Self-Healable, Stretchable, and Super-Soft Bottlebrush Polyester Elastomers for Highly Sensitive Flexible Sensors

Abstract

While much effort has been devoted to the creation of super-soft elastomers, there is a dearth of research aimed at self-healable and super-soft renewable elastomers. Herein, self-healing and super-soft renewable elastomers are developed based on bottlebrush architecture design and dynamic associative transesterification. The bottlebrush polymer precursors are generated by ring-opening metathesis polymerization (ROMP) of the norbornene-terminated macromonomer poly(ε-caprolactone-co-l-lactide) (PCLLA) (NB-PCLLA). After introducing alkyne groups onto the end of PCLLA side chains, the bottlebrush polymers are cross-linked to achieve elastomer networks via a UV-induced “click” thiol-yne reaction between the terminal alkyne groups and the dithiothreitol (DTT) additive. The resulting materials exhibit a shear modulus as low as 17 kPa, high stretchability with breaking strains as large as 315%, and a self-healing efficiency of 95.6% at an elevated temperature of 80 °C. Taking the super-softness advantage, flexible sensor devices are assembled based on the prepared elastomer, which are highly sensitive to deformation with a gauge factor of 0.347. This work demonstrates that high-performance biodegradable materials with unique properties that conventional linear polymers impossibly possess can be easily constructed by molecular architecture design using bottlebrush polymers as building blocks.

Self-Healing and Adhesive Supersoft Materials Derived from Dynamically Cross-Linked Bottlebrush Polymers for Flexible Sensors

“…Integration of alkene protons of the end NB moiety and the methylene protons neighboring to the ester group in P n BA segments was used to determine the degree of polymerization, and the value is about 20. Subsequent polymerization of P n BA via “grafting-through” ROMP provided the bottlebrush polymer precursor NB-P n BA-Br. , As shown in Figure B,C, the complete disappearance of the characteristic signals of alkene protons of NB terminal groups and SEC trace obviously shifting toward the higher molecular region as compared with the NB-P n BA-Br precursor indicate the successful fabrication of PNB-P n BA-Br.…”

“…As depicted in Figure A, the storage modulus ( G ′) of all these samples significantly is higher than their loss modulus ( G ″) in the plateau region, where sweeping amplitude remains below 50%. To assess the cross-linking densities, we quantified the normalized residual thickness (NRT) of the bottlebrush polymeric materials following the reported paper. , A higher NRT indicates a denser polymer network, with an NRT of 100% signifying complete cross-linking. The efficient thiol-bromo “click” reaction facilitated the achievement of high NRT values for both Brush-NM and Brush-DM, at 93.6 and 91.2%, respectively, confirming the successful formation of covalently cross-linked networks.…”

“…The bottlebrush polymer PNB-P n BA was synthesized via the ROMP method. , In a nitrogen atmosphere, macromonomer (PNB-P n BA-Br) (13.26 g, 1.93 mmol) was dissolved in 30 mL of dichloromethane (DCM), resulting in a 25 wt % macromonomer concentration. Simultaneously, G 2 (15 mg, 0.018 mmol) was dissolved in 1 mL of DCM in a scintillation vial and then added to the above solution.…”

“…Bottlebrush polymers with densely grafted side chains have an extended backbone resulting from the repulsion between the side chains. – As compared with their linear analogues, one unique attribute of bottlebrush polymers is their significantly suppressed chain entanglements in the networks. – Thus, lightly cross-linking bottlebrush polymers provide a promising avenue for achieving the solvent-free supersoft materials. , Progress has been made in the development of bottlebrush polymer-based high-performance materials, especially those with self-healing capability, which can repeatedly repair mechanical damages and restore their functionality, resulting in the enhanced durability of the materials with prolonged service lifetime. – However, the preparation process of dynamically cross-linked bottlebrush polymers mostly involves the tedious functional end-group transformation of side chains and/or synthesis of small molecular cross-linkers. , Meanwhile, the resultant materials usually fulfill the self-healing behavior under elevated temperature, thereby limiting their applications in practice. , It should be further noted that the bioelectronic devices need to have direct contact with the human skin for effective signal transduction. – To the best of our knowledge, few of literature bottlebrush polymer-based supersoft materials possess adhesive capability and adhesive tapes or binding bandages are needed to fix the fabricated wearable sensors onto the human skin. , Apart from consideration of simplifying the operation process, it is also difficult for them to perfectly detect microstrains and feeble physiological signals . Therefore, it still remains a challenge to integrate the combination of excellent self-healing capability and adhesiveness into one bottlebrush polymer-based supersoft material, which is critical for the development of next-generation flexible electronic devices with high-quality and stable electrophysiological recordings.…”

Strain-Stiffening, Self-Healing, and Low-Hysteresis Physically Dual-Cross-Linked Hydrogels Derived from Two Mechanically Distinct Hydrogen Bonds

“…49 Most importantly, this hydrogel exhibited the intriguing state-independent property, that is, the relative resistance changes only rely on the external strain and are not affected by the deformation state. 15,50 The hysteresis loop of the resistance−strain curve was almost negligible, and the resistance in the stretching process (R s ) was equal to the value in the releasing process (R r ). On the contrary, various reported hydrogels presented state-dependent characteristics, leading to poor sensing accuracy and limiting their application in human motion sensing (as illustrated in Figure 5D).…”