Unravelling the Mechanism of Viscoelasticity in Linear and Pendant Polymers with Phase Separated Dynamic Bonds

Incorporation of dynamic bonds within polymer structure enables properties such as self-healing and recyclability. These dynamic bonds, referred to as stickers, can form clusters by phase-segregation from the polymer matrix. These systems exhibit interesting viscoelastic properties with an unusually high and extremely long rubbery plateau. Understanding how viscoelastic properties of these materials are controlled by the hierarchical structure is crucial for engineering of materials for various future applications. Here we studied such systems made from telechelic polydimethylsiloxane chains, as well as pendant functionalized chains by employing a broad range of experimental techniques. We demonstrate that formation of a percolated network of interfacial layers surrounding clusters enhances mechanical modulus in these systems, whereas stickers hopping between the clusters results in terminal flow. Analysis also reveals that the concentration of stickers plays the critical role in viscoelastic properties of these materials, while specific placement of the stickers (chain ends or along the chain) only impacts the behavior on time scale between pulling the sticker out of the cluster and terminal relaxation. From our results, we formulate a general scenario describing viscoelastic properties of polymers with phase-separated dynamic bonds, including the role of architecture. This understanding will foster development of recyclable materials with tunable rheological properties.