Effects of boron compounds on thermal degradation behaviour of polymers involving ester linkages

Çetinkaya, Nezaket Nehir
Interest in polymer nanocomposites is growing exponentially across various scientific and engineering disciplines owing to their remarkable improvements in theirproperties 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 compositesin order to enhancethermal properties of polymers. Trans-esterificationand/or condensationreactions between the boron compounds andthe 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 likecondensed phase flame retardants and leadto the generationof boronic anhydrides and boroxines. They form a cross linked-boroxine network through water lossby assisting intermolecular interactions and so they are good char-yielding compounds. In this study, composites of polymers havingester 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 analyzedbyboth techniques. Thermal characteristics of the nanocomposites were investigatedby direct pyrolysis mass spectrometry (DP-MS) andthermal gravimetric analysis (TGA) techniques. The increase in thermal stabilities of PLA and PMMA wereassociated with generation of a crosslinked structure. On the other hand, the decrease in thermal stabilityof PCLupon incorporation of BDBA and/or C30Bwas 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.


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Citation Formats
N. N. Çetinkaya, “Effects of boron compounds on thermal degradation behaviour of polymers involving ester linkages,” M.S. - Master of Science, Middle East Technical University, 2021.