Dynamics of self-healing supramolecular guanine-modified poly(n-butyl methacrylate-co-hydroxyethyl methacrylate) copolymers

Abstract

Self-healing is a nature-inspired characteristic that is imparted in synthetic polymeric materials through the integration of reversible supramolecular bonds following different design concepts. Generally, the dynamics of supramolecular bonds regulates timescale of the self-healing process, specifically in polymeric systems with a homogeneous morphology. Herein, we explore the utility of guanine as a hydrogen bonding group to construct supramolecular polymeric systems based on poly (n-butyl methacrylate). For this purpose, we follow a three-step reaction approach, including a living radical copolymerization, deprotection of the functional comonomer, and grafting of the guanine group. The microstructure of obtained samples is assessed at each step by a combination of 1H NMR, FTIR, and GPC, and the homogeneity of morphologies is realized from the lack of secondary thermal transitions in DSC thermograms. To discover scaling concepts that govern such supramolecular materials, we systematically vary the structural parameters, including the chain length and the fraction of associative groups, and investigate their responses to the oscillatory shear deformation. The relaxation dynamics becomes significantly slower upon the introduction of transient bonds, which gets even more hindered when the chain length or the fraction of supramolecular groups are increased, following the scaling laws derived from the sticky reptation mechanism. Moreover, despite rheological measurements reveal that the network recovery after large deformations is not immediate, samples could completely heal a macroscopic scratch at 40 °C within 24 h, which is promising for the development of self-healing adhesives and coatings.