Enthalpy hysteresis (ΔH R ), an easily accessible quantity determined from a well-defined cooling and subsequent heating cycle of heat capacity curves, was recently reported to bear a proportional relationship with the α-related excess entropy of polymers at glass transition temperature( T g ). The kinetic fragility m of polymers was thus verified to link with thermodynamic parameters of T g •ΔC p /ΔH R , as predicted by the Adam−Gibbs equation. In this work, enthalpy hysteresis of poly(n-alkyl methacrylate)s was investigated systematically to clarify whether ΔH R is influenced by multifarious non-α-related contributions. The results showed that the ΔH R for higher poly(n-alkyl methacrylate)s is abnormally suppressed, as manifested by failure of the theoretic correlation between m and T g •ΔC p /ΔH R . The anomalous suppression appears non-related to the β JG relaxation but stems from nanophase separation of the alkyl sidechains. Once the PE-like nanophase is completely destroyed, either by increasing the steric hindrance of side groups or by introducing small molecule-bridged hydrogen bonds, ΔH R recovers, and the theoretic correlation between m and T g •ΔC p /ΔH R is re-established. Further experiments revealed that the abnormal ΔH R suppression occurs only when the periodicity of phase separation is comparable to the size of the cooperative rearrangement region of bulk α relaxation at T g . Accordingly, the deviation of m and T g •ΔC p /ΔH R correlations from the theoretic prediction must be related to the existence of two different but partly coupled glass transitions in higher poly(n-alkyl methacrylate)s. The extremely hindered and confined glass transition in the PE-like nanodomains is likely to cause the anomalous suppression of global enthalpy hysteresis.

In this work, metallic ions are introduced to polyacrylates to break the mutual limitation between damping peak width and height. It is found that all the ion-coordinated polymers exhibit two loss peaks. With the increase of concentration, coordination strength, and steric hindrance, the temperature gap between two damping peaks can be broadened significantly while the peak height is slightly decreased. We are surprised to find that the effective damping temperature region (peak height ≥0.3) for poly (butyl acrylate) ionomers with 100% neutralization and weak coordination strength can be more than 200 K. Moreover, the damping peak area also increases after the introduction of metallic ions. Our result provides a new strategy for developing novel damping materials with high performance.