Catalytic activity during the preparation of PE/clay nanocomposites by in situ polymerization with metallocene catalysts

Abstract

Catalytic activity during the formation of polyethylene (PE)/clay nanocomposites by in situ polymerization with metallocenes was studied. Ethylene polymerization was carried out with the homogeneous metallocene in the presence of the clay particles and using the clay-supported metallocene catalyst. It was found that the catalytic activity of the homogeneous metallocene does not decrease in the presence of the clay particles and only a slight decrease of activity occurs using the clay-supported catalyst. The modification of the clay with MAO cocatalyst as well as its intercalation with ODA surfactant were found to play an important role during the in situ formation of the PE/clay nanocomposite. ODA-intercalated clay apparently facilitates the activation and monomer insertion processes on zirconocene centers located in internal sites of the clay structure. Although metallocene supported on MAOtreated clay exhibited somewhat lower catalytic activity than that supported directly on the ODA-intercalated clay, both systems favored the production of PE nanocomposites containing highly exfoliated clay particles.

Polyethylene Nanocomposites Obtained by in situ Polymerization via a Metallocene Catalyst Supported on Silica Nanospheres

“…In recent years, particular interest has been devoted to discover an effective immobilization method for metallocene catalysts on inorganic materials 8, 9. The nature of the support and the method used for supporting the metallocene influence the catalytic activity and the final properties of the polymer, especially the polymer particle morphology and molecular weight distribution 10–15…”

Control of molecular weight and polydispersity in polyethylene/needle-like shaped clay nanocomposites obtained by in situ polymerization with metallocene catalysts

“…A decrease in chain transfer and termination reactions therefore occurred, which was produced by the polymer growth from the active metallocene centres located on the nanoclay surface [30,32]. This decrease gave an advantage to propagation reactions allowing the increase in molar mass.…”

“…The more co-catalyst is present in the medium, which increases the amount of produced PE, the higher is the amount of clay, i.e., higher concentrations of -OH groups on the surface. This may increase the termination reactions in addition to anchoring MAO onto fewer accessible sites in the clay [30]. Therefore, there is a compromise between the effects on productivity when the amount of clay increases in the polymerization.…”

“…Between the years 2008 and 2009 the first reports were published on controlling the molecular weight in in situ polymerization [29,30]. Most of these works concluded that transfer agents, such as hydrogen, should promote transference reactions and thus effectively control the molecular weight [31].…”

“…However, the productivity of the reaction was severely affected by the increase in hetero-atoms present in the reaction, which simultaneously caused a loss of catalytic activity. Therefore, the percentages of load in the synthesized materials were also very high (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) wt.%) [21,22] .…”