Preparation of cross-linked ultrathin films based on layer-by-layer assembly of polymers

Ultrathin cross-linked polymer films were prepared by means of two different assembly techniques. As one of the two approaches, alternate adsorption of poly(allylamine hydrochloride) (PAH) and glutaraldehyde, terephthalaldehyde, and valeraldehyde was studied. Cross-linked polymer layers regularly grow via condensation of glutaraldehyde with the adjacent polymer layers, as confirmed by UV, FT-IR, and XPS measurements. The resulting multilayer film has a nano-porous structure with density of 0.65 g/cm³, and unit thickness of ca. 45 angstroms. The hydrophobic interaction at the PAH surface modified with the aldehyde group appears to be crucial to the successful assembly. In the second approach, multilayer films were similarly prepared from PAH and (methyl vinyl ether)-alt-(monomethyl maleate) copolymer (MMC). Linear film growth is achieved only in limited pH ranges, pH 7-8 for MMC and pH 6 for PAH, to give unit bilayer (PAH+MMC) thickness of 26-33 angstroms. Upon heating in vacuo, more than half of the amino groups in PAH form the imide linkage with monomethyl maleate units of MMC. The cross-linked ultrathin polymer films prepared on a microporous polymer support display selective permeation of methyl orange against myoglobin.