Reversible adhesive compositions

Abstract

The present application disclosed adhesives and polymer networks curable under mild conditions and reversibly debondable under selected stimuli.

Description

[0001] REVERSIBLE ADHESIVE COMPOSITIONS TECHNOLOGICAL FIELD

[0002] The present invention relates to adhesive compositions and crosslinked polymer networks that are curable under mild conditions and reversibly de-bondable under selected stimuli.

[0003] BACKGROUND

[0004] From consumer electronics to aerospace, adhesives play an essential role in modern society. While the 2024 global adhesives market reached 92.6 billion dollars, or 122 billion dollars, including sealants, its reliance on irreversible and unrecyclable thermoset systems presents technical constraints, environmental and economic challenges, including material waste, and limitation of recycling processes.

[0005] Addressing these challenges, researchers have explored the dynamic and reversible chemistry, known as covalent adaptable networks (CANs) or vitrimers, to develop debonding-on-demand and recyclable adhesives, focusing on thermal -responsive bonds such as disulfides, P-hydroxy esters, or Diels-Alder or photo-responsive bonds like azobenzene, spiropyran, or [2 + 2] cycloaddition reactions. One example of such debondable adhesive has recently been introduced by Apple Inc. in their iPhone® 16, facilitating simple battery removal in case of a phone malfunction.

[0006] Current approaches for CANs-based applications can be categorized into two: The first involves distinct chemistries for bonding and debonding, resulting in high-performance adhesives, but often characterized by complex synthesis and reduced sustainability due to the adhesives' inability to completely dissociate from their substrates. The second approach utilizes a single bonding-debonding mechanism that typically requires extreme conditions, such as elevated temperatures or specialized activation techniques. These two approaches highlight the need for solutions balancing sustainability with performance.

[0007] SUMMARY OF THE INVENTION

[0008] Traditional adhesives rely upon irreversible covalent networks that, once cured, cannot be reshaped, reprocessed or removed without damaging the substrate. Such constraints severely limit their use in advanced applications including reusableelectronics, biomedical devices, textile assembly, robotics, composite manufacture, underwater repair, and ophthalmic or dental interfaces. The irreversible nature of conventional adhesives also impedes recyclability and the circular use of materials.

[0009] Dynamic covalent chemistry provides an emerging strategy for developing adhesives that combine the mechanical stability of conventional thermosets with the reconfigurability of thermoplastics. Within this field, bond-forming units that are capable of existing in a closed cyclic state and in an open bond-exchange state, such as disulfide-based systems, are particularly attractive because the bond forming unit can undergo exchange reactions under relatively mild physical or chemical stimuli. Lipoic acid has served as a model compound for such chemistry due to its five-membered cyclic disulfide ring.

[0010] The present invention expands the concept, recognizing that any five-, six- or seven-membered ring structure containing a bond-forming units such as an internal disulfide bond can participate in reversible polymer networks when equipped with appropriate reactive substituents. This allows tuning of mechanical properties, curing rates, optical characteristics, hydrophobicity, hydrophilicity, and thermal or microwave responsiveness. The present invention also recognizes that adhesive performance depends not only on the presence of dynamic units such as disulfide units but also on the architecture in which such units are embedded. A key insight is that bonding strength, reversibility and reprocessability are enhanced when the bond-forming unit is a cyclic disulfide unit that is incorporated into a carbon network that comprises at least two such bonds or rings and are further connected through a multifunctional core. This invention therefore enables a wide range of adhesive materials which properties can be precisely engineered by combining bond-forming units, such as disulfide-based ring motifs with multi-alcohol, multi -amine, multi -acid, multi-thiol or other multifunctional backbones.

[0011] The result is a new category of adhesives that cure rapidly, bond strongly, and yet can be debonded or reshaped when desired, in absence of a solvent, or a medium such as an organic solvent medium. These adhesives provide reversible adhesion to diverse substrates, including ceramics, metals, polymers, hydrogels, composite materials, glass, biological tissues, underwater surfaces and temperature-sensitive materials. They present a general and robust solution to the limitations of irreversible adhesives and meet the growing demand for materials that support repair, reconfiguration, recycling and sustainable manufacturing.Thus, in a general aspect of the invention, the invention concerns a material comprising a plurality of bond-forming units (such as S-S containing units) that are each capable of existing in a closed cyclic state and in an open bond-exchange state, wherein the bond-forming units undergo ring opening and form inter-unit linkages that create a cohesive and a substrate-adhering network (1st condition), and wherein the inter-unit linkages dissociate and the bond-forming units revert to their closed cyclic state (2nd condition), thereby reducing or eliminating adhesion; wherein the material is configured so that transitions between the closed cyclic state and the open bond-exchange state are reversible under different applied stimuli.

[0012] As exemplified herein, the material responds to an externally applied condition by transitioning from the closed cyclic state to the open bond-exchange state. This transition may be induced by a wide range of stimuli, such as thermal inputs, electromagnetic or microwave activation, irradiation with light of selected wavelengths, mechanical force, or exposure to chemical environments that promote ring opening and inter-unit coupling. The removal of the original stimulus or application of an alternative stimulus causes the material to return to the closed cyclic state, and this shift stabilizes the material and diminishes or eliminates its adhesion to the substrates.

[0013] The reversible transitions between ring opening and ring closing can endow the material with a self-healing behavior, such that disruptions or microfractures in the adhesive network can be repaired as the bond-forming units repeatedly cycle between the cyclic and open states. This self-healing effect may occur under ambient conditions or may be activated through controlled stimulation, depending on the design of the adhesive system.

[0014] The strength of the adhesive network and its cohesive integrity may be tailored by adjusting the relative concentration or spatial distribution of the at least two bond-forming units within the material. The adhesive can thus be engineered to function as a soft, compliant layer or as a rigid structural bonding interface. The network-forming process in the open bond-exchange state may involve the generation of short-lived intermediate species (such as S radicals or other S active species) that are capable of selectively linking with neighboring bond-forming units, thereby increasing the connectivity and cohesive properties of the material. Conditions such as reduced temperature, reduced electromagnetic flux, or altered chemical environment can favor formation of the closed cyclic state. Under such conditions, the adhesive network loses its inter-unit linkages, andthe material becomes non-adhesive or weakly adhesive, allowing clean release from a substrate without mechanical damage.

[0015] The material of the invention is an adhesive material specifically designed to reversibly bond to substrates. By inducing the open bond-exchange state, the material forms a network that conforms to and binds the substrate surface. When the so-called second condition above is applied, the inter-unit linkages dissociate, the closed cyclic structures reform, and the adhesive layer releases from the substrate. This behavior allows the adhesive to be used for temporary assembly, reversible fixtures, device repair, or substrate recycling.

[0016] The bond-forming units (e.g., S-S units) may be arranged along a polymer backbone, or generally along a carbon-based material, distributed as pendant moieties, incorporated into crosslink or chemical junctions, or introduced as part of an oligomeric system. Regardless of their arrangement, activation of the open bond-exchange state promotes formation of linkages between units located on different polymer chains or branches of the carbon-based material or network segments. These inter-chain linkages enhance the connectivity and strength of the material in its bonded state.

[0017] The reversible nature of the material allows selective debonding from substrates by applying a stimulus that triggers reversion to the closed cyclic state. This stimulus may be applied in a spatially controlled manner, allowing only selected regions of the adhesive layer to release while others remain bonded. This selective control supports advanced manufacturing workflows in which precise bonding and debonding patterns are desirable. The reversible transitions may be performed repeatedly without significant degradation of adhesive performance, thereby allowing the adhesive to be recycled. By cycling between the open and closed states, the material can be reused in multiple bonding and debonding cycles, supporting environmentally sustainable manufacturing practices. In some cases, the conditions that induce the transition occur at relatively low temperatures, enabling reversible adhesion to temperature-sensitive materials, electronic components, or biological tissues.

[0018] Additionally, the material may be engineered to allow temporal control of adhesion state transitions. By selecting conditions that trigger rapid ring opening or ring closing, the material may be programmed to bond or debond within specific time windows, enabling timed release or staged assembly processes.In some embodiments, the so-called first condition above comprises application of a first stimulus. In some embodiments, the first stimulus is application of energy selected from thermal, electromagnetic, photonic, mechanical, or chemical energy. In some embodiments, the first stimulus is application of a chemical condition such as changing pH, ionic strength, presence of a salt and others.

[0019] In some embodiments, the first stimulus may be a temperature between 70 and 130 °C; light irradiation at wavelengths above 365 or between 365 and 850 nm (e.g., when including a photoinitiator, such as a Noirish type I or type II); ultrasound at the range of 10-20 MHz, acidic conditions at pH values below 6 (e.g., including incorporation and use of latent acids such as photo-acid generators); and / or treatment with solvents that include high valence ions like calcium.

[0020] In some embodiments, the first stimulus comprises a temperature between 70 and 130 °C.

[0021] In some embodiments, the first stimulus comprises a temperature between 70 and 130 °C, with a radical thermo-initiator, such as a peroxide complex, an azo complex, or a persulphate salt. Non-limiting examples may include Lauroyl peroxide, Cumene hydroperoxide, Dicumyl peroxide, 2,2'-Azobis(2-methylpropionitrile)(AIBN), 1,1'-Azobis(cyclohexanecarbonitrile) (ACBN), ammonium persulfate, or sodium persulfate (SPS).

[0022] In some embodiments, the first stimulus comprises a temperature between 70 and 130 °C with a latent acid.

[0023] In some embodiments, the first stimulus comprises irradiation with a light source having a wavelength between 365 and 405 nm.

[0024] In some embodiments, the first stimulus comprises irradiation with a light source having a wavelength between 365 and 850 nm, in presence of a radical photoinitiator of Norrish type I, Noirish type II, or both.

[0025] Norrish type I photoinitiators may be selected from Trimethylbenzoyl Diphenylphosphine Oxide (TPO), Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (Phenylbis(2,4,6-trimethylbenzoyl)phosphinoxide, Irgacure 819), Bis(r|5-cyclopentadienyl)-bis(2,6-difluoro-3-(lH-pyrrol-l-yl)phenyl) titanium (Irgacure 784).

[0026] Norrish type II photoinitiators may be selected from photosensitizers, H-donors, which may optionally comprise an oxidizing agent serving also as a photoacid generator.Photosensitizers may be selected from 2-isopropylthioxanthone (ITX), camphorquinone, indocyanine green, acriflavine, riboflavin, zinc tetraphenyl porphyrin (ZnTPP), phthalocyanine complexes like zinc phthalocyanine, cupper phthalocyanine, or tin phthalocyanine, and dyes and pigments.

[0027] H-donors may be any tertiary amines, alcohols, or thiols, such as, but not limited to, triethylamine, triethanolamine, ethyl 4-(dimethylamino)benzoate (EDB).

[0028] Oxidizing agents may be photoacid generators such as diphenyliodonium nitrate, 4-Isopropyl-4'-methyldiphenyliodonium tetrakis(pentafhiorophenyl)borate (Speedcure 939), diphenyliodonium hexafluorophosphate, and Triarylsulfonium hexafluoroantimonate salts.

[0029] In some embodiments, the first stimulus comprises irradiation with a light source having a wavelength between 365 and 850 nm, optionally with a photoacid generator, with or without a photosensitizer, that are present with the adhesive material, as further disclosed herein.

[0030] In some embodiments, the so-called second condition comprises application of a second stimulus, being different than the first stimulus. In some embodiments, the second stimulus is application of energy selected from thermal, electromagnetic, photonic, mechanical, or chemical energy, each being different than that used for the first condition.

[0031] In some embodiments, the second stimulus may be a temperature between 150 and 200 °C; light irradiation at wavelengths below or equal to 365 nm or microwave radiation; a pH above 8, in aqueous solutions, in amine containing solvents such as dimethylformamide (DMF), or by using latent bases, such as, but not limited to, photobase generators or thermal latent bases; and / or ultrasound above 20MHz.

[0032] In some embodiments, the second stimulus is microwave radiation at 72 W, 2.45 GHz.

[0033] In some embodiments, the bond-forming units undergo ring opening and form inter-unit linkages that create a cohesive and a substrate-adhering network upon application of a stimulus selected from:

[0034] -a temperature between 70 and 130 °C;

[0035] -light irradiation with a light source having a wavelength above 365 nm;

[0036] -light irradiation with a light source having a wavelength between 365 and 850 nm, optionally in presence of a photoinitiator, such as a Norrish type I or a Norrish type II, or both;-ultrasound at the range of 10-20 MHz;

[0037] -acidic conditions at pH values below 6;

[0038] -a latent acid, such as, but not limited to, photo-acids generators, and / or -treatment with solvents including high valence ions.

[0039] In some embodiments, ring opening and formation of a cohesive adhering network is achievable by application a so-called first stimulus being or comprising irradiation with a light source having a wavelength between 365 and 850 nm.

