EP4688879A2 - Self-healing polymers and formulations for preparing self-healing polymers - Google Patents

Abstract

A thermally stable self-healing dual-capsule system that can withstand high temperatures during FROMP while remaining viable for an extended period of time prior to releasing its payload during a healing event is described. Particularly, a dual-capsule system comprising monomer microcapsules and catalyst microcapsules has been used to demonstrate self-healing of p(DCPD) with low catalyst loads achieving high repair efficacy and mechanical strength.

Description

SELF-HEALING POLYMERS AND FORMULATIONS FOR PREPARING SELF-

HEALING POLYMERS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. Provisional Application No. 63/454,806, filed March 27, 2023, the entirety of which is incorporated by reference herein for all purposes.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH

[0002] This invention was made with government support under award DE-AR0001330 awarded from the US Department of Energy. The government has certain rights in the invention.

BACKGROUND

[0003] Frontal polymerization (FP) is an energy efficient technique that involves an initial energy stimulus that fully cures the monomer resin in a self-propagating fashion at a steadystate front velocity. At the polymerization front, low-viscosity monomers transform into a cross-linked network quickly, creating a well-defined monomer-to-polymer interface.

[0004] As an example of FP, frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD) catalyzed by Grubbs-type ruthenium complexes has demonstrated that FROMP is compatible with a variety of applications, ranging from additive manufacturing techniques (e.g., 3D printing) to the fabrication of composite materials.

[0005] Poly(dicyclopentadiene) (p(DCPD)) materials have desirable properties, comparable or even superior to common bisphenol A (BP A) epoxies with thermochemical stabilities suitable for traditional manufacturing methods, but p(DCPD) materials can be damaged during their service lifetime due to factors such as thermal stress, continuous or high cycle fatigue loading, underwater conditions, high pressure, or corrosive environments.

[0006] Fail-safe features such as self-healing can extend the service life of thermosets by repairing minor damage or small fatigue cracks when they occur, thereby retarding their propagation to more catastrophic scope. Autonomous self-healing offers a cost-effective solution to prolong a material’s working lifetime in difficult-to-access areas, such as spacecraft or buried pipelines, where repairs or replacement are expensive. However, few strategies currently exist to non-invasively repair engineering materials damaged by extreme environments like space, offshore waters, and high-pressure applications.

[0007] Previous research has focused on self-healing of epoxy and epoxy vinyl ester thermosets and their composites using microencapsulated (or microvascularized) DCPD and various generations and derivatives of Grubbs catalysts (e.g., [(SIMes)Ru(=CHPh)(PCy3)C12]; G2), but the same cannot be achieved for a p(DCPD) matrix utilizing G2 or wax-coated catalyst particles due to their thermal and chemical instability during high-temperature fabrication (c.g, FROMP). Furthermore, limitations such as poor control over the size of the solid catalysts, inefficient mixing of the healing agents, and wax plasticization of the healed layer result in the need for excess amounts of catalyst (2.5 wt.%) to achieve satisfactory healing efficiency and peak loads of 50 N, as measured in tapered double cantilever beam (TDCB) tests.

SUMMARY

[0008] A thermally stable self-healing dual-capsule system that can withstand high temperatures during FROMP while remaining viable for an extended period of time prior to releasing its payload during a healing event is described herein. Particularly, a dual-capsule system comprising monomer microcapsules and catalyst microcapsules has been used to demonstrate self-healing of p(DCPD) with low catalyst loads achieving high repair efficacy and mechanical strength.

[0009] Thermally stable catalyst was used in dissolved form (e.g., about 1 wt.%), which ensured homogeneous mixing of the two-part healing system and allowed the stoichiometry of the healing agents to be tuned. Following optimization of encapsulation and microcapsule loading, the self-healing microcapsules exhibited thermal stability to FROMP conditions and facilitated self-healing efficiencies of 90% via tapered double cantilever beam tests. In one embodiment, stability was achieved through the use of a robust encapsulation system, a thermally resistant /v.s-N-heterocyclic (NHC) Ru-carbene pre-catalyst, and a Cu(I) activation coreagent.

[00010] In an aspect, a formulation for preparing a self-healing polymer comprises a polymer precursor liquid and a dual-capsule system dispersed in the polymer precursor liquid. The dual-capsule system includes monomer microcapsules each comprising a monomer solution and an activator encapsulated in a shell and catalyst microcapsules each comprising a ruthenium catalyst and a solvent encapsulated in a shell.

