In-situ intercalative polymerization

In this process, the modified montmorillonite clay is first added to the liquid monomer and dispersed using a mechanical stirrer or using ultrasonic mixer. A curing agent in the form of hardener or catalyst is added to initiate and to complete the curing reaction. The samples are cured either at room temperature or at high temperature in a mold to get the component of desired shape. 

Nanocomposites of thermoset polymers like unsaturated polyester and epoxy can be fabricated by this method. In this process, the monomers/ prepolymers are allowed to intercalate the layer spacing of the clay platelets. Polymerization will then be initiated either by the application of heat or radiation or by introducing suitable organic initiator. The intercalated monomer swells the clay and during polymerization increases the interlayer spacing and results in the formation of intercalated or exfoliated nanocomposites. 

In clay-polyamide nanocomposites, effective exfoliation and dispersion of clay can be obtained by in-situ polymerization technique. In this process, layered silicate particles are dispersed in the monomer and then polymerized. It is done by ring-opening polymerization of e-caprolactum in the presence of organically modified clay [7-8,40-41]. 

The modified montmorillonite prepared by cation exchange reaction with 12-aminolauric acid can chemically react with caprolactum molecules and makes the caprolactum polymer chain ends tethered to the silicate layers through the 12-aminolauric acid [41-42]. A. similar method has been used to prepare polyamide-6 nanocomposites [8,43-46]. 

In this mode of polymerization, the monomer is used to swell the layered silicate mineral. As the monomer has low molecular weight, it is more mobile in nature and can diffuse easily into the filler interlayers. During polymerization, the clay interlayers becomes trapped by the forming polymer chains and an 

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M. G. Kanatzidis, M. Humbbard, L. M. Tonge, T. J. Marks, H. 0. Marcy, C. R. Kannewurf, In situ intercalative polymerization as a route to layered conducting polymer-inorganic matrix microlaminates, polypyrrole and polythiophene in FeOCl, Synthetic Metals, vol. 28, pp. 89-95,1989. 

J. Zhang, L. Wang, A. Wang, Preparation and properties of chitosan-g-poly(acrylic acid)/montmorillonite superabsorbent nanocomposite via In situ intercalative polymerization, Ind. Eng. Chem Res., vol. 46, pp. 2497-2505, 2007. 

In Situ Intercalative Polymerization A variety of polymer nanocomposites have been prepared using this method, that is, PS/graphene, PMMA/expanded graphite, poly(styrene sulfonate) (PSS)/layered double hydroxyl (LDH), PI/LDH, and PET/LDH. 

The main techniques that can be used to prepare polymer/clay nanocomposites are (a) melt mixing the layered clay with polymer, (b) mixing the layered clay with solution of polymer followed by solvent removal, and (c) in situ intercalative polymerization, where the monomer is first intercalated in the clay and subsequently polymerized in situ. 

Besides melt intercalation, described above, in situ intercalative polymerization of E-caprolactone (e-CL) has also been used [231] to prepare polycaprolactone (PCL)-based nanocomposites. The in situ intercalative polymerization, or monomer exfoliation, method was pioneered by Toyota Motor Company to create nylon-6/clay nanocomposites. The method involves in-reactor processing of e-CL and MMT, which has been ion-exchanged with the hydrochloride salt of aminolauric acid (12-aminodecanoic acid). Nanocomposite materials from polymers such as polystyrene, polyacrylates or methacrylates, styrene-butadiene rubber, polyester, polyurethane, and epoxy are amenable to the monomer approach. 

Figure 6.1 Structural model for the Intercalated polypyrrole chains within the van der Waals gap of FeOCI. (Reprinted with permission from Solid State Ionics, In situ intercalative polymerization chemistry of FeOCI. Generation and properties of novel, highly conductive Inorganic/organic polymer microlaminates by M. G. Kanatzidis, H. O. Marcy, W. J. McCarthy et al., 594-608, 1-3. Copyright (1989) Elsevier Ltd)...

Okamoto, M., Morita, S., Taguchi, H., Kim, Y. H., Kotaka, T., and Tateyama, H., Synthesis and structure of smectic clay/poly(methyl methacrylate) and clay/polystyrene nanocomposites via in situ intercalative polymerization. Polymer, 41, 3887-3890 (2000). 

Uthirakumar, R, Hahn, Y. B., Nahm, K. S., and Lee, Y.-S., Preparation of polystyrene/ montmoriUonite nanocomposites using a new radical initiator-montmorillonite hybrid via in situ intercalative polymerization, Eur. Polym. J., 40, 2437-2444 (2004). 

Paul, M., Delcourt, C., Alexandre, M., Degee, P., Monteverde, R, Rulmont, A., and Dubois, P. (2005). (Plasticized) Polylactide/(organo-)clay nanocomposites by in situ intercalative polymerization. Macromol. Chem. Phvs.. 206,484-498. 

