The influence of the comonomer in the copolymerization of ethylene with α-olefins using C2H4[ind]2ZrCl2/methylaluminoxane as catalyst system

Copolymers based on ethylene with different incorporations of 1-hexene, 1-octene and 1-decene were obtained. There is not any marked variation of activity when different metallocenes were tested. The type and the concentration of the comonomer in the feed do not have a strong influence on the catalytic activity of the system, but the presence of the comonomer increases the activity compared with that in the absence of it. From ¹³C NMR it was found that below 8% of comonomer incorporated the comonomer units appear isolated between polyethylene blocks, sequences of the type ethylene-comonomer-ethylene-comonomer appear only above 8% of comonomer incorporated for all the systems studied. The reactivity of the comonomers for this particular system shows that the size of the lateral chain influences the percentage of comonomer incorporated, 1-hexene being the highest one incorporated. The crystallinity of the copolymers exerts a linear relation with the amount of comonomer incorporated, and it is independent of lateral chain lengths. The molecular weight of the copolymers obtained was found to be dependent on the comonomer concentration in the feed, showing that there is a transfer reaction with the comonomer. The polydispersity (M̄_w/M̄_n) of the copolymers is rather narrow and dependent on the concentration of the comonomer incorporated.