these were treated with dichloromethane solutions of BIP Fe Cl 2 [81]. Activation
with TIBA was successful in achieving ethylene polymerization activities in the
range of ton mol Fe
À1 h
À1 bar
À1 (Al/Fe ¼ 500–1,500/1). It was found of importance
to widen the layer distances in the supports by first exchanging the counterions with
Mg
2+ . The catalysts were active at 60
C and produced high molecular weight linear
products (M n ¼ 20–46 kg mol
À1
, M w ¼ 120–940 kg mol
À1 ) with large PDIs.
A variation of the approach uses an acetyliminopyridine iron(III) complex successfully [82], but the material properties are not reported.
An earlier report describes the use of montmorillonite charged with organic
ammonium ions as a starting material for the preparation of composites [83]. MAO
was absorbed into the clay and the resulting solid treated with a suspension of BI
iPr2
P
FeCl 2 . The activity of the catalyst system was found in the usual range of a homogeneous iron catalyst (0.5–1 ton mol Fe
À1 h
À1
) and was not dependent on the Al/Fe ratio
between 250 and 1,760. The products showed the typical bimodal distribution, with
the highest peak in the range of 50–150 kg mol
À1
. The higher the concentration of
clay, the lower the molecular weight. This was attributed to chain transfer reaction to
aluminum, and is in agreement with the processes shown in Scheme 1. It was found
that the crystal size of the linear PE was lower than that in pristine PE. Likewise, the
crystallinity was lower. This is explained by a (partial) exfoliation of the silicate
layers. A higher amount of clay resulted in a smaller amount of single layers and a
higher Al/Fe ratio, with a higher percentage of exfoliation. These observations are
probably related to the number of ethylene molecules that are polymerized between
the layers. A higher aluminum concentration leads to more active centers. Rheologic
studies show that a higher exfoliation leads to materials with higher storage moduli G
0
and G
00 . The better the clay was dispersed, the higher the moduli. Exfoliation was not
found when the catalyst was not previously absorbed onto the MAO-modified clay.
These are typical results for in situ polymerization on a solid surface, with a large
enhancement of the material properties.
We decided to use the catalytic properties of the BI
Cl2 P FeCl 2 complex to
prepare aluminum polymeryls and turn these into polymeryl alkoxides for use as
stabilizers for dispersing silica particles in polyethylene [49]. The objective was to
reach a stable and fine dispersion of filler at high concentration in polyethylene and
was addressed along different routes. Silica particles were chosen as generic filler
material because they are easily generated by the “Sto ¨ber” process [84]. The routes
are differentiated by the order of reactions. The first route comprises the steps of
generating an alkoxy-functionalized polyethylene, with subsequent in situ generation of silica particles. The second synthesis uses the procedure of in situ
polymerization.
The first route is based on generating sol–gel particles in an hydrophobic
medium. Since the Sto ¨ber process is based on water or alcohol solvents and uses
agents (ammonium hydroxide) that are not miscible with the polymerization
medium of toluene, adaption was necessary. Higher alcohol (butanol, pentanol,
octanol), toluene and toluene–ethanol mixtures were screened and, in addition to
TEOS, TBOS (tetrabutoxy silane) was used as precursor [85]. It was found that the
formation of defined and spherical particles is not easily achieved. For example, in a
356
R.S.A. Meyer and G.A. Luinstra
with TIBA was successful in achieving ethylene polymerization activities in the
range of ton mol Fe
À1 h
À1 bar
À1 (Al/Fe ¼ 500–1,500/1). It was found of importance
to widen the layer distances in the supports by first exchanging the counterions with
Mg
2+ . The catalysts were active at 60
C and produced high molecular weight linear
products (M n ¼ 20–46 kg mol
À1
, M w ¼ 120–940 kg mol
À1 ) with large PDIs.
A variation of the approach uses an acetyliminopyridine iron(III) complex successfully [82], but the material properties are not reported.
An earlier report describes the use of montmorillonite charged with organic
ammonium ions as a starting material for the preparation of composites [83]. MAO
was absorbed into the clay and the resulting solid treated with a suspension of BI
iPr2
P
FeCl 2 . The activity of the catalyst system was found in the usual range of a homogeneous iron catalyst (0.5–1 ton mol Fe
À1 h
À1
) and was not dependent on the Al/Fe ratio
between 250 and 1,760. The products showed the typical bimodal distribution, with
the highest peak in the range of 50–150 kg mol
À1
. The higher the concentration of
clay, the lower the molecular weight. This was attributed to chain transfer reaction to
aluminum, and is in agreement with the processes shown in Scheme 1. It was found
that the crystal size of the linear PE was lower than that in pristine PE. Likewise, the
crystallinity was lower. This is explained by a (partial) exfoliation of the silicate
layers. A higher amount of clay resulted in a smaller amount of single layers and a
higher Al/Fe ratio, with a higher percentage of exfoliation. These observations are
probably related to the number of ethylene molecules that are polymerized between
the layers. A higher aluminum concentration leads to more active centers. Rheologic
studies show that a higher exfoliation leads to materials with higher storage moduli G
0
and G
00 . The better the clay was dispersed, the higher the moduli. Exfoliation was not
found when the catalyst was not previously absorbed onto the MAO-modified clay.
These are typical results for in situ polymerization on a solid surface, with a large
enhancement of the material properties.
We decided to use the catalytic properties of the BI
Cl2 P FeCl 2 complex to
prepare aluminum polymeryls and turn these into polymeryl alkoxides for use as
stabilizers for dispersing silica particles in polyethylene [49]. The objective was to
reach a stable and fine dispersion of filler at high concentration in polyethylene and
was addressed along different routes. Silica particles were chosen as generic filler
material because they are easily generated by the “Sto ¨ber” process [84]. The routes
are differentiated by the order of reactions. The first route comprises the steps of
generating an alkoxy-functionalized polyethylene, with subsequent in situ generation of silica particles. The second synthesis uses the procedure of in situ
polymerization.
The first route is based on generating sol–gel particles in an hydrophobic
medium. Since the Sto ¨ber process is based on water or alcohol solvents and uses
agents (ammonium hydroxide) that are not miscible with the polymerization
medium of toluene, adaption was necessary. Higher alcohol (butanol, pentanol,
octanol), toluene and toluene–ethanol mixtures were screened and, in addition to
TEOS, TBOS (tetrabutoxy silane) was used as precursor [85]. It was found that the
formation of defined and spherical particles is not easily achieved. For example, in a
356
R.S.A. Meyer and G.A. Luinstra