Hydrogen bonding-induced anomalous dynamics of polyacrylates mixed with small molecules

Abstract

Enhancing the intermolecular interaction generally leads to an increased topological constraint, thus resulting in a decreased non-exponential parameter βKWW of segmental cooperative rearrangement during glass transition. In this report, we illustrate a counterintuitive case when the inter-chain interaction is strengthened by small molecule-bridged hydrogen bonds. It was found that hindered phenols capable of forming double hydrogen bonds per molecule can effectively narrow the dielectric loss peak of poly(ethyl acrylate) and the βKWW increases monotonically with the intermolecular hydrogen-bonding strength even if the small molecule (AO300) has a glass transition temperature Tg much higher than the host polymer. Further experiments revealed an increased Tg but a decreased dynamic fragility m, accompanied by gradual merging of the suppressed secondary relaxation toward the primary peak, demonstrating that introduction of AO300-bridged hydrogen bonds appears to enhance the intermolecular interaction, but actually reduces the inter-chain cooperativity. This anomalous dynamics stemming from hydrogen bonding was rationalized in terms of small molecule-alleviated chain connectivity, flexibility of bulky pendant groups and changes in enthalpic contributions to segmental cooperative rearrangement.