FIELD OF THE INVENTION The invention relates in general to epoxy resins, and in particular to branched epoxy resins that can exhibit self-healing properties. The invention further relates to a method of making, and also to repairing a defect in, such resins.

BACKGROUND OF THE INVENTION

Epoxy resins represent an important class of polymer which has widespread use in fibre- reinforced composite materials, coatings and adhesives.

The resins are typically prepared by reacting a compound bearing more than one epoxide group with a compound bearing more than one amine group (commonly referred to in the art as the "crosslinking agent"). The epoxide bearing compound may be a small molecule (such as bisphenol A diglycidyl ether) or a relatively large molecule (e.g. a prepolymer such as an oligomer of bisphenol A and epichlorohydrin). The so formed resins typically exhibit thermoset character in that they present an infusible, insoluble polymer chain network.

While thermoset polymers offer a number of advantages such as being rigid and durable, particularly when exposed to heat, pressur e and/or solvent, they typically can not be readily repaired upon developing defects such as micro-cracks, surface scratches etc because of their intractability.

Considerable research has therefore been directed toward developing epoxy resins with improved properties. Accordingly, a diverse range of epoxide and amine bearing compounds and other formulation components are now available for making these resins.

A particularly exiting field of epoxy resin research has been the development of so called "self-healing" epoxy resins. Self-healing polymers have the ability to substantially heal otherwise irreversible defects, such as microcracks and surface scratches, which can significantly reduce the load-bearing capacity properties of the polymers and shorten their lifetime, or alternatively may provide an undesirable appearance when the polymer is used as a coating. Self-healing properties have therefore shown particular promise in thermosetting materials such as epoxy resins.

A variety of approaches to forming self healing epoxy resins have been developed. For example, capsule-based healing systems, vascular healing systems and intrinsic healing systems are known.

An opportunity therefore remains to develop new epoxy resins and methods for their manufacture that demonstrate new and/or improved properties, and/or present advantages over or alternatives to known resins.

SUMMARY OF THE INVENTION

The present invention therefore provides a branched epoxy resin comprising a reaction product of a multi-epoxy compound and a multi-amine compound, wherein the reaction residue of the multi-amine compound comprises a Diels-Alder adduct which, upon undergoing a retro Diels-Alder reaction, will cleave a branch in the branched epoxy resin.

The present invention also provides a method of preparing a branched epoxy resin, the method comprising reacting a multi-epoxy compound with a multi-amine compound, wherein the multi-amine compound comprises a Diels-Alder adduct which, upon undergoing a retro Diels-Alder reaction, will cleave a branch in the so formed branched epoxy resin.

The present invention further provides use of a multi-amine compound to form a branched epoxy resin, the multi-amine compound comprising a Diels-Alder adduct which, upon undergoing a retro Diels-Alder reaction, will cleave a branch in the branched epoxy resin. It has now surprisingly been found that a multi-amine compound (commonly referred to in the art as the crosslinking agent) comprising a Diels-Alder adduct can be used in preparing branched epoxy resins to impart improved properties, such as self-healing properties. For example, through the application of heat to the so formed branched epoxy resin the Diels- Alder adducts can undergo a retro Diels-Alder reaction resulting in branches in the resin being cleaved. Cleavage of these branches can promote a transition in the resin from having thermoset character to having some thermoplastic character, which in turn enables the resin to develop self-healing properties. After self-healing has taken place, the Diels- Alder adducts can advantageously reform so as to reinstate thermoset character to the resin.

For example, a scratch may be introduced at the surface of a branched epoxy resin in accordance with the invention. Heat can then be applied to the resin so that the Diels- Alder adducts undergo a retro Diels-Alder reaction, the effect of which causes branches in the epoxy resin to be cleaved. In this state, the resin will develop some thermoplastic character which, with the assistance the applied heat and optionally applied pressure, enables polymer chains in the resin to flow and repair or heal the scratched surface. Cooling the resin enables the Diels-Alder adducts to reform so as to reinstate thermoset character to the resin.

Branched epoxy resins in accordance with the invention therefore advantageously have the potential to reversibly exhibit both thermoset and thermoplastic character. The present invention also provides a method of repairing a defect in a branched epoxy resin according to the invention, the method comprising heating the resin so that Diels- Alder adducts therein undergo a retro Diels-Alder reaction and cleave branches in the resin, wherein while at least some of the branches remain cleaved the defect is repaired. While use of Diels-Alder adducts in epoxy resins is known, such systems have typically employed specialty multi-epoxy compounds. This in turn has limited the application and use of such resins, and further, has limited the range of properties that can be derived from such resins.

In contrast, epoxy resins according to the present invention can be prepared using conventional and readily available multi-epoxy compounds. The present invention of course still requires the use of specialty multi-amine compounds (i.e. the comprising the Diels-Alder adduct). However, such multi-amine compounds are particularly versatile and can be more readily implemented into conventional epoxy resin technologies. Furthermore, incorporating the Diels-Alder adduct in the multi-amine compound has surprisingly been found to impart excellent self healing properties to the resin.

The present invention also provides a coating, adhesive or moulded product comprising an epoxy resin in accordance with the invention. Further aspects of the invention are described in more detail below.

BRIEF DESCRIPTION OF THE FIGURES

The present invention is described herein with reference to the following non-limiting drawings in which:

Figure 1 is a composite FTIR spectrum of an epoxy resin in accordance with the invention. The peak 694 cm ^'1 represents a carbon-hydrogen bond connected to a carbon-carbon double bond in the maleimide group of the Diels-Alder precursor. After the epoxy resin was heated at 140 °C for 30 minutes, the peak (b) is more intense than before heating (a), indicating that the content of maleimide had increased which is indicative that a retro Diels-Alder reaction has occurred. After the epoxy resin was cooled at 75 °C for 5 hours, the peak (c) became weaker, indicating that the content of maleimide had decreased which is indicative that the Diels-Alder adduct has reformed;

Figure 2(a) shows an image taken using an optical microscope of a cured sample of an epoxy resin of the invention having received a cut on the surface using a sharp blade. The scale on the image is 20 um and the cut is approximately 40 μπι in width; and

Figure 2(b) shows the sample epoxy resin depicted in figure 2(a), at the same scale, after having been subjected to heating at 140 °C for 30 minutes followed by cooling at 75°C for 5 hours.

All Figures have been filed in colour and are available on request. DETAILED DESCRIPTION OF THE INVENTION

As used herein, the expression "branched epoxy resin" refers to an epoxy resin which is substantially nonlinear and may be characterized by a degree of branch points in polymer chains. A "branch point" is section where at least three polymer chains emanate. The "section" may be an atom or group of atoms, for example an aryl group.

