Structure and thermal behavior of organic-inorganic PMMA-MMT-Na⁺ hybrids

Full text: Organic-inorganic polymer-clay hybrid nanocomposites were obtained using the grafting method and the study of their properties has been done through structural, thermal and mechanical characterizations. The methodology consisted of dispersion of sodic montmorillonite clay (MMT-Na⁺) in water and subsequent centrifugation. The supernatant was removed and the study of the particles dispersed in this medium was done using quasi-elastic light scattering (QELS). The average length of measured clay particles was 280 nm. This fraction of pretreated clay was dispersed in tetrahydrofuran (THF) using ultrasonic bath. The synthesis of the nanocomposite was performed in a reflux system at 70 °C: to a volumetric flask controlled amounts of the pretreated clay dispersed in THF, solution of sodium hydroxide (NaOH) and 3-(trimethoxysilyl)propyl methacrylate were added in defined amounts. The purpose of adding base and the alkoxysilane is the deprotonation of the OH groups present in the clay structure and the formation of a covalent bond between the alkoxysilane and the clay structure. [1] The next step was the addition of poly (methyl)methacrylate (PMMA) and benzoyl peroxide (BPO) attempt to connect the polymer to the precursor. The materials were characterized by XRD, SAXS, FTIR and thermogravimetric analysis. The XRD and SAXS results show that the interlayer spacing of the clay increases from 11.7 to 20 Å and a new crystalline phase is formed. FTIR shows the characteristics bands of the organic and inorganic phases and thermogravimetric analysis shows that increasing the clay loading tends to suppress the first stage of the polymer decomposition, increasing significantly its thermal stability. Reference: (1) Isoda, K., Kuruda, K. Interlamellar grafting of γ-methacryloxypropylsilys groups on magadiite and copolymerization with methyl methacrylate. Chem. Mater. 2000, 12, 1702. (author)