Accessibility of functional groups is an important concept in the mixing of polymers and involves factors such as chain connectivity, steric shielding, etc., all of which tend to limit the number of interchain contacts formed. Infrared spectroscopy is well suited to study functional group accessibility in carefully selected miscible hydrogen bonded polymer blend systems, because the fraction of interchain hydrogen bonded groups can be measured quantitatively. Such measurements have been made on blends consisting of a wide range of carbonyl containing (co)polymers with a 2,3-dimethylbutadiene-stat-4-vinylphenol containing 24 wt% 4-vinylphenol. Evidence has been obtained for decreasing accessibility of the carbonyl groups of the poly(n-alkyl methacrylate)s due to steric shielding from bulky side groups. Conversely, when these groups are spaced further apart in an ethylene-stat-vinyl acetate or ethylene-stat-methyl methacrylate copolymer chain, they become much more accessible. The effect of functional group accessibility on the scaling and transferability of self- and interassociation equilibrium constants is discussed, together with ramifications in terms of the prediction of miscibility windows and maps for hydrogen bonded polymer blends.