The branched epoxy resin may be cross-linked to varying degree. Typically the epoxy resin will contain a multitude of branches and cross-links such that the epoxy resin exhibits thermoset character. Where a cross-link is present in the epoxy resin, that cross-link may also provide for a branch point. In the context of the present invention, a cross-link may therefore also function as a branch. Cleavage of such branches in the epoxy resin can result in the resin developing some thermoplastic character such that polymer chains in the resin can flow, for example, upon being subjected to heat, pressure and/or solvent. As used herein the term "cross-link" or grammatical variants thereof such as "cross-links", "cross-linked", "cross-linking" etc refers to a section of the so formed branched epoxy resin from which at least four polymer chains emanate. The "section" may be an atom, a group of atoms, a number of branch points connected by bonds, groups of atoms or oligomeric chains.

As used herein, the expression "multi-epoxy compound" refers to a compound containing more than one epoxy group. For example, the multi-epoxy compound may comprise at least two epoxy groups. In some embodiments the multi-epoxy compound will contain two epoxy groups. More than one (e.g. two or more) of the epoxy groups in the "multi- epoxy compound" will of course be capable of reacting with an amine under conditions suitable for the formation of an epoxy resin. In one embodiment, at least two of the epoxy groups in the multi-epoxy compound are unsubstituted.

There is no particular limitation regarding the nature of multi-epoxy compound that can be used in accordance with the invention provided that it is capable of reacting with an amine under conditions suitable for the formation of an epoxy resin. Examples of multi-epoxy compounds include, for example, alicyclic and aromatic epoxides.

Examples of useful multi-epoxy alicyclic epoxides include monomeric alicyclic epoxides, oligomeric alicyclic epoxides, and polymeric alicyclic epoxides. Exemplary useful alicyclic epoxides monomers include epoxycyclohexanecarboxylates such as, for example, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate and 3,4-epoxy-2- methylcyclohexylmethyl 3,4-epoxy-2-methylcyclohexanecarboxylate; diglycidyl ether of cyclohexanedimethanol; hydrogenated bisphenol A diglycidyl ether; and combinations thereof.

Useful multi-epoxy aromatic epoxides include, for example, monomeric aromatic epoxides, oligomeric aromatic epoxides, and polymeric aromatic epoxides. Exemplary aromatic epoxides include the glycidyl ethers of polyhydric phenols such as bisphenol A- type resins and their derivatives; epoxy cresol-novolac resins; Bisphenol-F resins and their derivatives; epoxy phenol-novolac resins; and glycidyl esters of aromatic carboxylic acids (e.g., phthalic acid diglycidyl ester, isophthalic acid diglycidyl ester, trimellitic acid triglycidyl ester, and pyromellitic acid tetraglycidyl ester); and combinations thereof.

While not essential, a multi-epoxy compound used in accordance with the invention may comprise a Diels-Alder adduct, or one or both of a diene and dienophile capable of undergoing a Diels-Alder reaction to form a Diels-Alder adduct. In one embodiment, the multi-epoxy compound used in accordance with the invention does not comprise a Diels-Alder adduct, or one or both of a diene and dienophile capable of undergoing a Diels-Alder reaction to form a Diels-Alder adduct.

As used herein, the expression "multi-amine compound" refers to a compound containing more than one amine group. For example, the multi-amine compound may comprise at least two amine groups. In some embodiments the multi-amine compound will contain two amine groups. The amine groups will typically be primary or secondary amines such that each amine group possesses at least one N-H bond. In some embodiments the multi- amine compound will contain two, three, four, or more amine groups. In some embodiments the multi-amine compound will comprise at least three or at least four N-H bonds. Such N-H bonds will of course be capable of undergoing reaction with an epoxy group under conditions suitable for the formation of an epoxy resin.

In one embodiment, the multi-epoxy compound comprises two epoxy groups and the multi-amine compound comprises four N-H bonds.

For convenience, unless stated otherwise, reference herein to an "amine" group of the multi-amine compound is intended to be a reference to an amine group comprising at least one, if not two, N-H bonds capable of undergoing reaction with an epoxy group under conditions suitable for the formation of an epoxy resin.

In accordance with the invention, the branched epoxy resin comprises a reaction product of the multi-epoxy compound and the multi-amine compound. By the "reaction product" is meant the molecular structure formed by reaction of an epoxy group in the multi-epoxy compound and an amine group in the multi-amine compound. Those skilled in the art will appreciate that when a primary or secondary amine reacts with an epoxide, ring-opening of the epoxide yields an alcohol and a carbon-nitrogen bond is formed as depicted in Scheme 1 below:

Scheme 1: Reaction of an epoxide with an amine, where R is an organic substituent or hydrogen, and represents the remainder of the epoxide and amine compounds. The branched epoxy resin according to the invention therefore comprises the reaction residue of a multi-epoxy compound and a multi-amine compound that are covalently coupled through the so formed carbon-nitrogen bond shown in Scheme 1.

It will be appreciated from the reaction shown in Scheme 2 below that a primary amine may be capable of reacting with two epoxide groups so as to form two carbon-nitrogen bonds, whereas a secondary amine (as shown in Scheme 1 when R is an organic substituent) is capable of reacting with only one epoxide group.

In some embodiments the multi-amine compound contains two primary amine groups. In v

other embodiments the multi-amine compound contains three or more secondary amine groups. In yet further embodiments the multi-amine compound contains one or more primary amine groups and οηό or more secondary amine groups.

Where the multi-amine compound contains two primary amine groups and the multi-epoxy compound contains two epoxy groups, the compounds may react to form a structure represented below in Scheme 2 where and mmiiiii represent linking groups, and represents the remainder of the resin structure :

Scheme 2: Branched epoxy-resin according to the invention.

For clarity, the branched epoxy-resin illustrated in Scheme 2 does not depict specific Diels-Alder adducts. However, the lines represent linking groups associated with multi-epoxy compound reaction residues, and the _^ ΛΛΛ lines represent linking groups associated with multi-amine compound reaction residues. One or more linking groups associated with the multi-amine compound reaction residues will comprise one or more Diels-Alder adducts. Further detail in relation to the Diels-Alder adducts is provided below.

An important feature of the branched epoxy resin in accordance with the invention is that a reaction residue of a multi-amine compound comprises a Diels-Alder adduct. By the expression "reaction residue of the multi-amine compound" is meant the atoms in the multi-amine compound except those lost during reaction with the multi-epoxy compound.

By way of example, in those embodiments where the multi-amine compound contains two primary amine groups, following reaction with four epoxy groups, the reaction residue of the multi-amine shall consist of each of the atoms in the multi-amine compound except for the four hydrogen atoms originally bonded to the nitrogen atoms on each of the primary amine groups. Likewise, in those embodiments where the multi-amine compound contains four secondary amine groups, following reaction with four epoxy groups, the reaction residue of the multi-amine shall consist of each of the atoms in the multi-amine compound except for the four hydrogen atoms originally bonded to the nitrogen atoms on each of the secondary amine groups.

With reference to Scheme 2, those skilled in the art will readily appreciate that the reaction residue of the multi-amine compound is depicted by Ν·*~ ^» ~Ν. Accordingly, the Diels- Alder adduct is located in between the two nitrogen atoms of this residue. For avoidance of any doubt, in this context the term "between" refers specifically to the part of the reaction residue of the multi-amine compound linking the aforementioned two nitrogen atoms which consists of contiguous, covalently bonded atoms which couple a first nitrogen atom of the at least two nitrogen atoms to the second nitrogen atom of the at least two nitrogen atoms. The contiguous atoms may be optionally substituted, including providing branching, wherein in one or more of those branches, there may be one or more other Diels-Alder adducts, but at all times it must be possible to identify contiguous atoms which covalently bond the two nitrogen atoms and wherein the contiguous atoms comprise the Diels-Alder adduct.

