Debonding-on-demand adhesive

Abstract

Disclosed herein are compositions, systems, and methods for providing a crosslinked polymer that functions as a pressure sensitive adhesive before being exposed to a predetermined debonding stimulus, at which point, the material loses some or all adhesive properties. This is achieved by changing the crosslink density within the adhesive, the modulus of the adhesive, volume of the adhesive upon exposure to stimulus or combinations of crosslink density, modulus or volume listed above.

Description

DEBONDING-ON-DEMAND ADHESIVECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional application no. 63 / 657,183, filed on June 7, 2024, the content of which is hereby incorporated by reference in its entirety.FIELD

[0002] The present disclosure relates to adhesives, including pressure sensitive adhesives, and more particularly to adhesives designed to debond when exposed to a predetermined stimulus.BACKGROUND

[0003] Adhesives, including pressure sensitive adhesives (PSA) find use in a wide variety of modem industries, from everyday consumer use to use in the automotive and construction industry. PSAs are used in nearly all industrial segments in one form or another, as well as in consumer products, including household, office, personal care, and medical applications. On the industrial side, they are used for temporary surface protection (masking tape), packaging, labeling and the assembly of a wide variety of products such as automotive parts, toys, or electronic circuit boards, while plasters, surgical drapes, transdermal medicine delivery systems and biomedical electrodes are representatives of their application in the medical field. Moreover, PSAs are applied as decorative films, double or single sided adhesive tapes and sticky notes in household and office.

[0004] In many fields it would be beneficial for the adhesive to provide high holding power for reliable bonding during use while simultaneously displaying easy and clean removability at the end of the desired use. This can be achieved by adjustment of the adhesive's chemical composition or by the design of a release function, which enables the reduction of the adhesive strength by exposure to external triggers, or stimuli. One area that could benefit from improvements in on-demand debonding technology is labeling adhesives where current removal requires mechanical separation or volatile organic solvents for effective cleaning and removal of the label.SUMMARY

[0005] An unmet need exists for on-demand debonding adhesives that can provide adequate tack, adhesion, and shear resistance, while also providing easy on-demand debonding. One current concern in the field of recycling is easy, effective label removal. Because packaging materials and other products that use labels are often constructed from different materials than the labels attached thereto, it is often necessary to remove the label before the material (e g., a shipping box or plastic consumer product) can be recycled. The desirable adhesive properties of the adhesive (i.e., good tack, adhesion, and shear resistance) actually makes their inclusion more difficult when the time comes to recycle the product. Current technology has challenges removing labels from substrates or debonding two materials on-demand. The two main strategies, mechanical separation or volatile organics, each have their own drawbacks. Mechanical separation typically leaves residue on the substrate or is incompletely effective at removing the adhesive, and volatile organic chemicals add cost to the process and present their own sustainability challenges. Therefore, improved on- demand debonding adhesives could greatly improve recyclability of plastics and other commodity materials that use adhesives to attach labels. By being able to remove the label on demand by debonding the adhesive after application of stimulus, the commodity material can be recovered much more easily facilitating recycling and a circular economy. Similarly, debonding two substrates that are held together on demand would facilitate their reprocessing and use in subsequent applications.

[0006] Applicants have demonstrated that polymerization of an aliphatic acrylate (e.g., butyl acrylate) with a permanent crosslinker and a responsive crosslinker (e.g., a coumarin based crosslinker or coumarin monomer, a thermoresponsive crosslinker, etc.), as described herein, provides an adhesive that shows good tack, adhesion, and shear resistance, and which can also show reduced adhesive properties, including little or no adhesion, after exposure to a predetermined debonding stimulus.

[0007] The general inventive concepts are based, in part, on the discovery that an adhesive can be designed and synthesized that is crosslinked in all states and displays both good tack, adhesion, and shear resistance, while also showing on-demand debonding when exposed to apredetermined stimulus. The instant application describes adhesive compositions and methods which debond materials on-demand with better efficiency than mechanical separation while avoiding the use of volatile organic compounds. The inventive compounds align with current industry standard PSA structures and properties, without requiring complex multistep synthesis.

[0008] In certain exemplary embodiments, the general inventive concepts contemplate a debondable pressure-sensitive adhesive composition comprising the polymerized product of about 75 parts to about 95 parts of an aliphatic acrylic monomer; about 0.1 parts to about 3 parts of a permanent crosslinker; and about 2 parts to about 19 parts of a responsive crosslinker.

[0009] In certain exemplary embodiments, the general inventive concepts contemplate an article comprising a first substrate and a debondable pressure-sensitive adhesive composition bonded to a first surface of the first substrate, wherein the debondable pressure-sensitive adhesive composition comprises the polymerized product of about 75 parts to about 95 parts of an aliphatic acrylic monomer; about 0.1 parts to about 3 parts of a permanent crosslinker; and about 2 parts to about 19 parts of a responsive crosslinker.

[0010] In certain exemplary embodiments, the general inventive concepts contemplate a method of debonding an article, wherein the article comprises a first substrate and a debondable pressure-sensitive adhesive composition bonded to a first surface of the first substrate, the method comprises applying a predetermined amount of a debonding stimulus selected from UV irradiation and heat to the debondable pressure-sensitive adhesive composition such that the adhesive strength is reduced by at least 20%; wherein the debondable pressure-sensitive adhesive composition comprises about 75 parts to about 95 parts of an aliphatic acrylic monomer; about 0.1 parts to about 3 parts of a permanent crosslinker; and about 2 parts to about 19 parts of a responsive crosslinker.