[0040] In some embodiments, the debonding, wherein the inter-unit linkages dissociate and bond-forming units revert to their closed cyclic state occurs upon stimulation with a stimulus selected from:

[0041] -a temperature between 150 and 200 °C;

[0042] -light irradiation with light at a wavelength below or equal to 365 nm;

[0043] -microwave radiation at 72 W, 2.45 GHz;

[0044] -a pH above 8, in aqueous solutions, in amine containing solvents like dimethylformamide (DMF), or by using a latent base, including, but not limited to, photobase generators; and / or

[0045] -ultrasound above 20MHz.

[0046] In some embodiments, the debonding can be achievable by application of micro wave radiation at 72 W, 2.45 GHz.

[0047] In some embodiments, debonding may by achievable by changing the pH of the adhesive, by formation of acid or base by a trigger (such as heat, irradiation, or another stimulus) using a latent acid or base, such as, but not limited to, photoacids, photobases, hindered amines, or hindered acids.

[0048] In some embodiments, the material is capable of reversible bonding to a substrate by inducing the first stimulus to promote network formation at the adhesive-substrate interface and subsequently inducing the second stimulus to release the substrate, wherein the first and second stimuli are different.

[0049] In some embodiments, the cohesion of the material is tunable by adjusting the relative proportion or density of bond-forming units within the compound.

[0050] In some embodiments, the material is reprocessable by cycle-induced dissociation and re-formation of inter-unit linkages.

[0051] In some embodiments, the material transitions between a solid-like or gel-like state and a fluid-like or low-viscosity state.In some cases, the selection of the first and second stimulus may be based, at least in some part, on the nature of the substrate(s) to be associated. For example, where the substrates or one of the substrates is transparent, light irradiation or thermal conditions may be used. In cases where, for example, the substrate(s) is non-transparent, heat or ultrasound may be used.

[0052] The bond-forming units are typically disulfide (S-S) bonds that can exist in a closed cyclic state and in an open state, and which are capable of dissociating and reforming, thereby transitioning between an adhesive bond-exchanging state and a nonadhesive state. Thus, in some embodiments, the material comprising at least two ring structures each having an internal disulfide (S-S) bond, wherein the at least two ring structures are associated with a carbon framework, and are configured to undergo, in response to a first stimulus, ring opening and formation of new disulfide linkages between different ring structures, and further configured to undergo, in response to a second stimulus, reversion to the respective ring structures each having the internal S-S bond.

[0053] In another aspect there is thus provided a material comprising at least two ring structures, each having an internal disulfide (S-S) bond, wherein the at least two ring structures are associated with a carbon framework, and are configured to undergo, in response to a first stimulus, ring opening and formation of new disulfide linkages between different ring structures, and further configured to undergo, in response to a second stimulus, reversion to the respective ring structures each having the internal S-S bond.

[0054] The “ring structure having an internal disulfide (S-S) bond’ is a cyclic disulfide ring structure of five, six or seven atoms in total, two of which are sulfur atoms forming an internal S-S bond. These ring structures may be saturated or comprise an internal double bond. The ring structures may be fused, bridged or substituted. Each ring structure may be functionalized with at least one reactive substituent capable of engaging in bond formation with an atom of the carbon framework. Suitable substituents include hydroxyl, thiol, carboxyl, amine, amide, ester, thiocarboxylate, epoxide, halogen, acrylate, methacrylate, maleimide, vinyl or isocyanate groups, among others. In some cases, the ring structure is directly bonded to an atom of the carbon framework.

[0055]

[0056] The ring structure may be of the form , wherein n is an integer between 1 and 3, inclusive, and R is one or more ring substituents, one of which connecting the ring structure to the carbon framework.

[0057] The one or more substitutions on the ring (defined by one or more R groups) may be selected from halogen, Ci-Cioalkylene, C2-Cioalkyenylen, C2-Cioalkynylene, -ORi, -SRi, -NR1R2, -CN, -SCN, -NO2, -C(=O)Ri, -CO2R1, -C(=O)NRIR2, -OC(=O)Ri, -OCO2R1, -OC(=O)NRIR2, -NRIC(=O)RI, -NR1CO2R1, and -NRIC(=O)NRIR2, wherein each occurrence of Ri may be same or different and each occurrence of R2 may be same or different. Each occurrence of Ri and R2, independently, may be same or different and may be selected from -OH, -SH, -C(=O)OH, -NH2, -NHC(=O)H, ester, -C(=S)OH, halogen, acrylate, methacrylate, maleimide, vinyl or isocyanate groups.

[0058] Each occurrence of Ri and R2, independently, may be same or different and may be selected from hydrogen, Ci-Cealkyl, -OH, -SH, -NH2, -CN, -SCN, -NO2, -C(=O)H, -CO2H, -C(=O)NH2, -OC(=O)H, -OCO2H, -OC(=O)NH2, -NHC(=O)H, -NHCO2H, and -NHC(=O)NH2.

[0059] In some embodiments, the ring structure is selected from:

[0060]

[0061] more ring substituents, as defined and selected herein.

[0062] In some embodiments, in each of the structures, R is a single substituent that connects the ring to a carbon framework.

[0063] In some embodiments, the ring structure is saturated.

[0064] In some embodiments, the ring structure is fused to another ring structure, which

[0065] may or may not be aromatic. Examples of suitable fused systems include

[0066]

[0067]

[0068]

[0069] wherein each of R and n, independently, is as defined herein and wherein m is between 0 and 3.

[0070] In some embodiments, R is a single substituent provided at position 3 or 4 of the

[0071] ring structure:

[0072]

[0073] some embodiments, R is an atom or a group of atoms, as selected, associating the ring structure to the carbon framework.

[0074] In some embodiments, R is a substituted Ci-Cioalkylene, a substituted C2- Cioalkyenylen, or a substituted C2-Cioalkynylene. In some embodiments, R is a Ci-Cioalkylene substituted by a group capable of chemically associating with an atom of a carbon framework. The specific substitution may be selected to enable interaction with a native atom or substituent on the carbon framework used. Thus, in some embodiments, the substituent may be selected from halogen, -OH, -SH, -C(=O)OH, -NH2, -NHC(=O)H, ester, -C(=S)OH, halogen, acrylate, methacrylate, maleimide, vinyl or isocyanate groups.

[0075] In some embodiments, R is a Ci-Cioalkylene substituted by a group selected from halogen, OH, -SH, -C(=O)OH, -NH2, or -NHC(=O)H, to thereby generate an ether, thioether an ester, an amine or an amide bond with the carbon framework.

[0076] As used herein, the Ci-Cioalkylene group is a straight-chain or branched saturated divalent hydrocarbon group having between 1 and 10 carbon atoms, bonded at one end to the 1,2-dithiolane group and at the other end to an atom of the carbon framework.

[0077] The ''carbon framework refers to any carbon-containing molecular group, residue, moiety, scaffold, orbackbone comprising one, two or more carbon-based chains, branches, substituents, or structural segments, wherein each such chain, branch, or segment is capable of associating with, connecting to, or being bonded to, directly or indirectly, a bond-forming unit or a ring structure comprising a disulfide bond unit. The carbon framework may be linear, branched, cyclic, polycyclic, fused, or a combination thereof, and may include saturated, unsaturated, aromatic, or alicyclic carbon structures. Unless otherwise indicated, a carbon framework may also contain heteroatoms (e.g., O, N, S) provided that the framework remains predominantly carbon-based and may optionally include one or more functional groups that facilitate or modify the associationwith the ring structure. The carbon framework thus provides multiple points of attachment, connection, or linkage for the ring structures, allowing formation of di-, or poly-functional conjugates, crosslinked structures, or higher-order assemblies.

[0078] The carbon framework may be selected amongst polyhydric alcohol frameworks (polyols), substituted branched alkane or alkylene frameworks, substituted multifunctional alkyl and cycloalkyl cores, substituted aromatic or polycyclic carbon frameworks, dendrimer core units, carbohydrate frameworks and polymers, each of which having two or more groups or functionalities rendering possible association to two or more 1,2-dithiolane ring structures. In some cases, the substitution of the functionality is selected from halogen, -OH, -SH, -C(=O)OH, -NH2, -NHC(=O)H, ester, -C(=S)OH, halogen, acrylate, methacrylate, maleimide, vinyl or isocyanate groups, or any group or atom derived from the aforementioned, for example -O- derived from -OH, -NH- derived from an amine group, and a carboxylate derived from -C(=O)OH.

[0079] In some embodiments, the carbon framework is based on, or derived from, or having a carbon-skeleton and substituents of a material selected from glycerol, trimethylolpropane (TMP), trimethylol ethane (TME), pentaglycerol, sorbitol, mannitol, xylitol, inositol, pentaerythritol, ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), hexamethylenediamine (HMDA), putrescine, cadaverine, spermidine, spermine, tris (2-aminoethyl)amine, N,N-bis(3 -aminopropyl) methylamine, Jeffamine, diethylenetriamine-based hyperbranched polyamines, poly(allylamine), polyethylenimine (PEI), citric acid, tricarballylic acid, trimellitic acid (1,2,4-benzene tricarboxylic acid), hemimellitic acid (1,2,3-benzene tricarboxylic acid), trimesic acid (1,3,5-benzene tricarboxylic acid), ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), malic acid, tartaric acid, citramalic acid, isocitric acid, quinic acid, polyethyleneimine, triethylenetetraamine, ethoxylated bisphenol A, tetraglycidyl diaminodiphenyl methane (TGDDM), meta phenylenediamine (MPDA), polyethylene glycol, 1 ,3,5-triglycidyl isocyanurate, novolac, hydroquinone and others.

[0080] In some embodiments, the carbon framework is based on a polyol, such as but not limited to pentaerythritol.

[0081] In some embodiments, the material of the invention is of the general structure (I), or (II):

[0082]

[0083] wherein in each (I) and (II), independently:

[0084] n is 1, 2 or 3;

[0085] each of Xi and X2, independent, is -O-, -S-, -NH-, -N, -CH2-, or -CH;

[0086] each of R3 and R4, independently,

[0087]

[0088] defined here (including fused and substituted forms thereof);

[0089] or each of R3 and R4, independently, is selected from substituted or unsubstituted Ci-Cioalkylene, as defined herein, -OH, -SH, -C(=O)OH, -NH2, -NHC(=O)H, ester, -C(=S)OH, halogen, -ORi, -SRi, -NR1R2, -CN, -SCN, -NO2, -C(=O)Ri, -CO2R1, -C(=O)NRIR2, -OC(=O)RI, -OCO2R1, -OC(=O)NRIR2, -NRIC(=O)RI, -NR1CO2R1, and -NRIC(=0)NRIR2, wherein

[0090] each of Ri and R2, independently, is as defined herein; and

[0091] each of R5 and Rs, independently, is a chemical bond or group associating Xi or X2 to the ring structure, wherein Xi and Rs together, or X2 and R5 together, independently, form an ether bond, an ester bond, an amide bond, or a C-C single, double or triple bond.

[0092] In some embodiments, Xi and Rs together, and / or X2 and R5 together, form an ester bond.

[0093] In some embodiments of a material of structure (I) or (II), one or each of X5 and Xe is -O-.

[0094] In some embodiments of a material of structure (I) or (II), n is 1.

[0095] In some embodiments of a material of structure (I) or (II), n is 1 and each of X5 and Xe is -O-.

[0096] In some embodiments of a material of structure (II), Xi and Rs together, or X2 and R5 together, independently, form an ester bond.In some embodiments, the material of the invention has the structure (II), wherein

[0097] one or both

[0098]

[0099] defined here.

[0100] R

[0101]

[0102] In some embodiments of all materials of the invention, in the moiety , R is a Ci-Cioalkylene, wherein the alkylene may have between 1 and 3, or 1 and 4, or 1 and 5, or 1 and 6, or 1 and 7, or 1 and 8, or 1 and 9, or 2 and 10, or 2 and 9, or 2 and 8, or 2 and 7, or 2 and 6, or 2 and 5, or 2 and 4, or 3 and 10, or 3 and 9, or 3 and 8, or 3 and 7, or 3 and 6, or 3 and 5, or 4 and 10, or 4 and 9, or 4 and 8, or 4 and 7, or 4 and 6, or 5 and 10, or 5 and 9, or 5 and 8, or 5 and 7, or 6 and 10, or 6 and 9, or 6 and 8, or 7 and 10, or 7 and 9, or 8 and 10 carbon atoms.

[0103] In some embodiments, the alkylene may have between 2 and 6 carbon atoms. In some embodiments, R is Ci-Cioalkylene substituted by a group selected from -OH, -SH, -C(=O)OH, -NH2, -NHC(=O)H, -C(=S)OH, and halogen.

[0104] In some embodiments, a material of the invention is of structure (II), wherein Xi and Re taken together, and X? and R5 taken together, are each independently -Ci-Cioalkylene-C(=0)0-, wherein the alkylene has between 1 and 3, or 1 and 4, or 1 and 5, or 1 and 6, or 1 and 7, or 1 and 8, or 1 and 9, or 2 and 10, or 2 and 9, or 2 and 8, or 2 and 7, or 2 and 6, or 2 and 5, or 2 and 4, or 3 and 10, or 3 and 9, or 3 and 8, or 3 and 7, or 3 and 6, or 3 and 5, or 4 and 10, or 4 and 9, or 4 and 8, or 4 and 7, or 4 and 6, or 5 and 10, or 5 and 9, or 5 and 8, or 5 and 7, or 6 and 10, or 6 and 9, or 6 and 8, or 7 and 10, or 7 and 9, or 8 and 10 carbon atoms.

