WO2017096187A1 - Biobased epoxy monomers, compositions, and uses thereof - Google Patents

Abstract

A biobased epoxy compound, precursors, compositions, methods, and articles of manufacture related to the same. The biobased epoxy compound comprises an ether-bridged cycloaliphatic ring structure: where, each of R_a' and R_b' are selected from the group consisting of -H, branched and unbranched alkyl groups, fatty acid moieties, substituted or unsubstituted aliphatic cyclic rings, substituted or unsubstituted aromatic moieties, epoxy moieties, and combinations thereof, with the proviso that at least one of R_a' and R_b' each comprise an epoxy moiety.

Description

BIOBASED EPOXY MONOMERS, COMPOSITIONS, AND USES THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims the priority benefit of U.S. Provisional Patent Application Serial No. 62/263,437, filed December 4, 2015, entitled BIOBASED EPOXY MONOMERS, COMPOSITION, SYNTHESIS ROUTE, AND POTENTIAL APPLICATIONS, incorporated by reference in its entirety herein.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant No. 2012-10006-20230 awarded by United States Department of Agriculture. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to epoxy resins from renewable resources.

Description of Related Art

Epoxy resin is one of the most versatile polymers, accounting globally for approximately 70% of the market of thermosetting polymers (polyurethanes not included). The global market value of epoxy is projected to reach US $25.8 billion by 2018 for a range of applications including epoxy composites and the adhesive market. Bisphenol A diglycidyl ether (DGEBA) is the most popular epoxy monomer derived from the reaction of bisphenol A (BP A) and epichlorohydrin (ECH). The aromatic ring of BPA renders good thermal resistance and mechanical strength to the epoxy networks. However, the impacts of BPA on human health (e.g., alterations in both the immune and reproductive systems) limits the use of DGEBA, especially in food contact materials. The uncertainty in terms of price and availability of petroleum also urges the chemical industry to seek sustainable alternatives to petroleum chemicals.

Industry has been constantly seeking high bio-content alternatives to DGEBA, however, to date none of the bio-based epoxies developed in the past decades is entirely comparable to the commercial DGEBA. Starch- or sugar-derived epoxies could possess high mechanical strengths and low viscosities similar to DGEBA, however, the performance properties, especially the mechanical strength, rely on the combination of hardeners (generally petroleum-based anhydrides or amines with about 30-50 wt %). Aromatic ring-rich compounds from bio-based resources (i.e., natural polyphenols and woody biomass) have been investigated as building blocks for epoxy monomers. The intrinsic aromatic rings render rigid structures to the epoxy network, significantly improving the mechanical strength and thermal resistance as well as comparative glass transition temperature (Tg) to commercial DGEBA. However, because of the rigid aromatic rings, they restrict the mobility of epoxy chains that make the epoxy monomers highly viscous liquids or a solid at ambient temperature. Even though plant oil-derived epoxies have low viscosities, the poor thermo-mechanical properties limit the application.

SUMMARY OF THE INVENTION

The present invention is broadly concerned biobased epoxy compounds, precursors, compositions, methods, and articles of manufacture related to the same. In more detail, described herein is an epoxy resin comprising at least one biobased epoxy compound. The biobased epoxy compound c c ring structure:

where, each of Ra' and Rv are selected from the group consisting of -H, branched and unbranched alkyl groups, fatty acid moieties, substituted or unsubstituted aliphatic cyclic rings, substituted or unsubstituted aromatic moieties, epoxy moieties, and combinations thereof, with the proviso that at least one of Ra' and Rb' each comprise an epoxy moiety.

Articles of manufacture using the epoxy resin are also contemplated herein. The article comprises a substrate having a surface; and a layer of a biobased adhesive, coating, or film adjacent the substrate surface. This layer is formed from an epoxy resin according to any of the embodiments described herein.

