Facile synthesis of self‐healing gel via magnetocaloric bottom‐ignited frontal polymerization

Abstract

A series of the self-healing gels facilely fabricated by VI (N-vinyl imidazole) and MAH-b-CD (b-cyclodextrin grafted vinyl carboxylic acid groups) via bottom-ignited frontal polymerization (BIFP) initiated by magnetocaloric effect. Once ignited the bottom phase, the heat upward propagates to generate the "front" in the upper phase. Then, no further energy is added to maintain the reaction and the whole polymerization process experiences within minutes. In this system, the dependence of frontal velocity and temperature, along with morphology, swelling capacity, mechanical property, and self-healing efficiency, on the preparation parameters is investigated. Interestingly, the gels show good swelling capacity in the organic solvent, comparatively almost no absorption in water. Moreover, the as-prepared gels exhibit excellent auto-healing properties without any external stimuli at ambient temperature. The healed sample possesses 97% recovery of its tensile strength after 8 h healing time, which relies largely on the host-guest interaction between VI and MAH-b-CD. The results demonstrate that FP can be utilized as an efficient and energy-saving method to synthesize self-healing supramolecular gels.

Frontal polymerization for smart intrinsic self‐healing hydrogels and its integration with microfluidics

“…However, we found hydrogel samples without β‐CD do not possess self‐healing behavior. This reveals polymer chains are not long enough for the formation of hydrogen bond autonomously by accessing each other across the welded interface, consistent to the reported literature . The healing process was accelerated from 12 to 1 h with the application of an external heat on the healing site.…”

“…As shown in Figure (c), after mechanically cutting the hydrogel into two pieces, we brought them into contact and pressed for about 30 s. Then, the hydrogels with β‐CD show intrinsic auto‐healing after 12 h at ambient temperature without the need of any external stimulus. Analogous to the reported literatures, a unique size‐shape fit relationship exists. An imidazole moiety of VI monomers is physically inserted and included inside the void of the host β‐CD macrocyclic molecule via non‐covalent inclusion to form an imidazole inclusion complex.…”

“…FP is a self‐propagating reaction mode converting monomers to polymers via a localized reaction zone. Since discovered by Chechilo et al, FP has been employed effectively for the synthesis of quantum dot (QD)‐polymer composites, stimuli‐responsive hydrogels, gradient materials, and high‐mechanical performance self‐healing gels . In the available literatures, FP is classified into thermal frontal polymerization (TFP), photo frontal polymerization (PFP), and isothermal frontal polymerization (IFP) .…”

“…Herein, we report TFP synthesis of β‐cyclodextrin/poly(vinylimidazole‐ co ‐N‐vinylcaprolactam‐ co ‐acrylic acid) (β‐CD/p(VI‐ co ‐NVCL‐ co ‐AA)) copolymers based on host‐guest supramolecular interaction, where economical and biocompatible β‐CD host monomers entrap VI guest monomers . Such host‐guest interaction endows the fabricated polymers with self‐healing ability.…”

Synthesis and Characterization of pH‐sensitive Poly(IA‐co‐AAc‐co‐AAm) Hydrogels via Frontal Polymerization

“…Besides, a large amount of works have been devoted to developing new functional materials via FP . Among these, Chen and his research workers employed FP technique to prepare a range of functional gel materials, for instance, as mircomaterial transportation conveyer gel, artificial tongue‐like sensing materials, optoelectronic devices, superabsorbent hydrogels, and amphiphilic gel . Importantly, the FP can be a technique exploitable to obtain materials that cannot be prepared by the classical method .…”