Effect of the repeated unit length of guest polymers on the molecular motion of polymer blends within a miscible window

The effect of the repeated unit length on the substantially increasing molecular motion and entropy change (−TΔSm) of polymer blends was investigated with solid-state 13C 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 13C NMR spectra was weakened because of the reduction in the cross-polarization efficiency in highly mobile samples. The glass-transition 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 (−TΔSm) 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. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 679–686, 2003