The effect of the repeated unit length on the substantially increasing molecular motion and entropy change (-TDeltaS(m)) of polymer blends was investigated with solid-state C-13 NMR and differential scanning calorimetry within a miscible window. The hydrogen-bonding strength, from the formation of the phenolic-polyester interaction, was not high enough to overcome the breaking-off of the self-association of the phenolic. With respect to the increasing repeated unit length, the polyester resonance intensity of the solid-state C-13 NMR spectra was weakened because of the reduction in the cross-polarization efficiency in highly mobile samples. The glasstransition temperature of the blend and the proton spin-lattice relaxation time from NMR experiments were also reduced. The effect of the reduced hydrogen-bonding strength on blending brought about a tendency of higher entropy (-TDeltaS(m)) and higher molecular mobility of the blend. Accordingly, poly(decamethylene adipate) possessed the longest repeated unit length and exhibited the most mobile one in this phenolic/polyester blend family. The molecular segmental motion and entropy progressively increased while the repeated unit length of the guest polymers increased within a miscible window. (C) 2003 Wiley Periodicals, Inc.