6.1 Polyolefin/Clay Nanocomposites by In Situ
Polymerization of Olefins with a Coordination Catalyst
Polyolefins, which are normally defined as polymers based on alkene-1 monomers
or α-olefins, are the most widely used group of thermoplastic polymers today. The
use of many different coordination catalysts has been reported for the production of
polyolefin/clay nanocomposites. The methods of in situ synthesis of polyolefin/clay
nanocomposite by coordination catalysts mostly depends on the role of clay and
can be divided into three categories: (1) clay as polymer filler, (2) clay as catalyst
or cocatalyst support, and (3) Clay acts as a cocatalyst for coordination
polymerization.
6.1.1 Clay as Polymer Filler
Heinemann et al. [87] first reported this method for synthesis of ethylene/clay blended
nanocomposites in which the organically modified clay, the catalyst precursor, and the
cocatalyst are added to the reactor and the polymerization is started by introduction of
the olefin monomer. The authors found that in comparison to melt compounding,
in situ ethylene homo- and copolymerization, catalyzed with MAO-activated
zirconocene, nickel, and palladium catalysts with modified clay as filler, proved
more effective in nanocomposite formation. This was evidenced by larger interlayer
spacings and formation of exfoliated anisotropic nanosilicates with high aspect ratio.
Only a few reports [88–91] have been published investigating this method, which
seems to have the lowest polymerization activities compared with other methods. The
activity values and the microstructure of the resultant nanocomposites can be improved
by organic modification of MMT with polymerizable modifiers. Using this technique,
Ren et al. [91] showed that the polymerizable MMTs were more exfoliatable than
nonpolymerizable MMTs in the preparation of PE/MMT nanocomposites with very
high activity values. A schematic representation of the clay modification and effect of
amount of clay on nanocomposite microstructure is shown in Fig. 7.
Fig. 6 Representation of in situ polymerization with clay
Polyolefin/Layered Silicate Nanocomposites Prepared by In Situ Polymerization
323
Polymerization of Olefins with a Coordination Catalyst
Polyolefins, which are normally defined as polymers based on alkene-1 monomers
or α-olefins, are the most widely used group of thermoplastic polymers today. The
use of many different coordination catalysts has been reported for the production of
polyolefin/clay nanocomposites. The methods of in situ synthesis of polyolefin/clay
nanocomposite by coordination catalysts mostly depends on the role of clay and
can be divided into three categories: (1) clay as polymer filler, (2) clay as catalyst
or cocatalyst support, and (3) Clay acts as a cocatalyst for coordination
polymerization.
6.1.1 Clay as Polymer Filler
Heinemann et al. [87] first reported this method for synthesis of ethylene/clay blended
nanocomposites in which the organically modified clay, the catalyst precursor, and the
cocatalyst are added to the reactor and the polymerization is started by introduction of
the olefin monomer. The authors found that in comparison to melt compounding,
in situ ethylene homo- and copolymerization, catalyzed with MAO-activated
zirconocene, nickel, and palladium catalysts with modified clay as filler, proved
more effective in nanocomposite formation. This was evidenced by larger interlayer
spacings and formation of exfoliated anisotropic nanosilicates with high aspect ratio.
Only a few reports [88–91] have been published investigating this method, which
seems to have the lowest polymerization activities compared with other methods. The
activity values and the microstructure of the resultant nanocomposites can be improved
by organic modification of MMT with polymerizable modifiers. Using this technique,
Ren et al. [91] showed that the polymerizable MMTs were more exfoliatable than
nonpolymerizable MMTs in the preparation of PE/MMT nanocomposites with very
high activity values. A schematic representation of the clay modification and effect of
amount of clay on nanocomposite microstructure is shown in Fig. 7.
Fig. 6 Representation of in situ polymerization with clay
Polyolefin/Layered Silicate Nanocomposites Prepared by In Situ Polymerization
323