Several techniques such as intercalation of polymer from solution, in-situ intercalative polymerization, melt intercalation, direct mixture of polymer and particulates, template synthesis, in-situ polymerization and solgel process, are being employed for the preparation of polmer-layered silicate nanocomposites. Among them the most common and important approaches are in-situ polymerization, solution-induced intercalation method, and melt processing method, which are briefly discussed below. 

Zhang, R, Li, S., Karaki, T., and Adachi, M. 2005. Synthesis of p>olyethylene/montmorillon-ite nanocomposites by in-situ intercalative polymerization. J meseJomn ofj iedPltt/sics 44 658-661. 

He, A. H., Wang, L., Li, J., Dong, J.-Y, and Han, C. C. 2006. Preparation of exfoliated isotactic polypropylene/alkyl-triphenylphosphonium-modified montmorillonite nanocomposites via in situ intercalative polymerization. Polymer 47 1767-1771. 

When obtaining PLA/clay nanocomposites, three main techniques are frequently used to produce nanocomposites of this material, namely in situ intercalative polymerization, solution-casting and melt mixing. Of the three, the in situ intercalative polymerization method exhibits the highest performance, since it is the one that results in a higher degree of interaction... 

In the melt mixing method, nanoclays are incorporated into the polymer in the molten state. This technique has considerable advantages over either the in situ intercalative polymerization or polymer solution intercalation techniques. Firstly, this method is environmentally benign due to the absence of organic solvents. Secondly, melt processing is compatible with current industrial processes, such as extrusion and injection moulding. The melt intercalation method allows the use of biopolymers that were not suitable for in situ polymerization. This has been the most widely used method in the literature for obtaining PLA/clay nanocomposites. " ... 

Other techniques for obtaining PLA/clay nanocomposites have been recently explored, such as masterbatch, layer-by-layer and in situ intercalative polymerization in supercritical carbon dioxide. ... 

Table 8.2 Mechanical properties of clay nanocomposites of in situ intercalative polymerization [88]...

Bruzard, S. Levesque, G., Polysiloxane-g-TiNbO Nanocomposites Synthesis via In Situ Intercalative Polymerization and Preliminary Characterization. Chem. Mater. 2002,14, 2421-2426. 

The structure and dynamics of surfactant and polymer chains in intercalated poly(8-caprolactone)/ clay nanocomposites are characterized by P magic-angle spinning (MAS) and C cross-polarization MAS NMR techniques. To obtain hybrid materials with the low polymer content required for this study, in situ intercalative polymerization was performed by adapting a published procedure. After nanocomposite formation, the chain motion of the surfactant is enhanced in the saponite-based materials but reduced in the laponite ones. Compared to the initial clay, the trani -conformer population of the surfactant hydrocarbon chains in the nanocomposite decreases for the saponite systems. Mobility of the polymer chain is higher in the nanocomposites than in the bulk phase. The charge of the modified saponite does not significantly inflnence chain mobility in the nanocomposites. 

In the following section, the major research findings on polyamide in-situ intercalative polymerization are summarized, presenting different approaches per... 

To date, the in-situ intercalative polymerization technique is one of the most successful techniques for producing MMT nanocomposites on an industrial scale. The first step of this process, as shown in Figure 6.6, involves the intercalation of a monomer or low-molecular-weight precursor into the galleries of the silicates. 

Figure 6.6 Steps in the in-situ intercalative polymerization technique.

In-situ intercalative polymerization of layered silicates is perhaps the best example of reactive molding of nanocomposites today. In-situ interactive polymerization of layered silicates, which was discussed above, can be achieved either with thermosetting matrices, such as polyurethane and epoxy, or with thermoplastic systems, such as nylon-6 [4, 23]. A general requirement for reactive molding of nanocomposites is that the particulate phase of a PNC is compatible with the monomer phase of the reactive molding system, which acts as a polymerizable solvent This makes it possible to achieve and maintain a fine dispersion of the particulate phase in the monomer during matrix consolidation, resulting in excellent particle distribution in the final PNC. Above, it was noted that the hydroxylated surface of cellulose makes it reactive to isocyanate. Cellulose whiskers may therefore represent the ideal particulate phase for a nano-RIM process. For this to be achieved, the whisker-polyurethane system needs to be better characterized, so that the RIM process can be adapted to fabrication of cellulose whisker PNCs. 

The in-situ intercalative polymerization process, shown schematically in Figure 6.26, is especially favorable for the FA-MMT combination because MMT has the ability to catalyze the polymerization of FA to PFA which in turn drives the exfoliation process observed in XRD as discussed above. 

Figure 6.26 Schematic representation of in-situ intercalative polymerization.

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