[00011] In an embodiment, the shells of the monomer microcapsules and the catalyst microcapsules resist degradation to temperatures of at least 200 °C, the shells being thermally stable shells.

[00012] In an embodiment, a monomer solution comprises a monomer capable of ringopening metathesis polymerization (ROMP). For example, the monomer solution may include ring-strained unsaturated monomers such as, but not limited to, cyclopentadiene, cyclooctene, cyclooctadiene, dicyclopentadiene (DCPD), norbornene, and/or 5-ethylidene-2-norbornene (ENB). For example, the monomer solution may include the ENB at a concentration of up to 5 vol.%.

[00013] In an embodiment, the activator comprises a metal ion capable of participating in a transmetalation reaction. For example, the activator may include a Cu ion.

[00014] In an embodiment, the ruthenium catalyst comprises a thermally latent Grubbsbased complex, such as a thermally latent Grubbs-type complex bearing two N-heterocyclic carbene ligands.

[00015] In an embodiment, the solvent comprises a high boiling point organic solvent. For example, the solvent may include phenylcyclohexane.

[00016] In an embodiment, the monomer microcapsules, the catalyst microcapsules, or both have a nominal width or diameter in a range from 1 micron to 800 microns. In an embodiment, the monomer microcapsules and the catalyst microcapsules have a concentration in the polymer precursor liquid in a range from about 1 wt.% to about 40 wt.%. In an embodiment, the concentration is at least 15 wt.%.

[00017] In an embodiment, the shell of each of the monomer microcapsules and the catalyst microcapsules has a nominal thickness in a range from about 20 nm to about 10 microns. In an embodiment, the shell of each of the monomer microcapsules and the catalyst microcapsules has a multilayer structure. In an embodiment, the shell of each of the monomer microcapsules and the catalyst microcapsules includes one or more polymer layers and/or one or more ceramic layers. For example, the one or more polymer layers may comprise urea- formaldehyde, polymelamine, and/or polydopamine. In an embodiment, the one or more ceramic layers comprise silica.

[00018] In an embodiment, a polymer precursor liquid comprises a monomer capable of thermal curing and a ruthenium catalyst. For example, the ruthenium catalyst may be a Grubbsbased complex and the monomer may be capable of frontal ring-opening metathesis polymerization (FROMP). For example, the monomer may be dicyclopentadiene (DCPD) and/or 5-ethylidene-2-norbornene (ENB). In an embodiment, the polymer precursor liquid includes ENB at a concentration of up to 5 vol%.

[00019] In an embodiment, a polymer precursor liquid and a monomer microcapsule comprise the same monomer. In an embodiment, a polymer precursor liquid and a monomer microcapsule comprise different monomers.

[00020] In an embodiment, a rheology modifier, such as 5 wt.% fumed silica) is incorporated into the polymer precursor liquid to prevent or limit segregation (e.g., gravitational sedimentation) of microcapsules.

[00021] In an aspect, a method of producing a self-healing polymer comprises providing a formulation described herein and heating the polymer precursor liquid to effect polymerization, the monomer microcapsules and the catalyst microcapsules remaining intact during the heating, thereby forming a self-healing polymer.

[00022] In an embodiment, the step of heating the polymer precursor liquid to effect polymerization is a FROMP process. In an embodiment, the step of heating the polymer precursor liquid to effect polymerization comprises initiating an exothermal polymerization reaction in the polymer precursor liquid and generating a self-propagating polymerization front that moves through the polymer precursor liquid.

[00023] In an embodiment, the self-healing polymer comprises a thermoset polymer. In an embodiment, the self-healing polymer comprises polydicyclopentadiene (p(DCPD)).

[00024] In an aspect, a self-healing polymer comprises a polymer matrix and a dualcapsule system dispersed in the polymer matrix. The dual-capsule system comprises monomer microcapsules, each monomer microcapsule comprising a monomer solution and an activator encapsulated in a shell and catalyst microcapsules, each catalyst microcapsule comprising a ruthenium catalyst and a solvent encapsulated in a shell.

[00025] In an embodiment, the polymer matrix comprises a thermoset polymer, such as pDCPD. In an embodiment, the polymer matrix is an epoxy matrix, such as, but not limited to, Epon828 + Epikure3223.