Also described herein are methods of forming a biobased adhesive, coating, or film. The methods generally comprise providing an epoxy resin according to any of the embodiments described herein; applying the epoxy resin to a substrate; and exposing the epoxy resin to activating radiation to yield a cured biobased adhesive, coating, or film on the substrate.

Additional methods are described herein, including methods of forming a biobased epoxy precursor compound. The methods generally comprise reacting an alicyclic oxirane compound with a biobased unsaturated fatty acid or a biobased compound comprising an unsaturated fatty acid moiety under conditions to yield a biobased epoxy precursor compound. The precursor compound comprises an ether- ridged cycloaliphatic ring structure:

where, each of R_a and Rb are selected from the group consisting of -H, branched and unbranched alkyl groups, branched and unbranched alkenes, unsaturated fatty acid moieties, substituted or unsubstituted aliphatic cyclic rings, substituted or unsubstituted aromatic moieties, and combinations thereof, with the proviso that at least one of R_a and Rb each comprise an alkene.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

Figure (FIG.) 1 shows the reaction pathway for UA/ECP system. Solid arrows indicate the main reaction pathways; dash arrow indicates the additional reaction pathways;

FIG. 2 shows the reaction pathway for UA/MECP system;

FIG. 3 shows graphs of the time evolution of FTIR spectra for the stoichiometric UA/ECP system (A) and UA/MECP system (B) at 80 °C;

FIG. 4 shows graphs of Synchronous (A) and Asynchronous (B) 2D FTIR correlation spectra of UA /ECP system in the region of 1800-700 cm^"1. The unshaded and shaded areas in the contour maps represent positive and negative peaks, respectively;

FIG. 5 shows graphs of the ¹³C NMR spectra of (A) CUA and (B) MCUA;

FIG. 6 illustrates the transition states of cycloaliphatic epoxide isomers. Ri=H or CH₃, R₂=CH=CH₂ or C(CH₃)=CH₂; FIG. 7 illustrates the formation of isomers in CUA due to the stereoisomerism of ECP;

FIG. 8 illustrates the epoxidation of CUA and MCUA into (a) ECUA and (b) EMCUA;

FIG. 9 shows graphs of the ¹³C MR spectra of (a) ECUA and (b) EMCUA;

FIG. 10 is a graph of the complex viscosities (I]*) of various epoxies determined at 25 °C as a function of shear rate;

FIG. 11 is a graph of the exothermic behaviors of epoxy monomers containing of 3 wt% photo-initiator (PC-2506) radiated through UV light as a function of time;

FIG. 12 shows (a) a photograph of various epoxy resins after UV-curing and (b) a graph comparison of their % transmittance at various wavelengths;

FIG. 13 shows graphs of (A) Temperature dependence of storage moduli; and (B) loss factors for P-ESO, P-DGEBA, P-ECUA and P-EMCUA. (C) Schematic diagram demonstrating the key features of cured epoxy networks. Type I structure: ellipse shading; type II structure: rectangular shading; type III structure: square shading; type IV structure: round shading;

FIG. 14 illustrates the chain propagation mechanisms in the UV-curing process for epoxy monomers containing photo-initiator PC-2506;

FIG. 15 illustrates data on the mechanical property evaluation of cured epoxy resins. (A) Typical strain-stress curves. (B) Detailed mechanical results regarding elongation at break (%) and tensile strength (MPa);

FIG. 16 is a graphical illustration of the comprehensive performance comparison between DGEBA and bio-epoxies according to the invention;

FIG. 17 illustrates the (a) Synthetic pathway of MCCA (typical chemical structure is shown); and (b) Synthetic pathway of EMCCA (typical chemical structure is shown) and structural features of EMCCA;

FIG. 18 illustrates the synthesis of MCCA and EMCCA. Only typical chemical structures are shown due to the isomers in reagent and product;

FIG. 19 is a graph of the FTIR spectra of ECP-Amberlyst-15 system before and after being heated at 80 °C for 48h. Characteristic peak centered at 811 cm^"1 is attributed to the epoxy ring of ECP;