[0011] Other aspects and features of the general inventive concepts will become more readily apparent to those of ordinary skill in the art upon review of the following description of various exemplary embodiments in conjunction with the accompanying figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The general inventive concepts, as well as embodiments and advantages thereof, are described below in greater detail, by way of example, with reference to the drawings in which:

[0013] Figure 1 is bar graph showing tensile strength of exemplary debonding adhesives applied to a variety of substrates, including steel, polyethylene terephthalate (two different formulations), and high density polyethylene.

[0014] Figure 2A is a graph showing a rheological frequency sweep at 25 °C of an inventive adhesive (i.e., poly(BA89.5-EGDMAo.5-CMio ) at 25 °C prior to exposure to a debonding stimulus (e.g., ultraviolet light (UV)).

[0015] Figure 2B is a graph showing a rheological frequency sweep at 25 °C of an inventive adhesive (i.e., poly(BA89.5-EGDMAo.5-CMw) at 25 °C after to exposure to a debonding stimulus (e.g., ultraviolet light (UV)) with an emission peak near 360 nm. Increase in the plateau storage modulus at low frequency is observed compared to that of Figure 2A.

[0016] Figure 3 A is a graph showing a rheological frequency sweep at 25 °C of an inventive adhesive (i.e., poly(BA94-EGDMAi-CMs) at 25 °C prior to exposure to a debonding stimulus (e.g., ultraviolet light (UV)).

[0017] Figure 3B is a graph showing a rheological frequency sweep at 25 °C of an inventive adhesive (i.e., poly(BA94-EGDMAi-CM5) at 25 °C after to exposure to a debonding stimulus (e.g., ultraviolet light (UV)) with an emission peak near 360 nm. Increase in the plateau storage modulus at low frequency is observed compared to that of Figure 3 A.

[0018] Figure 4A is an image showing an inventive adhesive according to the general inventive concepts prior to exposure to a debonding stimulus. The adhesive is comprised of poly(BA94.5-EGDMAo.5-CM5) that is 94.5% butyl acrylate, 0.5% EGDMA and 5% coumarin monomer.

[0019] Figure 4B is an image showing an inventive adhesive according to the general inventive concepts after exposure to a debonding stimulus (UV irradiation of wavelength (X) ~ 360 nm upon exposure to UV with intensity of 4.8 ± 0.5 mW / cm2). Lack of tack and adhesion is observed after UV exposure.

[0020] Figure 5 is an image showing an inventive adhesive adhering two sections of material together and supporting the weight of a bottle filled with liquid of total weight of approximately 20 g.

[0021] Figure 6A is an image showing the experimental set-up for testing the bonding properties of the inventive adhesives between two PET substrates.

[0022] Figure 6B is an image showing the experimental test of Figure 6A after UV exposure at a wavelength ( ) of ~ 360 nm. Complete loss of adhesion and complete debonding is observed after the UV exposure.

[0023] Figure 7 is an image of photo-rheology data tracking storage modulus with sustained UV exposure for polymers containing different %wt. of coumarin acrylate (e.g., a coumarin-based crosslinker). The materials tested are poly(BA94.5-EGDMAo.5-CM5) (i.e., 94.5% BA, 0.5% EGDMA and 5% CM (in blue-the lower curve) and poly(BA84.5-EGDMAo.5-CMio) (i.e., 84.5% BA, 0.5% EGDMA and 10% CM (in red-the upper curve). Increase in modulus consistent upon UV exposure is observed.

[0024] Figure 8A is a graph showing the frequency sweeps of thermoresponsive pressure sensitive adhesives with thermal stimulus of 35 °C.

[0025] Figure 8B is a graph showing the frequency sweeps of thermoresponsive pressure sensitive adhesives after application of thermal stimulus of 110 °C for 12 h.

[0026] Figure 9 is a bar graph showing the adhesive strength of the PSAs with (a) stainless steel substrate with 5% VMA and thermoresponsive initiator (ACHN) (b) PET substrate with 10% VMA and light responsive BAPO initiator (c) stainless steel substrate with 10% VMA and thermoresponsive initiator (ACHN). BAPO is a light responsive initiator and the full name is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0027] Figure 10A shows a DSC plot before and after 360 nm UV exposure for poly(BA94.5- EGDMA0.5-CM5). Increase in the glass transition temperature is observed after UV exposure.

[0028] Figure 10B shows a DSC plot before and after 360 nm UV exposure for poly(BAs4.5- EGDMA0.5-CM10). Increase in the glass transition temperature is observed after UV exposure.

[0029] Figure 10C shows a DSC plot before and after 360 nm UV exposure for poly(BA94- EGDMA1-CM5). Increase in the glass transition temperature is observed after UV exposure.

[0030] Figure 10D shows a DSC plot before and after 360 nm UV exposure for poly(BAs4- EGDMAi-CMio). Increase in the glass transition temperature is observed after UV exposure.DETAILED DESCRIPTION

[0031] Several illustrative embodiments will be described in detail with the understanding that the present disclosure merely exemplifies the general inventive concepts. Embodiments encompassing the general inventive concepts may take various forms and the general inventive concepts are not intended to be limited to the specific embodiments described herein.

[0032] While various exemplary embodiments are described or suggested herein, other exemplary embodiments utilizing a variety of methods and materials similar or equivalent to those described or suggested herein are encompassed by the general inventive concepts.

[0033] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs.

[0034] As used herein, the term “debonding” refers to a measure of the reduction of adhesive strength relative to the initial or designed adhesive strength, including a reduction of 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and including a reduction of 100% (i.e., inadhesive) relative to the tested strength of the adhesive prior to exposure to the debonding stimulus. In certain embodiments, debonding is measured by lap shear or 180° peel.