[00026] In an aspect, a method of using a self-healing polymer comprises using a component comprising a self-healing polymer described herein in a remote location; during use of the component, exposing the self-healing polymer to mechanical forces or environmental conditions capable of inflicting damage; and during the exposure, forming a damaged region of the self-healing polymer, the monomer microcapsules and the catalyst microcapsules rupturing as a result of the damage, whereby the monomer solution, the activator, and the ruthenium catalyst are mixed in the damaged region, and ring-opening metathesis polymerization occurs in the damaged region, thereby effecting self-healing of the component. For example, the remote location may be undersea, underground, in space, or in a human body.

[00027] In an aspect, a formulation for preparing a self-healing polymer comprises a polymer precursor liquid, a thermally latent ruthenium catalyst dispersed directly in the polymer precursor liquid (with encapsulation), and monomer microcapsules dispersed in the polymer precursor liquid. The monomer microcapsules each comprise a monomer solution and an activator encapsulated in a shell.

BRIEF DESCRIPTION OF THE DRAWINGS

[00028] In order that the present disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings. The components in the figures are not necessarily to scale.

[00029] FIG. 1 illustrates a cross-sectional view of a self-healing polymer matrix comprising monomer microcapsules and catalyst microcapsules, according to an embodiment;

[00030] FIG. 2 illustrates an exemplary structure of a microcapsule;

[00031] FIG. 3 shows scanning electron micrographs of monomer microcapsules and catalyst microcapsules, according to some embodiments; [00032] FIG. 4 shows thermal gravimetric analysis (TGA) traces for exemplary monomer microcapsules and catalyst microcapsules;

[00033] FIG. 5 shows infrared spectra for exemplary monomer microcapsules and catalyst microcapsules;

[00034] FIG. 6 illustrates a schematic of frontal polymerization with microcapsules and scanning electron micrographs of a matrix containing intact microcapsules and the same matrix damaged by a razor blade to release healing agents from the microcapsules;

[00035] Fig. 7 shows the effect of incorporating microcapsules into a polymer precursor on FROMP fontal velocity (vf), frontal temperature (T_max) and glass transition temperature (T_g) as a function of microcapsule loading;

[00036] FIG. 8 illustrates a schematic of a self-healing polymer containing a dualcapsule system that is virgin, damaged, or repaired by self-healing, and subjected to a tapered double cantilever beam (TDCB) test;

[00037] FIG. 9 compares TDCB test results of virgin, healed and unhealed material, as well as a scanning electron micrograph of a healed material; and

[00038] FIG. 10 shows TDCB experimental results for control systems based on solvent welded materials that were injected at the crack site with exogenous monomer solution from a syringe.

[00039] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

[00040] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

[00041] The uses of the terms “a” and “an” and “the” and similar referents in the context of describing the present disclosure (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “plurality of’ is defined by the Applicant in the broadest sense, superseding any other implied definitions or limitations hereinabove or hereinafter unless expressly asserted by Applicant to the contrary, to mean a quantity of more than one. All methods described herein may be performed in any suitable order unless otherwise indicated herein by context.

[00042] As will be understood by one skilled in the art, for any and all purposes, all ranges recited herein also encompass any and all possible sub-ranges and combinations of subranges thereof, as well as the individual values making up the range, particularly integer values. It is therefore understood that each unit between two particular units is also disclosed. For example, if “10 to 15” is disclosed, then 11, 12, 13, and 14 are also disclosed, individually, and as part of a range. A recited range (for example, weight percentages or carbon groups) includes each specific value, integer, decimal, or identity within the range. Any listed range may be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As will also be understood by one skilled in the art, all language such as “up to,” “at least,” “greater than,” “less than,” “more than,” “or more,” and the like, include the number recited and such terms refer to ranges that may be subsequently broken down into sub-ranges. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio. Accordingly, specific values recited for radicals, substituents, and ranges are for illustration only; the specific values do not exclude other defined values or other values within defined ranges for radicals and substituents. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[00043] One skilled in the art will also readily recognize that where members are grouped together in a common manner, such as in a Markush group, the invention encompasses not only the entire group listed as a whole, but each member of the group individually and all possible subgroups of the main group. Additionally, for all purposes, the invention encompasses not only the main group, but also the main group absent one or more of the group members. The invention therefore envisages the explicit exclusion of any one or more of members of a recited group. Accordingly, provisos may apply to any of the disclosed categories or examples whereby any one or more of the recited elements, species, or examples may be excluded from such categories or examples, for example, for use in an explicit negative limitation.