FIG. 20 shows the (a) Kinetics of the variations of the epoxy ring (stretching C-O-C of epoxy group centered at 811 cm^"1) for Amberlyst-15a -A-(MCUA(10g)-ECP(2.5g)-Amberlyst- 15(1.2g) at 25°C), Amberlyst-15b -0-(MCUA(10g)-ECP(2.5g)-Amberlyst-15(1.2g) at 60°C) and Amberlyst-15c -•-(MCUA(10g)-ECP(2.5g)-Amberlyst-15(1.6g) at 60°C). (b) Typical chemical structures of MCUA and MCCA; the shadow regions represent the coupling areas of protons connected by hydroxyl, ether or ester groups with vicinity protons, (c) ¹H- MR and ¾-¾ COSY spectra of MCUA (d) ¾- MR and ¾-¾ COSY spectra of MCCA;

FIG. 21 shows the ¾- MR spectra of EMCUA and EMCCA. (typical chemical structures are shown). The NMR spectra of EMCUA presented here are for comparison purpose with EMCCA;

FIG. 22 shows a photograph of a cured epoxy resin and graph illustrating the transparency values of UV-cured EMCCA film in the light wavelength range of 300-700 nm;

FIG. 23 shows comparisons of (a) viscosities, (b) mechanical properties, (c) dynamic mechanical properties, and (d) creep behaviors of EMCUA and EMCCA. (e) Schematic diagram demonstrating the key features of cured epoxy networks. Type I structure: ellipse shading; type II structure: rectangular shading; type III structure: square shading; type IV structure: round shading;

FIG. 24 is a table of performance comparison of EMCCA with other typical counterparts containing fatty acid as building blocks;

FIG. 25 is (a) a graph of UV-curing reactivity comparison of epoxidized soybean oil (ESO) and EMCUA in the presence of 3 wt% photo-initiator (PC-2506); and (b) Chain propagation mechanisms in the UV-curing process for epoxy monomers based upon Example 1;

FIG. 26 is an illustration of the possibility of achieving new bio-based epoxy through the combination of building blocks from plant oil and terpene families for low viscosity, high mechanical strength and thermal resistance performances while maintaining a high bio-based content;

FIG. 27 shows photographs of MECP+Amberlyst-15(10wt%) after being heated at 60°Cfor 12h (left panel); and ECP+Amberlyst-15 (10wt%) after being heated at 60°Cfor 12h (right panel); and

FIG. 28 illustrates the reaction scheme to depict the acid-catalyzed epoxide ring-opening reaction.

DETAILED DESCRIPTION

The present invention is concerned with renewable epoxy resins, precursors thereof, cured epoxy compositions, and methods related to the same. In one or more embodiments, the materials are biobased and derived from plant-based materials. The inventive compositions can also be used to prepare coatings or films suitable for a variety of uses described herein.

The precursor compounds comprise a novel ether-bridged cycloaliphatic ring structure:

, where

each of Ra and Rb are selected from the group consisting of -H, branched and unbranched alkyl groups, branched and unbranched alkenes, unsaturated fatty acid moieties, substituted or unsubstituted aliphatic cyclic rings, substituted or unsubstituted aromatic moieties, combinations thereof, and the like, with the proviso that at least one of R_a and Rb each contain an alkene (e.g., vinyl moieties, unsaturated fatty acid moieties). Preferably, at least one Rb is an unsaturated fatty acid moiety. More preferably, the unsaturated fatty acid moiety is a linear moiety that comprises an alkene-terminated aliphatic chain. Thus, it will be appreciated that the resulting epoxidized compounds will also comprise this novel ether-bridged cycloaliphatic ring structure above, except that Ra' and Rb' are used to denote the epoxidized moieties, and at least one of R_a' and Rb' are each moieties comprising at least one epoxy group. Further any unsaturated groups would also be epoxidized in the epoxy resin (e.g., such as the terminal alkene of a fatty acid chain).

