The copolymerizations of ethylene with 1-hexene or 1-octene by using TiCl

4

/MgCl

2

/THF catalysts modified with different metal halide additives (ZnCl

2

SiCl

4

and the combined ZnCl

2

-SiCl

4

) were investigated based on catalytic activity and copolymer properties. It was found that the catalyst modified with mixed ZnCl

2

-SiCl

4

revealed the highest activities for both ethylene/1-hexene and ethylene/1-octene copolymerization. The increase in activities was due to the formation of acidic sites by modifying the catalysts with Lewis acids. Based on the FTIR measurements

the characteristic C—O—C peaks of the catalysts modified with metal halide additives were slightly shifted to lower wavenumber when compared to the unmodified catalyst. This showed that the modified catalysts could generate more acid sites in the TiCl

4

/MgCl

2

/THF catalytic system leading to an increase in activities as well as comonomer insertion (as proven by

13

C-NMR). However

Lewis acid-modifications did not affect the microstructure of the copolymers obtained. By comparison on the properties of copolymers prepared with the unmodified catalyst

it was found that polymers with ZnCl

2

and/or SiCl

4

modification exhibited a slight decrease in melting temperature

crystallinity and density. It is suggested that these results were obtained based on the different amount of

α

-olefins insertion

regardless of the types of Lewis acids and comonomer.