[0035] As used herein, the term “on-demand” refers to the targeted application of a stimulus to an adhesive according to the general inventive concepts. In certain exemplary embodiments, on-demand refers to a known or predetermined amount or time of exposure to a stimulus, including but not limited to seconds, minutes, hours, or days of exposure. In certain embodiments, the adhesive may be debonded multiple times (i.e., the debonded material may have its bonding / adhesive properties restored via exposure to a second / different stimulus that reverses at least a portion of the debonding crosslinking). For example, in certain exemplary embodiments, a photoresponsive adhesive may have its adhesive property restored by exposure to a predetermined amount of UV exposure at a wavelength of about 220 nm to about 290 nm.

[0036] As used herein, the term “responsive crosslinker” refers to a chemical reagent that joins or links two chemical compounds together upon exposure to an external stimulus. These stimuli could include but are not limited to photochemical stimuli, heat, chemical agents, mechanical forces, or ultrasonics. The external stimulus enables the formation of linkages (including covalent linkages) between the “responsive crosslinkers” thereby effecting a change in modulus and a reduction in adhesion. Examples of suitable responsive crosslinkers include, but are not necessarily limited to photoresponsive crosslinkers such as coumarin-based crosslinker(s) and thermoresponsive crosslinkers such as those containing pendant vinyl groups including vinyl methacrylate and furfuryl acrylate.

[0037] The term “coumarin-based crosslinker” refers to a responsive crosslinker that is a chemical reagent capable of crosslinking between two polymers or monomers and which has as its base a coumarin moiety. Coumarin is a chromene having a keto group at the 2-position. Thus, a coumarin-based crosslinker is a modified coumarin structure comprising a coumarin molecule which has been modified to further include a cross-linking moiety, for example, an acrylate or methacrylate moiety. Suitable examples of coumarin-based crosslinkers include acrylate and / or methacrylate substituted coumarin, including e.g., coumarin substituted with an acrylate functional group on one of more of the 5, 6, 7, or 8 position(s). One particularly suitable coumarin-based crosslinker is 2-oxo-2H-chromen-7yl acrylate. In certain exemplary embodiments, the term also refers to a coumarin monomer (CM). In certain exemplary embodiments, the coumarin-based crosslinker is an acrylate-substituted anthracene (e.g., an anthracene substituted with an acrylate or methacrylate functional group), including, but not limited to, 9-anthracenylmethyl (meth)acrylate.

[0038] As used herein, the term “permanent crosslinker” refers to a chemical reagent that, when activated, joins two or more chemicals by forming covalent bonds, which do not reverse under common chemical, thermal, or electromagnetic, conditions. Examples of suitable permanent crosslinkers include, but are not limited to, ethylene glycol dimethacrylate (EGMDA), diacrylates including 1,4-butanediol diacrylate, ethylene glycol diacrylate, bisphenol A-glycidyl methacrylate, and acrylic acid crosslinked with metals such as Al3+.

[0039] As used herein, the terms “stimulus” or “debonding stimulus” refer(s) to energy or force that is directed at an adhesive according to the general concepts and for which the inventiveadhesive is designed to change its adhesive properties when exposed thereto. In certain exemplary embodiments, the debonding stimulus increases a level of crosslinking in the adhesive leading to a corresponding decrease in bond strength and / or adhesive properties. In certain exemplary embodiments, the term also includes a predetermined time, distance, or concentration component. For example, exposure to a predetermined wavelength of light at a specific range of distance for a predetermined time. In certain exemplary embodiments, the term refers to at least one of UV irradiation, heat, electric current, piezoelectric, and application of a magnetic field.

[0040] The term “photoresponsive” refers to an adhesive that responds to a light-based stimulus, including UV irradiation. Thus, a photoresponsive pressure sensitive adhesive is one that, when exposed to a predetermined UV debonding stimulus, shows reduced adhesive properties such as bonding strength or lap shear (i.e., debonding). In certain embodiments a photoresponsive adhesive or photoresponsive pressure-sensitive adhesive comprises a photodimerizable unit pendant to the main polymer chains in the adhesive that can form new crosslinks when stimulated / activated (e.g., by UV light).

[0041] The term “thermoresponsive” refers to an adhesive that includes an initiator and responds to a heat-based stimulus, including increased heat (e.g., a temperature exposure of about 90 °C to about 150 °C). Thus, a thermoresponsive pressure sensitive adhesive is one that, when exposed to a predetermined amount of thermal debonding stimulus, shows reduced adhesive properties such as bonding strength or lap shear (i.e., debonding). In certain embodiments, a thermoresponsive adhesive or thermoresponsive pressure-sensitive adhesive comprises a heat- responsive radical initiator, e.g., a thermoinitiator. Suitable thermoinitiators include but are not limited to l,l'-azobis(cyclohexanecarbonitrile) (ACHN), tert-butyl peroxybenzoate, dicumyl peroxide, and tert-butyl peroxide. In certain embodiments a thermoresponsive adhesive or thermoresponsive pressure-sensitive adhesive comprises a dimerizable / polymerizable unit pendant to the main polymer chains in the adhesive that can form new crosslinks when stimulated / activated.

[0042] The term “photoinitiator-responsive” refers to an adhesive that includes a photoinitiator and responds to a light-based stimulus, including UV irradiation. Thus, a photoinitiator-responsive pressure sensitive adhesive is one that, when exposed to a predeterminedUV debonding stimulus, the photoinitiator forms radicals to facilitate secondary coupling and crosslinking of e.g., pendant vinyl groups in the polymer which, in turn, results in reduced adhesive properties such as bonding strength or lap shear (i.e., debonding). Suitable photoinitiators include but are not limited to phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), 2,2-dimethoxy- 2-phenylacetophenone (DMPA).