In one or more embodiments epoxy precursor compounds are prepared by reacting an alicyclic oxirane compound (aka cycloaliphatic epoxide) with an unsaturated fatty acid or compound comprising an unsaturated fatty acid moiety to yield a precursor compound comprising the ether-bridged cycloaliphatic ring structure above. Preferably, this reaction is carried out under conditions to facilitate competitive nucleophilic attack of the acid anion on the oxonium ion. In one or more embodiments, the reaction is carried out at temperatures ranging from about room temperature (e.g., about 20°C to about 25°C) up to elevated temperatures of about 160°C. The reaction time can range from about 30 minutes to about 72 hours. Advantageously, this reaction can be carried out without the use of a catalyst or solvents. In one or more embodiments, a heterogeneous catalyst can be used to facilitate the reaction. Exemplary catalysts include reusable ion exchange resins, and preferably strongly acidic cation exchange resins suitable for non-aqueous catalysis, such as AMBERLYST® 15 (strongly acid macro reticular polystyrene based ion exchange resin with strongly acidic sulfonic group).

Exemplary alicyclic oxirane compounds for use as the starting materials include cyclic epoxides with at least one unsaturated substitution, such as l,2-epoxy-4-vinylcyclohexane (also known as 4-ethenyl-7-oxabicyclo[4.1.0]heptanes ("ECP"), EP-101, or 4-vinyl-l-cyclohexene 1, 2-epoxide), 3,4-epoxy-l-cyclohexene, and substituted forms thereof. For example, methyl substituted forms, such as limonene 1, 2-epoxide (MECP), can be used to create linear precursor compounds. Advantageously, these linear precursor compounds can be further reacted with ECP to yield precursor compounds with the ether-bridged cycloaliphatic ring structure. Linear precursor compounds can also be used in the epoxy resins to modulate the properties of the resin.

Exemplary fatty acids for use as the starting materials include medium chain unsaturated fatty acids. In one or more embodiments, the fatty acids have an aliphatic chain length of from about 3 to about 24 carbons. Preferably, the fatty acids include a terminal alkene. Suitable fatty acids include 10-undecenoic acid, 8-nonenoic acid, 7-octenoic acid, and the like.

In one or more embodiments, epoxy precursor compounds according to embodiments of the invention include branched monomers:

where n is 1 to 21 (preferably 1 to 10), and any one of the cycloaliphatic rings in the foregoing structures may be substituted or unsubstituted. Precursor compositions can further include additional linear precursor monomers, such as:

where n is 1 to 21 (preferably 1 to 10), and any one of the cycloaliphatic rings in the foregoing structures may be substituted or unsubstituted.

Advantageously, these biobased epoxy precursor compounds can be epoxidized using any suitable reagent for epoxidation of alkenes, such as a peracid or a peroxy acid. Suitable reagents include meta-chloroperoxybenzoic acid (mCPBA), hydrogen peroxide, and the like.

Epoxy compounds formed according to embodiments of the invention include:

where n is 1 to 21 (preferably 1 to 10), and any one of the cycloaliphatic rings in the foregoing structures may be substituted or unsubstituted.

It will be appreciated that the properties of the epoxy composition can be adjusted by varying the relative amounts of branched and linear epoxy monomers. Advantageously, the resin is liquid under ambient conditions and can be mixed with additives, catalysts, initiators, preservatives, thickeners, plasticizers, and the like, without the need for a solvent system. However, in certain applications a solvent system may be desired and can optionally be included. In one or more embodiments, epoxy resins according to the invention consist essentially or even consist of one or more epoxy compounds listed above, and are substantially solvent-free. The term "substantially free," as used herein means that the composition contains less than about 1% by weight, and preferably less than about 0.1% by weight of that particular ingredient, based upon the total weight of the composition taken as 100% by weight.

