Aluminosilicate Nanocomposite Materials. Poly(ethylene glycol)−Kaolinite Intercalates

This paper reports the first example of the direct intercalation of an organic polymer into the interlamellar spaces of kaolinite. Poly(ethylene glycols) (PEG 3400 and PEG 1000) were intercalated into kaolinite by displacing dimethyl sulfoxide (DMSO) from the DMSO−kaolinite intercalate (Kao−DMSO). This was done directly from the polymer melt at temperatures between 150 and 200 °C. XRD showed that the intercalated oxyethylene units were arranged in flattened monolayer arrangements, such that the interlayer expansion was 4.0 Å. Infrared analysis of Kao−PEG 3400 supported the assignment of a trans conformation to at least a portion of the (O−CH2CH2−O) groups of the PEG polymer while 13C CP and DD/MAS NMR indicated that the polymer was intercalated intact and was more constrained in the interlamellar spaces of kaolinite than it was in its bulk form. TGA/DSC analysis revealed that the complete decomposition of the organic component of the oxyethylene-based organokaolinites did not occur until greater than 1000 °C. The formulas were estimated to be Al2Si2O5(OH)4(−OCH2CH2−)0.77(DMSO)0.27 and Al2Si2O5(OH)4(−OCH2CH2−)0.99(DMSO)0.17, respectively for the cases of PEG 1000 and PEG 3400. The calculated formulas for both samples are consistent with one unit of oxyethylene or DMSO per Al2Si2O5(OH)4 unit. Given the known density of hydroxyl groups on the aluminol surface, a polymer conformation where ethyleneoxy groups repeat every 2.8 Å with the oxygens all facing toward the hydroxyl surface should be favored. It is suggested that the polymer adopts a conformation TG2T'G2', in which the repeat unit per ethyleneoxy group is 2.94 Å, and all the oxygens are lined up on one side of the chain. The tension resulting from the imperfect fit could be relaxed by a certain degree of trans conformations.