[0043] The term “aliphatic acrylic monomer” refers to a molecule comprising a polymerizable acrylate functional group and a carbon chain having a length of 2 to 22 carbons (e.g., a C2-C22 moiety). As used herein, the following terms should be understood as follows: methyl, ethyl, n-Propyl, isopropyl, n-Butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl or octyl and all bond isomers are to be considered as (Ci-Cs)-alkyl and so on. In certain exemplary embodiments, the aliphatic acrylate is a C2-C22 acrylate, including a C2-C16 acrylate, and including a C2-C8 acrylate. One suitable aliphatic acrylic monomer is Butyl acrylate, which refers to a compound with the formula C4H9O2CCH=CH2.

[0044] Thus, in certain exemplary embodiments, the general inventive concepts contemplate compositions, systems, and methods wherein one or more stimuli (e.g., debonding stimuli) can be applied to change a material’s adhesive strength, converting a PSA to a nonadhesive or inconsequentially-low adhesive material, allowing for separation of (previously adhered) the substrates from each other with greater ease. The change in adhesion can be reversible, with the possibility of applying a different stimulus to return the PSA to an adhesive state.

[0045] The general inventive concepts are based, in part on the discovery that polymerization of an aliphatic acrylate in the presence of a permanent crosslinker, and a responsive crosslinker can provide a debonding on-demand adhesive as described herein.

[0046] In certain exemplary embodiments, the general inventive concepts contemplate a debondable pressure-sensitive adhesive composition comprising about 75 to about 95 parts of an aliphatic acrylic monomer; about 0.1 parts to about 3 parts of a permanent crosslinker; and about 2 parts to about 19 parts of a responsive crosslinker.

[0047] In certain exemplary embodiments, the aliphatic acrylic monomer is present in the debondable pressure-sensitive adhesive composition in an amount of from about 75 parts to about95 parts, including about 79 parts to about 92 parts, including about 82 parts to about 89 parts, and including about 84 parts to about 87 parts. In certain exemplary embodiments, the aliphatic acrylic monomer is present in the debondable pressure-sensitive adhesive composition in an amount of about 84 parts to about 95 parts of the composition.

[0048] In certain exemplary embodiments, the permanent crosslinker is present in the debondable pressure-sensitive adhesive composition in an amount of from about 0.1 parts to about 3 parts, including about 0.3 parts to about 2.6 parts, including about 0.6 parts to about 2.1 parts, including about 1.2 parts to about 1.7 parts. In certain exemplary embodiments, the permanent crosslinker is present in the debondable pressure-sensitive adhesive composition in an amount of from about 0.5 parts to about 1 parts of the composition.

[0049] In certain exemplary embodiments, the responsive crosslinker is present in the debondable pressure-sensitive adhesive composition in an amount of from about 2 parts to about 19 parts, including about 3.5 parts to about 15.8 parts, including about 4.2 parts to about 12.7 parts, including about 6.9 parts to about 9.3 parts. In certain exemplary embodiments, the responsive crosslinker is present in the debondable pressure-sensitive adhesive composition in an amount of from about 5 parts to about 10 parts of the composition.

[0050] In certain exemplary embodiments, a radical initiator is present in the debondable pressure-sensitive adhesive composition. In embodiments wherein the debondable pressuresensitive adhesive composition is thermoresponsive or photoinitiator-responsive a radical initiator promotes radical formation to help secondary coupling and crosslinking of e g., pendant vinyl groups in the polymer. When present, the radical initiator is present in an amount of from about 0.01 parts to about 1 parts, including about 0.04 parts to about 0.8 parts, including about 0.09 parts to about 0.7 parts, including about 0.15 parts to about 0.5 parts. In certain exemplary embodiments, radical initiator is present in the debondable pressure-sensitive adhesive composition in an amount of from about 0.1 parts to about 1 parts of the composition.

[0051] In certain exemplary embodiments, the general inventive concepts contemplate an article comprising a first substrate and a debondable pressure-sensitive adhesive composition bonded to a first surface of the first substrate, wherein the debondable pressure-sensitive adhesive composition comprises the reaction product of at least about 75 to about 95 parts of an aliphatic acrylic monomer; about 0.1 parts to about 3 parts of a permanent crosslinker; and about 2 parts toabout 19 parts of a responsive crosslinker. In certain exemplary embodiments, the article comprises a second substrate having a second surface and the first surface of the first substrate is bonded to the second surface of the second substrate by way of the debondable pressure-sensitive adhesive composition.

[0052] In certain exemplary embodiments, the general inventive concepts contemplate a method of debonding an article, wherein the article comprises a first substrate and a debondable pressure-sensitive adhesive composition bonded to a first surface of the first substrate, the method comprises applying a predetermined amount of a debonding stimulus selected from UV irradiation and heat to the debondable pressure-sensitive adhesive composition such that the adhesive strength is reduced by at least 20%; wherein the debondable pressure-sensitive adhesive composition comprises the reaction product of at least about 75 to about 95 parts of an aliphatic acrylic monomer; about 0. 1 parts to about 3 parts of a permanent crosslinker; and about 2 parts to about 19 parts of a responsive crosslinker.

[0053] In certain exemplary embodiments, when the debondable pressure-sensitive adhesive composition is photoresponsive, the debonding stimulus is UV radiation, including light with a wavelength of from about 300 nm to about 400 nm, including from about 310 nm to about 387 nm, including from about 328 nm to about 369 nm, including from about 341 nm to about 352 nm. In certain exemplary embodiments, the debonding stimulus is UV with a wavelength of from about 350 nm to about 360 nm.