The epoxy resin has a low viscosity of less than 5 Pa s, preferably less than 4 Pa s, and more preferably from about 1 Pa s to about 3 Pa s. The epoxy composition can be used in various applications, including any applications suitable for conventional epoxy compounds, for example as adhesives, films for flexible electronic devices (e.g., solar cell, semiconductor, organic light-emitting diode and display), reusable tapes, sticky notes, medical and pharmaceutical devices (e.g., electrodes, skin wound care, medical tapes, band-aids, etc.), and screen protectors for electronic displays (e.g., computers, tablets, phones, televisions, etc.). Thus, it will be appreciated that the epoxy compounds can be cured to create adhesives, films, coatings, elastomers, sealants, foams, composites, and the like. Thus, the composition can be applied to various substrates, or molded into a desired shape before curing.

Depending upon the initiator or catalyst chosen, the resultant epoxy resin can be cured using heat, radiation (e.g., UV or vis light), or under ambient conditions with the aid of a curing agent. It will be understood that references herein to "curing" in the context of epoxies refers to polymerization of the epoxy monomers and subsequent crosslinking between polymer chains to create the cured epoxy network. In some embodiments, the catalyst also functions as a crosslinking agent and participates in crosslinking. In other embodiments, the catalyst does not participate in crosslinking and does not function as a crosslinking agent. Regardless, in either embodiment, the composition is preferably substantially free of additional or any crosslinking agents. In other words, when a catalyst crosslinking agent is present, it is preferably the only crosslinking agent present in the composition, and no additional crosslinking agents are present. Where the catalyst does not function as a crosslinking agent, the composition is substantially free of any crosslinking agents at all. Exemplary "added" crosslinking agents that are preferably excluded in certain embodiments include aminoplasts/melamines, vinyl ethers, glycourils, multifunctional epoxies (unless also biobased), anhydrides, silanes, peroxides, thiadiazoles, and the like.

In one or more embodiments, the resultant epoxy resin is UV curable, preferably with the aid of a cationic photoinitiator. In one or more embodiments, the epoxy composition comprises one or more of the above epoxy compounds homogenously mixed with any suitable epoxy photoinitiator and optional solvent system. Suitable photoinitiators include low dose cationic photoinitiators, such as iodonium antimonate salts (e.g., PC-2506; Polyset company, Mechanicville, NY), radical photoinitiators, such as alpha hydroxyketones (e.g., DAROCUR® 1173; BASF resins, Wyandotte, MI), and the like. When present, the resin preferably comprises from about 1% to about 10% by weight photoinitiator, more preferably from about 3% to about 7% by weight, and even more preferably from about 3% to about 5% by weight photoinitiator, based upon the total weight of the resin taken as 100% by weight. The epoxy resins can also be thermally cured if desired.

In one use, a layer of the epoxy resin is formed on a substrate surface. The composition layer can be formed by brushing, rolling, spin-coating, pouring, and/or spraying the composition onto the substrate surface. Suitable substrates include virtually any solid surface, such as glass, paper, plastic, metal, silicon wafers, electronic displays, marbles, coated woods, composites, and combinations thereof. It will be appreciated that the thickness of the cured layer will depend upon the desired end-used of the composition. The cured layer preferably has a substantially uniform thickness across its surface area. Exposure to the UV radiation causes the cationic polymerization and self-crosslinking of the epoxy compounds. In some embodiments, the exposing process may be repeated multiple times until the desired level of curing is achieved. It will be appreciated that the total UV dose used for radiation will depend upon the end use (e.g., PSA vs. coating), as well as the thickness of the composition layer (to achieve complete through curing). The total radiation dose will generally range from about 1 to about 5 J/cm², more preferably from about 1 to about 3 J/cm², and even more preferably from about 1 to about 2 J/cm².

