Structure Property Relationships for Polymers Bearing Reversibly Associating Side-groups

The objective of this research is to establish structure-property relationships for macromolecules bearing reversibly associating side-groups. In previous studies we demonstrated shape-memory behavior for elastomer networks bearing strong ureidopyrimidinone (UPy) hydrogen-bonding side-groups. However, relationships between the underlying viscoelastic behavior and side-group features such as hydrogen bond strength, structure, the presence of a permanent network and distance of the binding group from the macromolecular chain are not well established. Further, while numerous studies focus on the associative behavior of polymers in solution, few have examined their bulk behavior. To address this need, copolymers bearing weak (H ~ 30kJ/mol) or strong hydrogen (H ~ 70kJ/mol) bonding side-groups (HBSGs) were copolymerized with a low glass transition (Tg) polymer backbone into linear and network polymers. For polymers bearing weak HBSGs the temperature dependence of viscosity could be attributed to the elevation of Tg alone whereas the rheological behavior of strong HBSG polymers could be attributed to side-group association. To explain our results, a “stateof-ease” model was developed that assumes continuous mechanical equilibrium between applied stress and the stresses arising from a permanent network and a second network that continuously reforms. The model is able to predict various rheological responses for UPy containing polymers such as dynamic mechanical and shape-memory behavior. The influence of micro-environment can also influence viscoelastic behavior. To assess the ability of a strong HBSG to dimerize within water swollen environments the swelling and