Monomer intercalation method

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. 

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. 

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. 

Lu et al. [95] have also prepared ER fluid based on PANI-MMT nanocomposite with small particles diameter about 100-200 nm by an emulsion intercalation method. No additional surfactant is used and the aniline monomer remains excess amount in their intercalation reaction, and thus, the positive charged aniline monomer can well replace the absorbed sodium ions in interlayer of MMT. In order to further reduce the conductivity of the PANI-MMT particles prepared by the chemical oxidation of aniline in the presence of acidic dopant, the PANI-MMT particles must be immersed in NH aqueous solution. This immersed time for controlling conductivity of this nanocomposite is longer (several hours) compared with immersed time (only several minutes) of pure PANI. This may be related to the protection function of MMT layer to PANI macromolecular. The yield stress of PANI-MMT ER fluid is 7.19 kPa at 3 kV/mm, which is much higher than that of pure MMT as well as that of the mixture of PANI with clay (PANI+MMT). 

Other methods to prepare nanocomposites include a solvent-assisted process, whereby a cosolvent is employed to help carry the monomer into the galleries and is subsequently removed from the polymer system, and direct polymer melt intercalation methods, which involve the direct addition of nanoclays to a polymer melt under shear conditions atelevated temperatures, allowing their direct exfoliationintothepolymer[5]. 

In-situ intercalation method was reported by Toyota researchers for the synthesis of polyamide nanocomposites that led to the exponential growth in the nanocomposites research. For generation of polymer nanocomposites by this method, the layered silicate mineral is swollen in monomer. After swelling, the polymerization of the monomer is initiated. As monomer is present in and out of the filler interlayers, therefore, the generated stmcture is exfoUated or significantly intercalated. As the rate or mechanism of polymerization in and out of the filler interlayers... 

PA 11-clay nanocomposites have also been reported through the in-situ intercalation method, by using 11-aminoundecanoic acid both as monomer and as clay organic modifier [63]. For less than 4wt% of clay loading, the nanofiller was uni-... 

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. 

From the above discussion, it can be seen that the method adopted to prepare nanocomposites is highly dependent on the nature of the polymer. When the polymers or monomers are water soluble, they can be incorporated into the pristine LDH without any organo-modification due to their good affinity with the LDH. Additionally, the aqueous environment is compatible with the condition for the synthesis of LDH materials. Therefore, water-soluble polymer-LDH nanocomposites can be prepared using some special methods such as in situ synthesis, ion exchange and reconstruction. In the case of water-insoluble polymers and monomers, their nanocomposites are usually prepared in orga-nosolvent (solution intercalation method, exfoliation-absorption method and in situ polymerization method) or molten polymer (melt intercalation method). However, emulsion polymerization and suspension polymerization are methods that allow the incorporation of a water insoluble polymer into an LDH in water. The following sections are devoted to polymer-LDH nanocomposites obtained via emulsion polymerization and suspension polymerization. 

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. ... 

ENGAGE is an ethylene-octene copolymer. Ray and Bhowmick [70] have prepared nanocomposites based on this copolymer. In this study, the nanoclay was modified in situ by polymerization of acrylate monomer inside the gallery gap of nanoclay. ENGAGE was then intercalated inside the increased gallery gap of the modified nanoclay. The nanocomposites prepared by this method have improved mechanical properties compared to that of the conventional counterparts. Preparation and properties of organically modified nanoclay and its nanocomposites with ethylene-octene copolymer were reported by Maiti et al. [71]. Excellent improvement in mechanical properties and storage modulus was noticed by the workers. The results were explained with the help of morphology, dispersion of the nanofiller, and its interaction with the mbber. 

NR, styrene-butadiene mbber (SBR), polybutadiene rubber, nitrile mbber, acrylic copolymer, ethylene-vinyl acetate (EVA) copolymer, and A-B-A type block copolymer with conjugated dienes have been used to prepare pressure-sensitive adhesives by EB radiation [116-126]. It is not necessary to heat up the sample to join the elastomeric joints. This has only been possible due to cross-linking procedure by EB irradiation [127]. Polyfunctional acrylates, tackifier resin, and other additives have also been used to improve adhesive properties. Sasaki et al. [128] have studied the EB radiation-curable pressure-sensitive adhesives from dimer acid-based polyester urethane diacrylate with various methacrylate monomers. Acrylamide has been polymerized in the intercalation space of montmorillonite using an EB. The polymerization condition has been studied using a statistical method. The product shows a good water adsorption and retention capacity [129]. 

In situ polymerization is generally a highly suitable method for the ob-tention of LDH/polymer nanocomposites. Various monomers can be intercalated and polymerized within the interlamellar space of LDH and this spatial confinement is believed to increase the degree of polymerization. Yet, the process is limited by two factors [43] ... 

Nucleic acids do not display the same promiscuous chemical reactivity of proteins. Instead, individual synthetic nucleotides can display a unique functional group that can be exploited even more for direct attachment of probes (117). The simplest method of labeling DNA uses high-affinity bis-intercalating dyes such as ethidium bromide, acridine, and thiazole orange monomers... 

Emulsion polymerization intercalation is an alternative method of PCN synthesis. This method is similar to in situ polymerization, but has several differences and limitations. In the emulsion polymerization method, micelle helps the polymer to be monodisperse, yet the micelles are limited in their ability to penetrate into the layer. Nonetheless, this method is attractive because of its use of a micelle as a targeted material, which helps the monomer or prepolymer to penetrate into the silicate layers. 

It should be noted that among the three different methods of PNC preparation mentioned above, the solution method and the in situ polymerization method have only limited applications because neither a compatible polymer-silicate solvent system nor a suitable monomer is always available. Moreover, they are not always compatible with current polymer processing techniques. Among all the methods to prepare PNCs, the approach based on direct melt mixing/intercalation is perhaps the most versatile and environmentally benign. 

Bissessur and coworkers explored the inclusion of poly(2-ethylaniline) (PEA) and poly(2-propylaniline) (PPA) into GO, in addition to polyaniline [90]. The technique of intercalation differed from previously reported methods. They showed that polyaniUnes can be directly inserted into GO without the preparation of precursor phases. The polymers were first prepared from the monomers by oxidation with ammonium peroxydisulfate in acidic medium. GO, synthesized by using the Hummers method, was dispersed in deionized water with the aid of sonication. Colloidal suspensions of the polymers in NMF were then added to the aqueous GO suspensions. The reaction mixtures were then acidified and heated at 60 °C for 90 min. The intercalated phases were isolated via freezedrying. A similar process was used to intercalate polypyrrole into GO [91]. 

The host components (Fig. la) are first reciystallized from usual solvents for isolation and purification. This operation produces host assemblies with or without the solvents (Fig. Ib). There are two methods for obtaining inclusion compounds with the monomers (Fig. Ic) by the addition of monomers into the solvents and by replacement of the guests with retention of the host assemblies, called intercalation. 

The manufacturing methods for PLA nanocomposites include intercalation of polymer from solution, polymer melt intercalation and intercalation of a suitable monomer and subsequent in situ polymerization. 

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