The fraction of directly-bound carbonyls of surface-adsorbed poly(methyl methacrylate) (PMMA) was determined using transmission Fourier-transform infrared (FTIR) spectroscopy. The small size of the silica used allowed these measurements to be made directly in the transmission mode from dried casts deposited on KBr salt plates. Curve fitting of the carbonyl-stretching region allowed the estimation of both the relative amounts and also the relative ratio of the absorption coefficients for the free and bound carbonyls. The bound-carbonyl fractions were found to vary smoothly from 0.3 to 0.1 for adsorbed amounts from 0.5 to 1.8 mg of PMMA/m 2 . The bound fractions depended primarily on the adsorbed amount of polymer. Only very small, perhaps even negligible, direct effects of the solvent composition (toluene vs. benzene/acetonitrile) or molecular mass (32 to 420 kg/mol) were observed.

The behavior of relatively monodisperse adsorbed poly(methyl methacrylate) (PMMA) samples, from 19 to 587 kDa on silica, was studied using modulated differential scanning calorimetry and FTIR. On untreated CabOSil silica, the glass transition temperatures (Tgs) were higher (by around 30 °C), and the transitions were significantly broader (by a factor of 5–6) than those for the corresponding bulk samples. While the Tgs for the bulk polymers showed the expected dependence on molecular mass, the polymers on untreated silica showed little dependence, i.e., at the same adsorbed amounts, the glass transitions were very similar. The FTIR spectra of the adsorbed PMMA (on untreated silica) showed the presence of at least two resonances, one for the bound (hydrogen bonded to surface silanols) and another for free carbonyls. Fitting of the spectra allowed the estimation of the bound fractions of carbonyls that were dependent on the adsorbed amount, but not molecular mass. On CabOSil treated with hexamethyldisilizane (HMDS), the adsorbed PMMA exhibited glass transition behavior with little molecular‐mass dependence; the Tgs for the different PMMA samples were very similar to those of the high‐molecular mass bulk polymer, but with additional broadening of about a factor of 2. FTIR spectra for the PMMA samples on the treated silica did not show significant amounts of any of the hydrogen‐bonded carbonyl groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 649–658, 2008