containing CaCO 3 and Al 2 O 3 · 2 H 2 O by immobilizing TiCl 4 /AlR 3 on the filler
surfaces [31, 32]. Supporting tetraalkyl zirconium on predried alumina did not
require the addition of aluminum alkyl cocatalysts [33–39]. In view of their
applications as implant material, the much more uniform filler dispersion and
improved mechanical properties of these UHMWPE composites show significant
advantages compared to conventional compounding and powder blends. This is in
accord with research reported by Dubois and coworkers, who demonstrated that the
performance of kaolin- and barite-composites was far superior to that of meltcompounded composites [40, 41]. Supporting single-site catalysts on fillers enabled
improved control of polyolefin molar mass and branching [42]. Kaminsky supported
Cp 2 ZrCl 2 /MAO on starch, cellulose, and aluminum flakes [43]. Extensive studies on
polymerization filling by means of filler-supported single-site catalysts were
published by the group of Dubois [44], who employed a variety of microfillers
such as kaolin, silica, glass beads [13], wollastonite, and magnesium hydroxide [45,
46]. Kaminsky and Zielonka [47] and Schoeppel and Reichert [48] reported the
application of in-situ polymerization to form disperse micron-sized zinc and aluminum particles in HDPE, isotactic polypropylene (iPP) and poly(cyclopentene). At
high metal content, the resulting Al/polyolefin composites exhibit metal-like high
thermal conductivity without the electrical conductivity typical for metals, owing to
the very effective encapsulation and insulation of the metal particles. However, at
high Al content, the fire retardancy was drastically lowered, causing intolerable fire
hazards in engineering applications. Similar polymerization filling strategies were
developed for producing cellulose/polyolefin composites [49], HDPE/CaCO 3
nanocomposites [50], as well as iPP nanocomposites containing nanometer-sized
alumina, magnesium oxide, and boron nitride [50]. The group of Marks exploited the
in situ polymerization in the presence of TiO 2 and BaTiO 3 to produce dielectric
polyolefin hybrid materials with high energy densities [51]. Recently, Rastogi et al.
reported on the formation of UHMWPE nanocomposites prepared by polymerization filling using salicylaldimine catalysts supported on TiO 2 , ZrO 2 , hydroxyapatite, and carbon nanotubes (CNT). The resulting nanocomposites exhibited
improved nanofiller dispersion and higher entanglement molar masses [52, 53].
With progress made in nanotechnology, polymerization filling has regained
attractiveness in recent years for formation of in situ nanocomposites. Among
nanoparticles, layered silicates such as clay minerals are of particular interest as
catalyst supports. Polymerization between the individual clay layers can promote
intercalation and exfoliation of individual layers, as reflected by dispersion of layer
stacks or individual silicate layers within in the polyolefin matrix [54–57]. Prior to the
in situ polymerization, the layered silicates such as montmorillonite are rendered
organophilic by exchanging sodium cations in the layers for alkyl ammonium
cations. A detailed overview on in situ polymerization based on organoclay and
layered silicate is presented in Chap. 17 by Woo et al. For instance, HDPE and
LLDPE nanocomposites containing exfoliated organophilic layered silicates were
prepared by in situ polymerization in the presence of MAO-activated metallocene
and diimine catalysts [58–60]. Half-sandwich-titanium complexes were supported on
hectorite and montmorillonite to produce HDPE nanocomposites [46, 61]. Supporting
Polyolefin Nanocomposites and Hybrid Catalysts
285
surfaces [31, 32]. Supporting tetraalkyl zirconium on predried alumina did not
require the addition of aluminum alkyl cocatalysts [33–39]. In view of their
applications as implant material, the much more uniform filler dispersion and
improved mechanical properties of these UHMWPE composites show significant
advantages compared to conventional compounding and powder blends. This is in
accord with research reported by Dubois and coworkers, who demonstrated that the
performance of kaolin- and barite-composites was far superior to that of meltcompounded composites [40, 41]. Supporting single-site catalysts on fillers enabled
improved control of polyolefin molar mass and branching [42]. Kaminsky supported
Cp 2 ZrCl 2 /MAO on starch, cellulose, and aluminum flakes [43]. Extensive studies on
polymerization filling by means of filler-supported single-site catalysts were
published by the group of Dubois [44], who employed a variety of microfillers
such as kaolin, silica, glass beads [13], wollastonite, and magnesium hydroxide [45,
46]. Kaminsky and Zielonka [47] and Schoeppel and Reichert [48] reported the
application of in-situ polymerization to form disperse micron-sized zinc and aluminum particles in HDPE, isotactic polypropylene (iPP) and poly(cyclopentene). At
high metal content, the resulting Al/polyolefin composites exhibit metal-like high
thermal conductivity without the electrical conductivity typical for metals, owing to
the very effective encapsulation and insulation of the metal particles. However, at
high Al content, the fire retardancy was drastically lowered, causing intolerable fire
hazards in engineering applications. Similar polymerization filling strategies were
developed for producing cellulose/polyolefin composites [49], HDPE/CaCO 3
nanocomposites [50], as well as iPP nanocomposites containing nanometer-sized
alumina, magnesium oxide, and boron nitride [50]. The group of Marks exploited the
in situ polymerization in the presence of TiO 2 and BaTiO 3 to produce dielectric
polyolefin hybrid materials with high energy densities [51]. Recently, Rastogi et al.
reported on the formation of UHMWPE nanocomposites prepared by polymerization filling using salicylaldimine catalysts supported on TiO 2 , ZrO 2 , hydroxyapatite, and carbon nanotubes (CNT). The resulting nanocomposites exhibited
improved nanofiller dispersion and higher entanglement molar masses [52, 53].
With progress made in nanotechnology, polymerization filling has regained
attractiveness in recent years for formation of in situ nanocomposites. Among
nanoparticles, layered silicates such as clay minerals are of particular interest as
catalyst supports. Polymerization between the individual clay layers can promote
intercalation and exfoliation of individual layers, as reflected by dispersion of layer
stacks or individual silicate layers within in the polyolefin matrix [54–57]. Prior to the
in situ polymerization, the layered silicates such as montmorillonite are rendered
organophilic by exchanging sodium cations in the layers for alkyl ammonium
cations. A detailed overview on in situ polymerization based on organoclay and
layered silicate is presented in Chap. 17 by Woo et al. For instance, HDPE and
LLDPE nanocomposites containing exfoliated organophilic layered silicates were
prepared by in situ polymerization in the presence of MAO-activated metallocene
and diimine catalysts [58–60]. Half-sandwich-titanium complexes were supported on
hectorite and montmorillonite to produce HDPE nanocomposites [46, 61]. Supporting
Polyolefin Nanocomposites and Hybrid Catalysts
285