[0054] In certain exemplary embodiments, when the debondable pressure-sensitive adhesive composition is thermoresponsive, the debonding stimulus is heat (i.e., increased heat), including heating the material(s) to a temperature of from about 75 °C to about 150 °C for a period of about 5 minutes to about 24 hours, including heating the material to a temperature of from about 90 °C to about 150 °C, including 106 °C to about 142 °C, including 119 °C to about 136 °C. Those of ordinary skill in the art will recognize that, generally speaking, when the temperature of the stimulus is greater, the corresponding time for debonding to occur will decrease, and vice versa. For example, a stimulus temperature of 137 °C would not be expected to require as much time as a stimulus temperature of 84 °C. The general inventive concepts also contemplate compositions that are responsive to more than one debonding stimulus, for example, a composition that is responsive to both thermal and photo stimulus.

[0055] All references to singular characteristics or limitations of the present disclosure shall include the corresponding plural characteristic or limitation, and vice versa, unless otherwise specified or clearly implied to the contrary by the context in which the reference is made.

[0056] The following examples illustrate features and / or advantages of the compositions, systems, and methods according to the general inventive concepts. The examples are given solely for the purpose of illustration and are not to be construed as limitations of the general inventive concepts, as many variations thereof are possible without departing from the spirit and scope of the general inventive concepts.EXAMPLES:

[0057] Photopolymerization of poly(EA / BA-EGDMA) materials

[0058] Butyl acrylate (4g) and 2,2-Dimethoxy-2-phenylacetophenone (DMPA) (40 mg) were added in a glass vial. In that mixture, ethylene glycol dimethylacrylate (EGDMA) crosslinker (0.02g, 0.04g, 0.08g, 0.2g, and 0.4g) was then added respectively to synthesize 0.5%, 1%, 2%, 5%, and 10% materials. The mixture was sonicated for 15 minutes for proper mixing / dissolution and then transferred to a Teflon mold for polymerization. The free radical polymerization was carried out at room temperature for 15 min. After the polymerization, the crosslinked material was removed from the mold and allowed to dry for 2 days at ambient condition. The materials were further dried overnight in a vacuum oven at 40 °C.

[0059] Photopolymerization of poly(BA)-with BDDA, BDDMA and TMPTA crosslinkers

[0060] Butyl acrylate (4g) and 2,2-Dimethoxy-2-phenylacetophenone (DMPA) (40 mg) were added in a glass vial. In that mixture, 1,4-butanediol diacrylate (BDDA) crosslinker (0.02g, 0.08g and 0.4g) was then added respectively to synthesize 0.5%, 2% and 10% materials. The mixture was sonicated for 15 minutes for proper mixing / dissolution and then transferred to a Teflon mold for polymerization. The free radical polymerization was carried out at room temperature for 15 min. After the polymerization, the crosslinked material was removed from the mold and allowed to dry for 2 days at ambient condition. The same procedure was used for the synthesis of poly (BA) with 1,4-butanediol dimethacrylate (BDDMA) crosslinker and poly (BA) with trimethylolpropane triacrylate (TMPTA) crosslinker. In these cases, BDDMA and TMPTA were respectively used in place of BDDA.

[0061] Synthesis of 2-oxo-2H-chromen-7-yl acrylate (Coumarin Monomer, CM)

[0062] l-Ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride EDC (29.25g, 0.1870 mol) and 150 mL of DCM was added into a 500 mL round bottom flask with a stir bar. The flask was put in an ice bath and 7-hydroxy coumarin (17.68g, 0.1210 mol) was added to the flask. Next, while stirring, acrylic acid (AA) (11.17g, 0.1550 mol) was added to the flask. Lastly, DMAP (0.95g, 0.0078 mol) was added. The flask was then sealed and stirred for 48 hours. Once the reaction finished, the reaction mixture was washed with 0.2 M HC1 (3x), brine (3x), saturated NaHCOs (3x), water (lx), and finally brine (3x). Separated organic phase was dried in MgSO4 and the solution was evaporated in vacuum to yield coumarin monomer 2-oxo2H-chromen-7-yl acrylate (CM) as slightly pinkish solid. (18.6 g .0864 mol, 72% yield)

[0063] ‘H-NMR (CDC13, 500 MHz): 5 ppm 7.70 (d, J = 9.56 Hz, 1H), 7.50 (d, J = 8.49 Hz, 1H), 7.17 (d, J = 2.25 Hz, 1H), 7.10 (dd, J = 8.56 Hz, 2.17 Hz, 1H), 6.66 (dd, J = 17.29 Hz, 1.02 Hz, 1H), 6.41 (d, J = 9.59 Hz, 1H), 6.33 (dd, J = 17.39 Hz, 10.41 Hz, 1H), 6.09 (dd, J = 10.43 Hz, 1.00 Hz, 1H).

[0064] Typical synthesis of poly (BA)-EGDMA-CM materials

[0065] Butyl acrylate (BA) (4g), 2,2'-Azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) (40 mg) and N,N-dimethylformamide (DMF) (8ml) were added in a glass vial. In that mixture, EGDMA (0.02g and 0.04g) and coumarin monomer (CM) (0.05g and 0.100g) was then added respectively to synthesize poly(BA-0.5%EGDMA-5%CM), poly(BA-0.5%EGDMA-10%CM), poly(BA-l%EGDMA-5%CM) and poly(BA-l%EGDMA-10%CM) materials. The mixture was sonicated for 10 minutes for proper mixing / dissolution and then transferred to a Teflon mold for polymerization. The free radical polymerization was carried out at 35 °C for 3h. After the polymerization, the crosslinked material was removed from the mold and allowed to dry for 3 days at ambient condition. The materials were further dried overnight in a vacuum oven at 40 °C.

