Polymeric/polymers polymer-matrix nanocomposites

Despite the enormous number of scientific papers and patents published recently concerning the preparation and characterization of polymer matrix nanocomposites reinforced and modified with intercalated or exfoliated clays, systems based on SBS as polymeric matrix are relatively poorly investigated. 

As mentioned above, the new method of cryochemical synthesis of polymer nanocomposite films has been developed based on co-deposition of M/ SC and monomer vapors at temperature 80K and subsequent low-temperature solid-state polymerization of monomer matrix ([2] and works cited herein). It has been established that a number of monomers (acrylonitrile, formaldehyde, /i-xylylene and its derivatives) polymerize in solid state in absence of thermal movement of molecules owing to own specific supra-molecular structure. When reaction is initiated by y- or UV-radiation the formation of a polymer matrix occurs even at the temperatures close to temperature of liquid helium [66-69]. 

Leszczynska, A., Njuguna, J., Pielichowski, K., and Banerjee, J. R. (a) Polymer/montmorillonite nanocomposites with improved thermal properties, Part I Factors influencing thermal stability and mechanisms of thermal stability improvement, Thermochim. Acta (2007), 453, 75-96. (b) Polymer/montmorillonite nanocomposites with improved thermal properties. Part II Thermal stability of montmorillonite nanocomposites based on different polymeric matrixes, Thermochim. Acta (2007), 454, 1-22. 

Better dispersion of MWNTs in the polymer matrix caused by the formation of the chemical bonds leads to uniform stress distribution and enhanced shape memory (23). Jana et al. prepared nanocomposites of PU and MWNTs via in-situ polymerization and conventional method (105). PU nanocomposites obtained via an in-situ method with PCL-g-MWNTs showed better shape recovery, compared to conventional nanocomposites. 

This bicontinuous-microemulsion polymerization method can also be used to synthesize polymer nanocomposites containing Si02 [101], Ti02, ZnO and many other semiconductors. The advantage of this method is that the nanoparticles of inorganic materials can be dispersed in the polymer matrix fairly uniformly. The only requirement is that nanomaterials should be first stabihzed... 

A dispersion of nanoparticles of Au or other metals in a polymer matrix may also be obtained by a one-pot process of microemulsion polymerization. For instance, the UV-polymerization of a microemulsion of 35 wt% MMA, 35 wt% AUDMAA and 30 wt% of 0.1 M HAUCI4 aqueous solution would produce a Au-polymer nanocomposite, as shown in Fig. 12 [104]. This TEM micrograph shows a microtoned thin film of the sample. It is clearly apparent that Au particles of about 10-15 nm are well dispersed in the polymer matrix. 

This volume is including information about thermal and thermooxidative degradation of polyolefine nanocomposites, modeling of catalytic complexes in the oxidation reactions, modeling the kinetics of moisture adsorption by natural and synthetic polymers, new trends, achievements and developments on the effects of beam radiation, structural behaviour of composite materials, comparative evaluation of antioxidants properties, synthesis, properties and application of polymeric composites and nanocomposites, photodegradation and light stabilization of polymers, wear resistant composite polymeric materials, some macrokinetic phenomena, transport phenomena in polymer matrix, liquid crystals, flammability of polymeric materials and new flame retardants. 

Generally, polymer nanocomposites can be obtained through two routes the first one is the polymerization of monomers in contact with the exfoliated clay and the second one uses existing transformation processes to produce nanocomposites, for example, by a reactive extrusion. There are, however, problems present due to the lack of affinity of the clay-polymer system because of the hydrophilic character of the particles. It is then necessary to treat the clay chemically to increase its affinity with the polymer matrix. This constitutes another whole area of research in the nanocomposites production. 

Metal-polymer nanocomposites can be obtained by two different approaches, namely, in situ and ex situ techniques. In the in situ methods, metal particles are generated inside a polymer matrix by decomposition (e.g., thermolysis, photolysis, radiolysis, etc.) or chemical reduction of a metallic precursor dissolved into the polymer. In the ex situ approach, nanoparticles are first produced by soft-chemistry routes and then dispersed into polymeric matrices. Usually, the preparative scheme allows us to obtain metal nanoparticles whose surface has been passivated by a monolayer of -alkanethiol molecules (i.e., Crfiin+i-SH). Surface passivation has a fundamental role since it avoids aggregation and surface oxidation/contamination phenomena. In addition, passivated metal particles are hydrophobic and therefore can be easily mixed with polymers. The ex-situ techniques for the synthesis of metal/polymer nanocomposites are frequently preferred to the in situ methods because of the high optical quality that can be achieved in the final product. 

A limited number of methods have been developed for the preparation of metal-polymer nanocomposites. Usually, such techniques consist of highly specific approaches, which can be classified as in situ and ex situ methods. In the in situ methods, two steps are needed First, the monomer is polymerized in solution, with metal ions introduced before or after polymerization. Then metal ions in the polymer matrix are reduced chemically, thermally, or by UV irradiation. In the ex situ processes, the metal nanoparticles are chemically synthesized, and their surface is organically passivated. The derivatized nanoparticles are dispersed into a polymer solution or liquid monomer that is then polymerized. 

The radiation synthesis of polymeric nanocomposites is one of the promising technologies in the production of polymeric nanomaterials (Taleb et al. 2012). Along with the polymerization of monomers in situ (Liu et al. 2001, Meszaros and Czvikovszky 2007), radiation-induced cross-linking leads to the reinforcement of the available polymeric matrix owing to additional bond formation both between polymer chains of the matrix (Glhsel et al. 2003, Sharif et al. 2007) and between the polymer matrix and filler particles (KrkljeS et al. 2007, Planes et al. 2010). It is a very useful technique to improve the thermal stability, stress crack resistance, solvent resistance, and... 

Figure 9.2 is a schematic representation of CdSe QDs dispersed in poly(hexyl methacrylate) by in situ polymerization. The polymer with long alkyl branches is expected to prevent or reduce phase separation of the QDs from the polymer matrix during polymerization. This technique resulted in the preparation of a series of QD-based nanocomposite materials for which laser scanned confocal microscopy imaging revealed a nearly uniform dispersion of nanoparticles within the polymethacrylate matrix (Fig. 9.3). Notably, the resulting macroscopic QD-polymer composites appeared to be clear and uniformly colored.

Up to now we considered pol5meric fiiactals behavior in Euclidean spaces only (for the most often realized in practice case fractals structure formation can occur in fractal spaces as well (fractal lattices in case of computer simulation), that influences essentially on polymeric fractals dimension value. This problem represents not only purely theoretical interest, but gives important practical applications. So, in case of polymer composites it has been shown [45] that particles (aggregates of particles) of filler form bulk network, having fractal dimension, changing within the wide enough limits. In its turn, this network defines composite polymer matrix structure, characterized by its fractal dimension polymer material properties. And on the contrary, the absence in particulate-filled polymer nanocomposites of such network results in polymer matrix structure invariability at nanofiller contents variation and its fractal dimension remains constant and equal to this parameter for matrix polymer [46]. 

---