Posttransfer modification of preformed Langmuir-Blodgett films of poly(tert-butyl methacrylate) and poly(tert-butyl acrylate) by gaseous hydrochloric acid yields films with layered architecture of poly(methacrylic acid) and poly(acrylic acid), respectively. X-ray reflectivity and infrared spectroscopy confirm monolayer by monolayer transfer of the source polymers and their transformation to acid multilayer assemblies with retention of low surface roughnesses. The incorporation of cross-linking groups into the system offers the possibility for further chemical modification to produce ultrathin films of model networks desirable for bioadsorption studies and as hydrophilic spacing layers for tethered membranes.
By employment of a strategy of post-transfer modification, precursor Langmuir-Blodgett (LB) films of poly(tert-butyl methacrylate) (PtBMA) and poly(tert-butylacrylate) (PtBA) can be converted to poly-(methacrylic acid) (PMAA) and poly(acrylic acid) (PAA) through acid-catalyzed hydrolysis in the gas phase. X-ray reflectivity studies show that these films possess surface roughnesses and controllable thicknesses, which are consistent with the retention of the "two-dimensional" configuration of the precursor polymers at the air/water interface. On this basis, the PMAA and PAA films with presumable layered architecture can be obtained, even though PMAA and PAA are too hydrophilic to undergo direct LB-multilayer formation. A combination of infrared spectroscopy, contact angle measurements, and sorption experiments confirms the chemical transformation and increased hydrophilicity of the films. Using the same approach, gasphase reactions with organic amines convert the reactive carboxylic acid groups to their corresponding ammonium salts, thereby leading to the formation of polyelectrolyte LB films. When these films are heated to elevated temperatures, amide bonds are formed. The use of difunctional amines opens up the possibility to cross-link the PMAA or PAA films efficiently. Fourier transform infrared measurements and X-ray reflectivity studies clearly indicate the conversion from PtBMA or PtBA LB films to ultrathin, highly swellable network films.
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