[0066] Typical synthesis of poly BA-AA-CM materials

[0067] Butyl acrylate (BA) (4.6g), Acrylic acid (AA) (150 mg), coumarin monomer (CM) (250 mg), n-dodecyl mercaptan (n-DDM, a chain transfer agent) (20 mg), and 2,2'-Azobis(4- methoxy-2,4-dimethylvaleronitrile) (V-70, a radical initiator) (25 mg) and N,N- dimethylformamide (DMF) (10 g) were added in a glass vial to synthesize poly(BA-3%AA-5%CM) polymer. The mixture was mixed for 1 min for proper mixing / dissolution, followed by N2 bubbling for 5 min to de-oxygenate the mixture. The free radical polymerization was carried out at 23 °C for 18h. After that the polymer was characterized by GPC / SEC for MW and GC for % conversion.

[0068] Post -polymerization crosslinking of BA-AA-CM materials

[0069] By avoiding the use of a multifunctional acrylate such as EGDMA during synthesis allowed the post polymerization crosslinking of the BA-AA-CM polymer by two different types of crosslinkers. In one example, 0.5% wt. (w.r.t. polymer) of aluminum acetyl acetonate (AAA) was added to the polymer solution, followed by a 50 micron fdm drawdown and subsequent drying + curing at 120 °C for 15 min. This formed dynamic metal-chelate cross-linked network. In another example, 0.6% wt. (w.r.t. polymer) of polyfunctional aziridine (CX100 from Covestro) was added to the polymer solution. Then a film drawdown of 50 micron and curing at 120°C for 15 min proceeded. Use of aziridine crosslinker formed a permanent covalent crosslinked network.

[0070] Characterization

[0071] Frequency sweep

[0072] Rheological frequency sweep experiments were carried out using a TA instrument (New Castle, DE) Discovery HR-1 rheometer. A 20 mm crosshatched plate geometry was used for all the experiments. In all cases, rheology disks were synthesized in a 20 mm diameter circular Teflon mold. Frequency sweep experiments were carried out from 0.1 to 500 Hz angular frequency with 0.5% applied strain at 25 °C. Rheological analysis giving viscous (G”) and elastic (G’) responses change with network composition, frequency or in this case UV irradiation is carried out. In general PSAs have rheological moduli below 100 kPa at room temperature and 1 Hz, (according to the Dahlquist criterion). The inventive materials have moduli of about 5-50 kPa before UV irradiation, which satisfies the Dahlquist criterion. Materials with moduli below 100 kPa give superior adhesion to a substrate and allow proper wetting of the substrate. In contrast, a modulus that is too low may lack shear resistance which can happen below 5 kPa. Figure 2 & 3 show frequency sweep plots before and after exposure to debonding stimuli (i.e., 360 nm UV) for the EGDMA-CM crosslinked networks. All of the samples exhibit typical viscoelastic solid behavior, as shown in Figure 2-3, where the storage modulus (G’) is higher than the loss modulus (G”) at low frequencies and transitions towards a glass transition-like behavior at higherfrequencies. As seen in Figure 2B & 3B, the EGDMA crosslinked networks all showed a notable increase in the storage modulus G’ after UV irradiation. Materials containing 10% CM (Fig. 2) showed an increase in G’ after UV than networks containing 5% CM (Fig. 3) due to higher % of CM in the polymer in Fig. 2.

[0073] Differential Scanning Calorimetry (DSC)

[0074] All glass transition temperatures (7g) were obtained using a TA instrument DSC Q2000. The data was obtained in a heat-cool -heat cycle ranging from -80 °C to 150 °C with 10 °C / min heating rate. Data from the second heating cycle was used to plot the curve. Differential scanning calorimetry (DSC) was used to investigate the thermal behavior of the coumarin- containing PSAs. Measuring glass transition temperature (Tg) is an indirect measure of a material’s ability to function as a PSA. If a material’s Tgincreases due to applied stimulus, the adhesive properties should decrease, due to reduced chain mobility.

[0075] As shown in Fig. 10, after UV irradiation networks with 10% coumarin had a larger increase in Tgcompared to materials with 5% coumarin moiety. This is expected because the increase in crosslink density is directly correlated with the coumarin monomer required for dimerization.

[0076] Lap Shear

[0077] Uniaxial tensile testing experiments were carried out using PET, HDPE, and stainless steel as the substrate. The network materials were sandwiched between two substrates of the same materials, and they were attached to Instron 3344 universal testing system equipped with a 2000 N load cell. The extension rate was 5 mm / s and data were collected until the material failed.

[0078] Debonding of Adhesives

[0079] The adhesive materials were sandwiched and bonded between two PET substrates and a roller of 4.5 lbs was rolled back and forth twice on the PET substrates containing the adhesive materials to obtain a firm bond between the adhesive material and the PET substrates. The adhesives were de-bonded from PET substrate using a photoreactor with UV lamps with a peak near 350 nm with intensity 2.6 ± 0.2 mW / cm2, measured as a straight-line intensity. To obtain 2+2 cycloaddition crosslinked polymers using UV light, the adhesive materials were irradiated with UV light of approximately 350 nm at ambient temperature and pressure. The distance between thePET substrate and the light source was 1 .57 inches and was kept constant till the experiment was ended after 24hr of UV irradiation. The resultant PET substrate was de-bonded from adhesive material. The reversibility of the crosslinked polymers was carried out under UV light of 250 nm at ambient temperature and pressure for 24 hr with the same experimental set up as the 350 nm UV.

