Monomers intercalation

Fig. 9 Scanning electron micrographs of a Zn2Al/Cl, and its PSS derivatives obtained b via monomer intercalation c followed by in situ polymerization, or d by direct polymer incorporation using the memory effect with e subsequent hydrothermal treatment and f after a delamination-restacking process. The bar represents 5 xm. Reprinted from [43] and [48] with permission from ACS and RSC, respectively...

Polypropylene (PP) is one of the most widely used plastics in large volume. To overcome the disadvantages of PP, such as low toughness and low service temperature, researchers have tried to improve the properties with the addition of nanoparticles that contains p>olar functional groups. An alkylammonium surfactant has been adequate to modify the clay surfaces and promote the formation of nanocomposite structure. Until now, two major methods, i.e., in-situ polymerization( Ma et al., 2001 Pirmavaia, 2000) and melt intercalation ( Manias et al.,2001) have been the techniques to prepare clay/PP nanocomposites. In the former method, the clay is used as a catalyst carrier, propylene monomer intercalates into the interlayer space of the clay and then polymerizes there. The macromolecule chains exfoliate the silicate layers and make them disperse in the polymer matrix evenly. In melt intercalation, PP and organoclay are compounded in the molten state to form nanocomposites. 

Abstract The development of polymer-clay nanocomposite materials, in which nano-meter-thick layers of day are dispersed in polymers, was first achieved about 15 years ago. Since then, the materials have gradually become more widely used in applications such as automotive production. The first practical nylon-clay nanocomposite was synthesized by a monomer intercalation technique however, the production process has been further developed and a compound technique is currently widely used. A polyolefin nanocomposite has been produced by the compound method and is now in practical use at small volume levels. In this review, which focuses on njdon- and polyolefin-nanocomposites, detailed explanations of production methods and material properties are described. This article contains mainly the authors work, but aims to provide the reader with a comprehensive review that covers the works of other laboratories too. Lastly, the challenges and directions for future studies are included. 

The first technique to be developed was the monomer intercalation method. This chapter describes the results of studies and experiments that we conducted to characterize this method. 

Figure 14.1 Changes in the silicate spacing as a consequence of monomer intercalation and subsequent polymerization.

Monomer Intercalation and Subsequent Controlled In Situ Polymerization... 

Nanocomposites are a relatively new class of hybrid materials characterized by an ultra fine dispersion of nanofillers into a polymeric matrix. As the result of this dispersion, these materials possess unique properties, behaving much diflferentiy than conventional composites or microcomposites, and offering new technological and economical opportunities. The first studies on nanocomposites were carried out in 1961, when Blumstein performed the polymerization of vinyl monomer intercalated into montmorillonite structure. Since then, clay-based polymer nanocomposites have emerged as a new class of materials and attracted considerable interest and investment in research and development worldwide (Schaefer and Justice 2007). 

Z. Chen, P. Luo, and Q. Fu, Preparation and properties of organo-modifier free PET/MMT nanocomposites via monomer intercalation and in situ polymerization. Polymers for Advanced Technologies, 20 (2009), 916-25. 

FIGURE 9.19 TEM micrographs of (a) a liquid epoxy monomer intercalated in MG61 -ABS (6.4 wt%) after swelling and (b) the same sample after curing with D230. (From Ref. 40, copyright 2005, Elsevier, with permission.)... 

In-situ polymerization is the most widely referred technique for preparation of LDH-based polymer nano composites. This process is solution-based and is usually carried out in an aqueous system. The scheme shown in Fig. 6 indicates the general principle for carrying out in-situ polymerization within the layers of LDH crystals. The primary step in this procedme is the preparation of monomer intercalated LDH hybrids, which are then subjected to excitation using heat [48,50], initiating chemicals [51], etc. to initiate the polymerization reaction. Various methods of intercalation of monomers into the interlayer space of LDH crystals and their subsequent polymerization have been reported in literature and are summarized in Fig. 6. 

The anionic interchange method involves the dispersion of LDH materials into a monomer solution, most often in aqueous mediiun (path 1 in Fig. 6) [52-54]. The dispersion is then stirred for several horns with mild heating. To be able to replace the interlayer anion, the monomer molecules should have such functionality as can stabilize the layered structure by neutralizing the excess charge on the hydroxide sheets of LDH. For example, acrylate anions are intercalated into Mg - Al LDH through ion exchange with Cl" or NO3" present in LDH. Lee and Chen reported intercalation of acrylate and 2-acryloamido-2-methyl propane sulfonate into hydrotalcite [51]. These intercalated hybrids are then dispersed in an alkah-neutralized solution of the monomer and the polymerization is carried out in the presence of an initiator. Leroux and coworkers prepared vinylbenzene sulfonate monomer intercalated Zn-Al LDH [52] and aminobenzene sulfonate monomer intercalated Cu-Cr LDH [53]. Further, Tanaka et al. reported acrylate ion intercalation within LDH by replacing the nitrate anion from Mg-Al LDH [54]. 

The abiUty of LDH materials to regenerate their layered structure from an aqueous dispersion of their mixed-oxide form is also applied to prepare the monomer-intercalated hybrids (path 3, Fig. 6). This is called the regeneration method, which is similar to the procedure used for converting C03 "-containing LDH to other forms. 

Polymerization of vinyl monomers intercalating into the montmorillonite (MMT) clay was first reported in the literature as early as 1961. The most recent methods to prepare polymer-layered-siUcate nanocomposites have primarily been developed by several other groups. In general these methods (shown in Fig. 5.1) are able to achieve molecular-level incorporation of the layered silicate (e.g. montmorillonite clay or synthetic layered silicate) in the polymer matrix by addition of a modified silicate either to a polymerization reaction (in situ method), to a solvent-swollen polymer (solution blending), or to a polymer melt (melt blending). Recently, a method has been developed to prepare the layered silicate by polymerizing silicate precursors in the presence of a polymer. ... 

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