Two different molecular weights of poly(methyl methacrylate) (PMMA) and PMMA containing polyhedral oligomeric silsesquioxane (PMMA-POSS) homopolymers have been prepared via the atom transfer radical polymerization (ATRP) technique. The miscibility and specific interaction behaviors of PMMA-POSS and PMMA with phenolic resin were investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). FTIR results reveal that at least three competing equilibriums are present in the phenolic/PMMA-POSS blend: self-association of phenolic (hydroxyl-hydroxyl), hydroxyl-siloxane interassociation between phenolic and POSS, and hydroxyl-carbonyl interassociation between phenolic and PMMA. Among these blends, single and higher T(g)s of these phenolic/PMMA-POSS blends were observed than the corresponding phenolic/PMMA blends at same composition, revealing that a stronger interassociation interaction of hydroxyl-siloxane than the hydroxyl-carbonyl interaction. Furthermore, we also found the screening effect in phenolic/LPMMA-POSS blends that tends to significantly decrease the hydrogen bond formation of the hydroxyl-carbonyl interassociation.