Advantageously, epoxies prepared according to embodiments of the invention have fast cure times (with UV cure times of less than 20 seconds). The cured biobased epoxy compositions are characterized by a number of additional beneficial features. For example, the cured biobased epoxy compositions possess a high tensile strength of at least about 40 MPa and up to about 65 MPa, depending upon the particular epoxy precursor compounds selected for the composition. The cured biobased epoxy also has a high glass transition temperature of from about 130 to about 160°C. The cured biobased epoxy also has high transparency in the visible region. More specifically, a 150-μπι layer of the cured composition will have a % light transmittance of at least about 80% at a wavelength of between 300-325 nm. Thus, in one or more embodiments, the composition is preferably substantially free of any pigments, dyes, chromophores, and/or other light attenuating moieties. Finally, the cured biobased epoxy is characterized by a biobased content of at least 50 wt %, preferably at least 75 wt%, and more preferably from about 80 to about 90 wt%, based upon the total composition taken as 100% by weight.

Notably, the foregoing mechanical properties are achieved without the use of a hardener or other similar additives in the uncured resin. Thus, in one or more embodiments, epoxy resins according to the invention are substantially free of any hardeners, extenders, and the like.

The cured composition will also preferably be substantially insoluble in organic solvents, including chloroform, methane chloride, tetrahydrofuran, ethyl acetate, methyl acetate, acetone, ethyl ether, dimethylformamide and hexane. The cured composition will also preferably be resistant to moisture and dissolution in water.

Additional advantages of the various embodiments of the invention will be apparent to those skilled in the art upon review of the disclosure herein and the working examples below. It will be appreciated that the various embodiments described herein are not necessarily mutually exclusive unless otherwise indicated herein. For example, a feature described or depicted in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the present invention encompasses a variety of combinations and/or integrations of the specific embodiments described herein.

As used herein, the phrase "and/or," when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing or excluding components A, B, and/or C, the composition can contain or exclude A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

The term "biobased" as used herein refers to renewable resources, particularly from plants, and excludes materials prepared or derived from petroleum or other non-renewable resources. Plant-based materials are particularly preferred biobased materials for use in the invention. The term "plant-based" material, refers to ingredients that are derived from plants, whether through chemical or biological processes. In other words, the compositions are preferably substantially free of non-plant-based materials, including petroleum-based compounds or synthetic polymers and/or elastomers, such as petrol-based acrylates, acrylics, silicones, synthetic rubbers (e.g., isoprenes, isobutylenes, ethylene propylene diene monomer, urethanes, butadienes), polypropylenes, and the like. In one or more embodiments, the compositions comprise greater than 50% by weight plant-based materials, preferably greater than about 75% by weight plant-based materials, and even more preferably greater than about 90% by weight plant-based materials, based upon the total weight of the solids in the composition taken as 100% by weight. In other embodiments, the compositions comprise greater than about 95% by weight plant-based materials, preferably greater than about 97% by weight plant-based materials, and even more preferably greater than about 99% plant-based materials, based upon the total weight of solids in the composition taken as 100% by weight.

The present description also uses numerical ranges to quantify certain parameters relating to various embodiments of the invention. It should be understood that when numerical ranges are provided, such ranges are to be construed as providing literal support for claim limitations that only recite the lower value of the range as well as claim limitations that only recite the upper value of the range. For example, a disclosed numerical range of about 10 to about 100 provides literal support for a claim reciting "greater than about 10" (with no upper bounds) and a claim reciting "less than about 100" (with no lower bounds).

EXAMPLES

The following examples set forth methods in accordance with the invention. It is to be understood, however, that these examples are provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention.

EXAMPLE 1

Bioepoxy derived from 10-undecenoic acid for high performance UV-curable resins In this example, 10-undecenoic acid (UA), a renewable derivate from castor oil, was used the building block for a biobased epoxy precursor. A one-step solvent-free chemical pathway was proposed to synthesize the bioepoxy precursor by utilizing a UA nucleophilic attack upon a cycloaliphatic oxide (4-ethenyl-7-oxabicyclo[4.1.0]heptanes, ECP), as depicted in FIG. 1. A hydroxyl group was formed during the formation of alkene-terminated epoxy precursor. Then, the hydroxyl group together with the UA nucleophilic group attacked the oxonium ion to obtain a novel ether-bridged cyclohexyl structure with more stiff chain segments and cross-linking sites:

