mechanism between silicate layers of MMT–OH. The polymerization of ethylene
was conducted by injecting ethylene into the catalyst slurry (30–50
C, 4 bar).
Comparison of the exfoliation characteristics of MMT–OH and nonintercalated
montmorillonite showed that the feasibility of exfoliation during ethylene polymerization was highly dependent on the catalyst fixation method.
Recently, our group [103] used TEA-modified MMT to prepare exfoliated
PMMA/clay nanocomposites by in situ polymerization using Ni(acac) 2 catalyst.
A schematic representation is given in Fig. 12. The PMMA/clay nanocomposites
are found to retain over 80% transparency, which is important for optical
applications. In addition, the tensile strength of nanocomposites is up to 70 MPa
for 7.26 wt% clay content, and the tensile modulus shows a value 20% higher than
that of neat PMMA.
6.1.3 Clay Acts as a Cocatalyst for Coordination Polymerization
During the mid-1990s, a research group at Mitsubishi discovered that certain clays
could be calcined and used to activate metallocenes [104]. McDaniel et al. [104]
proposed that the metallocenes may be activated by the reaction between the clay
cations and the metallocene, resulting in the formation “clay anions” and
metallocene cations and sodium chloride. In this way a neutral metallocene can
be activated, forming ion-pair active species such as metallocene cation and clay
anion. A schematic representation of activation of metallocene by clay is shown in
Fig. 13. The ion exchange of metallocenium cations with clay surfaces is also
C 14 N-2
H 3 N +
H 3 N +
H 3 N +
H 3 N +
NH 3
+
NH 3 +
NH 3 +
NH 3
+
CAT
CAT
('CAT')
CAT
CAT
Pd-2
Polyethylene Nanocomposite
Ethylene
O = Si
F
O
Mg/Li
MeO
O
1
Pd +
N
N
[B(C 6 H 3 (CF 3 ) 2 -3,5) 4 ]
-
Palladium
Catalyst (1)
=
=
=
Fig. 10 Route for the preparation of PE/organically modified fluorohectorite nanocomposite
using Brookhart’s single-component palladium complex. Reproduced with kind permission from
Bergman et al. [101]
Fig. 11 Mechanistic representation of the fixing of TiCl 4 between the silicate layers of
MMT–OH. Reproduced with kind permission from Jin et al. [102]
Polyolefin/Layered Silicate Nanocomposites Prepared by In Situ Polymerization
327
was conducted by injecting ethylene into the catalyst slurry (30–50
C, 4 bar).
Comparison of the exfoliation characteristics of MMT–OH and nonintercalated
montmorillonite showed that the feasibility of exfoliation during ethylene polymerization was highly dependent on the catalyst fixation method.
Recently, our group [103] used TEA-modified MMT to prepare exfoliated
PMMA/clay nanocomposites by in situ polymerization using Ni(acac) 2 catalyst.
A schematic representation is given in Fig. 12. The PMMA/clay nanocomposites
are found to retain over 80% transparency, which is important for optical
applications. In addition, the tensile strength of nanocomposites is up to 70 MPa
for 7.26 wt% clay content, and the tensile modulus shows a value 20% higher than
that of neat PMMA.
6.1.3 Clay Acts as a Cocatalyst for Coordination Polymerization
During the mid-1990s, a research group at Mitsubishi discovered that certain clays
could be calcined and used to activate metallocenes [104]. McDaniel et al. [104]
proposed that the metallocenes may be activated by the reaction between the clay
cations and the metallocene, resulting in the formation “clay anions” and
metallocene cations and sodium chloride. In this way a neutral metallocene can
be activated, forming ion-pair active species such as metallocene cation and clay
anion. A schematic representation of activation of metallocene by clay is shown in
Fig. 13. The ion exchange of metallocenium cations with clay surfaces is also
C 14 N-2
H 3 N +
H 3 N +
H 3 N +
H 3 N +
NH 3
+
NH 3 +
NH 3 +
NH 3
+
CAT
CAT
('CAT')
CAT
CAT
Pd-2
Polyethylene Nanocomposite
Ethylene
O = Si
F
O
Mg/Li
MeO
O
1
Pd +
N
N
[B(C 6 H 3 (CF 3 ) 2 -3,5) 4 ]
-
Palladium
Catalyst (1)
=
=
=
Fig. 10 Route for the preparation of PE/organically modified fluorohectorite nanocomposite
using Brookhart’s single-component palladium complex. Reproduced with kind permission from
Bergman et al. [101]
Fig. 11 Mechanistic representation of the fixing of TiCl 4 between the silicate layers of
MMT–OH. Reproduced with kind permission from Jin et al. [102]
Polyolefin/Layered Silicate Nanocomposites Prepared by In Situ Polymerization
327