Those skilled in the art will also readily appreciate that an inherent consequence of the epoxy resin according to the invention comprising a reaction product of a multi-epoxy compound and a multi-amine compound is that the resin will also comprise a reaction residue of the multi-amine compound and also a reaction residue of the multi-epoxy compound.

The multi-amine compound used in accordance with the invention comprises a Diels-Alder adduct. At its most basic level, a Diels-Alder (DA) reaction involves a [4+2] cycloaddition reaction between a diene moiety and a dienophile moiety to form a Diels-Alder adduct. In an all-carbon variant of the Diels-Alder reaction, the Diels-Alder adduct is discernible as a cyclohexene species. Modification of the substituents on the diene and dienophile moieties can affect the relative reactivity of the diene and dienophile species.

A Diels-Alder reaction is a reversible reaction wherein the Diels-Alder adduct may undergo a so-called retro Diels-Alder reaction (rDA) to reform the diene and dienophile moieties. An example of the reversibility of the Diels-Alder reaction is shown in Scheme 3 below, where heating the Diels-Alder adduct (on the right hand side of the reaction) to about 140 °C causes regeneration of the substituted furan (diene) and the substituted maleimide (dienophile) upon cooling.

Scheme 3: A Diels-Alder reaction (forward direction) and retro Diels-Alder reaction (backward direction). The Diels-Alder adduct comprises a cyclohexene ring.

The multi-amine compound used in accordance with the invention comprises a Diels-Alder adduct which, upon undergoing a retro Diels-Alder reaction, will cleave a branch in the branched epoxy resin. It will therefore be appreciated that the Diels-Alder adduct is not present in the multi-amine compound as a mere pendant group, but rather forms part of a continuous string of atoms located between at least two of the amine groups present in the multi-amine compound. In other words, the Diels-Alder adduct must form part of the molecular structure of the multi-amine compound such that when the Diels-Alder adduct undergoes a retro Diels-Alder reaction a branch in the epoxy resin is broken or cleaved.

By way of example only, the branched epoxy resin shown above in Scheme 2 contains Diels-Alder adducts in reaction residues of the multi-amine compounds, which, upon undergoing a retro Diels-Alder reaction, will cleave a branch in the branched epoxy resin. In that case, Scheme 4 below illustrates the process of branches being cleaved to yield the Diels-Alder precursors (i.e. the diene and dienophile moieties) shown schematically as circles:

Scheme 4: Branched epoxy resin on the left, and epoxy resin wherein branches have been cleaved on the right.

As can be seen from Scheme 4, following cleavage of branches in the branched epoxy resin a product remains that exhibits polymeric character as evidenced by the central polyarhine compound depicted horizontally and reproduced in isolation in scheme 5 below:

Scheme 5: Polyamine structure that remains after branches in the branched epoxy resin are cleaved.

In contrast, if the reaction residue of the multi-epoxy compound were to comprise a Diels- Alder adduct (i.e. where the linking groups associated with the multi-epoxy compounds comprise the Diels-Alder adduct), promoting a retro Diels-Alder reaction would provide for an entirely different composition as illustrated below in Scheme 6 (using similar symbols to that in Scheme 2, 4 and 5):

Scheme 6: An epoxy resin not prepared according to the present invention.

As can be seen form Scheme 6, fragmentation of the epoxy resin occurs when the Diels- Alder adduct undergoes a retro Diels-Alder reaction. However, in that case the product has no discernible polymer backbone. Without wishing to be limited by theory, it is believed the ability of branched epoxy resins according to the invention to undergo retro Diels-Alder reactions at or within the multi- amine reaction residue (in contrast to at or within the multi-epoxy reaction residue) provides for improved properties of the resin at least in part due to the resin retaining superior polymeric character upon undergoing a retro Diels-Alder reaction.

There is no particular limitation regarding the nature of the multi-amine compound that may be used, provided that it (i) can suitably react with the multi-epoxy compound to form the branched epoxy resin, and (ii) comprises a Diels-Alder adduct which, upon undergoing a retro Diels-Alder reaction, will cleave a branch in the branched epoxy resin.

The multi-amine compound may comprise two primary amine groups as depicted schematically below in Scheme 7, wherein the oval represents the Diels-Alder adduct:

Scheme 7: A multi-amine compound that may be used in accordance with the present invention.

The multi-amine compound may comprise primary and secondary amine groups as depicted schematically below in Scheme 8, wherein the oval represents the Diels-Alder adduct and each R (e.g. optionally substituted alky) may be the same or different and each R is not hydrogen:

RHN RHN NHR

RHN RHN NHR

Scheme 8: A multi-amine compound that may be used in accordance with the present invention.

It will be recognised that in each of these multi-amine compound examples, the multi- amine compound possesses two nitrogen-hydrogen bonds on each side of the molecule relative to the Diels-Alder adduct. This arrangement is particularly favourable to formation of the branched epoxy resins of the invention, since in the production of these types of resins each nitrogen atom depicted above forms part of a polymer backbone that remains intact following the reto Diels-Alder reaction.

In some embodiments, the multi-amine compound comprises at least two nitrogen- hydrogen bonds, wherein one of the nitrogen-hydrogen bonds is separated from the other nitrogen-hydrogen bond by a moiety comprising a Diels-Alder adduct such that upon the adduct undergoing a retro Diels-Alder reaction one nitrogen-hydrogen bonds remain with one of the so formed diene or dienophile and the other nitrogen-hydrogen bond remains with the other of the so formed diene or dienophile. In other embodiments, the multi-amine compound comprises at least three nitrogen- hydrogen bonds, wherein two of the nitrogen-hydrogen bonds are separated from the third nitrogen-hydrogen bond by a moiety comprising a Diels-Alder adduct such that upon the adduct undergoing a retro Diels-Alder reaction two nitrogen-hydrogen bonds remain with one of the so formed diene or dienophile and the third nitrogen-hydrogen bond remains with the other of the so formed diene or dienophile.

In further embodiments, the multi-amine compound comprises at least four nitrogen- hydrogen bonds, wherein two of the nitrogen-hydrogen bonds are separated from the other two nitrogen-hydrogen bond by a moiety comprising a Diels-Alder adduct such that upon the adduct undergoing a retro Diels-Alder reaction two nitrogen-hydrogen bonds remain with one of the so formed diene or dienophile moieties and the other two nitrogen- hydrogen bonds remain with the other of the so formed diene or dienophile moieties.

In some embodiments it may be desirable to utilise multi-amine compounds that possess a plurality of Diels-Alder adducts, including asymmetrical and symmetrical multi-amine compounds. For example, the multi-amine compound may have a structure schematically illustrated below in below Scheme 9 wherein each oval represents a Diels-Alder adduct:

Scheme 9: A multi-amine compound that may be used in accordance with the present invention.