[0105] In some embodiments, the alkylene has between 2 and 6 carbon atoms.

[0106] In some embodiments, a material of the invention is of structure (II), wherein Xi and Re taken together, and X2and R5 taken together, are each independently -C2-C5alkylene-C(=O)O-.

[0107] In some embodiments, a material of the invention is of structure (II), wherein Xi and Re taken together, and X2and R5 taken together, are each independently -Ci-Cioalkylene-C(=0)0-, and wherein each n is 1.

[0108] In some embodiments, a material of the invention is of structure (III):

[0109]

[0110] of structure (IV): (IV), wherein n is 1, 2 or 3, z is an integer between zero and 8, and wherein •'vw designates a bond of connectivity to the oxygen atom(s) of structure (III).

[0111] In some embodiments, two of X3, X4, X5 and Xe, independently, are moieties of structure (IV), which may be same or different.

[0112] In some embodiments, three of X3, X4, X5 and Xe, independently, are moieties of structure (IV), which may be same or different.

[0113] In some embodiments, each of X3, X4, X5 and Xe, independently, is a moiety of structure (IV), which may be same or different.

[0114] In some embodiments, two, or three or all of X3, X4, X5 and Xe are moieties of structure (IV), wherein n is i and z is 2.

[0115] In some embodiments, a material of the invention is of structure (V), (VI) and

[0116]

[0117] selected herein;

[0118]

[0119] (VII).

[0120] The invention further provides a material being one or more of:

[0121]

[0122] wherein n is between 1 and 100;

[0123]

[0124] , wherein n is between 1 and 100

[0125]

[0126] independently, is between 1 and 30;

[0127]

[0128]

[0129] As may be understood from the discussion herein, materials of the invention are adhesive materials which properties can be precisely engineered by selecting the bondforming units as well as the carbon backbone or framework to which the units may be associated. This results in adhesives that cure rapidly, bond strongly, and yet can be debonded or reshaped when desired. These adhesives provide reversible adhesion to diverse substrates, including metals, polymers, hydrogels, composite materials, glass, biological tissues, underwater surfaces and temperature-sensitive materials. The substrate may alsobe a transparent or a non-transparent object, and is not necessarily flat or substantially 2-dimentional. In some cases, the substrates to be associated may be three dimensional.

[0130] The invention thus provides a solvent-free adhesive, the adhesive being a material accoridng to the invention.

[0131] The term “solvent free ' refers to an adhesive or an adhesive composition that is substantially free of volatile organic solvents or other added liquid carriers which primary function is to dissolve, dilute, or disperse the adhesive components and which are expected to evaporate during or after application. A solvent-free adhesive is one which comprises no intentionally added organic solvents, and not more than trace or incidental amounts of solvent (typically less than 1% by weight, and often 0.1% or less) arising from residuals, impurities, or manufacturing byproducts. Unless otherwise indicated, “solvent-free” excludes both volatile organic solvents, such as alcohols, ketones, esters, aromatics, ethers, hydrocarbons, chlorinated solvents, and others, and aqueous carriers.

[0132] Materials and adhesives of the invention, by virtue of their unique combination of mechanical robustness and controlled reconfigurability, are suitable for use across a wide range of industrial, biomedical, electronic, robotic, structural, and consumer applications.

[0133] The adhesives may be utilized in assemblies requiring periodic disassembly, rework, or component replacement, including consumer electronics, wearable devices, sensing modules, printed circuit board substructures, and housings for portable equipment. The adhesive provides thermoset-level mechanical and thermal stability during device operation, while allowing reversible bonding through localized heating, light activation, or other triggers, thereby enabling repair, refurbishment, or recycling of electronic components without destructive mechanical force.

[0134] In mechanical assemblies, such as robotic systems, including soft-robotics actuators, end-effectors, sensing skins, and modular robotic components, the adhesive offers strong structural integrity under dynamic load and repeated bending, while permitting reconfiguration of joints, flexible housings, and embedded electronics. The ability to reprocess or reshape the adhesive network allows robots to be modified, repaired, or retooled without discarding existing parts. In soft robots, the adhesive may secure elastomeric components while maintaining compliance and stretchability.

[0135] The adhesives are further useful in medical and biomedical systems requiring secure yet reconfigurable interfaces. In implantable devices, prosthetics, wearable biosensors, wound-closure systems, or drug-delivery platforms, the adhesive canmaintain strong, durable adhesion within physiological environments, while permitting controlled debonding or repositioning to accommodate tissue healing, device adjustment, patient comfort, or scheduled replacement. In temporary implants or surgical tools, the adhesive may be configured to soften or reflow under clinically acceptable conditions, enabling atraumatic removal.

[0136] In ophthalmic devices, such as contact lens assemblies, ocular patches, therapeutic inserts, or interfaces the adhesive may be used for sensor-bearing lenses, where a secure, biocompatible, yet repositionable bond is beneficial. The adhesive may permit gentle removal or reactivation under mild temperature conditions compatible with ocular tissues. Similarly, in dental applications, the adhesives may be used in provisional restorations, orthodontic brackets, aligner attachments, prosthetic interfaces, coating systems, or oral devices. They provide strong adhesion in the oral environment while enabling clean debonding or reconfiguration without mechanical trauma to enamel or dentin. Their ability to self-heal or reflow may reduce microcrack formation or leakage at bonded interfaces.

[0137] The adhesives may also be used in the manufacture of textiles, garments, and composite fabrics, particularly where flexible, wash-resistant, and thermally stable bonding is desired. The adhesive enables bonding of fibers, seams, electronic textile components, or layered fabric structures while preserving softness and flexibility. Because the adhesive can be reworked or debonded, it facilitates repair of garments, repositioning of components, modular fashion systems, or integration of e-textile elements without damaging the underlying fabric.

[0138] The adhesives may serve as matrix binders, interlaminar coupling agents, or structural adhesives in the production of fiber-reinforced composites, laminates, and sandwich structures. They provide the mechanical performance of crosslinked thermosetting resins, enabling load-bearing composite structures, while their dynamic bonding capability allows for post-forming, reshaping, crack-healing, or repair of composite parts. This is beneficial in aerospace, automotive, marine, and industrial composite applications where maintenance access is limited and component longevity is critical.

[0139] Uniquely, adhesives of the invention may be formulated for wet-surface adhesion, enabling their use in underwater construction, pipe repair, marine structures, submerged equipment, and emergency sealing applications. Once applied, the adhesive behaves as adurable thermoset, resisting hydrolysis, pressure, and temperature fluctuation. When maintenance is required, the reversible bonding chemistry allows in-situ reconfiguration, patching, or removal, even in environments where conventional adhesives fail or become permanently set.

[0140] In some embodiments, the adhesive may be used in electronics, advanced packaging, electric vehicle batteries, automotive and transportation, and in consumer goods.

[0141] In some embodiments, the adhesive may be used in wafer thinning (a process necessary for Wafer-Level Packaging to achieve thinner and more compact chips).

[0142] In some embodiments, the adhesive may be used in micro-electro-mechanical Systems (MEMS) and sensors are increasingly used in loT devices, wearables, and automotive systems.

[0143] In some embodiments, the adhesive may be used in display panels, such as OLED display panels.

[0144] In some embodiments, the adhesive may be used in smartphone devices such in smartphone screens binding and battery bonding.

[0145] In some embodiments, the adhesive may be used in bonding batteries in a variety of devices.

[0146] In some embodiments, the adhesive may be used in Cell-to-Module (C2M) bonding.

[0147] In some embodiments, the adhesive may be used in Module-to-Pack (M2P) Bonding.

[0148] In some embodiments, the adhesive may be used in Thermal Interface Materials (TIMs).

[0149] In some embodiments, the adhesive may be used in Structural Bonding in Pack Assembly Used in pack casing, lid sealing, or tray bonding.

[0150] The solvent-free adhesive may be presented or provided in a variety of forms, including without limitation a liquid form, a gel form, a film form, a tape form (e.g., as a single-sided tape, a double-sided tape or a transfer tape), a coating form, or a solid resin form.

[0151] The invention further provides an adhesive system comprising:-a solvent-free adhesive comprising or being a material accoridng to the invention (the material having two or more ring structures, each containing a disulfide bond, as defined herein);

[0152] -a first stimulant as defined herein (e.g., being selected from heat, light, electromagnetic radiation, mechanical force, redox activator, or a chemical catalyst), the first stimulant being effective to open the two or more ring structures (thereby generate an adhesive framework comprising reactive sulfide or thiolate groups capable of forming intermolecular disulfide linkages); and

[0153] -optionally a second stimulant distinct from the first stimulant, and as defined herein (e.g., the second stimulant being effective to promote re-closure of the ring structures and thereby reverse or reduce disulfide crosslinking, enabling debonding or weakening of the adhesive network).

[0154] The invention further provides a method of bonding two substrates, the method comprising applying a solvent-free adhesive accoridng to the invention between the substrates, applying a first stimulus to induce formation of an adhesive network, and optionally applying a second stimulus to cause reversion of the formation of the network and debond the adhesive.

[0155] The application of the solvent-free adhesive may be to the complete surface of the substrate, or to any part thereof. In some cases, the adhesive may be patterned on the surface, wherein patterning may be achievable by a variety of application methodologies and for a variety of purposes.

[0156] Also provided is an adhesive kit comprising:

[0157] -a first container containing a solvent-free adhesive accoridng to the invention; -a second container holding a first stimulant effective to induce formation of an adhesive network; and

[0158] -optionally a third container holding a second stimulant effective to debond the adhesive;

[0159] wherein the kit is configured to permit end-user formation and subsequent release of an adhesive bond, and

[0160] instructions for applying the adhesive to a substrate, activating the adhesive bond using the first stimulant, and releasing the bond using the second stimulant.

[0161] In some embodiments, the kit comprises the adhesive as a liquid, a gel, a film, a tape, a coating, or a solid resin.In some embodiments, the kit is packaged for reversible bonding of surf aces / sub states as disclosed herein, e.g., metals, polymers, ceramics, glass, composites, wood, or electronic components.

[0162] In invention further provides a method of bonding two substrates, the method comprising placing an adhesive according to the invention between the two substrates and applying a stimulus to cause formation of an adhesive framework holding the two substrates to each other.

[0163] In some embodiments, the method comprises contacting the adhesive with at least one of the substrates, applying a first stimulus selected from heat, light, electromagnetic radiation, mechanical force, chemical activator, or a combination thereof, thereby opening the ring structure to generate an adhesive framework comprising reactive sulfide or thiolate groups and allowing or promoting intermolecular bond formation between neighboring sulfide or thiolate groups, thereby forming intermolecular disulfide linkages that crosslink the adhesive framework, producing an adhesive network that bonds the at least one surface with another and optionally, releasing or debonding the adhesive by applying a second stimulus that induces re-closure of the ring structures, thereby reversing at least a portion of the disulfide crosslinks and reducing adhesion between the surfaces.

[0164] The invention further provides an article comprising two or more substrates bonded by an adhesive accoridng to the invention, wherein the substrates can be separated, repositioned, or rebonded by activating dynamic bond exchange within the adhesive.

[0165] In some embodiments, the adhesive permits repeated cycles of reconfiguration without significant loss of mechanical strength.

[0166] In some embodiments, the substrates are selected as herein.

[0167] The invention further provides:

[0168] A material comprising at least two ring structures each having an internal disulfide (S-S) bond, wherein the at least two ring structures are associated with a carbon framework, and are configured to undergo, in response to a first stimulus, ring opening and formation of new disulfide linkages between different ring structures, and further configured to undergo, in response to a second stimulus, reversion to the respective ring structures each having the internal S-S bond.In some embodiments of any material according to the invention, the material has a surface bonding or adhesive properties when forming new disulfide linkages between different ring structures, and debonding or non-adhesive properties when in the ring structures having the internal S-S bond.

[0169] In some embodiments of any material according to the invention, the ring structure having an internal disulfide (S-S) bond is a cyclic disulfide ring structure of five, six or seven atoms.

[0170] In some embodiments of any material according to the invention, the ring structure is saturated or comprises an internal double bond.

[0171] In some embodiments of any material according to the invention, the ring structure is fused, bridged or substituted.

[0172] In some embodiments of any material according to the invention, the ring structure is directly bonded to an atom of the carbon framework.

[0173] In some embodiments of any material according to the invention, the ring R

[0174]

[0175] structure is a of the form , wherein n is an integer between 1 and 3, inclusive, and R is one or more ring substituents, one of which connecting the ring structure to the carbon framework.

[0176] In some embodiments of any material according to the invention, the one or more ring substitutions being selected from halogen, Cl-ClOalkylene, C2-C10alkyenylen, C2-ClOalkynylene, -OR1, -SRI, -NR1R2, -CN, -SCN, -NO2, -C(=O)R1, -C02R1, -C(=O)NR1R2, -OC(=O)R1, -0C02R1, -OC(=O)NR1R2, -NR1C(=O)R1, -NR1C02R1, and -NR1C(=O)NR1R2, wherein each occurrence of R1 is same or different and each occurrence of R2 is same or different.