[0080] Thermally Responsive Debonding-on-Demand Pressure Sensitive Additives PSAs Materials

[0081] All starting materials, solvents, and reagents were purchased from commercial sources and used directly without further purification unless when otherwise stated. Thermal initiator 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) was obtained from Fujifilm Wako and l,r-azobis(cyclohexanecarbonitrile) (ACHN) was obtained from Sigma- Aldrich. Butyl acrylate (BA), vinyl methacrylate (VMA) and furfuryl methacrylate (FMA) were obtained from ACROS Organics. In certain embodiments, vinyl methacrylate and furfuryl methacrylate are the cross linkers that are used in thermal debonding. Upon heat (in the presence of ACHN thermal initiator) they crosslink to increase crosslink density and reduce adhesion.

[0082] Polymer synthesis

[0083] Typical synthesis of poly(BA-VMA) materials

[0084] BA (8.75g), vinyl methacrylate (VMA) (g), V-70 (0.1g), ACHN (0.1 g) and N,N- dimethylformamide (DMF) (10ml) were added in a glass vial. The mixture was sonicated for 10 minutes for proper mixing / dissolution and then transferred to a Teflon mold for polymerization. The free radical polymerization was carried out at 35 °C for 3h. After the primary polymerization was completed, the polymer was removed from the mold and allowed to dry for 3 days at ambient condition. After drying, adhesive strength experiment, differential scanning calorimetry (DSC), rheological characterization and debonding experiment were carried out on the PSAs.

[0085] Characterization

[0086] Rheology

[0087] Rheological frequency sweep experiments were carried out using a TA instrument (New Castle, DE) Discovery HR-1 rheometer. A 20 mm crosshatched plate geometry was used for all the experiments. In all cases, rheology disks were synthesized in a 20 mm diameter circularTeflon mold. Frequency sweep experiments were carried out from 0.1 to 600 Hz angular frequency with 0.5% applied strain at 25 °C. See Fig. 8A-8B.

[0088] Lap Shear

[0089] Uniaxial tensile testing experiments were carried out using PET, HDPE, and stainless steel as the substrate. The network materials were sandwiched between two substrates of the same materials, and they were attached to Instron 3344 universal testing system equipped with a 2000 N load cell. The extension rate was 5 mm / s and data were collected until the material failed. See Fig. 9.

[0090] Debonding of Adhesives

[0091] The adhesive materials were sandwiched and bonded between two stainless steel (SS) substrates and a roller of 4.5 lbs was rolled back and forth twice on the SS substrates containing the adhesive materials to obtain a firm bond between the adhesive material and the SS substrates. To obtain secondary polymerization / crosslinking which ultimately leads to debonding of the PSA from the substrate due to reduce adhesive strength, ACHN thermal initiator was fully activated by heating the PSA sandwiched between SS in the oven for 12 hours at 110 °C . After that, it was allowed to cool to room temperature then lap shear test was carried out.

[0092] All combinations of method or process steps as used herein can be performed in any order, unless otherwise specified or clearly implied to the contrary by the context in which the referenced combination is made. All references to methods or processes are intended to comprise and encompass each embodiment of the compositions described herein, including those described in the examples.

[0093] All ranges and parameters, including but not limited to percentages, parts, and ratios, disclosed herein are understood to encompass any and all sub-ranges assumed and subsumed therein, and every number between the endpoints. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more (e.g., 1 to 6.1), and ending with a maximum value of 10 or less (e.g., 2.3 to 9.4, 3 to 8, 4 to 7), and finally to each number 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 contained within the range.

[0094] The compositions, systems, and corresponding methods of the present disclosure can comprise, consist of, or consist essentially of the essential elements and limitations of the disclosure as described herein, as well as any additional or optional ingredients, components, or limitations described herein or otherwise useful in the general inventive concepts.

[0095] The compositions of the present disclosure may also be substantially free of any optional or selected component or feature described herein, provided that the remaining composition still contains all of the required elements or features as described herein. In this context, and unless otherwise specified, the term “substantially free” means that the selected composition contains less than a functional amount of the optional component, typically less than 0.1% by weight, and also including zero percent by weight of such optional or selected component.

[0096] To the extent that the terms “include,” “includes,” or “including” are used in the specification or the claims, they are intended to be inclusive in a manner similar to the term “comprising” as that term is interpreted when employed as a transitional word in a claim. Furthermore, to the extent that the term “or” is employed (e.g., A or B), it is intended to mean “A or B or both A and B.” When the Applicant intends to indicate “only A or B but not both,” then the term “only A or B but not both” will be employed. Thus, use of the term “or” herein is the inclusive, and not the exclusive use. In the present disclosure, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular.

[0097] In some aspects, it may be possible to utilize the various inventive concepts in combination with one another. Additionally, any particular element recited as relating to a particularly disclosed embodiment should be interpreted as available for use with all disclosed embodiments, unless incorporation of the particular element would be contradictory to the express terms of the embodiment. Additional advantages and modifications will be readily apparent to those skilled in the art. Therefore, the disclosure, in its broader aspects, is not limited to the specific details presented therein, the representative composition, or the illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general inventive concepts.

[0098] While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It should be understood that only the exemplary embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.

Claims

Claims:

1. A debondable pressure-sensitive adhesive composition comprising the polymerized product of at least: about 75 to about 95 parts of an aliphatic acrylic monomer; about 0.1 parts to about 3 parts of a permanent crosslinker; and about 2 parts to about 19 parts of a responsive crosslinker.