In one embodiment, the multi-amine compound comprises one or more Diels-Alder adducts that are a reaction product of a substituted furan with a substituted maleimide.

The multi-amine compound may be represented by a compound of formula (I):

RHN— L-DAA L— NHR (I)

where each R is the same or different and is selected from an organic substituent and hydrogen; each L is the same or different and is a linking group selected from a divalent form of optionally substituted: alkyl, alkenyl, alkynyl, aryl, acyl, carbocyclyl, heterocyclyl, heteroaryl, alkyloxy, alkenyloxy, alkynyloxy, aryloxy, acyloxy, carbocyclyloxy, heterocyclyloxy, heteroaryloxy, alkylthio, alkenylthio, alkynylthio, arylthio, acylthio, carbocyclylthio, heterocyclylthio, heteroarylthio, alkylalkenyl, alkylalkynyl, alkylaryl, alkylacyl, alkylcarbocyclyl, alkylheterocyclyl, alkylheteroaryl, alkyloxyalkyl, alkenyloxyalkyl, alkynyloxyalkyl, aryloxyalkyl, alkylacyloxy, alkyloxyacylalkyl, alkylcarbocyclyloxy, alkylheterocyclyloxy, alkylheteroaryloxy, alkylthioalkyl, alkenylthioalkyl, alkynylthioalkyl, arylthioalkyl, alkylacylthio, alkylcarbocyclylthio, alkylheterocyclylthio alkylheteroarylthio, alkylalkenylalkyl, alkylalkynylalkyl, alkylarylalkyl, alkylacylalkyl, arylalkylaryl, aryialkenylaryl, arylalkynylaryl, arylacylaryl, arylacyl, arylcarbocyclyl, arylheterocyclyl, arylheteroaryl, alkenyloxyaryl, alkynyloxyaryl, aryloxyaryl, arylacyloxy, arylcarbocyclyloxy, arylheterocyclyloxy, arylheteroaryloxy, alkylthioaryl, alkenylthioaryl, alkynylthioaryl, arylthioaryl, arylacylthio, arylcarbocyclylthio, arylheterocyclylthio, and arylheteroarylthio; and DAA is a Diels- Alder adduct. In one embodiment, each linking group L is independently selected from optionally substituted Ci-i ₂ alkylene, optionally substituted Ci-^alkenylene, optionally substituted Ci. nalkynylene, and optionally substituted C ₆ .igarylene.

In another embodiment, each linking group L is independently selected from optionally substituted Ci.^alkylene.

Where R is an organic substituent, it may itself be independently selected from optionally substituted: alkyl, alkenyl, alkynyl, aryl, acyl, carbocyclyl, heterocyclyl, heteroaryl, alkyloxy, alkenyloxy, alkynyloxy, aryloxy, acyloxy, carbocyclyloxy, heterocyclyloxy, heteroaryloxy, alkylthio, alkenylthio, alkynylthio, arylthio, acylthio, carbocyclylthio, heterocyclylthio, heteroarylthio, alkylalkenyl, alkylalkynyl, alkylaryl, alkylacyl, alkylcarbocyclyl, alkylheterocyclyl, alkylheteroaryl, alkyloxyalkyl, alkenyloxyalkyl, alkynyloxyalkyl, aryloxyalkyl, alkylacyloxy, alkyloxyacylalkyl, alkylcarbocyclyloxy, alkylheterocyclyloxy, alkylheteroaryloxy, alkylthioalkyl, alkenylthioalkyl, alkynylthioalkyl, arylthioalkyl, alkylacylthio, alkylcarbocyclylthio, alkylheterocyclylthio alkylheteroarylthio, alkylalkenylalkyl, alkylalkynylalkyl, alkylarylalkyl, alkylacylalkyl, arylalkylaryl, arylalkenylaryl, arylalkynylaryl, arylacylaryl, arylacyl, arylcarbocyclyl, arylheterocyclyl, arylheteroaryl, alkenyloxyaryl, alkynyloxyaryl, aryloxyaryl, arylacyloxy, arylcarbocyclyloxy, arylheterocyclyloxy, arylheteroaryloxy, alkylthioaryl, alkenylthioaryl, alkynylthioaryl, arylthioaryl, arylacylthio, arylcarbocyclylthio, arylheterocyclylthio, and arylheteroarylthio.

In one embodiment, R is independently selected from alkyl, alkylaryl, arylalkyl, and aryl.

In another embodiment, R is independently selected from optionally substituted Cj.i ₂ alkyl, optionally substituted Ci-^alkenyl, optionally substituted Ci-^alkynyl, and optionally substituted Ce-isaryl.

In yet another embodiment, R is independently selected from optionally substituted C _\ . i ₂ alkyl.

Where the multi-amine compound is of formula (I), the resulting branched epoxy resin will comprise a moiety of formula (II): where each L is as herein defined; DAA is a Diels-Alder adduct; and represents the remainder of the epoxy resin structure.

Use of the expression " represents the remainder of the epoxy resin structure" is intended to simplify the formula without depicting the potential complex remaining structure of the resin. The "epoxy resin structure" includes moieties such as organic (R) and hydrogen (H) substituents as herein defined.

The multi-amine compound may also be represented by a compound of formula (III):

RH — L-DAA— L— DAA L— NHR (ΠΙ) where each R is as herein defined; each L is as herein defined; and each DAA is the same or different and is a Diels-Alder adduct. WWhheerree tthhee mmuullttii--aammiinnee ccoommppoouunndd iiss ooff ffoorrmmuullaa ((IIII)),, tthhee rreessuullttiinngg bbrraanncchheedd eeppooxxyy rreessiinn w wiillll ccoommpprriissee aa mmooiieettyy ooff ffoorrmmuullaa ((IIVV))::

where each L is as herein defined; each DAA is the same or different and is a Diels- Alder adduct; and represents the remainder of the epoxy resin structure.

In one embodiment, the Diels Alder adduct (DAA) in formula (I)-(IV) is represented by moiety of formula (V):

where each * is the point of attachment to L in each of formula (I)-(IV).

More specific examples of a multi-amine compounds that may be used in accordance with the present invention can be represented by general formulae (VI) and (VII) below:

(VII) where L is a linking group as herein defined.

For example, the multi-amine compound may be of formula (VIII):

In one embodime la (IX):

where each R is the same or different and is as herein defined; each R* is the same or different and is R or represents, together with , the remainder of the epoxy resin structure; each L is as herein defined; DAA is a Diels-Alder adduct; and represents, optionally together with R*, the remainder of the epoxy resin structure. In another embodiment, the branched epoxy resin comprises a moiety of formula (X):

where each R is the same or different and is as herein defined; each R* is the same or different and is R or represents, together with , the remainder of the epoxy resin structure; each L is as herein defined; each DAA is the same or different and is a Diels- Alder adduct; and represents, optionally together with R*, the remainder of the epoxy resin structure. In a further embodiment, DAA in formula (IX) and (X) is represented by a moiety of formula (V)

where * is the point of attachment to L in each of formula (IX) and (X).

