Synthesis and properties of styrene-based polymer-montmorillonite nanocomposites

Abstract

Styrene monomer was mixed with quaternary ammonium montmorillonites (org-MMTs) and polymerized in the presence of radical initiator. The intercalated and exfoliated structures of polymerized polystyrene/org-MMT nanocomposites were identified by XRD and TEM. TEM was employed to examine the microstructures of ordered intercalates as well as exfoliated MMT layers. The observed microstructures were compared with those concluded from XRD results. The radical polymerization of the styrene penetrated between the interlayers of org-MMT has resulted in intercalated PS/org-MMT hybrid. The intercalated nanocomposites exhibited the microstructures which is very similar to that of the unintercalated organically modified layered silicate (org-MMT). The X-ray diffraction study on PS/org-MMT nanocomposite revealed the distance of MMT interlayers increased from 11.8Å for Na-MMT and to 34Å for PS/org-MMT nanocomposite. This finite layer expansion associated with polymer intercalation resulted in the appearance of a new basal reflection corresponding to the larger gallery height. This result was in good agreement with the interlayer spacing determined by transmission electron microscope (TEM). Fourier transform infrared (FTIR) spectra further confirmed the formation of polystyrene in the MMT gallery. The ratio of intercalated PS to MMT ranged from 0.62 to 0.94 g-PS / 1g-MMT depending on the structure of organic group in org-MMT and on the amount of MMT. These intercalated nanocomposites exhibited higher thermal stability compared with the virgin polystyrene (PS) or PS/pristine-MMT microcomposites. PS/Bz-MMT, containing benzyl-unit similar to styrene in org-MMT, exhibited higher decomposition temperature even for MMT loading content as low as 0.3 wt.% compared with other PS/org-MMT nanocomposites. Therefore, intercalation of the MMT particles in the polymer matrix is dependent on the accessibility of the monomers to the MMT galleries. It was found that the structural affinity be...