[0177] In some embodiments of any material according to the invention, each occurrence of R1 and R2, independently, is same or different and is selected from hydrogen, Cl-C6alkyl, -OH, -SH, -NH2, -CN, -SCN, -NO2, -C(=O)H, -C02H, -C(=0)NH2, -OC(=O)H, -0C02H, -0C(=0)NH2, -NHC(=O)H, -NHC02H, and -NHC(=0)NH2.

[0178] In some embodiments of any material according to the invention, the ring structure is selected from:

[0179]

[0180] , wherein R is one or more ring substituents, as defined herein.

[0181] In some embodiments of any material according to the invention, the ring structure is saturated.

[0182] In some embodiments of any material according to the invention, the ring structure is fused to another ring structure, which is optionally aromatic.

[0183] In some embodiments of any material according to the invention, the ring

[0184] structure i

[0185]

[0186] wherein R is as defined herein.

[0187] In some embodiments of any material according to the invention, the ring structure is directly associated to the carbon framework via group R.

[0188] In some embodiments of any material according to the invention, R is a Cl-ClOalkylene substituted by a group selected from halogen, OH, -SH, -C(=O)OH, -NH2, and -NHC(=0)H, said group generating an ether, a thioether, an ester, an amine or an amide bond with the carbon framework.

[0189] In some embodiments of any material according to the invention, the carbon framework is a carbon-containing molecular group, residue, moiety, scaffold, or backbone comprising two or more carbon-based chains, branches, substituents, or structural segments, each being capable of associating, directly or indirectly, to the ring structure.

[0190] In some embodiments of any material according to the invention, the carbon framework is a linear, branched, cyclic, polycyclic, fused, or a combination thereof.

[0191] In some embodiments of any material according to the invention, the carbon framework is selected amongst polyhydric alcohol frameworks (polyols), substituted branched alkane or alkylene frameworks, substituted multi-functional alkyl and cycloalkyl cores, substituted aromatic or polycyclic carbon frameworks, dendrimer core units, carbohydrate frameworks and polymers, each of which having two or more groups or functionalities rendering possible association to two or more ring structures.

[0192] In some embodiments of any material according to the invention, the carbon framework is based on a material selected from glycerol, trimethylolpropane (TMP),trimethylolethane (TME), pentaglycerol, sorbitol, mannitol, xylitol, inositol, pentaerythritol, ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), hexamethylenediamine (HMDA), putrescine, cadaverine, spermidine, spermine, tris (2-aminoethyl)amine, N,N-bis(3 -aminopropyl) methylamine, Jeffamine, diethylenetriamine-based hyperbranched polyamines, poly(allylamine), polyethylenimine (PEI), citric acid, tricarballylic acid, trimellitic acid (1,2,4-benzene tricarboxylic acid), hemimellitic acid (1,2,3-benzene tricarboxylic acid), trimesic acid (1,3,5-benzene tricarboxylic acid), ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), malic acid, tartaric acid, citramalic acid, isocitric acid, quinic acid, polyethyleneimine, triethylenetetraamine, ethoxylated bisphenol A, tetraglycidyl diaminodiphenyl methane (TGDDM), meta phenylenediamine (MPDA), polyethylene glycol, 1 ,3,5-triglycidyl isocyanurate, novolac, and hydroquinone.

[0193] In some embodiments of any material according to the invention, the carbon framework is based on a polyol.

[0194] In some embodiments of any material according to the invention, the polyol is pentaerythritol.

[0195] In some embodiments of any material according to the invention, the material is of general structure (I), or (II):

[0196]

[0197] wherein

[0198] n is 1, 2 or 3;

[0199] each of XI and X2, independent, is -O-, -S-, -NH-, -N, -CH2-, or -CH;

[0200] each of R3 and R4, independently,

[0201]

[0202] defined herein; or each of R3 and R4, independently, is selected from substituted or unsubstituted Cl-ClOalkylene, -OH, -SH, -C(=O)OH, -NH2, -NHC(=O)H, ester, -C(=S)OH, halogen, -OR1, -SRI, -NR1R2, -CN, -SCN, -NO2, -C(=O)R1, -C02R1, -C(=O)NR1R2, -OC(=O)R1, -0C02R1, -OC(=O)NR1R2, -NR1C(=O)R1, -NR1C02R1, and -NR1C(=O)NR1R2, wherein R1 and R2, independently, is as defined herein; and

[0203] each of R5 and R6, independently, is a chemical bond or group associating XI or X2 to the dithiolane ring structure, wherein XI and R6 together, or X2 and R5 together, independently, form an ether bond, an ester bond, an amide bond, or a C-C single, double or triple bond.

[0204] In some embodiments of any material according to the invention, XI and R6 together, and X2 and R5 together, form an ester bond.

[0205] In some embodiments of any material according to the invention, in a material of structure (I) or (II), one or each of X5 and X6 is -O-.

[0206] In some embodiments of any material according to the invention, in a material of structure (I) or (II), n is i.

[0207] In some embodiments of any material according to the invention, in a material of structure (I) or (II), n is 1 and each of X5 and X6 is -O-.

[0208] In some embodiments of any material according to the invention, in a material of structure (II), XI and R6 together, or X2 and R5 together, independently, form an ester bond.

[0209] In some embodiments of any material according to the invention, in the material R

[0210] of the structure (II), one or both of R3 and R4 is (s

[0211] In some embodiments of any material according to the invention, in the moiety R

[0212] (Ls, R is a Cl-ClOalkylene, wherein the alkylene is between 1 and 3, or 1 and 4, or 1 and 5, or 1 and 6, or 1 and 7, or 1 and 8, or 1 and 9, or 2 and 10, or 2 and 9, or 2 and 8, or 2 and 7, or 2 and 6, or 2 and 5, or 2 and 4, or 3 and 10, or 3 and 9, or 3 and 8, or 3 and 7, or 3 and 6, or 3 and 5, or 4 and 10, or 4 and 9, or 4 and 8, or 4 and 7, or 4 and 6, or 5 and 10, or 5 and 9, or 5 and 8, or 5 and 7, or 6 and 10, or 6 and 9, or 6 and 8, or 7 and 10, or 7 and 9, or 8 and 10 carbon atoms.

[0213] In some embodiments of any material according to the invention, the alkylene has between 2 and 6 carbon atoms.In some embodiments of any material according to the invention, R is Cl-ClOalkylene substituted by a group selected from -OH, -SH, -C(=O)OH, -NH2, -NHC(=O)H, -C(=S)OH, and halogen.

[0214] In some embodiments of any material according to the invention, in a material of structure (II), XI and R6 taken together, and X2 and R5 taken together, are each independently -Cl-C10alkylene-C(=O)O-, wherein the alkylene has between 1 and 3, or 1 and 4, or 1 and 5, or 1 and 6, or 1 and 7, or 1 and 8, or 1 and 9, or 2 and 10, or 2 and 9, or 2 and 8, or 2 and 7, or 2 and 6, or 2 and 5, or 2 and 4, or 3 and 10, or 3 and 9, or 3 and 8, or 3 and 7, or 3 and 6, or 3 and 5, or 4 and 10, or 4 and 9, or 4 and 8, or 4 and 7, or 4 and 6, or 5 and 10, or 5 and 9, or 5 and 8, or 5 and 7, or 6 and 10, or 6 and 9, or 6 and 8, or 7 and 10, or 7 and 9, or 8 and 10 carbon atoms.

[0215] In some embodiments of any material according to the invention, the alkylene has between 2 and 6 carbon atoms.

[0216] In some embodiments of any material according to the invention, in a material of structure (II), XI and R6 taken together, and X2 and R5 taken together, are each independently -C2-C5alkylene-C(=O)O-.

[0217] In some embodiments of any material according to the invention, in a material of structure (II), XI and R6 taken together, and X2 and R5 taken together, are each independently -Cl-C10alkylene-C(=O)O-, and wherein each n is 1.

[0218] In some embodiments of any material according to the invention, the material is of structure (III):

[0219] s

[0220]

[0221] tructure (): (), weren n s , or , z s an nteger etween zero and 8, and wherein designates a bond of connectivity to the oxygen atom(s) of structure (III).

[0222] In some embodiments of any material according to the invention, two of X3, X4, X5 and X6, independently, are moieties of structure (IV), which are same or different.

[0223] In some embodiments of any material according to the invention, three of X3, X4, X5 and X6, independently, are moieties of structure (IV), which are same or different.In some embodiments of any material according to the invention, each of X3, X4, X5 and X6, independently, is a moiety of structure (IV), which are same or different.

[0224] In some embodiments of any material according to the invention, two, or three or all of X3, X4, X5 and X6 are moieties of structure (IV), wherein n is 1 and z is 2.

[0225] In some embodiments of any material according to the invention, the material being of structure (V), (VI) or (VII):

[0226]

[0227] A material is provided, being one or more of:

[0228]

[0229]

[0230] independently, is between 1 and 30;

[0231]

[0232]

[0233] bonds of connectivity;

[0234]

[0235] In all embodiments of material according to the invention, the material is for use as a reversible adhesive.

[0236] In all embodiments of material according to the invention, the material is for reversible adhesion of substrates.

[0237] In all embodiments of material according to the invention, the substrate is of a material selected from ceramics, metals, polymers, hydrogels, composite materials, glass, biological tissues, underwater surfaces and temperature-sensitive materials.

[0238] In all embodiments of material according to the invention, the substrate is transparent or non-transparent object, having a substantially 2-dimentional surface of a 3-dimentional surface.

[0239] In all embodiments of material according to the invention, the first stimulus is or comprises (i) application of a temperature between 70 and 130 °C; (ii) light irradiation with a light source having a wavelength above 365 or between 365 and 850 nm; (iii) application of ultrasound at a range of 10-20 MHz; (iv) application of acidic conditions at pH values below 6; and (v) treatment with a solvent including high valence ions.

[0240] In all embodiments of material according to the invention, the first stimulus is or comprises irradiation with a light source having a wavelength between 365 and 850 nm.

[0241] In all embodiments of material according to the invention, the second stimulus is or comprises (i) application of a temperature between 150 and 200 °C; (ii) light irradiation with light source at a wavelength below or equal to 365 nm; (iii) application of microwaveradiation at 72 W, 2.45 GHz;(iv) application of basic conditions at pH above 8, in an aqueous solution; and (v) application of ultrasound above 20MHz.

[0242] In all embodiments of material according to the invention, the second stimulus is or comprises application of microwave radiation at 72 W, 2.45 GHz.

[0243] Also provided is a solvent-free adhesive, the adhesive being a material accoridng to the invention.

[0244] In some embodiments of any adhesive according to the invention, the adhesive is for use in mechanical assemblies, in medical and biomedical systems, in ophthalmic devices, in manufacturing of textiles, garments, and composite fabrics, or for wet-surface adhesion.

[0245] In some embodiments of any adhesive according to the invention, the adhesive is for use in electronics, advanced packaging, electric vehicle batteries, automotive and transportation, and in consumer goods.

[0246] In some embodiments of any adhesive according to the invention, the adhesive is for use in wafer thinning.

[0247] In some embodiments of any adhesive according to the invention, the adhesive is for use in micro-electro-mechanical systems (MEMS) and sensors.

[0248] In some embodiments of any adhesive according to the invention, the adhesive is for use in display panels.

[0249] In some embodiments of any adhesive according to the invention, the adhesive is for use in smartphone devices.

[0250] In some embodiments of any adhesive according to the invention, the adhesive is for use in bonding batteries.

[0251] In some embodiments of any adhesive according to the invention, the adhesive is provided in a liquid form, a gel form, a film form, a tape form, a coating form, or a solid resin form.

[0252] An adhesive system is provided which comprises:

[0253] -a solvent-free adhesive according to the invention;

[0254] -a first stimulant; and

[0255] -optionally a second stimulant distinct from the first stimulant.

[0256] A method is provided for bonding two substrates, the method comprising applying a solvent-free adhesive accoridng to the invention between the substrates, applying a firststimulus to induce formation of an adhesive network, and optionally applying a second stimulus to cause reversion of the formation of the network and debond the adhesive.

[0257] In some embodiments of any method according to the invention, the first stimulus is or comprises (i) application of a temperature between 70 and 130 °C; (ii) light irradiation with a light source having a wavelength above 365 or between 365 and 850 nm; (iii) application of ultrasound at a range of 10-20 MHz; (iv) application of acidic conditions at pH values below 6; and (v) treatment with a solvent including high valence ions.

[0258] In some embodiments of any method according to the invention, first stimulus is or comprises irradiation with a light source having a wavelength between 365 and 850 nm or between 365 and 405 nm.

[0259] In some embodiments of any method according to the invention, the second stimulus is or comprises (i) application of a temperature between 150 and 200 °C; (ii) light irradiation with light source at a wavelength below or equal to 365 nm; (iii) application of microwave radiation at 72 W, 2.45 GHz;(iv) application of basic conditions at pH above 8, in an aqueous solution; and (v) application of ultrasound above 20MHz.

