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43609-GB7
Spectroscopic Studies of Adsorbed Vinyl Polymers
We have been investigating the conformation of polymers adsorbed onto inorganic substrates, primarily silica (SiO2). These two years of support have provided research opportunities for four undergraduates (three at William Paterson University; one at Fairleigh Dickinson University) and one graduate student (at Fairleigh Dickinson, who was continuing from his undergraduate research at Paterson). Unfortunately, continuity has been an issue, because the principal investigator had to change institutions twice during the grant period. However, in spite of these challenges, we have acquired enough data for several presentations, and anticipate that a number of publications will result from this work. Furthermore, because of this support, the Brandolini's laboratory at Ramapo College of New Jersey is already active, and will involve two undergraduates this year.
In summary, the main accomplishments over the past two years have been:
1. We have devised a method for estimating relative amounts of adsorbed polymer, and a curve-fitting scheme which separates an infrared absorbance band into two Gaussian components, corresponding to bound and unbound polymer-chain segments. Adsorption behavior is described by the fit parameters.
2. We have nearly completed a study of the adsorption of several poly(alkyl methacrylates) onto silica. By analyzing the infrared (IR) absorption of the pendant carbonyl, we find that both the size and shape of the pendant groups determine the conformation of the adsorbed polymer chain.
3. The observation reported last year, that oxygenated solvents inhibit the adsorption of polymethacrylates, has been confirmed for several different solvent types.
4. Originally, we had proposed to study adsorption of polystyrene, but this material does not appear to adsorb onto silica in any significant amount. Instead, we have started to investigate the adsorption of other carbonyl-containing polymers. This promises to be a very fruitful direction.
5. We have also begun to look at the adsorption of PMMA onto other supports, such as aluminum oxide, titanium oxide, calcium carbonate, clays, and polysaccharides. Poly(methyl methacrylate) only adsorbs onto some of these materials, indicating a lack of suitable interaction sites on some surfaces.
The relative amounts of polymer adsorbed onto silica can be determined by comparing the total area of the polymer carbonyl band to a nearby silica-related band. The bound and unbound polymer segments can be described by fitting the observed absorbance as two overlapping Gaussians. This procedure yields several fit parameters – peak positions, intensities, and widths – for each component. The peak shift (difference between the positions of the bound and unbound) and the component areas can be calculated.
This data analysis was applied to spectra of several poly(alkyl methacrylates) – methyl (PMMA), ethyl, propyl (n- and iso-), butyl (n-, sec-, iso-, and tert-), neopentyl, cyclohexyl, and 2,2,2-trifluoroethyl (PTFEMA). By far, PMMA and PTFEMA are the most strongly adsorbed. The behavior of PMMA is easily explained by the pendant group's small size, which allows for close approach. This is clearly not the case for PTFEMA; the fluorines likely facilitate adsorption in some way. There is surprisingly little variation among the other pendant groups. We have prepared samples and recorded spectra of polymethacrylates with other ester types (e.g., longer alkyls, aromatics, and halogenated aromatics). Lineshape analyses of these spectra are in progress.
Not surprisingly, we observe strong adsorption onto silica from other carbonyl-containing polymers, such as poly(vinyl ester)s, aliphatic polyesters, poly(vinyl ketone)s and cellulose esters. Curve-fitting analysis of these spectra is in progress. Interestingly, we observed that poly(vinyl methyl ketone), which is originally a white solid, turns yellow when adsorbed onto silica. This color change will be further studied.
Investigations into the effect of varying the support material have also been initiated. We find that PMMA adsorbs very differently onto diverse supports, such as oxides, carbonates, sulfates, phosphates, etc. PMMA does not appear to adhere to cellulose and related materials at all. An interesting extension of this work involves adsorption of polymethacrylates, poly(vinyl esters), and polyesters onto the components of concrete, to simulate polymer-concrete composites.
Solid-state NMR studies of these systems were originally proposed to be done during the summers, but that work could not be pursued as planned. During the summer of 2006, the Brandolini was not affiliated with an institution, and no students were interested in full—time work on this project in 2007.
The results obtained to date have been presented at several different venues. Undergraduate students have done both oral and poster presentations at local American Chemical Society meetings. Brandolini delivered a paper, with three student co-authors, at the 2006 Eastern Analytical Symposium. The latest developments will be presented by another student at an upcoming meeting of the Polymer Topical Group of the North Jersey ACS. Several papers will eventually result from this work, and students will be co-authors on all of them.
