Distinct Aggregation Behaviors and Rheological Responses of Two Terminally Functionalized Polyisoprenes with Different Quadruple Hydrogen Bonding Motifs

Abstract Though a series of studies have introduced non-covalent branched networks to enhance the properties of polyisoprene (PIP) based on structural mimic of natural rubber (NR), it is still a challenge to reveal the relationship between properties of modified PIP and the aggregation behaviors of end groups. Herein, two quadruple hydrogen bonding motifs 2-ureido-4-1[H]-pyrimidinones (UPy) and α-alanine tetrapeptide (4A) were introduced into into the end of model PIP polymers. Branched networks of terminal groups were prepared by self-assembly of quadruple hydrogen bonding motifs, which elucidated the key role of the terminal structures in the PIP chain. Previous work has demonstrated that the branched network intensifies the entanglement between polymer chains, thereby resulting in higher modulus and shear viscosity of the branched polymers compared to the linear polymers. Due to the stable aggregation of 4A, the mechanical properties of PIP-4A are superior to those of PIP-UPy. Rheological analysis and 2D FTIR spectroscopy collaboratively demonstrate that PIP-UPy and PIP-4A both exhibit two-step dissociation processes. These results expand our understanding on the role of the aggregation structures of PIP terminal and provide insight into the generic design of mechanically strong rubber.