[00044] As used herein, the terms “comprise(s),” “include(s),” “having,” “has,” “may,” “contain(s),” and variants thereof, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The present description also contemplates other examples, “comprising,” “consisting of,” and “consisting essentially of,” the examples or elements presented herein, whether explicitly set forth or not.

[00045] In describing elements of the present disclosure, the terms “1^st,” “2^nd,” “first,” “second,” “A,” “B,” “(a),” “(b),” and the like may be used herein. These terms are only used to distinguish one element from another element, but do not limit the corresponding elements irrespective of the nature or order of the corresponding elements.

[00046] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meanings as those generally understood by those skilled in the art to which the present disclosure pertains. Such terms as those defined in a generally used dictionary are to be interpreted as having meanings equal to the contextual meanings in the relevant field of art.

[00047] As used herein, the term “about,” when used in the context of a numerical value or range set forth means a variation of ±15%, or less, of the numerical value. For example, a value differing by ±15%, ±14%, ±10%, or ±5%, among others, would satisfy the definition of “about,” unless more narrowly defined in particular circumstances.

[00048] The term “frontal polymerization,” refers, unless otherwise stated, to a process in which the polymerization reaction propagates through a vessel or a substance. There are three types of frontal polymerizations: thermal frontal polymerization (“TFP”) that uses an external thermal energy source to initiate the front; photofrontal polymerization (“PFP”), in which the localized reaction is driven by an external UV source; and isothermal frontal polymerization (“IFP”), which relies on the Norrish-Trommsdorff, or gel effect, that occurs when monomer and initiator diffuse into a polymer seed (small piece of polymer). Thermal frontal polymerization begins when a heat source contacts a solution of monomer and a thermal initiator or catalyst. Alternatively, a UV source may be applied if a photoinitiator is also present. The area of contact (or UV exposure) has a faster polymerization rate, and the energy from the exothermic polymerization diffuses into the adjacent region, raising the temperature and increasing the reaction rate in that location. The result is a localized reaction zone that propagates down the reaction vessel as a thermal wave.

[00049] The term “ring-opening metathesis polymerization” (“ROMP”), refers, unless otherwise stated, to a type of olefin metathesis chain-growth polymerization that may produce industrially important products. The driving force of the reaction is relief of ring strain in cyclic olefins, which may be referred to as “functionalized cycloalkenes.” Thus, “frontal ringopening metathesis polymerization” (“FROMP”) entails the conversion of a monomer into a polymer via a localized exothermic reaction zone that propagates through the coupling of thermal diffusion and Arrhenius reaction kinetics. The pot life, gel time, and reaction kinetics may be controlled through various modifications of the polymerization chemistry.

[00050] As used herein, a “polymer precursor liquid” is a liquid at or near room temperature comprising chemical reagents, such as monomers, oligomers, and optionally catalysts, that react to form a solid polymer network. In most cases, the chemical reagents react only after a stimulus, such as heat or light, is applied to the liquid.

[00051] As used herein, “transmetalation” describes an organometallic reaction that involves the transfer of ligands from one metal to another metal.

[00052] As used herein, an “activator” is an element, ion or compound that initiates a polymerization reaction. For example, an activator for a ROMP reaction may be a metal or metal ion capable of participating in a transmetalation reaction with a ruthenium catalyst.

[00053] Examples of functionalized cycloalkenes for a FROMP reaction may include, but are not limited to: dicyclopentadiene; norbomene; and

5 -ethylidene-2-norbomene.

[00054] In an example, a molar ratio of the amount of the catalyst to the amount of the functionalized cycloalkene may be less than about 1 : 100, or less than about 1 :200, or less than about 1 :300, or less than about 1 :400, or less than about 1 :500, or less than about 1 :600, or less than about 1 :700, or less than about 1 :800, or less than about 1 :900, or less than about 1 : 1000, or less than about 1 :2000, or less than about 1 :3000, or less than about 1 :4000, or less than about 1 :5000, or less than about 1 :6000, or less than about 1 :7000, or less than about 1 :8000, or less than about 1 :9000, or less than about 1 : 10000; or a range made from any two of the foregoing ratios; and including any sub-ratios therebetween.

