ANALYSIS OF THE MOLECULAR-WEIGHT DISTRIBUTION (MWD) IN POLYMERIZATIONPROCESSES - CONTRIBUTION OF DIFFERENT FAMILIES OF ACTIVE-SITES TO THEMWD OF POLYETHYLENE PREPARED USING SUPPORTED TRANSITION-METAL CATALYSTS

The broad molecular weight distribution (MWD) curves obtained by gel-p ermeation chromatography (GPC) of polyethylenes prepared in the presen ce of MgCl2 supported monometallic (Ti or Hf) and bimetallic (Ti/Hf) c atalysts were analyzed by deconvolution into component curves. The MWD curves of the monometallic catalysts can be accounted for with only t hree component curves associated with three distinct families of activ e sites. The term family is used to indicate a group of relatively sim ilar active sites producing a polymer with (M) over bar(w)/(M) over ba r(n) < 3. This approach seems valid for both Ti and Hf catalysts in sp ite of the different characteristic values; indeed we have for the for mer system 1 < (M) over bar(w)/10(5) < 2,5 with 6 < (M) over bar(w)/(M ) over bar(n) < 10, whereas for the latter (M) over bar(w) approximate to 7 x 10(5) and (M) over bar(w)/(M) over bar(n) approximate to 18. I n the case of the bimetallic Ti/Hf system with 1,9 < (M) over bar(w)/1 0(5) < 2,6 and (M) over bar(w)/(M) over bar(n) approximate to 17, the MWD distribution can be better accounted for on the basis of 6 familie s of active sites, corresponding to the linear combination of the bala nced contributions from both Ti and Hf sites.