| Three series of doped supports were prepared by means of ball milling or precipitation in this paper, and about 42 kinds of catalysts based on the doped supports were prepared by impregnating process. The rules of olefin (propene, 1-hexene) polymerization, the active center distribution and the isotacticity of polymer, et al, were studied. It was attempted to find the new access to accommodate the active center distribution of Ziegler-Natta catalyst and the molecular weight distribution of PR, acquire the principle, and provide the supporting information of developing new PP products.The NaC1 doped supports were prepared by co-ball milling of NaCl and MgCl2-EtOH adducts, and a series of catalysts were prepared. The XRD of supports showed that two mixed-crystals (Na2MgCl4 and NaMgCl3) formed in the case of NaCl dosage was 16mol%, which was backed up by both the electron diffraction and TG-DSC analysis of the support. It was proved that the NaCl crystal hardly appeared in the support with 16mol% NaCl. XRD manifested that the diffraction of NaCl appeared when the dosage was up to 32mol%, and the more NaCl was in the support, the stronger was the diffraction signal. The mixed crystals did not exist in the catalysts based on XRD. There were diffractions of NaCl itself in all of catalysts. However, the relative strength of the diffractions were changed very much, thereinto the 16mol% dosage and 72-hour-milling support's catalyst was changed most. Only two of four characteristic diffractions appeared very weakly. The SEM of catalysts showed that NaCl existed in catalysts in the form of surface adsorption.The NaCl doped catalysts was applied to 1 -hexene polymerization, and the non-linear-fitting of polyhexene's MWD showed that the supports' doping and co-catalysts affected the active center distribution. The microstructure analysis of polyhexene proved that the supports' doping could improve the isotacticity of polyhexene produced in (j-Bu)3Al activated system. The active centers of doped supports' catalysts were decreased to 2 and one of them produced polymer more than 80%, which was very close to the single-site system.IVThe propene polymerization result by the NaCl doped supports' catalysts showed that the catalysts' activity was decreased and the isospecificity was improved by the doping. The molecular weight was lower and the polydispersity was broader at the relatively less dosage, whereas the molecular weight was higher and the polydispersity was narrower at the relatively more dosage. The prolonging of ball-milling time improved the catalysts' activity and the PP's isotacticity. When EtsAl was used as co-catalyst, the isotacticity of PP was relatively higher and the molecular weight was lower; when (/-BuAl was used as co-catalyst, the activity was relatively higher, the isotacticity of PP was lower and the molecular weight was higher. The non-linear-fitting analysis of MWD proved that was the result of the change of active center distribution made by the doping of supports. The active center distribution of catalyst was changed most in the case of which NaCl dosage was 16mol%, which was broaden as the system was activated by EtsAl and was narrowed as the system was activated by (/-BuAl. The soluble and insoluble in the boiling n-heptane of PP were analyzed by DSC, and the result proved that the doping of supports could increase the crystallinity and the isotacticity, and it also could extend the isotactic chain segment.The influence of NaCl on the support's surface was discussed based on the experimental. It was considered that NaCl could adsorb on MgCl2 surface and the Cl" could migrate on the catalyst's surface and affect the property of active centers. The effect of support's doping was selective to some extent for the migration of Cl" and the asymmetry of NaCl aggregated particle's size. The effect on the (110) face of MgCl2 was more than which on the (100) face. Simultaneously, for the coordinating capacity and the steric hindrance of the co-catalysts, the effect of the doped particle on the active...
|
PDF Full Text Request