The fraction of directly-bound carbonyls of surface-adsorbed poly(methyl methaerylate) (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 us. benzene/acetonitrile) or molecular mass (32 to 420 kg/mol) were observed. (c) 2006 Wiley Periodicals, Inc.