In another embodiment, the branched epoxy resin comprises a moiety of formula (XI):

where each R is the same or different and is as herein defined; each R* is the same or different and is R or represents, together with , the remainder of the epoxy resin structure; each L is as herein defined; and represents, optionally together with R*, the remainder of the epoxy resin structure.

In further embodiment, the branched epoxy resin comprises a moiety of formula (XII):

where each R is the same or different and is as herein defined; each R* is the same or different and is R or represents, together with , the remainder of the epoxy resin structure; each L is as herein defined; and represents, optionally together with R*, the remainder of the epoxy resin structure. The multi-amine compounds may be prepared using techniques well known to those skilled in the art. For example, an amine substituted furan compound (the diene) and an amine substituted maleimide compound (the dienophile) may be reacted through a Diels Alder reaction to form the multi-amine compound.

- ^'

The epoxy resin according to the invention may also comprise a reaction product of a multi-epoxy compound and a multi-amine compound, wherein the reaction residue of the multi-amine compound does not comprise a Diels-Alder adduct. In other words, the epoxy resin may be prepared using a combination of a multi-amine compound comprising a Diels-Alder adduct as described herein and a conventional multi-amine compound that does not comprise a Diels-Alder adduct. Generally, of the total amount of multi-amine compound used to prepare an epoxy resin according to the invention, at least 20 mol%, or at least 30 mol%, or at least 40 moI%, or at least 50 mol%, or at least 60 mol%, or at least 70 mol%, or at least 80 mol%, or at least 90 mol%, or at least 95 mol%, or 100 mol% is a multi-amine compound comprising a Diels-Alder adduct as described herein. Accordingly, of the total amount of multi-amine compound reaction residue in the epoxy resin according to the invention, at least 20 mol%, or at least 30 mol%, or at least 40 mol%, or at least 50 mol%, or at least 60 mol%, or at least 70 mol%, or at least 80 mol%, or at least 90 mol%, or at least 95 mol%, or 100 mol% is a multi-amine compound reaction residue comprising a Diels-Alder adduct as described herein.

For convenience and avoidance of any doubt, unless otherwise specified reference herein to "the multi-amine compound" is intended to mean a multi-amine compound comprising a Diels-Alder adduct as described herein.

A method according to the invention comprises reacting the multi-epoxy compound with the multi-amine compound. To form the required branched epoxy resin, those skilled in the art will appreciate that a number of factors need to be considered, such as the number of nitrogen-hydrogen ( H) bonds in the multi-amine compound, the number of epoxy groups in the multi-epoxy compound, and the ratio of multi-amine compound and multi- epoxy compound used. For example, a branched epoxy resin will not be formed by reacting a multi-amine compound comprising two secondary amine groups with multi- epoxy compound comprising two epoxy groups. It is well within the knowledge of those skilled in the art to suitably select the NH bond and epoxy group requirements so as to prepare the branched epoxy resin.

As outlined above, it is important that the multi-amine compound used comprises a Diels- Alder adduct which, upon undergoing a retro Diels-Alder reaction, will cleave a branch in the branched epoxy resin. Accordingly, a Diels-Alder adduct must be suitably located between at least two NH bonds of amine groups in the multi-amine compound.

In one embodiment, the multi-amine compound used comprises at least four NH bonds, wherein two of the NH bonds are separated from the other two NH bond by a moiety comprising a Diels-Alder adduct such that upon the adduct undergoing a retro Diels-Alder reaction two NH bonds remain with one of the so formed diene or dienophile moieties and the other two NH bonds remain with the other of the so formed diene or dienophile moieties. In that case, the method of the invention may comprise reacting the multi-amine compound with a multi-epoxy compound comprising two epoxy groups in a ratio of aboutl :4. The method of preparing a branched epoxy resin in accordance with the invention can advantageously be performed using techniques, equipment and reagents similar to those employed in making conventional epoxy resins.

Having said this, unlike conventional epoxy resin systems, reagents used to prepare the epoxy resin systems of the present invention include multi-amine compound comprising a Diels-Alder adduct. Those skilled in the art will therefore appreciate that when the resin of the invention is prepared, it will be desirable that the manufacturing temperature remains below the temperature at which the Diels-Alder adduct undergoes a retro Diels-Alder reaction. In one embodiment, the method of the invention therefore comprises reacting the multi- epoxide compound with the multi-amine compound at a temperature that is below the temperature at which the Diels-Alder adduct undergoes a retro Diels-Alder reaction. The branched epoxy resins in accordance with the invention can advantageously exhibit self healing properties. By "self healing properties" is meant that the resin has an inherent capacity to repair defects including micro-cracks and surface spratches that occur in or on the resin. In the case of the present invention, the self-healing properties are provided by the resins ability to initiate cleavage of the branched polymer structure so as to provide or improve its thermoplastic character. While at least some of the branches remain in a cleaved state (i.e. where at least some of the so formed diene and dienophile pairs have not reformed Diels- Alder adducts), the improved thermoplastic character of the resin (i.e. relative to the resin when the branches have not been cleaved) enables the resin to more readily flow on a molecular level and repair defects such as micro-cracks and surface scratches. Reformation of the Diels-Alder adducts in turn reforms the branches and can "lock in" the repaired state of the resin. As discussed, cleavage of branches in the epoxy resin occurs by Diels-Alder adducts in the reaction residue of the multi-amine compound undergoing a retro Diels-Alder reaction. The retro Diels-Alder reaction is typically promoted by heating the epoxy resin. The temperature, required to promote a given retro Diels-Alder reaction will vary depending upon the nature of the Diels-Alder adduct, and can be readily determined by those skilled in the art. For example, promotion of a retro Diels-Alder reaction can be studied as a function of temperature using Infrared spectroscopy.

The invention therefore further provides a method of repairing a defect in the branched epoxy resin, the method comprising heating the resin so that Diels-Alder adducts therein undergo a retro Diels-Alder reaction and cleave branches in the resin, wherein while the branches remain cleaved the defect is repaired. There is not particular limitation regarding the technique used to heat the epoxy resin in order to promote the retro Diels-Alder reaction. For example, the epoxy resin may be heated (directly or indirectly) by convection, conduction or radiation.

In one embodiment, the epoxy resin comprises within its polymeric matrix susceptor particles (i.e. particles of matter that can absorb electromagnetic radiation and convert it to heat). In that case, the resin may be heated by exposing these particles to an appropriate electromagnetic radiation frequency, for example ultraviolet (UV), radiofrequency (RF) or microwave radiation. Examples of susceptor materials include metals, metal oxides, metal sulfides, and ceramics.

Those skilled in the art will appreciate that a specific class of susceptor material are so called "photo thermal particles" which can undergo an increase in temperature upon being exposed to UV radiation. Examples of photo-thermal particles include titanium dioxide, zinc oxide, gold, cobalt, cadmium oxide, cadmium sulfide and sodium tantalite (NaTaCh).