[0260] In some embodiments of any method according to the invention, the second stimulus is or comprises application of microwave radiation at 72 W, 2.45 GHz.

[0261] An adhesive kit is provided which comprises:

[0262] -a first container containing a solvent-free adhesive accoridng to the invention; -a second container holding a first stimulant effective to induce formation of an adhesive network; and

[0263] -optionally a third container holding a second stimulant effective to debond the adhesive;

[0264] wherein the kit is configured to permit end-user formation and subsequent release of an adhesive bond, and

[0265] instructions for applying the adhesive to a substrate, activating the adhesive bond using the first stimulant, and releasing the bond using the second stimulant.

[0266] In some embodiments of any kit according to the invention, the kit comprises the adhesive as a liquid, a gel, a film, a tape, a coating, or a solid resin.

[0267] An article is provided which comprised two or more substrates bonded by an adhesive accoridng to the invention, wherein the substrates are separated, repositioned, or rebonded by activating dynamic bond exchange within the adhesive.In some embodiments of an article of the invention, the adhesive permits repeated cycles of reconfiguration without significant loss of mechanical strength.

[0268] BRIEF DESCRIPTION OF THE DRAWINGS

[0269] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0270] Figs. 1A-C. Monomer synthesis and bulk characterization. A, Schematic illustrations of the monomer synthesis (I) (Fig. 2) and the curing process (II). B, A photograph represents the curing process of TetraALA. On the left, the monomer in its liquid form flows to the bottom of the vial. After irradiation for 30sec (when the vial's black lid is on top), the monomer solidifies and remains on the bottom of the vial. C, Tensile tests of the cured monomer after 30 seconds at 405 nm.

[0271] Figs. 2A-C. Synthesis of TetraALA. A, a schematic illustration of the monomer synthesis. B, 'H-NMR spectroscopy at CDCh. C, ATR-IR.

[0272] Figs. 3A-B. Curing conversion analysis of TetraALA. A, Conversion (%) Vs. irradiation time. The light grey shade represents the standard deviation after three tests for each period. B, A representative ATR-IR spectroscopy of all irradiation periods. All tests were conducted using 405 nm LED (5.13 mW cm'2).

[0273] Fig.4. Dynamic mechanical analysis (DMA) results for pristine sample. The test was conducted in tensile mode heating at 3 °C min'1.

[0274] Figs. 5A-E. Adhesion analysis. A, Schematic illustration of the adhesion system, including an adhesive layer placed between two substrates, cured by irradiation. B, the visible spectrum (in a greyscale) and the four photoinitiators that were used in this study (from 1 to 4) with their operative wavelength: Phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide (BAPO, also referred to as Irgacure 819), Bis(.eta.5-2,4-cylcopentadien-l-yl)-bis(2,6-difluoro-3-(lH-pyrrol-l-yl)phenyl) titanium (IR 784), Zinc (II) tetraphenylporphyrin (ZnTPP, both for 3 and 4). C, Lap shear results for different substrates irradiated with BAPO under 405 nm for 30 seconds. D, Shear strength to glass of TetraALA compared to commercial non-reversible adhesives and literature-reported reversible adhesives (all raw data is available at Table 2). E, Lap shear results on treated glass substrates under different wavelengths. All specimens were irradiated for 30seconds. All lap shear tests presented in this figure were pre-treated by mercapto-silane. All raw data for the lap shear tests are available in Table 3.

[0275] Figs. 6A-B. Silane Treatment. A, Lap shear strength of glass substrates irradiated at 405 nm for 30 s before and after the silane treatment. B, Changes within the contact angles of different substrates before (pale colors) and after the silane treatment (dark colors): Glass, aluminum, Polycarbonate, and FR4. This figure also presents the contact angle of pristine and recycled bulk polymer.

[0276] Figs. 7A-B. UV-NIR Spectra. A, Absorbance spectra of the TetraALA (solid line) used photoinitiators: BAPO (short dash dot), IR 784 (dots), ZnTPP (dash). B, light transmittance of three of the used substrates, excluding aluminium that is non-transparent.

[0277] Figs. 8A-C. Lap-shear specimens. A, The lap-shear specimens’ dimensions. B, Lap-shear specimens with BAPO as photoinitiator. The adhesion area is -6.45 cm2(1 inch2), according to the ASTM standards. As shown in the photos, the adhesive forms thin transparent layers that maintain its shape even after several weeks. C, Specimens that were irradiated under 405 nm wavelength after failure. All specimens, apart from the glass, underwent cohesive failures. All glass specimens underwent a substrate failure (the adhesion area remained untacked).

[0278] Fig. 9. Cure Depth analysis. Glass slides were adhered together, with each slide connected to the next by a 200 pm adhesive layer. The upper slide was then irradiated using 405, 470, 530, and 630 nm wavelengths. The lower slides were removed until reaching the fully cured slides. At this point, the height of the adhesive structure was measured.

[0279] Figs. 10A-E. Recycling of TetraALA. A, A schematic illustration of the recycling process. B, a cured polymer (left) transformed back into liquid (right) after 30 seconds in a 7 W microwave irradiation. C, Photocuring conversion (405 nm, round dots) and recycling conversion (microwave, triangular dots) as a function of irradiation time. D, 'H-NMR of pristine (lower spectrum) sample and after the 3rdrecycling cycle (upper spectrum). E, properties comparison of pristine and 4th cured samples.

[0280] Figs. 11A-D. Recycling conversion analysis of TetraALA and thermal dissipation during the process. A, recycling conversion (%) Vs. irradiation time at the microwave oven (72 W). The pale shade represents the standard deviation after three tests for each period. B, A representative ATR-IR spectroscopy of all irradiation periods. C and D, Thermal photos of the samples before (I) and after (II) the 30 s recycling process.Figs. 12A-B. Spectroscopy comparison of pristine and recycled samples. A, Full 'H-NMR spectra of pristine (lower spectrum) and 4thcured (upper spectrum) samples. B, ATR-IR spectra of pristine (pale spectrum) and 4thcured (dark spectrum) samples.

[0281] Figs. 13A-D. Bulk comparison of pristine and recycled samples. Tensile tests of pristine (A) and recycled (B, 4thcuring cycle) specimens. Dynamic mechanical analysis (DMA) of pristine (C) and recycled (D, 4thcuring cycle) samples.

[0282] Fig. 14. Swell tests (left columns) and gel content (right columns) calculations for pristine and recycled (4thcuring cycle) samples

[0283] Figs. 15A-B. Viscoelastic properties of pristine and recycled samples. A, Creep analysis for 60 min. B, stress relaxation. For both tests, pristine is presented in pale grey whereas the recycled sample is presented in black.

[0284] Figs. 16A-F. TetraALA potential applications. A, A schematic illustration of the water-effect analysis. 1, the adhesive is applied on one of the substrates. 2, the two substrates are forced together inside a water bath, forming a thin adhesive layer between them while irradiating under 405 nm. 3, the cured samples are left in water for several hours\ days. B, Water (TDW - triangle and tap water - circle) effect on adhesion force to glass under irradiation of 405 nm: C, An example of chicken skin lap shear specimen and its test. D, the light transmittance of TetraALA thin film (200 pm). E, 22 glass slides that adhere to each other show the transparency of TetraALA, as the green laser (535 nm) does not scatter. F, A beam splitter device - two silicone triangular prisms pressed together without (I) and with TetraALA (II).

[0285] Figs. 17A-C. Water effect analysis. ATR-IR spectra of samples swelled in water for 48 h (A) and 72 h (B). Three measurements are presented: “Initial” - representing the sample before immersing in water, “Wet” - a sample that has been taken from water and immediately weighed, and “Dry” - a sample weighed after drying in a vacuum oven at room temperature for two hours followed by 48 h drying in a desiccator. These graphs contain the average curves of three samples each. Color maps are from pale to dark in the following order: samples before swelling, samples after swelling, and the darkest are samples after drying for 48 h under vacuum in a desiccator. C, Swelling measurements of the samples in water.

[0286] Fig. 18. Emission spectra of the different LEDs used in this study.DETAILED DESCRIPTION OF EMBODIMENTS

[0287] Synthesis and Characterization

[0288] Tetr a AL A Synthesis

[0289] TetraALA (Fig. 2) was synthesized from pentaerythritol, a-lipoic acid (ALA), and tin (II) chloride (SnCh) as a catalyst. At first, 0.05 mol of pentaerythritol, 0.21 mol of ALA and 0.002 mol of SnCh were added to an open round flux. Then, 0.02 mol of tri ethylamine (TEA), 10 ml of acetone and 4 ml of 1,4-di oxane were added. The mixture was stirred with a magnetic stirrer (350 Hz) at 160 °C for 3.5 h using a metallic holder and then let to cool down to room temperature. The sample system was covered with aluminum foil during the entire process to avoid light exposure. The resulting yellow viscous liquid was then analyzed using 'H-NMR (Fig. 2B) and ATR-IR (Fig. 2C). 'H NMR (400 MHz, CDCh): 4.13 (t, J = 3.96 Hz, 8H), 3.58 (t, J = 7.75 Hz, 8H), 3.15 (m, 8H), 2.47 (m, 4H), 2.35 (m, 8H), 1.92 (m, 8H), 1.68 (m, 8H), 1.35 (m, 8H). As the used lipoic acid is not 100% pure and has some different isomers, the splitting does not entirely fit the theoretical prediction, resulting in more multiplets. Moreover, a small amount of residual ionized TEA was observed, affecting the integration of the signals. A 100 % conversion of the Pentaerythritol can be concluded as no residual hydroxyl groups were observed. However, since ALA was added in small excess, some free ionized lipoic carboxylates still exist, as shown in the IR spectrum at 1548 cm'1. IR (ATR-IR, cm'1): 2928, 2854 (C-H stretching), 1729 (C=O stretching), 1548 (residual COO' stretching from free ionized lipoic), 1425 (C-H bending), 1243 (C-0 stretching), 1170 (C-O-C stretching), 1045 (C-O-C Stretching), 890 (C-H out-of-plane bending), 740 (C-H out-of-plane bending). As no OH was observed, it can be concluded that all the Pentaerythritol reacted; thus, a 100% conversion can be concluded. UV-Vis Spectroscopy:max (nm) = 341, 200.

[0290] A fully recyclable thermoset adhesive can only be obtained while incorporating fully reversible bonds in the cross-links or backbone. This study has focused on exploring the potential of cyclic disulfides, specifically a-Lipoic Acid (ALA), a naturally occurring carboxylic acid that contains a cyclic disulfide functional group. However, more than one functional group is required to achieve a cross-linked thermoset-like structure. To address this, ALA was esterified by reacting it with pentaerythritol. A simple “one-pot” synthesis method was used (Fig. 1A, Fig. 2A), which involves mixing the two reagents along with tin (II) chloride (SnCh) as a catalyst, tri ethylamine (TEA) as a weak base and co-catalyst,acetone as a solvent, and 1,4-di oxane as a co-solvent. Since water, acetone, TEA, and 1,4-di oxane all have boiling points below 160 °C, they are easily removed upon completion of the reaction, which is performed in an open flux. 'H-NMR (Fig.2B) and ATR-IR (Fig.

[0291] 2C) evaluation of the resulting monomer (TetraALA) indicate a complete conversion of the pentaerythritol’ s hydroxyl groups. However, as an excess of ALA was used, a small amount of non-esterified ALA remained in the form of ionized carboxylates after reacting with TEA. Furthermore, the process, characterized as a "one-pot" single-step synthesis utilizing only commercially available and relatively cost-effective raw materials (Table 1), alongside the absence of purification requirements, holds industrial potential regarding viability and scalability.

[0292]

[0293] Cost Cost

[0294] Cost

[0295] Unit Price (formulation with (formulation with IR

[0296] Material Qty (kg) (Type II formulation)

[0297] (USD Kg1) IR 819) 784)

[0298] USD Kg1USD Kg'1USD Kg1

[0299] a-Lipoic Acid (ALA) 093 3400 31.62 31.62 31.62 Pentaerythritol 007 1 50 0105 0.105 0105 Irgacure 819 0.01 (only in formulation 819) 5.00 0.05 0 0

[0300] Irgacure 784 0.01 (only in formulation 784) 10.00 0 0.10 0 Diphenyliodonium

[0301] 0.01 (only in formulation II) 0.10 0 0 0.001 hexafluorophosphate

[0302] Triethanolamine (TEA) 0.01 (only in formulation II) 1.30 0 0 0.013

[0303] Zinc meso-tetraphenylporphyrin 0.01 (only in formulation II) 11000 0 0 110

[0304] (ZnTPP)

[0305] Total "" **** 31.8 31.8 141.7Table 1. Materials’ cost estimations. Note that cheaper or more expensive prices can be found, depending on the materials’ purity and quality purchased.

