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.