Intercalation of the polymer from solution is based on a solvent system in which
the polymer or pre-polymer is soluble and the silicate layers are swellable. The
layered silicate is first swollen in a solvent such as water, chloroform, or toluene.
When the polymer and layered silicate solutions are mixed, the polymer chains
intercalate and displace the solvent within the interlayer of the silicate. Upon
solvent removal, the intercalated structure remains, resulting in PLS
nanocomposite. The drawback of this method is the requirement for a suitable
solvent. It has been shown that intercalation only occurs for certain polymer/solvent
or monomer/solvent pairs [49].
In melt intercalation, the polymer and layered silicate mixture is annealed above
the T g in either static or flow conditions. Modified layered silicates are usually
employed to promote intercalation. The polymer chains spread from the molten
mass into the silicate galleries to form either intercalated or delaminated hybrids
according to the degree of penetration. The critical factor that determines which
type is obtained is probably linked to thermodynamic factors. This method is
environmentally benign due to the absence of organic solvents. Furthermore, it is
compatible with current industrial processes such as extrusion and injection molding. However, very careful attention has to be paid to finely tune the processing
conditions to increase the compatibility of the clay layer surfaces with the polymer
matrix.
The template synthetic method is based on the in situ hydrothermal crystallization of clay mineral layers (from a gel) using selected water-soluble polymers as
templates [61]. Template synthesis is essentially limited to water-soluble polymers,
and the synthetic clay mineral formed under the conditions described by the authors
is a poorly ordered fluorohectorite. On the other hand, the method is potentially
capable of promoting the dispersion of silicate layers in a one-step process.
In situ polymerization of monomers confined in molecule-sized spaces has been
used to synthesize stereospecific polymers [62]. In this method, the layered silicate
is swollen within the liquid monomer or a monomer solution so that polymer
formation can occur between the intercalated sheets. Polymerization can be
initiated either by heat or radiation, by the diffusion of a suitable initiator, or by
an organic initiator or catalyst fixed through cation exchange inside the interlayer
before the swelling step, as shown in Fig. 6.
Various in situ polymerization methods have been used in the production of
well-dispersed silicate layers, including ROP [63–66] and ROMP [67–69]; controlled radical polymerization [63, 70–78] such as ATRP, NMP, and RAFT;
cationic polymerization [79–81]; living anionic polymerization [82, 83]; and coordination polymerization [56, 60, 84–86]. In addition to the above in situ methods,
nanocomposite preparations involving multimode [63] and click chemistry [69]
have also been reported.
The scope of this contribution is limited to polyolefin nanocomposites prepared
by in situ coordination polymerization techniques. Special emphasize is devoted to
the synthetic routes and the resultant morphology of the nanocomposites prepared
using the above-mentioned polymerization mechanism.
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N.H. Tarte et al.
the polymer or pre-polymer is soluble and the silicate layers are swellable. The
layered silicate is first swollen in a solvent such as water, chloroform, or toluene.
When the polymer and layered silicate solutions are mixed, the polymer chains
intercalate and displace the solvent within the interlayer of the silicate. Upon
solvent removal, the intercalated structure remains, resulting in PLS
nanocomposite. The drawback of this method is the requirement for a suitable
solvent. It has been shown that intercalation only occurs for certain polymer/solvent
or monomer/solvent pairs [49].
In melt intercalation, the polymer and layered silicate mixture is annealed above
the T g in either static or flow conditions. Modified layered silicates are usually
employed to promote intercalation. The polymer chains spread from the molten
mass into the silicate galleries to form either intercalated or delaminated hybrids
according to the degree of penetration. The critical factor that determines which
type is obtained is probably linked to thermodynamic factors. This method is
environmentally benign due to the absence of organic solvents. Furthermore, it is
compatible with current industrial processes such as extrusion and injection molding. However, very careful attention has to be paid to finely tune the processing
conditions to increase the compatibility of the clay layer surfaces with the polymer
matrix.
The template synthetic method is based on the in situ hydrothermal crystallization of clay mineral layers (from a gel) using selected water-soluble polymers as
templates [61]. Template synthesis is essentially limited to water-soluble polymers,
and the synthetic clay mineral formed under the conditions described by the authors
is a poorly ordered fluorohectorite. On the other hand, the method is potentially
capable of promoting the dispersion of silicate layers in a one-step process.
In situ polymerization of monomers confined in molecule-sized spaces has been
used to synthesize stereospecific polymers [62]. In this method, the layered silicate
is swollen within the liquid monomer or a monomer solution so that polymer
formation can occur between the intercalated sheets. Polymerization can be
initiated either by heat or radiation, by the diffusion of a suitable initiator, or by
an organic initiator or catalyst fixed through cation exchange inside the interlayer
before the swelling step, as shown in Fig. 6.
Various in situ polymerization methods have been used in the production of
well-dispersed silicate layers, including ROP [63–66] and ROMP [67–69]; controlled radical polymerization [63, 70–78] such as ATRP, NMP, and RAFT;
cationic polymerization [79–81]; living anionic polymerization [82, 83]; and coordination polymerization [56, 60, 84–86]. In addition to the above in situ methods,
nanocomposite preparations involving multimode [63] and click chemistry [69]
have also been reported.
The scope of this contribution is limited to polyolefin nanocomposites prepared
by in situ coordination polymerization techniques. Special emphasize is devoted to
the synthetic routes and the resultant morphology of the nanocomposites prepared
using the above-mentioned polymerization mechanism.
322
N.H. Tarte et al.