[0306] To evaluate the curing rate of the adhesive, the sample was subjected to irradiation at 405 nm for different periods, resulting in 92.7 ± 2.7 % conversion after 30 seconds (Fig- 3). As shown in Fig. IB, the monomer is a liquid that flows to the bottom of the vial, and after irradiation (when the vial's black lid is on top), the monomer solidifies and remains on the bottom of the vial, forming a brittle yellow solid. Once the photocuring of the composition was established, the cured polymer's glass transition temperature (Tg) was analyzed through dynamic mechanical analysis (DMA, Fig. 4). The Tgwas found to be 37°C, meaning that unlike many reported disulfide-containing thermosets, this polymer is in its glassy state at room temperature, correlated with its brittleness. Due to the lack of solvents in the composition, the tensile strength of the cured bulk polymer was very high, 5.6 ± 0.5 MPa (Fig. 1C), stronger than any other reported ALA-based polymers.

[0307] Adhesion Evaluation

[0308] The adhesion performance of TetraALA was evaluated using lap shear tests (a schematic illustration of irradiating the two substrates at the test configuration is shown in Fig. 5A). As typically used in the adhesives industry, prior to the adhesion process, a primer was applied to the tested substrates to ensure covalent bonding at the interface. In this case, (3-Mercaptopropyl)trimethoxysilane, a commonly used silane primer for epoxy resins, was selected due to its commercial availability and because it had been previously reported in thiol-ALA reactions (Fig. 6). This specific primer also ensures that the adhesive will bond to the primer with reversible bonds rather than traditional non-reversible covalent bonding.

[0309] Following the primer treatment, a layer of pre-cured monomer, at a thickness of 180-200 pm, was applied to one of the substrates. The two substrates were pressed together and irradiated for 30 seconds. Initially, four substrates were tested: glass, which is commonly used for optical applications; FR4, which is a common substrate in the printed circuit boards industry; aluminum, as a representative of metals, and polycarbonate (PC), a transparent, strong amorphous polymer. Due to aluminum being non-transparent for all tested wavelengths (Fig. 7), the adhesion strength to this substratewas conducted on specimens consisting of glass slides and aluminum. Fig.5C shows that almost similar strength was observed for all substrates irradiated under 405 nm. It should be noted that the glass substrates broke under the test conditions; thus, the real adhesion force to the glass was very high and could not be measured. All other substrates showed cohesion failure (Fig. 8). The similarities between the substrates are probably a result of pre-treatment, which forms a thiol layer on the surface. Moreover, as demonstrated in Table 2, the measured adhesion strength to glass is in line with commercial non- reversible polyurethane adhesives and higher than most literature reported CANs-based\ recyclable adhesives described in the literature (Fig. 5D and Table 2).

[0310]

[0311]

[0312] and literature reversible (CANs) adhesives.

[0313] One of the drawbacks of ALA-based adhesives is their dependency on irradiation at a narrow range of light spectrum. Thus, this study used four visible-light wavelengthsto cure TetraALA: 405, 470, 530, and 630 nm. Achieving curing under different wavelengths requires some modifications to the adhesive composition. Based on their light absorbance spectra (Fig. 7), BAPO (Fig. 5B1) was chosen for 405 nm, IR 784 (Fig.

[0314] 5B2) was chosen for 470 nm, and ZnTPP (Fig. 5B3-4) was selected for both 530 and 630 nm. Unlike the first two, ZnTPP is a Norrish type II photoinitiator and requires triethanolamine (TEOA) and diphenyl iodonium (Ph2I+) salt as proton donors and acceptors. Lap shear tests (Fig. 5E) were performed for all four wavelengths on glass substrates, resulting in somewhat similar strength (> 4 MPa) with a slightly lower value for 405 nm. Initially, this difference was hypothesised to result from different curing penetration depths. However, the penetration depth only at 470 nm was significantly larger (Fig. 9). Thus, as will be discussed later for underwater specimens, , and as demonstrated for previously reported ALA-based adhesives, it is more likely a result of coordination bonds between ALA’s carboxylate or esters groups and the multi -valence metal ions that reinforced the adhesive.

[0315] Recycling

[0316] Most CANs-based adhesives reported in the literature rely until now on one (or more) of the following stimuli for recycling: high temperatures, adding solvents, or deep UV (200-280 nm) irradiation. Specifically, ALA-based polymers are recycled by heating to >150 °C, in a solution with reducing agents, or in highly basic solvents. Trying to avoid the need for solvents or elevated temperatures, this study has addressed the recycling challenge through a different approach; based on previous studies by our group, it was hypothesized that molecular vibrations resulting from microwave irradiation would cause dissociation of the disulfide bonds to promote depolymerization (Figs. 10A,B).

[0317] Therefore, cured samples were placed in a microwave oven at low intensity - to avoid heating - for various durations. ATR-IR measurements revealed that 93.7 ± 0.5% of the polymer was converted to the monomer after only 30 seconds (Fig. 10C, Fig. 11), demonstrating the efficiency of the microwave recycling approach. This was also substantiated by 'H-NMR, even after several recycling cycles, as discussed below (Fig.

[0318] 9D, Fig. 12) To confirm that these results are not due to heating during the microwave irradiation, thermal images (Fig. 11) of samples before and after recycling were taken using a thermal camera, showing the samples’ temperature increased only to ~47 °C, which is too low to cause any thermal dissociation.Although a direct assessment of the microwave effect on the molecules cannot be performed inside the microwave oven, the changes observed within the IR spectrum after varying irradiation periods may clarify the underlying mechanism. As illustrated in Fig.

[0319] 11, the IR spectrum provides no evidence of thiol group formation, effectively ruling out the possibility of reduction being involved. Nonetheless, some alterations are detected in the C-S vibrations (-930 cm-1). These changes may suggest the proposed mechanism involving the vibrations of the S-S bonds and the linked C-S bonds during microwave irradiation (Fig. 10A). Such vibrations destabilize the chemical structure, leading to ringclosing depolymerization and the reformation of the liquid monomeric form, as demonstrated by the IR and NMR spectra. In addition to the points mentioned above, the involvement of the photoinitiators in the recycling process cannot be completely ruled out, despite the lack of spectroscopic evidence supporting their effect. Nonetheless, because the initiators are essential for the curing process, it would have been impossible to prepare a comparable control system without them. Furthermore, it was postulated that lowering bond energies can make dynamic bonds more reversible under mild conditions, mainly if the bonds’ exchanges occur through a dissociative mechanism. Thus, vibrational energy could dissociate bonds by lowering bond exchange energy, resulting in recycling, bonds-cleavage, or self-healing.

[0320] Specifically, disulfide bonds were shown to react with microwave irradiation, leading to their cleavage. For example, it was demonstrated that microwave irradiation can cleave ALA’s disulfide bonds, although they used it for polymerization and surface treatments rather than recycling. Singh et al. also studied the effect of microwave irradiation on disulfide bonds, presenting the use of microwave irradiation to induce self-healing in disulfide-containing polymers Their study showed that microwave irradiation can induce cleavage and reformulation of disulfide bonds, thus resulting in self-healing in their case.

[0321] By repeating the photocuring-depolymerization for several cycles, it was found that TetraALA can be recycled and reused up to four times before adding more photoinitiators is required, which is in line with previously reported recyclable adhesives [36,72-74] Te reqUiremenfor the addition of photoinitiators after four cycles is due to the decomposition and depletion of the Noirish Type I photoinitiators (BAPO, IR 784) or the photobleaching of the Type II (ZnTPP) during the photocuring process. It should be noted that the latter is evident, since a color change is observed upon light irradiation.Attempting to cure the samples without adding photoinitiators resulted in a very slow and partial curing. To understand the recycling process’s effect on the chemical composition, 'H-NMR and IR evaluation of a pristine sample and a sample after the third recycling was conducted (Fig.9D, Fig. 12), showing no significant changes, proving the reforming of the monomer. Then, the 3rdrecycled samples were tested after another (4th) curing cycle and were compared with the pristine bulk properties. As shown in Fig. 9E, no significant changes were observed either. These similarities between the pristine and the 4-times cured material are also manifested in the adhesion strength: when testing it on glass, the adhesion strength remained without significant changes, emphasizing the recyclability of TetraALA using the microwave.

[0322] Further evaluations were conducted as the only observed changes were noted in the bulk elongation (Fig. 13), which increased after recycling. First, a swell test with an ethanol-acetone mixture was conducted (Fig. 14), showing small changes within the swell ratios (SR) and the gel-content (GC). It was found that the cross-linking density was slightly reduced after recycling, resulting in an increase in the SR and a decrease in the GC of ~35 %. As no evidence for hydrolysis or disulfide reduction was found in IR and NMR spectroscopies, these changes are more likely a result of some other side reactions, like disulfide exchanges, which may have occurred during the recycling process. These reactions may cause internal re-configurations in the cross-links, in a way that may reduce the effective cross-links. However, as the amount of disulfide did not change, these changes did not affect the adhesion strength or the bulk mechanical properties. Some evidence for these changes may be found in the samples' creep compliance and stress relaxation (Fig. 15). The pristine sample experienced lower creep compliance and lower stress relaxation than the 4threcycled one, pointing to higher cross-linking density.

[0323] Potential applications

[0324] An essential feature of a good adhesive is its ability to function not only in air but also in humid environments, including underwater bonding. First, TetraALA was used to bond two glass substrates while being immersed in water. Lap shear specimens were formed from glass substrates and cured in tri-distilled water (TDW) for 30 seconds at 405 nm. Then, the specimens were left for 24, 48, 72 and 168 h, for evaluating the water effect on adhesion over time (Fig. 16A). As shown in Fig. 16B, the adhesion strength was similar to that obtained in air, and the immersion in water for a prolonged duration hadno effect. It should be noted that due to the interference of the glass slides with the IR spectrum, as the adhesive itself forms only a -200 pm film between the two slides, a direct measurement of the conversion could not be performed. Nonetheless, since the resulting mechanical under dry conditions are similar to that in underwater experiments, it can be assumed that the conversion is similar.

[0325] Further evaluation was made using tap water, following the same procedure. Surprisingly, the tap water did not decrease the adhesion force, but increased it by about 60 %, reaching an equilibrium at 48 h (Fig. 16B). Following the differences in the adhesion strength observed after using the organo-metallic complexes IR 784 and ZnTPP compared to the organic BAPO, it was hypothesised that high-valence ions which are present in the tap water replaced the ionized TEA, further strengthening the inter and intra-molecular bonds and thus the adhesive strength. It should be noted that after soaking the sample for 48 h and 72 h, only 2.8 ± 0.5 % and 3.3 ± 0.1 % swelling was observed, respectively (Table C in Fig. 17). These small swelling levels are in line with the relative hydrophobicity of TetraALA; yet they indicate that the multivalent ions in the tap water can penetrate the adhesive layer. Furthermore, ATR-IR spectral analysis (Fig. 17) showed notable changes in the carboxylates’ vibrations and several key regions after water exposure, indicating ion exchange between single-valence TEA and multi-valent tap water ions, such as calcium, affecting the material's bonding and properties. These observations demonstrate that introducing high valence ions, such as calcium and iron, reinforces lipoic-based materials.

[0326] After observing the good results in water, the adhesive was also tested on chicken skin, representing wet tissues (Fig. 16C, Table 3). The skin's partial transparency to visible light necessitated using the adhesive for 630 nm irradiation, which was irradiated for 1 minute. Applying the adhesive proved challenging, due to the oily nature of the skin tissue leading to some incompatibility issues. Despite this, the adhesive's strength was 144.7 ± 17.2 kPa, a superior shear strength compared to other lipoic acid-based adhesives

[0036] . The achieved strength, which is within the range reported for commercial cyanoacrylate-based adhesives, opens the door to future biomedical applications. Nonetheless, as it is outside this study’s scope, a further evaluation of biocompatibility of this system is required while taking into consideration the specific requirements of the intended biomedical application.Sample

[0327] Untreated Glass Treated Glass

[0328] Al-Glass

[0329] FR4 Polycarbonate Recycled (4th curing) 470 nm

[0330] 530 nm

[0331] 630 nm

[0332] Dry

[0333] 24h in tap water 48h in tap water 72h in tap water 168h in tap water 24h in TDWb

[0334] 48h in TDWb

[0335] 72h in TDWbChicken Skin3

[0336] 1.502.953.043.833.243.273454.174.022.952.934.644.854882.743.22308155.62

[0337] 21.292.672.523.242.722.985125.914.822.673.374.044.504662.702.76342159.46

[0338] 31.242.962.532.992.883.214594.654.192.963.344.835.354643.143.22297138.94

[0339] 41.773.603.223.693.343.355064.334.223.602.945.485.005303.183.08313117.18

[0340] 516529730730331934551140842029733648544945830630029515233

[0341] 64.203.504.445.215232.90312

[0342] Mean

[0343] 1.53.02.93.53.13.3474.64.33.03.24.84.9493.03.131144.7

[0344] MPa

[0345] SD 0.20.30.30.50.30.2070.70.30.30.20.50.4030.20.20217.2Table 3. Raw data of all lap shear tests. All results in MPa except of Chicken skin that is in kPa. All specimens were tested until a complete failure of either the adhesive (cohesive failure) or the substrate.