The size of susceptor particles used will generally fall within the range of 1 nm to I mm. To promote even heat distribution, the particles will generally be distributed substantially uniformly throughout the polymeric matrix of the epoxy resin.

In one embodiment, the epoxy resin is coated on a susceptor substrate. In that case, the resin may be heated by exposing the susceptor substrate to an appropriate electromagnetic radiation frequency, for example radiofrequency (RF). By exposing the susceptor substrate, for example a metal substrate, to the appropriate electromagnetic radiation frequency the substrate will increase in temperature and inturn transfer that heat to the coated resin.

In one embodiment, a branched epoxy resin in accordance with the invention is heated to about 140° C to promote the retro Diels-Alder reaction. After heating the epoxy resin to promote the retro Diels-Alder reaction, the resin can be held at this temperature for a time sufficient for the resin to undergo the required degree of self-healing. If required, pressure may also be applied to the resin at this stage to assist the self-healing process.

Once self-healing has occurred, it will typically be desired to reform the cleaved branches in the epoxy resin. In that case, the resin can be cooled so as to reform the Diels-Alder adduct. The epoxy resin will of course be cooled to a temperature below that which is required to promote the retro Diels-Alder reaction. For example, the resin can simply be cooled to ambient temperatures. Having said this, to improve the efficiency of the Diels- Alder reaction it may be desirable to hold the resin at an elevated temperature (e.g. above ambient temperature) that is below the temperature at which the retro Diels-Alder reaction occurs. Reforming the Diels-Alder adducts can advantageously reinstate thermoset character to the resin.

In one embodiment, the epoxy resin in accordance with the invention is heated to about 75° C to reform the Diels-Alder adduct.

The term "alkyl" includes saturated aliphatic groups, including straight-chain alkyl groups (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, etc.) and branched-chain alkyl groups (isopropyl, tert-butyl, isobutyl, etc.). In some embodiments "alkyl" refers to straight chained alkyl. The expression "C _x . _y alkyl", wherein x is 1-5 and y is 2-12 indicates an alkyl group (straight- or branched-chain) containing the specified number of carbon atoms. For example, the expression Ci^alkyl includes, but is not limited to, methyl, ethyl, propyl, butyl, isopropyl, tert-butyl and isobutyl. The term "alkylene" refers to a divalent alkyl group.

In one embodiment, a straight chain or branched chain alkyl has 12 or fewer carbon atoms (ie C1.12). In some embodiments a straight chain or branched chain alkyl has 8 or fewer carbon atoms (ie d-s).

The term "alkenyl" includes unsaturated aliphatic groups analogous in length and possible substitution to the alkyls described above, but which contain at least one double bond. For example, the term "alkenyl" includes straight-chain alkenyl groups (e.g., ethenyl, propenyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, etc.) and branched-chain alkenyl groups. In some embodiments "alkenyl" refers to straight chained alkenyl. In certain embodiments, a straight chain or branched chain alkenyl grou has 12 or fewer carbon atoms in its backbone (e.g., C2-C12 for straight chain, C3-C12 for branched chain). The term C ₂ -Ci2 includes alkenyl groups containing 2 to 12 carbon atoms. The term "alkenylene" refers to a divalent alkenyl group.

The term "alkynyl" includes unsaturated aliphatic groups analogous in length and possible substitution to the alkyls described above, but which contain at least one triple bond. For example, the term "alkynyl" includes straight-chain alkynyl groups (e.g., ethyriyl, propynyl, butynyl, pentynyl, hexynyl, heptynyl, octynyl, nonynyl, decynyl, etc.) and branched-chain alkynyl groups. In some embodiments "alkynyl" refers to straight chained alkynyl. In certain embodiments, a straight chain or branched chain alkynyl group has 12 or fewer carbon atoms in its backbone (e.g., C2-C12 for straight chain, C2-C12 for branched chain). The term C2-C12 includes alkynyl groups containing 2 to 12 carbon atoms. The term "alkynylene" refers to a divalent alkynyl group.

The term "carbocyclyl" includes any of non-aromatic monocyclic, polycyclic, fused or conjugated hydrocarbon residues, preferably C3 _-2 o (e.g. C _3- io or C _3- 8). The rings may be saturated, e.g, cycloalkyl, or may possess one or more double bonds (cycloalkenyl) and/or one or more triple bonds (cycloalkynyl). Particularly preferred carbocyclyl moieties are 5-, 6-membered or 9-10 membered ring systems. Suitable examples include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cyclopentenyl, cyclohexenyl, cyclooctenyl, cyclopentadienyl, cyclohexadienyl, cyclooctatetraenyl, indanyl, decalinyl and indenyl. A carbocyclyl group may be optionally substituted by one or more optional substituents as herein defined. The term "carbocyclylene" is intended to denote the divalent form of carbocyclyl. The term "cycloalkyl" includes saturated cyclic aliphatic groups (cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl). The term C3-6cycIoalkyl includes, but is not limited to, cyclopropyl, cyclopentyl, and cyclohexyl. Likewise, preferred cycloalkyls have from 4-7 carbon atoms in their ring structure, and more preferably have 5 or 6 carbons in the ring structure. As used herein the term "heterocycloalkyl" refers to a cycloalkyl group containing one or more endocyclic heteroatoms. Likewise, cycloalkenyl groups may have from 3-8 carbon atoms in their ring structure, and more preferably have 5 or 6 carbons in the ring structure.

The term "heteroatom" includes atoms of any element other than carbon or hydrogen. Preferred heteroatoms are nitrogen, oxygen, sulfur and phosphorus. Particularly preferred heteroatoms are nitrogen and oxygen. The term "amine" or "amino" should be understood as being broadly applied to both a molecule, or a moiety or functional group, as generally understood in the art, and may be primary, secondary, or tertiary. The term "amine" or "amino" includes compounds where a nitrogen atom is covalently bonded to at least one carbon or hydrogen. As used herein, the term "optionally substituted" typically refers to where a hydrogen atom on a group has been substituted with a non-hydrogen group. Unless the context requires otherwise, such as where the optional substituent has been explicitly referred to, examples of optional substituents are detailed below. Any optionally substituted group may bear one, two, three or more optional substituents.

In some embodiments the optional substituents are selected from: optionally substituted Ci. ₆ alkyl; optionally substituted C _6- ioaryl; halogen; -OH; -NH ₂ ; -N0 ₂ ; -S0 ₂ NH ₂ ; -COOH; -COO(C^alkyl); -NHCOO(C^alkyl); -NH-COR ⁹ wherein R ^a is H or Ci^alkyl; -NR R ^b wherein R ^a is H or -C(0)NR ^a R ^b , wherein R ^a is H or Ci. ₆ alkyl and R ^b is H, Ci-ealkyl; -C(0)R ^a wherein R ^a is H or Ci^alkyl; or -Y-Q wherein:

Y is selected from: -0-, -NH-, -N(C^alkyl)-, -NHS0 ₂ -, -S0 ₂ NH-, -NHCONH-, -NHCON(C _1-6 alkyl)-, -S(0)„- wherein q is 0, 1 or 2, -C(0)NH-, -C(0)N(CH ₃ )-, -NHC(O)-, -C(O)-, -NHC(NH)NH-, or absent, and

Q is selected from: optionally substituted C6-ioaryl; optionally substituted 5-10 membered Ci.9heteroaryl; optionally substituted 3-10 membered Q. 9heterocyclyl; optionally substituted C3-iocycloalkyl; optionally substituted

Ci-ealkyl; optionally substituted Ci-ealkylacyl; optionally substituted C ₂ . ealkenyl; optionally substituted C ₂ ^alkynyl; and hydrogen.

