Hydrogen Bonding-Induced Alleviation of Topological Constraints in Acrylic Polymers Mixed with Small Molecules

Intermolecular hydrogen bonds (inter-HBs) typically act as transient cross-linkers and can enhance the intermolecular interactions. Herein, we report a counterintuitive scenario that interchain constraints of polyacrylates are alleviated by adding hindered phenols capable of forming strong inter-HB interactions with the host polymer, even if a small molecule-bridged inter-HB network apparently increases the glass transition temperature (Tg) of the hybrids. The less-constrained segmental dynamics is confirmed enthalpically by the enhanced dynamic homogeneity (i.e., an increase in nonlinearity parameter x and stretching exponential parameter β) of α-relaxation together with a remarkable increase in the physical aging rate at (Tg – 10) K. Further results clarified that x and β values are primarily governed by the strength of inter-HB interactions (Δυi), and a stronger Δυi results in a larger x or β value. The present work provides solid experimental evidence and new molecular-level insights for the less-constrained segmental dynamics in such HB-driven hybrids in terms of the balanced flexibility between side groups and the backbone, the reduction of energy barriers hindering the cooperative motions, and the alleviation of long-chain connectivity.