Blends of poly(N-methyldodecano-12-lactam) PMDL with poly(4-vinyphenol) PVPh have been studied by the DSC and ATR FTIR methods. The difference in glass transition temperature T(g) between the components is 206 degrees C. A single composition-dependent T(g) suggests miscibility of the system, that is, homogeneity on the scale of about 10 nm. Fitting of the equation of Brostow et al. to the T(g) data indicates relatively strong specific interactions and high complexity of the system. The Schneider's equation applied separately to low-and high-PVPh regions provides good agreement with experiment; the calculated curves cross at the point of PVPh weight fraction 0.27. In the low-PVPh region, the analysis indicates weak interactions with predominance of segment homocontacts and strong involvement of conformational entropy. In the high-PVPh region, strong specific interactions predominate and entropic effects are suppressed. Composition dependences of the heat capacity difference at T(g) and the width of glass transition indicate strong interactions in the system and existence of certain heterogeneities on segmental level, respectively. According to ATR FTIR, hydrogen bonds between PVPh as proton donor and PMDL as proton acceptor induce miscibility in blends of higher PVPh content (above about 0.28 weight fraction). In low-PVPh blends, it is conformational entropy that enables intimate intermolecular mixing. Hydrogen bonds adopt several (distorted) geometries and are on average stronger than average hydrogen bonds formed in self-associating PVPh. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1031-1040, 2011