Synthesis of Polymer-Clay Nanocomposites

There are three general approaches to the synthesis of polymer-clay nanocomposites. In the first approach, a monomer or precursor is mixed with organophilic clay and followed by polymerization. This in situ polymerization technique was first developed by the... 

K.A. Cairado, L. Xu, In Situ synthesis of polymer-clay nanocomposites from silicate gels. Chemistry of Materials 10 (1998) 1440-1445. 

Templated synthesis of polymer-clay nanocomposites Synthetic flnoro-smectite/ polyvinylpyrrolidone Carrado and Xu (111)... 

Kaminsky [92] was the first to report a method in which the filler surfaces were treated with metallocene-based catalyst for the production of filled polyolefins. In this method, at first under inert atmosphere, the clay surface is treated with an alkylaluminum compound to reduce the residual water content. In the second step, the catalyst or cocatalyst solution is impregnated onto the clay surface followed by washing with an anhydrous solvent to avoid excess catalyst leaching from the support during the polymerization. Additional alkylaluminum compounds may be used during the course of polymerization. This polymerization-filling technique is a widely used procedure for the synthesis of polymer/clay nanocomposites using coordination catalysts [60, 93, 94]. 

In situ emulsion polymerization in aqueous solution is an effective and successful method for the synthesis of polymer-clay nanocomposites. The structure of the nanocomposites formed is usually characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD offers a convenient method to determine the position, shape and intensity of the nanofillers. The XRD patterns shows a basal (001) reflection when the spacing between the clay layers is small. However, X-rays cannot detect the (001) reflection when the layers are exfoliated in the composite. An increase in spacing between layers is correlated with an increase in the degree of exfoliation. In contrast, TEM observation gives a direct view of the internal structure, spatial distribution of the various phases and defect structures. By combining these methods, the structure of polymer nanocomposites can be determined. 

The present review aims to cover and discuss recent developments in the synthesis of polymer-clay nanocomposites through emulsion polymerization. The first part summarizes the research status of in situ emulsion polymerization performed in the presence of pristine or organically modified clays (either MMT or Laponite). Then, the chapter highlights work on the synthesis of clay-armored latexes through soap-free polymerization. It reports the state of the art in the field and presents recent advances in the synthesis and characterization of high solids content latexes stabilized by Laponite clay platelets, with particular attention to mechanistic aspects and properties of the film materials issued from... 

Meneghetti, P. and Qutubuddin, S. 2006. Synthesis, thermal properties and applications of polymer-clay nanocomposites. Thermochimica Acta 442 74-77. 

Ramazani, A. 2010. Synthesis of polypropylene/clay nanocomposites using bisupported Ziegler-Natta catalyst. Journal of Applied Polymer Science 115 308-314. 

Bottcher and coworkers were the first to report the preparation of polymer clay nanocomposites by ATRP [20]. ATRP initiator-modified layered silicate was prepared by ion exchange between clay and l,T-(N,N,N-trimethylammonium bromide)undecanyl-2-bromoisobutyrate in-situ ATRP was carried out to grow polymer chains from the clay surface. In-situ ATRP between individual silicate layers leads to the direct synthesis of dispersed silicate nanocomposites. Their kinetics study and molecular weight analysis demonstrated that the polymerization followed the ATRP mechanism. 

Zhang and coworkers [27] reported the synthesis of SBR/clay nanocomposites by anionic polymerization, as shown in Scheme 11.2. The clay used is an OC modified by the intercalation of a quaternary long ammonium salt The fiUer is stirred into a 51 polymerization kettle filled with both styrene and butadiene monomer, THF, and cyclohexane. After stirring for 3 h, n-BuLi (THF/n-BuLi = 25) was added and the polymerization was carried out at 50 °C for 3 h. The authors found that the addition of the inorganic filler to the reaction mixture did not change the total conversion of both monomers, leading to the synthesis of SBR nano-composites with almost the same polymer composition as that of the materials... 

Nanoclays. Nanocomposites are materials that contain nanofillers, or fillers of nanometer dimensions. The successful synthesis of nylon-clay nanocomposites (57-59) ushered in nylon nanocomposites that could attain high modulus, heat distortion temperature, dimensional stabiUty, impermeabiUty, and strength with only a few percent modified clay nanofillers. Although it has been long known that poljuners could be mixed with appropriately modified clay minerals and synthetic clays, the field of polymer-layered silicate nanocomposites has gained... 

Kormann X, Lindberg H, Berglund LA (2001) Synthesis of epoxy-clay nanocomposites. Influence of the nature of the curing agent on structure. Polymer 42 4493-4499... 

Polyolefins, which are normally defined as polymers based on alkene-1 monomers or a-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 pol5nner filler, (2) clay as catalyst or cocatalyst support, and (3) Clay acts as a cocatalyst for coordination polymerization. 

So far, most studies have concerned polymer nanocomposites containing only one type of nanofiller. Lin and co-workers reported the synthesis of polymer-clay-silica ternary nanocomposites by in situ emulsion polymerization... 

Among the variety of inorganic solids e.g. silica, iron oxides, titanium dioxide, metals), clay minerals have recently attracted considerable attention. Indeed, polymer-clay nanocomposites (PCNs) have been the topic of extensive research worldwide since scientists at the Toyota Central Research laboratories reported 10 years ago that the incorporation of small amounts of montmorillonite (MMT) into nylon-6 resulted in a remarkable enhancement of the thermal and mechanical properties of the nanocomposite material. Whereas there has been a tremendous number of studies on the synthesis, properties and applications of polymer-clay nanocomposites in the recent literature, surprisingly only a small number of reports have dealt with emulsion polymerization. 

This book covers both fundamental and applied research associated with polymer-based nanocomposites, and presents possible directions for further development of high performanee nanocomposites. It has two main parts. Part I has 12 chapters which are entirely dedicated to those polymer nanocomposites containing layered silicates (clay) as an additive. Many thermoplastics, thermosets, and elastomers are included, such as polyamide (Chapter 1), polypropylene (Chapter 4), polystyrene (Chapter 5), poly(butylene terephthalate) (Chapter 9), poly(ethyl acrylate) (Chapter 6), epoxy resin (Chapter 2), biodegradable polymers (Chapter 3), water soluble polymers (Chapter 8), acrylate photopolymers (Chapter 7) and rubbers (Chapter 12). In addition to synthesis and structural characterisation of polymer/clay nanocomposites, their unique physical properties like flame retardancy (Chapter 10) and gas/liquid barrier (Chapter 11) properties are also discussed. Furthermore, the crystallisation behaviour of polymer/clay nanocomposites and the significance of chemical compatibility between a polymer and clay in affecting clay dispersion are also considered. 

As reflected in this chapter, most of the published literature on polymer-clay nanocomposites focuses on synthesis and characterization. Future work should address is-... 

Usuki, A., Hasegawa, N. and Kato, M. Polymer-Clay Nanocomposites. Vol. 179, pp. 135-195. Uyama, H. and Kobayashi, S. Enzymatic Synthesis and Properties of Polymers from Polyphenols. Vol. 194, pp. 51-67. 

---