Lamellar polysilicate nanocomposite materials: Intercalation of polyethylene glycols into protonated magadiite

Abstract

This paper reports the direct intercalation of organic polymers into the interlamellar spaces of the layered polysilicate magadiite. Poly(ethylene glycols) (PEG 3400 and PEG 1000) were intercalated into acidified magadiite (H-magadiite) by displacing a dipolar aprotic solvent (e.g., dimethylsulfoxide (DMSO)) from the H-magadiite – DMSO intercalate. This was done directly from the polymer melt at 155°C. The polysilicid acid (H-magadiite) was obtained by HCl titration of the sodic form of magadiite obtained by hydrothermal synthesis. Dipolar aprotic solvents (dimethylsulfoxide, N-methylformamide, and hexamethylphosphorictriamide) were intercalated in the interlamellar spaces of H-magadiite. PEG 3400 and PEG 1000 were then intercalated by dispersing the H-magadiite intercalates in a large excess of the polymers heated above their fusion temperature, without any solvent. The resulting polymer intercalated H-magadiite nanocomposites were isolated and purified and were shown by chemical analysis to have chemical formulae of H2Si14O29(-OCH2CH2-)3.1 and H2Si14O29(-OCH2CH2-)2.9, respectively, in agreement with a structure in which one unit cell of magadiite corresponds to three oxyethylene units. The dipolar aprotic solvents have been completely removed from the interlamellar spaces. 13C NMR dipolar diphasing techniques show that the polymer chains in the interlamellar spaces of H-magadiite are more constrained than in the bulk polymer. 29Si NMR spectra show that the structure of magadiite is unchanged by the two processes of intercalation. The polymer intercalates are characterized by interlamellar spacings of 4.6 and 4.4 Å, as determined by XRD. These values correspond to a flattened arrangement of the polymer chains in the interlamellar spaces. This is also in agreement with DSC data, which demonstrate that the polymer chains are no longer in the aggregation state characteristic of the bulk polymer.Key words: lamellar polysilicates, polyethylene glycols, nanocomposite materials, polymer intercalation, magadiite.