[00055] In an example, the catalyst may be a Grubbs or Grubbs-type catalyst. Examples of suitable catalysts may include: and

[00056] In an example, heating the mixture may include applying a heat source to the mixture at a temperature of from about 50 to about 500° C, including, for example, from about 75° C, or from about 100° C, or from about 125° C, or from about 150° C, or from about 175° C, or from about 200° C, or from about 225° C, or from about 250° C, or from about 275° C, or from about 300° C, or from about 325° C, or from about 350° C, or from about 375° C, or from about 400° C, or from about 425° C, or from about 450° C, or from about 475° C; or to about 75° C, or to about 100° C, or to about 125° C, or to about 150° C, or to about 175° C, or to about 200° C, or to about 225° C, or to about 250° C, or to about 275° C, or to about 300° C, or to about 325° C, or to about 350° C, or to about 375° C, or to about 400° C, or to about 425° C, or to about 450° C, or to about 475° C; or any range of temperatures made from any two of the foregoing temperatures; including any sub-ranges therebetween.

[00057] FIG. 1 illustrates a cross-sectional view of a self-healing polymer 100 comprising a polymer matrix 102, monomer microcapsules 104, and catalyst microcapsules 106. As shown, the microcapsules 104, 106 are evenly distributed throughout the matrix, although alternative distributions, such as gradient distributions, are possible.

[00058] FIG. 2 illustrates components of an exemplary microcapsule, which may be a catalyst microcapsule 106 or a monomer microcapsule 104. The microcapsule comprises a self-healing core, which is typically a liquid core. For example, the self-healing core may include a monomer solution and an activator in the case of a monomer microcapsule 104 or a ruthenium catalyst and a solvent in the case of a catalyst microcapsule 102. The self-healing components in the core are surrounded by an encapsulation layer(s) that resists degradation (i.e., is stable) at FROMP conditions that form a solid polymer matrix 102.

[00059] FIG. 3 shows scanning electron micrographs of monomer microcapsules 104 and catalyst microcapsules 106, according to some embodiments. The monomer microcapsules shown have a solution of DCPD monomers within a UF/SiCh shell in an epoxy matrix. The catalyst microcapsules shown have a thermally-latent Grubbs-type complex dissolved in solvent (phenylcyclohexane) within a UF shell in an epoxy matrix. The microcapsules contain agents that undergo a ring-opening metathesis-based (ROMP -based) self-healing process when the microcapsules rupture and agents from their cores mix. The liquid cores ensure homogeneous mixing of the two-part healing system. Accordingly, the liquids in the cores of the monomer and catalyst microcapsules are typically miscible with one another.

[00060] Thermal stability of the microcapsules was demonstrated by thermal gravimetric analysis (TGA). FIG. 4 shows TGA traces for the monomer microcapsules and catalyst microcapsules, as well as a comparison of monomer microcapsules having a single UF shell versus a double shell of UF/SiCh. All of the microcapsules are thermally stable to about 300°C. FIG. 5 shows infrared spectra for the monomer microcapsules and catalyst microcapsules.

[00061] FIG. 6 illustrates a schematic of frontal polymerization with microcapsules dispersed in the polymer precursor (DCPD). When heat, indicated by a flame symbol, is applied to initiate FROMP, a polymer front advances away from the heat source in the direction indicated by the propagation arrow, and p(DCPD) is formed behind the front. Scanning electron micrographs show a matrix containing intact catalyst and monomer microcapsules that survived FROMP at about 200°C, and release of healing agents from the microcapsules when the same matrix is scratched by a razor blade.

[00062] Fig. 7 shows the effect of incorporating microcapsules into a polymer precursor on FROMP fontal velocity (vf), frontal temperature (T_max) and glass transition temperature (T_g) as a function of microcapsule loading. The frontal velocity and frontal temperature both decreased as a function of microcapsule loading, and the glass transition temperature of the microcapsule-containing polymer was approximately 95°C at all loadings relative to about 130°C in the absence of microcapsules.

[00063] FIG. 8 illustrates a schematic of a self-healing polymer containing a dualcapsule system that is virgin, damaged, or repaired by self-healing, and subjected to a tapered double cantilever beam (TDCB) test. Self-healing decreased the crack length and changed the slope in the load-displacement curve. Healing efficiencies (r ) were calculated using the internal work (or strain energy) from virgin and healed fracture tests.