[0346] Taking advantage of the transparency (Fig. 16D) and the high refractive index (1.62) of TetraALA, it was also assessed as a potential adhesive for optical applications. First, it was tested for optical devices requiring high transparency so that no light scattering would occur. Thus, 22 glass slides were adhered together with a 200 pm adhesive layer between each glass. After curing for 30 seconds at 405 nm, no scattering of a visible light laser (532 nm) was observed (Fig. 16E). As the light penetrates the glass, some reduction in its intensity was observed. Thus, a comparison of 22 glass slides with and without the adhesives’ layers was evaluated. Surprisingly, compared to the nonadhered glass slides, the measured intensity of the light beam after penetrating the adhesive-containing slides exhibited a seven times lower reduction in the light intensity due to lower light reflection, emphasizing the potential of TetraALA for such optical applications. The second test was using the adhesive layer for making a beam splitter. Beam splitters are devices that split a light beam into transmitted and reflected beams, usually with 90 ° splitting. These devices are key factors in many applications, such as optical fibers and interferometers. The most common structure for such devices is two right-angled triangular prisms, forming a cube with a thin adhesive layer between them. The two prisms were made from transparent silicone (SYLGARD™ 184). As shown in Fig. 16F, a 532 nm laser beam is split into two distinctive beams with 90 ° between them, opening the door for further investigations of this adhesive's optical properties and application in optics industries.

[0347] Conclusions

[0348] The adhesives industry mainly comprises thermosets as raw materials, resulting in economic shortcomings and environmental challenges. This study presents a fully recyclable, solvent-free, visible-light-curable adhesive based on an a-lipoic acid derivative. The proposed adhesive cures rapidly under a wide spectral range of visible light, achieving strong and constant adhesion to various substrates, even underwater. Recycling is performed using a low-intensity house microwave while avoiding the typical need in reversible adhesives for adding solvents or recycling at elevated temperatures,while maintaining the adhesion performance following multiple adhesion-debonding cycles.

[0349] By combining rapid curing, mechanical robustness, and closed-loop recyclability, this adhesive exemplifies a sustainable approach to thermosets-based adhesives. Its compatibility with biomaterials, optical systems, and underwater applications highlights its potential for further advancements in adhesive design and material sustainability.

[0350] Future studies should elaborate on the microwave-induced recycling mechanism, employing computational chemistry and other complementary measurements. In view of industrial application of microwave recycling, the proposed approach presents various challenges that should be addressed in the future, for example, suitability to a variety of substrates and to non-planner substrates, and the optimal ways for recovering the recycled adhesive from the bonded laminates.

[0351] Methods

[0352] Materials

[0353] Pentaerythritol (98+%), zinc meso-tetraphenylprophine (ZnTPP), triethylamine (TEA), and Diphenyliodonium hexafluorophosphate (Ph2l+) were supplied by Tzamal D-Chem, Israel. a-Lipoic Acid (ALA) was purchased from Aaron Chemicals, USA. Tin (II) chloride anhydrous (SnCL, 99%) and 1,4-di oxane were supplied by Rhenium, Israel. (3-mercaptopropyl)trimethoxysilane was supplied by Gelest through Tzamal D-Chem, Israel. Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO, also referred to as Irgacure 819) and Bis(.eta.5-2,4-cylcopentadien-l-yl)-bis(2,6-difluoro-3-(lH-pyrrol-l-yl)phenyl) titanium (Irgacure 784, IR 784), were supplied by IGM Resins, the Netherlands. Ethanol (technical grade, 96%) and acetone (technical grade) were purchased from Bio-Lab, Israel. Triethanolamine (TOHA) was supplied by Sigma-Aldrich, Israel, was purchased from Dow Chemicals. All chemicals were used without further purification.

[0354] FR4 (GIO epoxy glass laminates) and aluminum (Al) substrates (2.5 cm x 10.1 cm x 2 mm Width x Length x Thickness) were supplied by Arch Materials Services. Polycarbonate (PC) substrates (2.5 cm X10.1 cm X 4 mm W x L x T) were purchased from Dow Chemicals. For glass substrates, standard microscope slides were used. Chicken skin was bought from the local butcher shop and then cut into samples similarin size to the aluminum and FR4 ones. Before been used, the chicken skin samples were washed carefully with water and dish soap.

[0355] Structural Analysis

[0356] Chemicals’ compositions were analyzed using IR and NMR spectroscopy. IR spectroscopy was recorded using ATR-IR method from 400 to 4000 cm'1on Bruker Alpha-P machine (Brucker, USA). 'H-NMR spectroscopy was performed using 400 Hz spectrometer (Ascend™ 400 Neo by Brucker, USA) using tetramethylsilane (TMS) as an internal reference and CDCh as a solvent.

[0357] All Absorbance and transmittance spectra were recorded using a UV-Vis spectrophotometer (UV-1800, Shimadzu, Japan) from 1000 to 190 nm using ethanol as a solvent (3.75- 10'6g ml'1) (Fig. 7). Transmittance of cured thin-filmed (Fig. 15D) was recorded using 200 pm film between two poly(ethylene terephthalate) films (75 pm), which were also recorded as the reference during the measurement.

[0358] Swell tests (Fig. 14) were conducted to further evaluate the differences between pristine and recycled materials. According to ASTM D2765-16, the samples were immersed in a 50:50 ethanol and acetone mixture for 48 h at room temperature. After swelling, the samples were filtered using a Buchner funnel with cellulose filter paper and immediately weighed. The wet samples were then dried in a vacuum oven at 30 °C for 14 hours and weighed again. Swelling ratio (SR) and gel-content (GC) were calculated according to equations 1 and 2.

[0359] Swelled sample's weight

[0360] (i) (%) = ■ 100

[0361] Samples' original weight

[0362] Samples' weight after drying

[0363] (2) GC (%) = ■ 100

[0364] Samples' original weight

[0365] Swell test in tri-distilled and tap water was conducted for 48 and 72 h, using 200 p inch2square specimens, representing the adhesive layer in lap shear specimens. All samples were weighed before the test, after the swelling, and after drying in a vacuum oven at room temperature for two hours followed by 48 h drying in a desiccator. All 18 samples were analyzed in ATR-IR spectroscopy, following the same method mentioned above.Curing Analysis

[0366] Conversion of the curing process (Fig. 3) was conducted by recording the changes within the IR spectrum over time. Since both the monomer and the cured polymer contain disulfide bonds, the conversion was calculated by evaluating the changes in the ester bonds (C-O) and C-S bonds, as after curing their mobility reduced, resulting in changes within the signals’ integrals at -930 cm'1. These signals were normalized to the C-H signals’ integrals at -2990 cm'1. The IR was recorded after 0, 1, and 2-30 seconds with measurements every two seconds. These tests were performed three times each irradiation time.

[0367] The cure depth evaluation (Fig. 11) at the various wavelengths and with the different photoinitiators was conducted by bonding glass slides, with each slide bonded to the next by a 200 pm adhesive layer. The upper slide was then irradiated. The lower slides were systematically removed until reaching the fully cured slides that remained bonded to each other. At this point, the height of the adhesive structure was measured and recorded as the curing depth for that specific wavelength.

[0368] Adhesion

[0369] Curing of TetraALA was conducted under four wavelengths: 405 nm (405 LED lamp with 5.13 mW cm'2) using 1 wt% BAPO as a photoinitiator, 470 nm (470 LED flashlight with 3.62 mW cm'2) using 1 wt% IR 784 as a photoinitiator, 530 nm (520-540 nm LED flashlight with 3.38 mW cm'2), and 630 (630 LED flashlight with 3.63 mW cm'2), both using 1 wt% ZnTPP as a Norrish type-II photoinitiator with 1 wt% TOHA and 1 wt% Ph2l+. LEDs’ light intensities were measured using THORLabs’ P400 Opitcal Power Meter with 500 mW sensor. LEDs’ emission spectra were measured using StellarNet Spectrometer (Fig. 18).

[0370] All adhesion tests were performed using lap shear samples made according to ASTM D5868-01, D3163-01, orD1002-10, depending on the substrates. The underwater samples were prepared following the same procedure, though the irradiation took place when the samples were located underwater (TDW or tap water). Then, the samples were left under water for 24, 48, 72, and 168 h, and immediately tested to measure the water effect on the adhesion strength. Further information may be found in the Supporting Information.Mechanical and Viscoelasticity Analysis

[0371] Tensile tests of the pristine and recycled samples (Fig. 13) were performed on thin-films dog-bones like specimens following ASTM D638 type V standard. The tensile tests were performed using a Dynamic Mechanical Analysis (DMA) instrument (TA Instruments’ DMA Q800 V21.3 Build 96, TA Instruments, USA, equipped with 18 N load cell) in a controlled force mode (static) at room temperature with ramp force of 1 N min'1.

[0372] Lap shear tests (Table 3) were conducted following ASTM D5868, D3163, or D1002, depending on the substrates (Fig. 8), using a mechanical tester (INSTRON 4481, Instron, USA) equipped with a load cell of 500 N for the pre-treated glass samples and the chicken skin samples and 5kN for the rest of the samples. All tests were performed at 5 mm min'1. All tests were performed up to failure.

[0373] Creep analysis (Fig. 15) was performed using a parallel-plates rheometer (Discovery HR-1, TA Instruments, USA), applying a constant force of 100 kN for 60 min. Stress relaxation (Fig. 15) was performed using the same instrument, though at a constant strain of 5% for 60 min.

[0374] Thermal Analysis

[0375] Transition temperatures were analyzed using a DMA instrument (TA Instruments’ DMA Q800 V21.3 Build 96, TA Instruments, USA, equipped with 18 N load cell) in a tensile mode, heating from -50 to 150 °C at 3 °C min'1with an amplitude displacement of 15 pm and a frequency of 1 Hz (Figs.2 and 12). Samples’ temperature dissipation during the recycling process was evaluated using a thermal camera (FLIR-E63900, FLIR, Sweden) (Fig. 11).

[0376] Optical Samples Preparation

[0377] The adhesive's visible light transmittance was demonstrated using 22 glass slides bonded with a 200 pm layer of adhesive between each slide. The adhesive layers were irradiated simultaneously under 405 nm for 30 seconds. The scattering of a laser pointer (532 nm, 5 mW output) was then analyzed as it passed through the glass structure. A beam splitter device was manufactured to demonstrate the adhesive's suitability as an alternative to traditional adhesives for beam splitter devices. First, two right-angle triangular prisms were constructed from SYLGARD™ 184. The two prisms were thenjoined using a 120 gm adhesive layer and cured for 30 seconds under 405 nm. The final beam splitter device size was 1 cm3.

[0378] Recycling

[0379] TetraALA's recyclability was analyzed using samples irradiated in a silicone mold for 30 seconds. The cured samples were then placed in glass vials and heated in a microwave oven (Sauter's microwave, 720 W, Sauter, China) for various durations, using 10% of the microwave's maximum power (72 W, 2.45 GHz). No sample was continuously irradiated for more than ten seconds to prevent overheating. Furthermore, each 10 seconds of irradiation was followed by a 10-second cooling period for extended irradiation periods. Overall, the energy input was equal to 3000 J.

[0380] The conversion of the recycled samples (Fig. 10, Fig. 11) was calculated using the same method as for the pre-recycled samples. This method involved evaluating the changes in the signals’ integrals around 930 cm'1normalized to the C-H signals’ integrals at approximately 2990 cm'1, resulting in a recycling conversion of 93.7 ± 0.5% after 30 seconds. Since it was observed that after four recycling processes, the addition of a photoinitiator was necessary for curing, this research focused on properties after a maximum of four curing cycles.

Claims

1. CLAIMS:

1. A material comprising at least two ring structures each having an internal disulfide (S-S) bond, wherein the at least two ring structures are associated with a carbon framework, and are configured to undergo, in response to a first stimulus, ring opening and formation of new disulfide linkages between different ring structures, and further configured to undergo, in response to a second stimulus, reversion to the respective ring structures each having the internal S-S bond.

2. The material according to claim 1, having a surface bonding or adhesive properties when forming new disulfide linkages between different ring structures, and a debonding or non-adhesive properties when in the ring structures having the internal S-S bond.

3. The material according to claim 1 or 2, wherein the ring structure having an internal disulfide (S-S) bond is a cyclic disulfide ring structure of five, six or seven atoms.

4. The material according to claim 3, wherein the ring structure is saturated or comprise an internal double bond.

5. The material according to any one of the preceding claims, wherein the ring structure is fused, bridged or substituted.

6. The material according to any one of claims 1 to 5, wherein the ring structure is directly bonded to an atom of the carbon framework.

7. The material according to any one of claims 1 to 6, wherein the ring structure is a R(sof the form , wherein n is an integer between 1 and 3, inclusive, and R is one or more ring substituents, one of which connecting the ring structure to the carbon framework.

8. The material according to claim 7, wherein the one or more ring substitutions being selected from halogen, Cl-ClOalkylene, C2-C10alkyenylen, C2-C10alkynylene, -OR1, -SRI, -NR1R2, -CN, -SCN, -NO2, -C(=O)R1, -C02R1, -C(=O)NR1R2, -OC(=O)R1, -0C02R1, -OC(=O)NR1R2, -NR1C(=O)R1, -NR1C02R1, and -NR1C(=O)NR1R2, wherein each occurrence of R1 is same or different and each occurrence of R2 is same or different.

