Citation:
FAN Zhiqiang, M.CarmelaSacchi, PaoloLocatelli. EFFECTS OF EXTERNAL DONOR ON ACTIVE CENTER DISTRIBUTION OF SUPPORTED ZIEGLER-NATTA CATALYST[J]. Chinese Journal of Polymer Science,
;1997, 15(3): 217-225.
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The composition distribution (CD) and microisotacticity distribution (ID) of propene/1-hexene copolymer synthesized by MgCl2/DIBP/TiCl4 (DIBP: diisobutyl phthalate) weredetermined by fractionating the copolymers according to crystallinity and characterizingthe fractions by 13CNMR. The effects of two alkoxysilane donors, triethoxyphenylsilane(PTES) and dimethoxydi-tert-butylsilane (TBMS), on CD and ID of the copolymrs werecompared. Three main parts in the CD diagram of each copolymer were distinguished,which were correlated to active center distribution (ACD) based on three groups of different active centers.By studying the changes in 1-hexene content,microisotacticity and reactivity ratio product of three typical fractions,the effects of external donor on ACD were better elucidated.It was found that TBMS shows much stronger effects on ACD than PTES.In the former system,most fractions were produced on active centers with relatively lower r1 r2,higher reactivity to 1-hexene,and higher stereospecificity as compared to the system without external donor.It is concluded that the observed very extensive changes in ACD are mainly resulted by the formation of new types of active centers,possibly by coordination of external donor to certain positions on the catalyst.
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