β<sub>fast</sub> Relaxation Governs the Damping Stability of Acrylic Polymer/Hindered Phenol Hybrids
Gaopeng Shi, Yuanbiao Liu, Guozhang Wu
Abstract
Hindered phenols remarkably enhance the sound attenuation and vibration damping of acrylic polymers. However, this novel damping material suffers from gradual degradation during long-term use because of potential self-aggregation and crystallization of small molecules. In this work, the effects of small molecule size, hydrogen bonding strength, and mobility of the pendant group of acrylic matrices on the long-term damping stability were investigated. The results were correlated to the hierarchical relaxation of acrylic mixtures. We were surprised by the findings that the damping degradation dynamics appears to be governed by βfast relaxation instead of α and/or βJG relaxation of the polymer matrix. Further experiments revealed that the long-distance diffusion of small molecules to self-aggregation and subsequent crystallization is regulated by βJG relaxation, but dissociation of the intermolecular hydrogen bonding between the hydroxyl group of phenols and the carboxyl group of acrylates during physical aging plays the decisive role in damping degradation. We supposed that the small molecule’s fluctuation-induced dissociation of hydrogen bonding is limited within a sub-Å amplitude and therefore couples with the cage-breaking motion of βfast relaxation. These results clarify the mechanism of small-molecule-enhanced damping and provide a strategy for the rapid evaluation of the service life of novel damping materials and a thermodynamic criterion k0 for the future design of small molecules and long-term stable damping materials.