9. The material according to claim 7, wherein each occurrence of R1 and R2, independently, is same or different and is selected from hydrogen, Cl-C6alkyl, -OH, -SH, -NH2, -CN, -SCN, -NO2, -C(=O)H, -C02H, -C(=0)NH2, -OC(=O)H, -0C02H, -0C(=0)NH2, -NHC(=O)H, -NHC02H, and -NHC(=0)NH2.

10. The material according to any one of claims 1 to 9, wherein the ring structure is selected from:R R R5swherein R is one or more ring substituents, as defined in claim 15.

11. The material according to any one of claims 1 to 10, wherein the ring structure is saturated.

12. The material according to any one of claims 1 to 10, wherein the ring structure is fused to another ring structure, which is optionally aromatic.

13. The material according to any one of claims 1 to 12, wherein the ring structure iswherein R is as defined in claim 8.

14. The material according to claim 13, wherein the ring structure is directly associated to the carbon framework via group R.

15. The material according to claim 13, wherein R is a Cl-ClOalkylene substituted by a group selected from halogen, OH, -SH, -C(=O)OH, -NH2, and -NHC(=O)H, said group generating an ether, a thioether, an ester, an amine or an amide bond with the carbon framework.

16. The material according to any one of claims 1 to 15, wherein the carbon framework is a carbon-containing molecular group, residue, moiety, scaffold, or backbone comprising two or more carbon-based chains, branches, substituents, or structural segments, each being capable of associating, directly or indirectly, to the ring structure.

17. The material according to claim 16, wherein the carbon framework is a linear, branched, cyclic, polycyclic, fused, or a combination thereof.

18. The material according to any one of claims 1 to 17, wherein the carbon framework is selected amongst polyhydric alcohol frameworks (polyols), substitutedbranched alkane or alkylene frameworks, substituted multi-functional alkyl and cycloalkyl cores, substituted aromatic or polycyclic carbon frameworks, dendrimer core units, carbohydrate frameworks and polymers, each of which having two or more groups or functionalities rendering possible association to two or more ring structures.

19. The material according to any one of claims 1 to 18, wherein the carbon framework is based on a material selected from glycerol, trimethylolpropane (TMP), trimethylolethane (TME), pentaglycerol, sorbitol, mannitol, xylitol, inositol, pentaerythritol, ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), hexamethylenediamine (HMDA), putrescine, cadaverine, spermidine, spermine, tris (2-aminoethyl)amine, N,N-bis(3 -aminopropyl) methylamine, Jeffamine, diethylenetriamine-based hyperbranched polyamines, poly(allylamine), polyethylenimine (PEI), citric acid, tricarballylic acid, trimellitic acid (1,2,4-benzene tricarboxylic acid), hemimellitic acid (1,2,3-benzene tricarboxylic acid), trimesic acid (1,3,5-benzene tricarboxylic acid), ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), malic acid, tartaric acid, citramalic acid, isocitric acid, quinic acid, polyethyleneimine, triethylenetetraamine, ethoxylated bisphenol A, tetraglycidyl diaminodiphenyl methane (TGDDM), meta phenylenediamine (MPDA), polyethylene glycol, 1 ,3,5-triglycidyl isocyanurate, novolac, and hydroquinone.

20. The material according to any one of claims 1 to 19, wherein the carbon framework is based on a polyol.

21. The material according to claim 20, wherein the polyol is pentaerythritol.

22. The material according to any one of the preceding claims, the material is of general structure (I), or (II):whereinn is 1, 2 or 3;each of XI and X2, independent, is -O-, -S-, -NH-, -N, -CH2-, or -CH;each of R3 and R4, independently,defined in claim 8; or each of R3 and R4, independently, is selected from substituted or unsubstituted Cl -Cl Oalkylene, -OH, -SH, -C(=O)OH, -NH2, -NHC(=O)H, ester, -C(=S)OH, halogen, -OR1, -SRI, -NR1R2, -CN, -SCN, -NO2, -C(=O)R1, -CO2R1, -C(=O)NR1R2, -OC(=O)R1, -OCO2R1, -OC(=O)NR1R2, -NR1C(=O)R1, -NR1C02R1, and -NR1C(=O)NR1R2, wherein R1 and R2, independently, is as defined in claim 8; andeach of R5 and R6, independently, is a chemical bond or group associating XI or X2 to the dithiolane ring structure, wherein XI and R6 together, or X2 and R5 together, independently, form an ether bond, an ester bond, an amide bond, or a C-C single, double or triple bond.

23. The material according to claim 22, wherein XI and R6 together, and X2 and R5 together, form an ester bond.

24. The material according to claim 22, wherein in a material of structure (I) or (II), one or each of X5 and X6 is -O-.

25. The material according to claim 22, wherein in a material of structure (I) or (II), n is 1.

26. The material according to claim 22, wherein in a material of structure (I) or (II), n is 1 and each of X5 and X6 is -O-.

27. The material according to claim 22, wherein in a material of structure (II), XI and R6 together, or X2 and R5 together, independently, form an ester bond.

28. The material according to claim 22, wherein in the material of the structure (II),R(one or both of R3 and R4 isn29. The material according to any one of claims 7 to 28, wherein in the moiety R([J n Ss, R is a Cl -Cl Oalkylene, wherein the alkylene is between 1 and 3, or 1 and 4, or 1 and 5, or 1 and 6, or 1 and 7, or 1 and 8, or 1 and 9, or 2 and 10, or 2 and 9, or 2 and 8,or 2 and 7, or 2 and 6, or 2 and 5, or 2 and 4, or 3 and 10, or 3 and 9, or 3 and 8, or 3 and 7, or 3 and 6, or 3 and 5, or 4 and 10, or 4 and 9, or 4 and 8, or 4 and 7, or 4 and 6, or 5 and 10, or 5 and 9, or 5 and 8, or 5 and 7, or 6 and 10, or 6 and 9, or 6 and 8, or 7 and 10, or 7 and 9, or 8 and 10 carbon atoms.

30. The material according to claim 29, wherein the alkylene has between 2 and 6 carbon atoms.

31. The material according to claim 29, wherein R is Cl-ClOalkylene substituted by a group selected from -OH, -SH, -C(=O)OH, -NH2, -NHC(=O)H, -C(=S)OH, and halogen.

32. The material according to any one of claims 22 to 31, wherein in a material of structure (II), XI and R6 taken together, and X2 and R5 taken together, are each independently -Cl-C10alkylene-C(=O)O-, wherein the alkylene has between 1 and 3, or 1 and 4, or 1 and 5, or 1 and 6, or 1 and 7, or 1 and 8, or 1 and 9, or 2 and 10, or 2 and 9, or 2 and 8, or 2 and 7, or 2 and 6, or 2 and 5, or 2 and 4, or 3 and 10, or 3 and 9, or 3 and 8, or 3 and 7, or 3 and 6, or 3 and 5, or 4 and 10, or 4 and 9, or 4 and 8, or 4 and 7, or 4 and 6, or 5 and 10, or 5 and 9, or 5 and 8, or 5 and 7, or 6 and 10, or 6 and 9, or 6 and 8, or 7 and 10, or 7 and 9, or 8 and 10 carbon atoms.

33. The material according to claim 32, wherein the alkylene has between 2 and 6 carbon atoms.

34. The material according to any one of claims 22 to 33, wherein in a material of structure (II), XI and R6 taken together, and X2 and R5 taken together, are each independently -C2-C5alkylene-C(=O)O-.

35. The material according to any one of claims 22 to 33, wherein in a material of structure (II), XI and R6 taken together, and X2 and R5 taken together, are each independently -Cl-C10alkylene-C(=O)O-, and wherein each n is 1.

36. The material according to any one of the preceding claims, wherein the material is of structure (III):"structure (): (), weren n s , or , z s an nteger etweenzero and 8, and wherein designates a bond of connectivity to the oxygen atom(s) of structure (III).

37. The material according to claim 36, wherein two of X3, X4, X5 and X6, independently, are moieties of structure (IV), which are same or different.

38. The material according to claim 36, wherein three of X3, X4, X5 and X6, independently, are moieties of structure (IV), which are same or different.

39. The material according to claim 36, wherein each of X3, X4, X5 and X6, independently, is a moiety of structure (IV), which are same or different.

40. The material according to claim 36, wherein two, or three or all of X3, X4, X5 and X6 are moieties of structure (IV), wherein n is i and z is 2.

41. The material according to any one of the preceding claims, being of structure (V), (VI) or (VII):

42. A material being one or more of:, wherein n is between 1 and 100;independently, is between 1 and 30;43. The material according to any one of the preceding claims, for use as a reversible adhesive.

44. The material according to any one of the preceding claims for reversible adhesion of substrates.

45. The material according to claim 44, wherein the substrate is of a material selected from ceramics, metals, polymers, hydrogels, composite materials, glass, biological tissues, underwater surfaces and temperature-sensitive materials.

46. The material according to claim 44 or 45, wherein the substrate is transparent or non-transparent object, having a substantially 2-dimentional surface of a 3-dimentional surface.

47. The material according to any one of the preceding claims, wherein the first stimulus is or comprises (i) application of a temperature between 70 and 130 °C; (ii) light irradiation with a light source having a wavelength above 365 or between 365 and 850 nm; (iii) application of ultrasound at a range of 10-20 MHz; (iv) application of acidic conditions at pH values below 6; and (v) treatment with a solvent including high valence ions.

48. The material according to any one of the preceding claims, wherein the first stimulus is or comprises irradiation with a light source having a wavelength between 365 and 850 nm.

49. The material according to any one of the preceding claims, wherein the second stimulus is or comprises (i) application of a temperature between 150 and 200 °C; (ii) light irradiation with light source at a wavelength below or equal to 365 nm; (iii) application of microwave radiation at 72 W, 2.45 GHz;(iv) application of basic conditions at pH above 8, in an aqueous solution; and (v) application of ultrasound above 20MHz.

50. The material according to any one of the preceding claims, wherein the second stimulus is or comprises application of microwave radiation at 72 W, 2.45 GHz.

51. A solvent-free adhesive, the adhesive being a material accoridng to any one of claims 1 to 50.

52. The adhesive according to claim 51, for use in mechanical assemblies, in medical and biomedical systems, in ophthalmic devices, in manufacturing of textiles, garments, and composite fabrics, or for wet-surface adhesion.

53. The adhesive according to claim 51 or 52, for use in electronics, advanced packaging, electric vehicle batteries, automotive and transportation, and in consumer goods.

54. The adhesive according to claim 51, for use in wafer thinning.

55. The adhesive according to claim 51, for use in micro-electro-mechanical systems (MEMS) and sensors.

56. The adhesive according to claim 51, for use in display panels.

57. The adhesive according to claim 51, for use in smartphone devices.

58. The adhesive according to claim 51, for use in bonding batteries.

59. The adhesive according to any one of claims 51 to 58, provided in a liquid form, a gel form, a film form, a tape form, a coating form, or a solid resin form.

60. An adhesive system comprising:-a solvent-free adhesive according to claim 51;-a first stimulant; and-optionally a second stimulant distinct from the first stimulant.

61. A method of bonding two substrates, the method comprising applying a solvent-free adhesive accoridng to claim 51 between the substrates, applying a first stimulus to induce formation of an adhesive network, and optionally applying a second stimulus to cause reversion of the formation of the network and debond the adhesive.

62. The method according to claim 61, wherein the first stimulus is or comprises (i) application of a temperature between 70 and 130 °C; (ii) light irradiation with a light source having a wavelength above 365 or between 365 and 850 nm; (iii) application of ultrasound at a range of 10-20 MHz; (iv) application of acidic conditions at pH values below 6; and (v) treatment with a solvent including high valence ions.

63. The method according claim 61, wherein the first stimulus is or comprises irradiation with a light source having a wavelength between 365 and 850 nm or between 365 and 405 nm.

64. The method according to claim 61, wherein the second stimulus is or comprises (i) application of a temperature between 150 and 200 °C; (ii) light irradiation with light source at a wavelength below or equal to 365 nm; (iii) application of microwave radiation at 72 W, 2.45 GHz;(iv) application of basic conditions at pH above 8, in an aqueous solution; and (v) application of ultrasound above 20MHz.

65. The method according to claim 61, wherein the second stimulus is or comprises application of microwave radiation at 72 W, 2.45 GHz.

66. An adhesive kit comprising:-a first container containing a solvent-free adhesive accoridng to claim 51;-a second container holding a first stimulant effective to induce formation of an adhesive network; and-optionally a third container holding a second stimulant effective to debond the adhesive;wherein the kit is configured to permit end-user formation and subsequent release of an adhesive bond, andinstructions for applying the adhesive to a substrate, activating the adhesive bond using the first stimulant, and releasing the bond using the second stimulant.

67. The kit according to claim 66, comprising the adhesive as a liquid, a gel, a film, a tape, a coating, or a solid resin.

68. An article comprising two or more substrates bonded by an adhesive accoridng to claim 60, wherein the substrates are separated, repositioned, or rebonded by activating dynamic bond exchange within the adhesive.

69. The article according to claim 68, wherein the adhesive permits repeated cycles of reconfiguration without significant loss of mechanical strength.

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