Boron bileşiklerinin, ester bağı içeren polimerlerin ısıl bozunum davranışları üzerindeki etkileri

Interest in polymer nanocomposites is growing exponentially across various scientific and engineering disciplines owing to their remarkable improvements in their properties compared to micro- and macro- conventional composites. Although polymers having good physical properties are commercially available, they are mostly hampered by their low melting temperatures, poor mechanical or barrier properties. Therefore, there is a considerable work on improvement of the properties of polymers, and development of polymer nanocomposites. Several studies were concentrated on boron compounds in polymer composites in order to enhance thermal properties of polymers. Trans-esterification and/or condensation reactions between the boron compounds and the polymers involving COO, OH or CONH groups may take place and support to improve thermal characteristics. Boronic acid groups release water upon thermolysis and behave like condensed phase flame retardants and lead to the generation of boronic anhydrides and boroxines. They form a cross linked-boroxine network through water loss by assisting intermolecular interactions and so they are good char-yielding compounds. In this study, composites of polymers having ester group along the main change such as poly(lactic acid), PLA and poly(caprolactone), PCL, or along the side chain such as poly(methyl methacrylate), PMMA and poly(n-butyl methacrylate), PnBMA with methyl tallow bis-2-hydroxyethyl ammonium modified montmorillonite, Cloisite 30B (C30B) and Cloisite 15A (C15A) and boron compounds (benzene-1,4-diboronic acid (BDBA), boric acid (BA) and zinc borate (ZB)) were prepared and characterized with the use of transmission electron microscopy (TEM) and x-ray diffraction (XRD) analyses. Dispersion of clay in the polymer matrices and intercalated and partially exfoliated clay layers were analyzed by both techniques. Thermal characteristics of the nanocomposites were investigated by direct pyrolysis mass spectrometry (DP-MS) and thermal gravimetric analysis (TGA) techniques. The increase in thermal stabilities of PLA and PMMA were associated with generation of a crosslinked structure. On the other hand, the decrease in thermal stability of PCL upon incorporation of BDBA and/or C30B was attributed to lower probability of crosslinking in the presence of long alkyl chains along the polymer backbone. Generation of boron network structure was detected for PMMA-BDBA and PCL-BDBA composites. For PnBMA, although addition of C30B increased the thermal stability, addition of clay with BDBA caused any noticeable change in thermal stability. Trans-esterification reactions between BDBA and C30B and ester groups of polymer matrices were also determined.