[00064] FIG. 9 compares TDCB test results of virgin, healed and unhealed material to determine microcapsule loading needed to restore mechanical properties. A microcapsule loading of 15 wt.% or greater restored the original mechanical properties to p(DCPD). A scanning electron micrograph shows that healing agent covered the fracture plane and repaired the damaged material.

[00065] In comparison the self-healing polymers described herein, FIG. 10 shows TDCB experimental results for solvent welded materials that were injected at the crack site with exogenous monomer solution from a syringe. The solvent welding effect was not significant, providing less than 5% healing efficacy. In contrast, use of the same ROMP chemistry for both matrix fabrication and healing -as disclosed herein - resulted in a well- formed interface that enhanced the overall self-healing performance.

[00066] The compositions and methods described above may be better understood in connection with the following Examples. In addition, the following non-limiting examples are an illustration. The procedures described as general methods describe what is believed will be typically effective to prepare the compositions indicated. However, the person skilled in the art will appreciate that it may be necessary to vary the procedures for any given example of the present disclosure, for example, vary the order or steps and/or the chemical reagents used.

EXAMPLES

[00067] Catalyst microcapsules were prepared from a catalyst / solvent mixture that was vigorously emulsified in a neutralized 1.75 wt% poly(ethylene maleic anhydride) (EMA) surfactant solution using a homogenizer for 10 min.

[00068] Monomer microcapsules were prepared from an activator (e.g., CuCl) and monomer DCPD/PCH (95/5 wt%) mixture containing 2 wt% antioxidant that was stirred vigorously using an overhead mixer in a neutralized 1 wt% EMA aqueous solution followed by dissolving in ascorbic acid.

[00069] Microcapsule shells were fabricated as follows. Prepolymer of ureaformaldehyde (UF) was synthesized by preparing formaldehyde solution of pH 8 using triethanolamine and dissolving urea therein. The mixture was reacted at 70 °C for one hour. The prepolymer solution was added into the emulsified mixture followed by dissolving 0.38 g of resorcinol. After stabilizing for 10 min, the emulsion was heated up to 35 °C, and pH was adjusted to 2.5 using formic acid when the temperature reached 30°C. The reaction completed after 5 hours.

[00070] An additional coating of SiCh was added when pre-hydrolyzed TEOS was added after the UF reaction and reacted at 55 °C for 5 hours.

[00071] The synthesized microcapsules were washed via centrifuge and spray dried (Buchi mini spray dryer B-290) yielding a free-flowing microcapsule powder.

[00072] Fabrication of a self-healing polymer involved mixing a desired weight percentage of catalyst microcapsules and monomer microcapsules (e.g., 1 wt.% and 7.5 wt.%, respectively) in a polymer precursor liquid and applying an appropriate stimulus (e.g., heat or light) to initiate the frontal polymerization reaction.

[00073] Exemplary systems and methods are described in Lee, Y.B. et al., Adv. Mater. 2024, 36, 2309662, which is hereby incorporated by reference herein.

[00074] Although the present disclosure has been described with reference to examples and the accompanying drawings, the present disclosure is not limited thereto, but may be variously modified and altered by those skilled in the art to which the present disclosure pertains without departing from the spirit and scope of the present disclosure.

[00075] In addition to the features mentioned in each of the independent aspects enumerated above, some examples may show, alone or in combination, the optional features mentioned in the dependent aspects and/or as disclosed in the description above and shown in the figures.

Claims

CLAIMS What is claimed is:

1. A formulation for preparing a self-healing polymer, the formulation comprising: a polymer precursor liquid; and a dual-capsule system dispersed in the polymer precursor liquid, the dual-capsule system comprising: monomer microcapsules each comprising a monomer solution and an activator encapsulated in a shell; and catalyst microcapsules each comprising a ruthenium catalyst and a solvent encapsulated in a shell.

2. The formulation of claim 1, wherein the shells of the monomer microcapsules and the catalyst microcapsules resist degradation to temperatures of at least 200 °C, the shells being thermally stable shells.

3. The formulation of claim 1 or 2, wherein the monomer solution comprises a monomer capable of ring-opening metathesis polymerization (ROMP).

