In situ intercalative polymerization method

In this method, the layered silicate is swollen within the liquid monomer or a monomer solution, so the formation cannot occur between the intercalated sheets. Polymerization can be initiated by heat or radiation, by the diffusion of a suitable initiator, or by an organic initiator or catalyst fixed through cation exchange inside 

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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... 

The use of toxie organometallic catalysts and initiators in polymerization, as well as bulk solvents for monomer solutions, are among the industrial limitations of the in situ intercalative polymerization method, despite its reported advantage of good nanofiller dispersion in nanocomposite production. ... 

Tudor et al. [95] first used the in situ intercalative polymerization method for the preparation of PP/clay nanocomposites. They demonstrated the ability of soluble metallocene catalysts to intercalate inside silicate layers, and to promote the coordination polymerization of propylene. The silicate layers were modified by... 

Among the methods used for the addition of such fillers, only a small number of studies in the literature describe the preparation of these materials by in situ polymerization. Cho and coworkers [78] first utilized the in situ intercalative polymerization method for the preparation of polymer-clay nanocomposite consisting of conducting PAni and MMT. 

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. 

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. 

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. 

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. " ... 

A number of methods have frequently been employed in the production of nanocomposite materials. These include solution intercalation, melt intercalation, polymerization, sol-gel, deposition, magnetron sput-tering, laser, ultrasonication, supercritical fluid, etc. In PHA nanocomposite fabrication, solution intercalation and melt intercalation methods are the most widely explored procedures. However, use of in situ intercalative polymerization, supercritical fluids and electrospinning are shown to be promising and emerging techniques. The performance and quality of a nanocomposite depends on how well the nanofillers disperse or blend into the matrix. Therefore, these methods constitute different strategies to improve the composites thermo-mechanical and physico-chemical properties by enhancing efficient interactions between the nanofiller and the polymer matrices. 

Three different methods have been used to prepare polymer-clay nanocomposites. In the in situ intercalative polymerization, the first method, a precursor solution (monomer liquid or monomer solution) is inserted into the basal spaces of expanding clay layers, followed... 

Accordingly, a two-step method, named masterbatch process, has been approached for the preparation of PCL layered silicate nanocomposites by combining the in-situ intercalative polymerization and the melt blend intercalation process d. In such a process, a highly clay-filled (organo-modified) PCL is first prepared by in-situ intercalation pol)mierization of e-CL, followed by its addition as masterbatch, that is blended with the molten polyester matrix (commercial PCL CAPA 650). As it will be shown, this method permits to prepare PCL-based nanocomposites with a high degree of exfoliation, which cannot be achieved by directly mixing PCL and clay. 

A demonstrated method to insert polymer chains into host structures is by in-situ intercalative polymerization of a monomer using the host itself as the oxidant. FeOCl is one of the most convenient redox-intercalation hosts for a great variety of molecules including conducting polymers. The in-situ intercalative polymerization of pyrrole, 2,2 -bithiophene and aniline in the interlayer space of this material has been reported. The resulting intercalation compounds are composed... 

Traditionally, organoclay-polymer nanocomposites were synthesized by either the solution intercalation method or in-situ intercalative polymerization. However, it was the possibility of direct melt intercalation by... 

Three main methods have been developed to prepare polymer-clay nanocomposites.The first is exfoliation-adsorption the layered clay is exfoliated into a single layer in solvent in which the polymer can dissolve. Owing to the weak forces between the clay layers, the polymer enters between the delaminated layers and, when the solvent is evaporated, the nanocomposites are formed. The second is melt intercalation the polymer, in the molten state, is incorporated with the layered clay. The polymer then crawls into the interlayer space, causing the layers to separate and form nanocomposites. These two methods are physical and no chemical reaction occurs. The third method in situ intercalative polymerization the modified layered clay absorbs the liquid monomer and polymerization can be carried out between the intercalated sheets as shown in Figure 8.2. So far, many polymer-clay nanocomposites have been prepared through in situ intercalative polymerization initiated by chemical agents but very few by irradiation. ... 

Melt rheological properties of PCL-based nanocomposites were first reported by Krishnamoorti and Giannelis in the case of delaminated structures prepared by in-situ intercalative polymerization. Recently, Lepoittevin et a/. reported the detail melt rheology properties of PCL-based nanocomposites prepared by melt intercalation method. The rheological behaviour of the PCL filled with 3wt.% of MMT-AIk and MMT-(OH)2 was significantly different compared to the unfilled PCL and PCL/MMT-Na nanocomposites, for which the power law observed at low frequencies agrees with expectation for thermoplastics. The frequency dependence of G and G" was, however, perturbed by organically modified MMT. The effect was dramatic in the case of G which drops from 2 to 0.14 and 0.24 for MMT-(OH)2 and MMT-AIk, respectively. 

In situ polymerisation of the polymer matrix is an attractive method of preparing graphene-based composites although often solvents are used to reduce the viscosity of the dispersions. For example, intercalative polymerisation of methyl methacrylate and epoxy resins has been achieved with graphene oxide to produce nanocomposites with enhanced properties. It has also been possible to use in situ polymerization produce polyethylene- and polypropylene-matrix graphene oxide nanocomposites. The technique of grafting poly(methyl methacrylate) chains onto graphene oxide has also been employed to make the filler compatible with the polymer matrix. " ... 

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