of composite material development, it was observed by Friedlander [1] that montmorillonite (MMT) could catalyze the polymerization of butadiene and 4-vinyl
pyridine. Subsequently, styrene could be polymerized [2–4] by mixing the monomer with dry, acid-washed MMT. Similarly, styrene could spontaneously polymerize when mixed with (dry) kaolinite and palygorskite [5]. However, the field of
polymer-layered silicate (PLS) nanocomposites has gained momentum recently
because two major findings have stimulated the revival of interest in these
materials. First, the Toyota group [6] developed an attractive design for a Nylon6 (N6)/clay nanocomposite in which individual silicate layers of about 1 nm
thickness are homogeneously dispersed in a continuous matrix of Nylon-6. Very
small amounts of layered silicate loadings resulted in pronounced improvement of
thermal and mechanical properties. The second major finding was the observation
by Vaia et al. [7] that it is possible to melt-mix polymers with layered silicates,
without the use of organic solvents Today, efforts are being conducted globally,
using almost all types of polymer matrices.
Polyethylene (PE) and polypropylene (PP) occupy about half the total production
capacity in synthetic plastics. Having been an important field in both academy and
industry for more than half a century, polyolefin nanocomposites are still attracting
interest from numerous researchers due to their superior properties. Furthermore,
preparation of coordination polymerization-induced PLS nanocomposites has many
advantages, which include: (1) no unfavorable thermodynamic requirement for melt
intercalation; (2) facile adjustment of clay loading and the accompanying
nanocomposite properties; (3) no special demand on polyolefin molecular weights
and no need for introduction of olefin oligomer modifiers; and (4) more homogeneous
dispersion of clay layers in the polymeric matrix.
PLS nanocomposites are a relatively new class of materials that exhibit ultrafine
phase dimensions, typically in the range of 1–100 nm [8]. Because of their nanometer
size features, nanocomposites possess unique properties typically not shared by their
more conventional microcomposite counterparts and, therefore, offer new technology
and business opportunities [9–11]. For instance, many of the polymer properties can
be significantly altered at very low clay loadings (2–8 wt%) in the nanocomposites
whereas 30–40 wt% of the microfillers are required for the same effect in the case of
conventional composites [11, 12]. PLS nanocomposites exhibit ultrafine phase
dimensions, typically with 1–10 nm thickness [8]. The high aspect ratio (i.e., length:
thickness ratio of about 100–1,000) of the clay platelets provides a large surface area
and is considered to be responsible for the highly improved properties of these
nanocomposites. These improvements can include better tensile strength and moduli
[13–15], increased strength and heat resistance [12], decreased thermal expansion
coefficient [14], decreased gas permeability [14, 16, 17], decreased flammability [18,
19], increased swelling resistance [13], biodegradability of biodegradable polymers
[20], and enhanced ionic conductivity [21, 22]. The nanocomposites also show
unusual chemical and physical phenomenon, such as highly anisotropic electrical
conductivity [23] and photoactivity [24–26]. On the other hand, they are also considered to be unique model systems for the study of the structure and dynamics of
polymers in confined environments.
Polyolefin/Layered Silicate Nanocomposites Prepared by In Situ Polymerization
313
pyridine. Subsequently, styrene could be polymerized [2–4] by mixing the monomer with dry, acid-washed MMT. Similarly, styrene could spontaneously polymerize when mixed with (dry) kaolinite and palygorskite [5]. However, the field of
polymer-layered silicate (PLS) nanocomposites has gained momentum recently
because two major findings have stimulated the revival of interest in these
materials. First, the Toyota group [6] developed an attractive design for a Nylon6 (N6)/clay nanocomposite in which individual silicate layers of about 1 nm
thickness are homogeneously dispersed in a continuous matrix of Nylon-6. Very
small amounts of layered silicate loadings resulted in pronounced improvement of
thermal and mechanical properties. The second major finding was the observation
by Vaia et al. [7] that it is possible to melt-mix polymers with layered silicates,
without the use of organic solvents Today, efforts are being conducted globally,
using almost all types of polymer matrices.
Polyethylene (PE) and polypropylene (PP) occupy about half the total production
capacity in synthetic plastics. Having been an important field in both academy and
industry for more than half a century, polyolefin nanocomposites are still attracting
interest from numerous researchers due to their superior properties. Furthermore,
preparation of coordination polymerization-induced PLS nanocomposites has many
advantages, which include: (1) no unfavorable thermodynamic requirement for melt
intercalation; (2) facile adjustment of clay loading and the accompanying
nanocomposite properties; (3) no special demand on polyolefin molecular weights
and no need for introduction of olefin oligomer modifiers; and (4) more homogeneous
dispersion of clay layers in the polymeric matrix.
PLS nanocomposites are a relatively new class of materials that exhibit ultrafine
phase dimensions, typically in the range of 1–100 nm [8]. Because of their nanometer
size features, nanocomposites possess unique properties typically not shared by their
more conventional microcomposite counterparts and, therefore, offer new technology
and business opportunities [9–11]. For instance, many of the polymer properties can
be significantly altered at very low clay loadings (2–8 wt%) in the nanocomposites
whereas 30–40 wt% of the microfillers are required for the same effect in the case of
conventional composites [11, 12]. PLS nanocomposites exhibit ultrafine phase
dimensions, typically with 1–10 nm thickness [8]. The high aspect ratio (i.e., length:
thickness ratio of about 100–1,000) of the clay platelets provides a large surface area
and is considered to be responsible for the highly improved properties of these
nanocomposites. These improvements can include better tensile strength and moduli
[13–15], increased strength and heat resistance [12], decreased thermal expansion
coefficient [14], decreased gas permeability [14, 16, 17], decreased flammability [18,
19], increased swelling resistance [13], biodegradability of biodegradable polymers
[20], and enhanced ionic conductivity [21, 22]. The nanocomposites also show
unusual chemical and physical phenomenon, such as highly anisotropic electrical
conductivity [23] and photoactivity [24–26]. On the other hand, they are also considered to be unique model systems for the study of the structure and dynamics of
polymers in confined environments.
Polyolefin/Layered Silicate Nanocomposites Prepared by In Situ Polymerization
313