Molecular weight distribution with heterogeneous catalysts

Me) was R = Me > Bu > Pr-opposite to that observed for the heterogeneous system. In addition, the supported catalysts produced polyethylene with higher molecular weights, narrower molecular weight distributions and higher bulk densities than that produced by the homogeneous systems. 

Tagata and Homma47 analyzed in the aforementioned manner the compositional heterogeneity of two typical commercial SBR samples, E-SBR and S-SBR, which had 23.5 and 20.0 average styrene wt.%, and were produced by an emulsion polymerization and by a solution polymerization with an organometallic catalyst, respectively. The result was that the former gave a distinctly narrower compositional distribution than the latter. GPC experiments on these samples were also carried out, which indicated that the above situation was just the opposite for the molecular-weight distributions. 

Heterogeneous Ziegler-Natta catalysts composed of titanium trichloride and alkylaluminum have been used to prepare block copolymers of ethylene with a-olefins 44-46), even though there is no known example of such a catalyst meeting the requirement for a living polymerization. The produced block copolymers have broad molecular weight distributions (Mw/Mn = 4 20) and are present in small concentrations... 

Chromocene) deposited on silica reaction of the metallocene with hydroxyl gronps on the silica snrface generates the active catalyst (eqnation 15). These ill-defined heterogeneous systems give high-density polyethylene with broad molecular weight distributions, indicative of multisited catalysts. 

Hs)4 for styrene [278], Ti(On-Bu)4/AlEtj for butadiene (125) or (7T-C4H7 1)2 or butadiene [61] molecular weight distributions are fairly narrow (Mw/M = 1—2), where the propagating species have long lifetimes and their concentrations remain reasonably constant throughout the polymerization. The soluble catalysts based on vanadium compounds likewise give relatively narrow distributions with ethylene or ethylene/ propene (M / n 2). Polymers prepared with heterogeneous catalysts... 

In contrast to the heterogeneous catalysts which produce polymers with a broad molecular weight distribution MJMf) of 5-30, the compounds containing vanadium produce polymers with a narrow MJM of 2-4. 

Bochmann [184] developed a heterogeneous catalyst system of silica-supported neodymium amides (Scheme 28) that in conjunction of TIBA displayed activity for the copolymerization of ethylene and butadiene to give copolymer with relatively broad molecular weight distribution and fra i -l,4-regulatedbutadiene sequences. 

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