effective than long sequence copolymer on improving the toughness of polypropylene. Compared with mechanical blend, the PP reactor alloy showed better impact property due to its more uniform dispersion of copolymer phase. Therefore, reactor alloy exhibited perfect balance between toughness and rigidity.Spherical porous polypropylene particles containing a certain amount of hydroxyl groups were prepared with the copolymerization of propylene and triethyaluminum treated dihydromyrcene alcohol by Z-N catalyst. These particles were efficient in supporting metallocene catalyst (rac-Et(Ind)2ZrCl2) by chemical anchoring and were applied to ethylene and propylene slurry copolymerization to produce PP/m-EPR reactor alloys. It was found that the copolymerization activity of metallocene supported PP particles increased with the increase of MAO/Zr ratios and ethylene content in feed, and the composition of m-EPR formed could be adjusted by monomer composition in feed. Ethylene-propylene copolymers in reactor alloys obtained from metallocene supported PP particles showed much more random features than that prepared with conventional Z-N catalyst. Under appropriate reaction conditions, well scattered spherical particles of PP/m-EPR reactor alloy were obtained. PP/m-EPR reactor alloy prepared with (CH3Ind)2ZrCl2/PP system at proper conditions showed good impact property.PP/EPR reactor alloys were prepared with a metallocene/Ziegler-Natta hybrid catalyst system (rac-Et(Ind)2ZrCl2/Z-N) using a process composed of three stages: propylene homopolymerization, metallocene activation, and ethylene-propylene copolymerization. In the homopolymerization stage, polypropylenes synthesized by the hybrid catalyst with TEA as single cocatalyst showed high isotacticity without agglomerazation. It was shown that Metallocene/Ziegler-Natta hybrid system exhibited the features of both metallocene and Ziegler-Natta catalysts during copolymerization. The hybrid catalyst had better ability in incorporating a-olefin than the Z-N catalyst owing to the action of metallocene active sites. The effects of MAO/Zr ratio and monomer composition on the copolymerization activity and the copolymer properties in the alloys were investigated. EPR in the alloy became random with increased MAO/Zr ratio due to the increased metellocene activity. In addition, reducing ethylene content in the feed decreased the activity and promoted the production of random copolymers. The PP particles prepared by the hybrid catalyst system were spherical and porous, and the PP/EPR reactor alloy maintained the spherical shape of the PP particles. PP/EPR reactor alloy prepared with (CH3Ind)2ZrCl2/Z-N hybrid catalyst system at proper conditions showed good impact property.