Polimer/kil nanokompozitlerin hazırlanmasında yeni yöntemler

Polymer/clay nanocomposites have exhibited immensely enhanced properties and higher performance as compared to both their conventional polymer composites and pure polymers. Currently polymer/clay nanocomposites can be prepared by three ways such as solution mixing, melt blending, and in-situ polymerization. Solution mixing method consists to solubilize polymer in an organic solvent, then the clay is dispersed in the obtained solution and subsequently either the solvent is evaporated or the polymer precipitated. The large quantities of volatile solvent necessary for this approach make it less attractive as an industrial process. Melt blending is a solvent-free method to enable mixing of the layered silicate with the polymer matrix in the molten state. However, very careful attention has to be paid to finely tune the processing conditions to increase the compatibility of clay layer surfaces with the polymer matrix. In the in-situ polymerization technique, the monomer, together with the initiator and/or catalyst, is intercalated within the silicate layers and the polymerization is initiated by external stimulation such as thermal, photochemical or chemical activation. The chain growth in the clay galleries triggers the clay exfoliation and hence the nanocomposite formation.The in-situ polymerization can be initiated by externally stimulation such as thermal, photochemical or chemical activation. The growth of polymer chains within the clay galleries may lead to the clay exfoliation and hence the nanocomposite formation.Recently, a highly efficient method, namely copper (I) catalyzed azide/alkyne cycloaddition (CuAAC) "click" reaction, in which exfoliation is rooted in the functional groups of the intercalant that readily react with the antagonist groups of the preformed polymershas been established. To take advantage of click chemistry, azide and alkyne partners could each be incorporated in either the clay surface or polymer chain. The quantitative efficiency of coupling reaction coupled with tolerance to a wide variety of functional groups and reaction conditions make this coupling process highly attractive for the nanocomposite preparation. However, there are limited examples in the literature to date regarding the preparation of polymer/clay nanocomposites via the CuAAC click reactions. In the first part of thesis,an efficient protocol, atom transfer radical nitroxide coupling chemistry (ATNRC), for the preparation of polymer/clay nanocomposites via grafting-onto strategy with well-defined polymer synthesized via atom transfer radical polymerization has been described. The highly efficient ATNRC chemistry was based on mixing a nitroxide-containing organoclay with corresponding halide-containing polystyrene in the presence of Cu(I)Cl/PMDETA catalytic system was developed.The radical coupling, taking place between the clay layers, not only leads to attach the polymer chain but also successful nanocomposite formation with highly exfoliated morphology. Spectroscopic and microscopic investigations revealed that successful nanocomposite formation has been achieved by this method. By addition of small amounts of layered silicate loadings resulted in remarkable improvements of thermal properties of nanocomposites. In the second part of thesis,a series of A3-type star poly(methylmethacrylate)/clay nanocomposites has been prepared by in-situ atom transfer radical polymerization (ATRP) initiated from organomodified montmorillonite containing quaternary trifunctional ATRP initiator. The first order kinetic plot showed a linear behavior, indicating the controlled character of the polymerization. The resulting nanocomposites were characterized by spectroscopic, thermal and microscopic analyses. Spectroscopic and microscopic investigations revealed a complex morphology, with partial intercalation/exfoliation, which depends on the concentration of clay.The exfoliated nanocomposite was obtained when polymerization was conducted with 1% of organic clay loading.However, with increasing the clay loading to 3, 6 and 10%, the degree of exfoliation of the nanocomposites decreased, which confirmed by both spectroscopic and microscopic analyses. Thermal analyses show that all nanocomposites had higher glass transition values and thermal stabilities compared to neat polymer. In the third part of thesis, the preparation of polymer/clay nanocomposites by specific hydrogen bonding interactions between surface functionalized silica nanoclays and 2-ureido-4[1H]pyrimidinone-bonded supramolecular poly(ethylene glycol) or poly(ɛ-caprolactone)s, which has self-association capability through quadruple hydrogen bonds was described. An 2-ureido-4[1H]pyrimidinone (UPy) motif with self-association capability (through quadruple hydrogen bonds) was successfully anchored onto montmorillonite clay layers. Polymer/clay nanocomposites were prepared by specific hydrogen bonding interactions between surface functionalized silica nanoclays and UPy-bonded supramolecular poly(ethylene glycol) or poly(ɛ-caprolactone). The mixed morphologies including intercalated layers with a non-uniform separation and exfoliated single layers isolated from any stack were determined by combined spectroscopic and microscopic analyeses. Thermal measurements showed that all nanocomposites have higher decomposition temperatures and thermal stabilities comparedto neat polymer. Thedifferential scanning calorimetry data implied that thecrystallinity of polymers did not show essential changes upon introduction of organomodified UPy clays.