Solution polymer intercalation

A second major area in which the CD observed in a solute-polymer system has proven to be very useful in studies of the interactions has been for the particular instance where the polymer was an oligonucleotide. This area is also characterized by an extremely large literature, so in the present work we will restrict our focus on the CD induced in planar aromatic molecules which may or may not intercalate in the oligonucleotide structure. Perrin and Hart have reviewed the work performed prior to 1970 [67], and the focus of the current review will be on later works. 

The solution technique [Table 1(H)] is similar to that of the in situ process. Here, the organoclay is dispersed first in a toluene or A,A-dimethylformamide. The alkylammonium ions treated clays will then considerably swell to form gel structures. Later, polymer is added into the solution, which intercalates between the clay layers. Finally, the solvent is removed via evaporation (usually under a vacuum). 

The intercalation of polymer or prepolymer from the solution is described via minimum free energy principle. The driving force of polymer intercalation is the entropy from the solvent desorption. Several researchers investigated the thermodynamics properties of PCN with homo polymeric systems in a confined geometry. However, Lim et al. investigated ternary systems, and explained that the intercalation distance of poly-(methyl methacrylate) (PMMA)/organic-modified clay (OMMT) nanocomposite is larger than that for the... 

The general idea underlying the preparation of layered clay-polymer intercalates follows the simple rules of ion exchange. In most cases, the synthesis involves either intercalation of a polymer from solution or a suitable monomer followed by subsequent polymerization. But for more technologically important polymers, both approaches are limited since neither a suitable monomer nor a compatible polymer host solvent system is always available. 

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. 

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. 

This solution-induced intercalation process has the novelty to swell and disperse clays into a polymer solution. This process is difficult to carry out commercially because of the high cost factor of the solvents. In addition, phase separation in this process is quite tedious for solvent separation from the phase. There are also health and safety concerns associated with the application of this technology. However, this technology is exclusively applicable to water soluble polymers. As the solvent used in this process is water, which is a low-cost as well as an eco-friendly solvent with minimum... 

The insertion of PEO into mica-like sheet silicates in the reactions of a melt of the polymer with the host Na - or NH4 -exchanged lattice is one of tiie few examples of direct polymer intercalation. Poly(ethylene oxide) is also inserted into the lamellar networks of V205-nH20, MoOs," " - MnPSj, CdPSj, " etc. Thus an aqueous solution of PEO (M = 10 ) reacts with an aqueous gel of V2O5 nH20 to form a composite after removal of water. In this case, the interlayer distance increases from 1.155 to 1.32nm. Alkali metal ions react with PEO to form inclusion compounds. These can also be inserted into layers of ionic silicates, for example, into MMN. The distance between the layers of the PEO-Li salt complexes intercalated into MMN is 0.8 nm, the PEO chain adopts a slightly strained helicoid conformation in these locations. 

When layered silicates are used, the weak forces that stack the layers together can be easily dispersed in an adequate solvent. After the clay/organoclay has swollen in the solvent, the polymer is added to the solution and intercalates between the clay layers (in this case, the method is called intercalation of polymer from solution). 

One may address this phenomenon with thermodynamic arguments similar to those developed in Chapter 3 for the formation of solutions. The intercalation of a liquid or polymer melts into the clay presumably between the silicate layers require that... 

In-situ polymerisation, solvent intercalation/exfoliation and melt intercalation/exfoliation are the three major pathways for the formation of nanocomposites. In-situ polymerisation involves the combination of clay and monomer, followed by the polymerization of the monomer, which ideally locks the exfoliated clay particles in the resulting polymer matrix. In solvent intercalation die clay is first swollen in a solvent and the polymer (intercalant) is dissolved in die solvent. Both solutions are then combined and the polymer chains intercalate and displace the solvent within the interlayer of the clay (Shen et al, 2002). 

In the solution intercalation process, organically modified LDHs are first dispersed in a solution containing the desired polymer, followed by aging with stirring under a nitrogen atmosphere to accomplish polymer intercalation. This method was first used to disperse ZnAl-LDH into polyethylene By... 

In this method, the organo-modified LDH is swollen within the liquid monomer solution. When polymerization is initiated, the intercalated monomer can convert to polymer intercalated to the interlayer of LDH and thus forms a nanocomposite. Normally, only intercalated nanocomposites were obtained via this method if the organo-modified LDH was simply dispersed in acrylate and styrene monomers.O Leary et al reported the first exfoliated polymer-LDH nanocomposite prepared by the in situ polymerization method. In their work, MgAl-LDH intercalated with dodecyl sulfate (DS) also underwent... 

Melt intercalationRecently, the melt intercalation technique has become the standard for the preparation of polymer/layered silicate nanocomposites and is also quite compatible with the recent industrial techniques. During polymer intercalation from solution, a relatively large... 

Polyimide-clay nanocomposites constitute another example of the synthesis of nanocomposite from polymer solution [70-76]. Polyimide-clay nanocomposite films were produced via polymerization of 4,4 -diaminodiphenyl ether and pyromellitic dianhydride in dimethylacetamide (DMAC) solvent, followed by mixing of the poly(amic acid) solution with organoclay dispersed in DMAC. Synthetic mica and MMT produced primarily exfoliated nanocomposites, while saponite and hectorite led to only monolayer intercalation in the clay galleries [71]. Dramatic improvements in barrier properties, thermal stability, and modulus were observed for these nanocomposites. Polyimide-clay nanocomposites containing only a small fraction of clay exhibited a several-fold reduction in the... 

Reactions (5.5.30) and (5.5.31) proceed prevailingly during intercalation from solid or polymer electrolytes (cf. Section 2.6) or melts. When using common liquid electrolyte solutions, a co-insertion of solvent molecules (and/or intercalation of solvated ions) very often occurs. The usual products of electrochemical intercalation are therefore ternary compounds of a general composition ... 

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