heptane gives a catalyst that has high (70–200 kg g Fe
À1 h
À1 bar
À1 ) and
longstanding (>60 min) activity at temperatures higher than 60
C. The polyethylene is linear and is monomodal, although broadly distributed. Hydrogen is tolerated
by the catalyst and increases the activity, as observed before, yet without a
molecular weight regulation. 1-Olefins deactivate the catalyst system, possibly by
allylic abstraction reactions and regeneration of the active center. In the latter case,
the vinyl content per chain increases accordingly. The molecular weight of the
product decreases with temperature from 415 to 16 kg mol
À1 from 70
C to 90
C,
respectively. The termination reactions at this low concentration of cocatalyst are
basically only β-hydrogen eliminations. This may also explain the monomodal
distribution.
The BIP iron catalyst on a support can be used to prepare in situ 1-olefins from
ethylene. These can used to prepare PE–LLDs from ethylene through the action of a
further catalyst. Fused silicas and MCM-41 were used as supports for the preparation of a catalyst capable of generating PE–LLD from ethylene. The catalyst was
prepared by pretreating the silica particles with TMA and subsequently with
gaseous H 2 O to obtain a Lewis acidic and alkylating layer [78]. Titanocene and/
or zirconenes in combination with a BIP catalyst were added either simultaneously
or subsequently to the treated support. PE with several microstructures and
distributions could be obtained in this way. Ethylene oligomerization with the
supported iron catalyst is very effective (>50 ton mol Fe
À1 h
À1 ) and yields a
products with M n of 1,430 and PDI of about 10.
2.5 Nanocomposites by BIP FeCl 2 Catalysis
The generation of in situ composites – polymerizing ethylene in the presence of or
on the surface of a filler – is a potentially efficient route for production of high
performance polyolefin composites [79]. Of course, firstly, fragmentation of the
filler particle needs to be kept within certain limits and, secondly, to avoid reactor
fouling caused by melting of the polymer-filler ensemble, the activity of the
resulting supported catalyst should be correspondingly lower (e.g., [7]). The BIP
iron catalysts have been successfully used for the preparation of such composites.
Phyllosilicates like glimmer (mica), montmorillonite, and/or saponite were used in
some studies with the objective of achieving exfoliation and by that a molecular
dispersion of silicate layers. In the case of mica, the catalyst was formed inside the
silicate [80]. In a first step, iron(III) ions were loaded between the fluorotetrasilyllic
layers and subsequently treated with BI
Me2(p-Me) P, BI
Me2 P, or BI
iPr2 P ligands to
locally prepare the BIP Fe complex. The resulting intercalated iron complex with
BI
Me2(p-Me) P was in this series particular active for the polymerization of ethylene
after activation with MAO, TEA, or TIBA (500–890 g PE g Fe
À1 ). The molecular
weights were in the range of 20–30 kg mol
À1 . The morphology of the mica particles
were replicated in the polymeric product. In another approach to the preparation of
polyethylene composites from layered clays (mica, montmorillonite, saponite),
Iron Catalyst in the Preparation of Polyolefin Composites
355
À1 h
À1 bar
À1 ) and
longstanding (>60 min) activity at temperatures higher than 60
C. The polyethylene is linear and is monomodal, although broadly distributed. Hydrogen is tolerated
by the catalyst and increases the activity, as observed before, yet without a
molecular weight regulation. 1-Olefins deactivate the catalyst system, possibly by
allylic abstraction reactions and regeneration of the active center. In the latter case,
the vinyl content per chain increases accordingly. The molecular weight of the
product decreases with temperature from 415 to 16 kg mol
À1 from 70
C to 90
C,
respectively. The termination reactions at this low concentration of cocatalyst are
basically only β-hydrogen eliminations. This may also explain the monomodal
distribution.
The BIP iron catalyst on a support can be used to prepare in situ 1-olefins from
ethylene. These can used to prepare PE–LLDs from ethylene through the action of a
further catalyst. Fused silicas and MCM-41 were used as supports for the preparation of a catalyst capable of generating PE–LLD from ethylene. The catalyst was
prepared by pretreating the silica particles with TMA and subsequently with
gaseous H 2 O to obtain a Lewis acidic and alkylating layer [78]. Titanocene and/
or zirconenes in combination with a BIP catalyst were added either simultaneously
or subsequently to the treated support. PE with several microstructures and
distributions could be obtained in this way. Ethylene oligomerization with the
supported iron catalyst is very effective (>50 ton mol Fe
À1 h
À1 ) and yields a
products with M n of 1,430 and PDI of about 10.
2.5 Nanocomposites by BIP FeCl 2 Catalysis
The generation of in situ composites – polymerizing ethylene in the presence of or
on the surface of a filler – is a potentially efficient route for production of high
performance polyolefin composites [79]. Of course, firstly, fragmentation of the
filler particle needs to be kept within certain limits and, secondly, to avoid reactor
fouling caused by melting of the polymer-filler ensemble, the activity of the
resulting supported catalyst should be correspondingly lower (e.g., [7]). The BIP
iron catalysts have been successfully used for the preparation of such composites.
Phyllosilicates like glimmer (mica), montmorillonite, and/or saponite were used in
some studies with the objective of achieving exfoliation and by that a molecular
dispersion of silicate layers. In the case of mica, the catalyst was formed inside the
silicate [80]. In a first step, iron(III) ions were loaded between the fluorotetrasilyllic
layers and subsequently treated with BI
Me2(p-Me) P, BI
Me2 P, or BI
iPr2 P ligands to
locally prepare the BIP Fe complex. The resulting intercalated iron complex with
BI
Me2(p-Me) P was in this series particular active for the polymerization of ethylene
after activation with MAO, TEA, or TIBA (500–890 g PE g Fe
À1 ). The molecular
weights were in the range of 20–30 kg mol
À1 . The morphology of the mica particles
were replicated in the polymeric product. In another approach to the preparation of
polyethylene composites from layered clays (mica, montmorillonite, saponite),
Iron Catalyst in the Preparation of Polyolefin Composites
355