How Dynamic Bond results in the unique viscoelastic behavior of the associating polymers

Associating polymer is a special kind of polymer possessing transient reversible bonds in addition to the conventional covalent bonds. The reversible bonds provide unique dynamics and fascinating viscoelastic properties, resulting in attractive applications for these polymers, such as self-healing and shape memory materials. Despite many years of studies, the understanding of dynamics of polymers with reversible bonds, especially on molecular level, is still in the rudimentary stage, preventing the rational design of the potential novel functional materials based on associating polymers. In this dissertation, we provide a detailed and quantitative understanding of the dynamics and viscoelastic properties of associating polymers. The functional groups form both binary association and microphase separation. For the associating polymer with binary association, the bond lifetime renormalization model was experimentally tested on telechelic associating polymers with PDMS and PPG backbone, different chain length and different H-bonding functional groups, unravelling the mechanism of how bond dissociation results in the network rearrangement in such system. For associating polymers forming microphase separation, the microphase separated structure was characterized through X-ray scattering. In addition, a layer of polymer segments with restricted mobility was found at the interface of the microphase separated clusters and the polymer matrix through the dielectric measurements. The layer plays a critical role in mechanical reinforcement of the associating polymers with microphase separation. In addition, we unraveled the mechanism of how network rearrangement happens in associating polymers. Finally, a general vi molecular picture of stress relaxation mechanism in such associating polymer system was proposed. The microscopic understanding of the dynamics and viscoelastic behavior of associating polymers is instructive for rational design of novel functional polymeric materials, i.e, how to control viscoelasticity by tuning the structure and position of the functional groups in such materials. In addition, the research can be essential for the understanding of the dynamics of general soft matter, and even biological materials in which dynamic bonds play an important role.