Ring-and-Lock Interactions in Self-Healable Styrenic Copolymers

Abstract

Commodity copolymers offer many useful applications, and their durability is critical in maintaining desired functions and retaining sustainability. These studies show that primarily alternating styrene/n-butyl acrylate [p(Sty/nBA)] copolymers self-heal without external intervention when monomer molar ratios are within the 45:55–53:47 range. This behavior is attributed to the favorable interchain interactions between aliphatic nBA side groups being sandwiched by aromatic rings forming ring-and-lock associations driven by pi–sigma–pi (π–σ–π) interactions. Guided by molecular dynamics (MD) simulations combined with spectroscopic and thermomechanical analysis, the ring-and-lock interchain van der Waals forces between π orbitals of aromatic rings and sigma components of aliphatic side groups are responsible for self-healing. Despite the frequent occurrence of these interactions in biological systems (proteins, nucleic acids, lipids, and polysaccharides), these largely unexplored weak and ubiquitous molecular forces between the soft acid aliphatic and soft base aromatic electrons may be valuable assets in the development of polymeric materials with sustainable properties.

Dynamic Interfaces in Self-Healable Polymers

“…When plotted against the copolymer monomer molar ratio, the CED values exhibit a linear dependence that gradually increases with one component’s increasing molar fraction. However, near the self-healing copolymer composition, , the CED values reach maxima. This behavior usually occurs in a narrow compositional range for preferentially alternating/random copolymer topologies and is attributed to energetically favorable interchain forces.…”

“…The elevated cohesive-energy density (CED) stabilizes the vdW forces between adjacent copolymers. A similar strategy was utilized develop slef-healable poly­(styrene/ n -butyl acrylate) p­(Sty/nBA) copolymers, which also exhibit self-healing properties in relatively narrow monomer molar ratios . In this case, styrene’s electron-rich groups contributed to of pi-sigma-pi (π–σ–π) vdW interactions between aromatic rings and aliphatic side groups in driving favorable “ ring-and-lock ” associations facilitating self-healing (Figure b).…”

“…(a) Key-and-lock associations in self-healable p­(MMA/nBA) copolymer . (b) Ring-and-lock associations in self-healable p­(Sty/nBA) copolymer . (c) Graphical illustration of interchain vdW interactions between neighboring p­(MMA/nBA) copolymer chains containing 420 water molecules (H 2 O: MMA/nBA = 1:1) .…”

Macromolecular Postpolymerization of Siloxane Exchange to Assemble Multiple Siloxane Linkages

“…The possibilities of polymerization, and the variety of products that can be gained, are greatly increased when polymerization is carried out in a mixture of two or more monomers, for the copolymer chain can now contain arrangements of various monomer units. − Moreover, copolymerization brings flexibility to tailor polymer properties (such as Tg , surface energy, rheological properties, and so on) to meet the needs of a wide range of applications. − However, copolymerization is a more challenging research topic than homopolymerization, because it requires a comprehensive consideration of the relative polymerization activity of monomers, monomer feeding ratios, and dosing methods, and the distribution of monomers (random, block, or alternating) in the polymer chain. − Therefore, numerous efforts have been devoted to the development of catalysts and polymerization methods to surmount the varied polymerization activity of the monomers and to achieve the controllability of the copolymerization, thus modulating the properties of the synthesized polymers. , Such challenges are also encountered with polysiloxanes, − a polymer formed out of silicon and oxygen atoms alternately arranged in the backbone and organic groups attached to the silicon atoms, which serve as a critically important material bridge between inorganic and organic polymers.…”

The Importance of Bulk Viscoelastic Properties in “Self-Healing” of Acrylate-Based Copolymer Materials

“…Recently, an intriguing approach to realize van der Waals-based dynamic-bond-type interactions was proposed in which the deliberate placing of pendant groups in copolymers gives rise to a microstructure with increased CED via “key-and-lock” or “ring-and-lock” interactions. − In 2018, Urban and co-workers observed that copolymers based on n -butyl acrylate (BA) and methyl methacrylate (MMA) with about equimolar composition (50–55 mol % BA), synthesized via atom transfer radical polymerization (ATRP), featured self-healing . Assuming a random sequence of copolymers, the authors proposed “key-and-lock” interactions between alternating BA/MMA repeats to raise the CED and promote “self-heal ability”.…”