In other embodiments the optional substituents are selected from: optionally substituted C _\ . ₆ alkyl; optionally substituted C ₆ .i ₀ aryl; halogen; -OH; -NH ₂ ; -COOH; -COO(Ci. ₆ alkyl); -NR ^a R ^b wherein R ^a is H or d-ealkyl and R ^b is H or Ci. ₆ alkyl; -NH-COR ³ wherein R ^a is H or Ci-ealkyl; -C(0)NR ⁸ R ^b , wherein R ^a is H or C _1-6 alkyl, and R ^b is H, C^alkyl; C(0)R ^a wherein R ^a is H or Ci-ealkyl; or -Y-Q, wherein:

Y is selected from: -0-, -NH-, -N(C alkyl)-, -NHCONH-, -S-, -C(0)NH-, -C(0)N(CH ₃ )-, -NHC(0)-, -C(O)-, -NHC(NH)NH-, or absent, and

Q is selected from: C -io ryl optionally substituted with -OH; 5-10 membered Ci- 9heteroaryl; 3-10 membered C3.iocycloalkyl; Ci. 6alkylacyl; C^alkenyl; C ₂ .6alkynyl; and hydrogen. The term "amide," "amido" or "aminocarbonyl" includes compounds or moieties which contain a nitrogen atom which is bound to the carbon of a carbonyl or a thiocarbonyl group.

The term "aryl" refers to aromatic monocyclic (e.g. phenyl) or polycyclic groups (e.g., tricyclic, bicyclic, e.g., naphthalene, anthryl, phenanthryl). Aryl groups can also be fused or bridged with alicyclic or heterocyclic rings which are not aromatic so as to form a polycycle (e.g., tetralin, methylenedioxyphenyl).

The term "heteroaryl", as used herein, represents a monocyclic or bicyclic ring, typically of up to 7 atoms in each ring, wherein at least one ring is aromatic and contains from 1 to 4 heteroatoms selected from the group consisting of O, N and S. Heteroaryl groups within the scope of this definition include but are not limited to: benzimidazole (otherwise known as benzoimadazole), acridinyl, carbazolyl, cinnolinyl, quinoxalinyl, pyrrazolyl, indolyl, benzotriazolyl, furanyl, thienyl, benzothienyl, benzofuranyl, quinolinyl, isoquinolinyl, oxazolyl, isoxazolyl, indoiyl, pyrazinyl, pyridazinyl, pyridinyl, pyrimidinyl, pyrrolyl, tetrahydroquinoline. As with the definition of heterocycle below, "heteroaryl" is also understood to include the N-oxide derivative of any nitrogen-containing heteroaryl. In cases where the heteroaryl substituent is bicyclic and one ring is non-aromatic or contains no heteroatoms, it is understood that attachment is via the aromatic ring or via the heteroatom containing ring, respectively.

The term "heterocycle" or "heterocyclyl" as used herein is intended to mean a 5- to 10- membered aromatic or nonaromatic heterocycle containing from 1 to 4 heteroatoms selected from the group consisting of O, N and S, and includes bicyclic groups. "Heterocyclyl" therefore includes the above mentioned heteroaryls, as well as dihydro and tetrathydro analogs thereof. Further examples of "heterocyclyl" include, but are not limited to the following: benzoimidazolyl, benzofuranyl, benzofurazanyl, benzopyrazolyl, benzotriazolyl, benzothiophenyl, benzoxazolyl, carbazolyl, carbolinyl, cinnolinyl, furanyl, imidazolyl, indolinyl, indoiyl, indolazinyl, indazolyl, isobenzofuranyl, isoindolyl, isoquinolyl, isothiazolyl, isoxazolyl, naphthpyridinyl, oxadiazolyl, oxazolyl, oxazoline, isoxazoiine, oxetanyl, pyranyl, pyrazinyl, pyrazolyl, pyridazinyl, pyridopyridinyl, pyridazinyl, pyridyl, pyrimidyl, pyrrolyl, quinazolinyl, quinolyt, quinoxalinyl, tetrahydropyranyl, tetrazolyl, tetrazolopyridyl, thiadiazolyl, thiazolyl, thienyl, triazolyl, azetidinyl, 1 ,4-dioxanyl, hexahydroazepinyl, piperazinyl, piperidinyl, pyridin-2-onyI, pyrrolidinyl, mocpholinyl, thiomorpholinyl, dihydrobenzoimidazolyl, dihydrobenzofuranyl, dihydrobenzothiophenyl, dihydrobenzoxazolyl, dihydrofuranyl, dihydroimidazolyl, dihydroindolyl, dihydroisooxazolyl, dihydroisothiazolyl, dihydrooxadiazolyl, dihydrooxazolyl, dihydropyrazinyl, dihydropyrazolyl, dihydropyridinyl, dihydropyrimidinyl, dihydropyrrolyl, dihydroquinolinyl, dihydrotetrazolyl, dihydrothiadiazolyl, dihydrothiazolyl, dihydrothienyl, " dihydrotriazolyl, dihydroazetidinyl, methylenedioxybenzoyl, tetrahydrofuranyl, and tetrahydrothienyl, and N-oxides thereof. Attachment of a heterocyclyl substituent can occur via a carbon atom or via a heteroatom. A referred to herein "heterocycloalkyl" refers to a saturated heterocyclyl group. In some embodiments the heterocycloalkyl group is optionally substituted with one or more OH and/or C¾OH. An example of such a group is the simple sugar ribose.

The term "acyl" includes compounds and moieties which contain the acyl radical (CH3CO-) or a carbonyl group such as CH ₃ CH ₂ CH ₂ CO-.

The term "alkoxy" includes substituted and unsubstituted alkyl, alkenyl, and alkynyl groups covalently linked to an oxygen atom. Examples of alkoxy groups include methoxy, ethoxy, isopropyloxy (isopropoxy), propoxy, butoxy, and pentoxy groups and may include cyclic groups such as cyclopentoxy.

