ABSTRACTS: Three poly(methyl methacrylates) (PMMA) with a racemic fraction ranging from 0.25 to 0.91 have been adsorbed from a chloroform solution on γ-alumina and studied by diffuse reflectance infrared spectroscopy (DRIFT) and solid-state 13C NMR spectroscopy. From DRIFT spectra, it is seen that the fraction of carbonyl groups bonded to the surface goes from 0.29 for s-PMMA to 0.41 for i-PMMA, but there is a larger amount of s-PMMA retained on the surface (at any given solution concentration). NMR spectroscopy indicates, from shifts of the methylene and α-methyl carbon peaks (due to the γ-gauche effect), that the adsorption is accompanied by changes in conformation, with an increase in the number of trans conformers, particularly with i-PMMA. These results indicate that s-PMMA adsorbs on γ-alumina in a brush-like configuration, with a relatively small number of groups attached to the surface, and tails and loops sticking out of the surface, whereas i-PMMA adsorbs in a sheet-like configuration, with a greater number of interacting groups. In both cases, the adsorption is accompanied with an increase in the number of trans conformers as compared to the bulk conformation.
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Grohens et al. (1999) studied this question.
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