2. The debondable pressure sensitive adhesive of claim 1, wherein the adhesive is selected from a thermoresponsive adhesive, a photoresponsive adhesive, and a photoinitiator- responsive adhesive.

3. The debondable pressure sensitive adhesive of claim 1, wherein the adhesive is a photoresponsive pressure sensitive adhesive.

4. The debondable pressure sensitive adhesive of claim 1, wherein the adhesive is a thermoresponsive pressure sensitive adhesive.

5. The debondable pressure sensitive adhesive of claim 4, wherein the responsive crosslinker is selected from vinyl acrylate and furfuryl acrylate and the adhesive further comprises a radical initiator in an amount of about 0.01 parts to about 1 part.

6. The debondable pressure sensitive adhesive of claim 1, wherein the aliphatic acrylic monomer is a C2-C22 aliphatic acrylic monomer.

7. The debondable pressure sensitive adhesive of claim 6, wherein the aliphatic acrylic monomer is a C2-C8 aliphatic acrylic monomer.

8. The debondable pressure sensitive adhesive of claim 1, wherein the aliphatic acrylic monomer is butyl acrylate.

9. The debondable pressure sensitive adhesive of claim 1, wherein the permanent crosslinker is selected from ethylene glycol dimethacrylate (EGMDA), diacrylates including 1,4- butanediol diacrylate, ethylene glycol diacrylate, bisphenol A-glycidyl methacrylate, acrylic acid crosslinked with Al3+, and combinations thereof.

10. The debondable pressure sensitive adhesive of claim 9, wherein the permanent crosslinker is EGDMA.

11. The debondable pressure sensitive adhesive of claim 1, wherein the responsive crosslinker is a coumarin-based crosslinker.

12. The debondable pressure sensitive adhesive of claim 1, further comprising a radical initiator selected from phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), 2,2'- Azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1 '-azobis(cyclohexanecarbonitrile), tertbutyl peroxybenzoate, dicumyl peroxide, tert-butyl peroxide, and combinations thereof.

13. An article comprising a first substrate and a debondable pressure-sensitive adhesive composition bonded to a first surface of the first substrate, wherein the debondable pressure-sensitive adhesive composition comprises the polymerized product of at least: about 75 to about 95 parts of an aliphatic acrylic monomer; about 0.1 parts to about 3 parts of a permanent crosslinker; and about 2 parts to about 19 parts of a responsive crosslinker.

14. The article of claim 13, wherein the debondable pressure-sensitive adhesive is selected from a thermoresponsive adhesive, a photoresponsive adhesive, and a photoinitiator- responsive adhesive.

15. The article of claim 13, wherein the debondable pressure-sensitive adhesive is a photoresponsive pressure sensitive adhesive.

16. The article of claim 13, wherein the debondable pressure-sensitive adhesive is a thermoresponsive pressure sensitive adhesive.

17. The article of claim 13, wherein the aliphatic acrylic monomer is a C2-C22 aliphatic acrylic monomer.

18. The article of claim 13, wherein the aliphatic acrylic monomer is butyl acrylate.

19. The article of claim 13, wherein the permanent crosslinker is selected from ethylene glycol dimethacrylate (EGMDA), diacrylates including 1,4-butanediol diacrylate, ethyleneglycol diacrylate, bisphenol A-glycidyl methacrylate, acrylic acid crosslinked with Al3+, and combinations thereof.

20. The article of claim 13, wherein the responsive crosslinker is 2-oxo-2H-chromen-7-yl acrylate.

21. The article of claim 13, wherein the responsive crosslinker is selected from vinyl acrylate and furfuryl acrylate.

22. The article of claim 13 further comprising a second substrate having a second surface and the first surface of the first substrate is bonded to the second surface of the second substrate by way of the debondable pressure-sensitive adhesive composition.

23. A method of debonding an article, wherein the article comprises a first substrate and a debondable pressure-sensitive adhesive composition bonded to a first surface of the first substrate, the method comprising: applying a predetermined amount of a debonding stimulus selected from UV irradiation, heat, and combinations thereof to the debondable pressure-sensitive adhesive composition such that the adhesive strength is reduced by at least 20%; wherein the debondable pressure-sensitive adhesive composition comprises the polymerized product of at least: about 75 to about 95 parts of an aliphatic acrylic monomer; about 0.1 parts to about 3 parts of a permanent crosslinker; about 2 parts to about 19 parts of a responsive crosslinker.

24. The method of claim 23, wherein the debonding stimulus is selected from at least one of UV irradiation, heat, electric current, piezoelectric, and application of a magnetic field.

25. The method of claim 23, wherein the debonding stimulus is UV.

26. The method of claim 25, wherein the debonding stimulus is UV at a wavelength of about 300 nm to about 400 nm.

27. The method of claim 25, wherein the debonding stimulus is UV at a wavelength of about 350 nm to about 360 nm.

28. The method of claim 23, wherein the debonding stimulus is heat.

29. The method of claim 28, wherein the debonding stimulus comprises heating the article to a temperature of about 75 °C to about 150 °C.

30. The method of claim 29 comprising heating the article for a period of about 5 minutes to about 24 hours.

31. The method of claim 23, wherein the stimulus is applied such that the adhesive strength is reduced by about 30% to about 100%.

32. The method of claim 23, wherein the article further comprises a second substrate having a second surface and the first surface of the first substrate is bonded to the second surface of the second substrate by way of the debondable pressure-sensitive adhesive composition.

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