The term "carbonyl" or "carboxy" includes compounds and moieties which contain a carbon connected with a double bond to an oxygen atom, and tautomeric forms thereof. Examples of moieties that contain a carbonyl include aldehydes, ketones, carboxylic acids, amides, esters, anhydrides, etc. The term "carboxy moiety" or "carbonyl moiety" refers to groups such as "alkylcarbonyl" groups wherein an alkyl group is covalently bound to a carbonyl group, "alkenyl carbonyl" groups wherein an alkenyl group is covalently bound to a carbonyl group, "alkynylcarbonyl" groups wherein an alkynyl group is covalently bound to a carbonyl group, "arylcarbonyl" groups wherein an aryl group is covalently attached to the carbonyl group. Furthermore, the term also refers to groups wherein one or more heteroatoms are covalently bonded to the carbonyl moiety. For example, the term includes moieties such as* for example, aminocarbonyl moieties, (wherein a nitrogen atom is bound to the carbon of the carbonyl group, e.g., an amide), aminocarbonyloxy moieties, wherein an oxygen and a nitrogen atom are both bond to the carbon of the carbonyl group (e.g., also referred to as a "carbamate"). Furthermore, aminocarbonylamino groups (e.g., ureas) are also include as well as other combinations of carbonyl groups bound to heteroatoms (e.g., nitrogen, oxygen, sulfur, etc. as well as carbon atoms). Furthermore, the heteroatom can be further substituted with one or more alkyl, alkenyl, alkynyl, aryl, aralkyl, acyl, etc. moieties. The term "thiocarbonyl" or "thiocarboxy" includes compounds and moieties which contain a carbon connected with a double bond to a sulfur atom. The term "thiocarbonyl moiety" includes moieties that are analogous to carbonyl moieties. For example, "thiocarbonyl" moieties include aminothiocarbonyl, wherein an amino group is bound to the carbon atom of the thiocarbonyl group, furthermore other thiocarbonyl moieties include, oxythiocarbonyls (oxygen bound to the carbon atom), aminothiocarbonylamino groups, etc. The term "ester" includes compounds and moieties that contain a carbon or a heteroatom bound to an oxygen atom that is bonded to the carbon of a carbonyl group. The term "ester" includes alkoxycarboxy groups such as methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, etc. The alkyl, alkenyl, or alkynyl groups are as defined above.

The term "hydroxy" or "hydroxyl" includes groups with an -OH.

The term "halogen" includes fluorine, chlorine, bromine and iodine. In some embodiments halogen refers to fluorine or chlorine.

The terms "polycyclyl" or "polycyclic" include moieties with two or more rings (e.g., cycloalkyls, cycloalkenyls, cycloalkynyls, aryls and/or heterocyclyls) in which two or more carbons are common to two adjoining rings, e.g., the rings are "fused rings". Rings that are joined through non-adjacent atoms are termed "bridged" rings.

It is to be understood that all of the compounds of the invention will further include bonds between adjacent atoms and or hydrogens as required to satisfy the valence of each atom. That is, double bonds and/or hydrogen atoms are typically added to provide the following number of total bonds to each of the following types of atoms: carbon: four bonds; nitrogen: three bonds; oxygen: two bonds; and sulfur: two, four or six bonds. It is also to be understood that definitions given to the variables of the generic formulae described herein will result in molecular structures that are in agreement with standard organic chemistry definitions and knowledge, e.g., valency rules.

It will be noted that the structures of some of the compounds of this invention include asymmetric carbon atoms. It is to be understood accordingly that the isomers arising from such asymmetry (e.g., all enantiomers, stereoisomers, rotamers, tautomers, diastereomers, or racemates) are included within the scope of this invention. Such isomers can be obtained in substantially pure form by classical separation techniques and by stereochemically controlled synthesis. Furthermore, the structures and other compounds and moieties discussed in this application also include all tautomers thereof. Compounds described herein may be obtained through synthetic strategies known in the art.

The invention will now be described with reference to the following non-limiting example: Example 1

Synthesis of 2^Z'-(octane-l,8-diyl)bis(4-(aminomethyl)hexahydro-lH-4,7 epoxy

l,l'-(octan-l,8-diyl)bis(lH-pyrrole-2,5-dione) (4.36 g, 14.3 mmol) and tert-butyl (furan-2- ylmethyl)carbamate (14.13 g, 71.7 mmol) were combined in ethyl acetate (130 mL). The solution was stirred at 70 °C overnight, before the ethyl acetate was evaporated and acetone was added to the residue to precipitate out the solid. The solid was filtered, dried under vacuum before being dissolved in acetone (25 mL) and mixed with cone. HC1 (125 mL) and stirred at 70 °C for 2 days. After the reaction, the acetone was evaporated and the remained solid was washed with dichloromethane, and dissolved in water (50 mL) with sodium hydroxide (0.1 N) to neutralize the product. Dichloromethane was used to extract the final product, 2,2'-(octan-l,8-diyl)bis(4-(aminomethyl)hexahydro-lH-4,7 epoxyisoindole-l,3(2H)-dione) (63 %). Exo and endo ratio of the compound was determined by Ή NMR as exo/endo = 6.7:1. Exo isomer: Ή NMR (400 MHz, CDC1 ₃ ) δ 6.54 (d, J= 5.7 Hz, 2H), 6.50 (dd, J= 5.7, 1.6 Hz, 2H), 5.20 (d, J = 1.7 Hz, 2H), 3.43 (t, J = 8.0 Hz, 4H), 3.34 - 3.11 (m, 4H), 2.94 (d, J= 6.4 Hz, 2H), 2.83 (d, J= 6.4 Hz, 2H), 1.55 - 1.39 (m, 4H), 1.24 (s, 8H). ^,3 C NMR (100 MHz, CDC1 ₃ ) δ 176.27, 175.36, 138.57, 137.08, 92.45, 91.97, 82.99, 80.80, 50.46, 48.06, 41.46, 39.74, 28.94, 27.59, 26.55. ESI- MS ( /z): [M + H] ⁺ calc. for CzeHssWe 499.3, found 499.1. FTIR v (cm- ¹ ) 3373, 2932, 2857, 1768, 1692, 1439, 1402, 1153, 731.

Synthesis of the branched epoxy resin

: * ^* polymer

2,2'-(octan-l,8-diyl)bis(4-(aminomethyl)hexahydro-lH-4,7 epoxyisoindole-l,3(2H)-dione) (0.051 g, 0.1 mmol) and the diglycidyl ether of bisphenol-A (0.070 g, 0.2 mmol) were mixed directly without solvent at 80° C for 12 hr to provide the epoxy resin.

Assessment of the self healing properties of the branched epoxy resin

A sample of the epoxy resin was cut on its surface using a sharp blade. The cut was approximately 40 μπι in width (see Figure (2a). The damaged epoxy resin was subjected to heating at 140 °C for 30 minutes followed by cooling at 75°C for 5 hours. The cut was completely healed (see Figure (2b)) Figure 1 is a composite FTIR spectrum of an epoxy resin in accordance with the invention. The peak 694 cm ^"1 represents a carbon-hydrogen bond connected to a carbon-carbon double bond in the maleimide group of the Diels-Alder precursor. After the epoxy resin was heated at 140 °C for 30 minutes, the peak (b) is more intense than before heating (a), indicating that the content of maleimide had increased which is indicative that a retro Diels-Alder reaction has occurred. After the epoxy resin was cooled at 75 °C for 5 hours, the peak (c) became weaker, indicating that the content of maleimide had decreased which is indicative that the Diels-Alder adduct has reformed; Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.