Complicated Effects of Intermolecular Interaction and Chain Rigidity on the Glass Formation of Acrylic Networks

The knowledge of molecular dynamics induced by noncovalent bonding is important for the fabrication of high-performance polymeric materials. However, little attention is paid to the segmental dynamics triggered by the π–π stacking interactions and fluorinated polar interactions. Here, the complicated effects of rigidity and intermolecular interaction on the dynamic fragility m and glass transition temperature T_g are systematically investigated in acrylic networks. It is found that fluorinated structures have minor effects on m and T_g due to their relatively weak intermolecular interaction strength, whereas m increases with the growth of T_g after the introduction of rigid aromatic structures. In contrast, the further addition of hindered phenols or metallic ions leads to an increased T_g while m is reduced. Based on the generalized entropy theory (GET) of glass formation, it can be concluded that polymers with rigid structures but weak interaction strength tend to be fragile due to the almost constant cohesive energy densities. Although the hydrogen bonding and ionic interactions act as transient cross-linkers, the cohesive energy densities also increase because of their high polarities, thus leading to decreased fragilities. These results not only help further clarify the relationship between structures and dynamics on glass formation but also provide fundamental experimental benefits for verifying the predictions of GET and molecular dynamic simulations of glass-forming polymer materials.