4. The formulation of any preceding claim, wherein the monomer solution comprises dicyclopentadiene (DCPD).

5. The formulation of any preceding claim, wherein the monomer solution comprises 5- ethylidene-2-norbornene (ENB).

6. The formulation of claim 5, wherein the monomer solution includes the ENB at a concentration of up to 5 vol.%.

7. The formulation of any preceding claim, wherein the activator comprises a metal ion capable of a transmetalation reaction.

8. The formulation of any preceding claim, wherein the activator comprises a Cu ion.

9. The formulation of any preceding claim, wherein the ruthenium catalyst comprises a thermally latent Grubbs-based complex.

10. The formulation of any preceding claim, wherein the monomer microcapsules have a nominal width or diameter in a range from 1 micron to 800 microns.

11. The formulation of any preceding claim, wherein the catalyst microcapsules have a nominal width or diameter in a range from 1 micron to 800 microns.

12. The formulation of any preceding claim, wherein the monomer microcapsules and the catalyst microcapsules have a concentration in the polymer precursor liquid in a range from 1 wt.% to 40 wt.%.

13. The formulation of any preceding claim, wherein the shell of each of the monomer microcapsules and the catalyst microcapsules has a nominal thickness in a range from 20 nm to 10 microns.

14. The formulation of any preceding claim, wherein the shell of each of the monomer microcapsules and the catalyst microcapsules has a multilayer structure.

15. The formulation of any preceding claim, wherein the shell of each of the monomer microcapsules and the catalyst microcapsules includes one or more polymer layers and/or one or more ceramic layers.

16. The formulation of claim 15, wherein the one or more polymer layers comprise ureaformaldehyde, polymelamine, and/or polydopamine.

17. The formulation of claim 15 or 16, wherein the one or more ceramic layers comprise silica.

18. The formulation of any preceding claim, wherein the polymer precursor liquid comprises: a monomer capable of thermal curing; and a ruthenium catalyst.

19. The formulation of claim 18, wherein the ruthenium catalyst comprises a Grubbs-based complex.

20. The formulation of claim 18 or 19, wherein the monomer is capable of frontal ringopening metathesis polymerization (FROMP).

21. The formulation of any one of claims 18-20, wherein the monomer comprises dicyclopentadiene (DCPD).

22. The formulation of any one of claims 18-21, wherein the polymer precursor liquid comprises 5-ethylidene-2-norbornene (ENB).

23. The formulation of claim 22, wherein the polymer precursor liquid includes the ENB at a concentration of up to 5 vol%.

24. A method of producing a self-healing polymer, the method comprising: providing the formulation of any preceding claim; and heating the polymer precursor liquid to effect polymerization, the monomer microcapsules and the catalyst microcapsules remaining intact during the heating, thereby forming a self-healing polymer.

25. The method of claim 24, wherein the step of heating the polymer precursor liquid to effect polymerization comprises: initiating an exothermal polymerization reaction in the polymer precursor liquid; and generating a self-propagating polymerization front that moves through the polymer precursor liquid.

26. The method of claim 24 or 25, wherein the self-healing polymer comprises a thermoset polymer.

27. The method of any one of claims 24-26, wherein the self-healing polymer comprises polydicyclopentadiene (pDCPD).

28. A self-healing polymer comprising: a polymer matrix; a dual-capsule system dispersed in the polymer matrix, the dual-capsule system comprising: monomer microcapsules, each monomer microcapsule comprising a monomer solution and an activator encapsulated in a shell; and catalyst microcapsules, each catalyst microcapsule comprising a ruthenium catalyst and a solvent encapsulated in a shell.

29. The self-healing polymer of claim 28, wherein the polymer matrix comprises a thermoset polymer.

30. The self-healing polymer of claim 28 or 29, wherein the polymer matrix comprises polydicyclopentadiene (pDCPD).

31. A method of using a self-healing polymer, the method comprising: using a component comprising the self-healing polymer of any one of claims 28-30 in a remote location; during use of the component, exposing the self-healing polymer to mechanical forces or environmental conditions capable of inflicting damage; and during the exposure, forming a damaged region of the self-healing polymer, the monomer microcapsules and the catalyst microcapsules rupturing, whereby the monomer solution, the activator, and the ruthenium catalyst are mixed in the damaged region, and ring-opening metathesis polymerization occurs in the damaged region, thereby effecting self-healing of the component.

32. The method of claim 31, wherein the remote location is undersea, underground, in space, or in a human body.