CUA Monomer

In association with the UA flexible aliphatic chains, we achieved an ideal structure for bioepoxy with balanced stiffness and flexibility. Furthermore, we used limonene 1,2-epoxide (MECP), a terpene-derived material, to replace the ECP to hinder the CNA reaction and achieved a fully biorenewable linear-structured epoxy precursor (FIG. 2):

MCUA

With this unique and environmentally friendly processing approach, we anticipated achieving a high performance UV-curable bioepoxy with superior mechanical strength and high thermal resistance properties comparable to commercial DGEBA epoxy.

Results and Discussion

Synthesis of Branched Epoxy Precursor - CO A Monomer

The epoxy ring of cycloaliphatic oxide is prone to be protonated, resulting in the formation of oxonium ion intermediate. This intermediate has a fused six- and three- membered ring with high strain. Nucleophiles, such as fatty acid anion, can attack the three-membered ring, realizing an effective connection of fatty acid chain and cycloaliphatic ring. Here, 10-undecenoic acid (UA) and 4-ethenyl-7-oxabicyclo[4.1.OJheptanes (ECP) were used as the building blocks for a bioepoxy with a flexible aliphatic chain and a stiff ether-bridged cyclohexyl structure (FIG. 1). The successful reaction was indicated by the decrease of the bands centered at 809 cm^"1 (stretching C-O-C of epoxy group) and 2678 cm^"1 (stretching O-H of carboxylic acid dimer) respectively, combined with the increase of the band centered at 3454 cm^"1 (stretching O-H of hydroxyl group) (FIG. 3A). This result confirmed the nucleophilic attack of UA upon the epoxide ring of ECP and formation of new hydroxyl groups. The epoxy peak (centered at 809 cm^"1) almost disappeared after a 48-hour reaction, while the carboxylic acid dimer peak (centered at 2678 cm^"1) was still observable. Since the stoichiometric coefficient of UA to ECP is equal to one, the disappearance of epoxy peaks should be theoretically equal to the depletion of carboxylic acid peaks if the reaction proceeded in accordance with the molar ratio of 1 : 1. Therefore, it appeared that a complex reaction pathway existed in the UA/ECP system.

2D FTIR correlation spectra of the UA/ECP system (0-48h) in the region of 1800-700 cm^"1 were derived from the corresponding ID FTIR spectra (Fig. 2). In the synchronous map (FIG. 4A), positive correlation intensities were observed at 1732, 1260-1000 cm^"1 and 1704, 809 cm^"1, and negative correlation intensities were observed at 1732, 1704 cm^"1, 1732, 809 cm^"1, 1704, 1260-1000 cm^"1 and 1260-1000, 809 cm^"1. In the asynchronous map (FIG. 4B), positive correlation intensities were observed at 1732, 1704 cm^"1, 1732, 1260-1000 cm^"1 and 1704, 809 cm^"1, and negative correlation intensities were observed at 1732, 809 cm^"1, 1704, 1260-1000 cm^"1 and 1260-1000, 809 cm^"1. According to the Noda rule, the reaction sequence of 1704, dimeric carboxylic carbonyl→ 1727, dissociated carboxylic carbonyl→ 1200-1000, oxonium ion→ 805, epoxy ring cm^"1 seemed to have occurred. Therefore, the following reaction orders were concluded: dimeric carboxylic dissociation, proton transfer to cycloaliphatic epoxy ring, formation of oxonium ion, and nucleophilic attack of 10-undecenoic acid anion upon the protonated epoxide. Moreover, the resulting hydroxyl group derived from the foregoing nucleophilic attack was also involved in the competitive reaction against 10-undecenoic acid anion for the epoxide ring-opening. The result was the formation of CUA monomers featuring the ether-bridged cyclohexyl structure with multi-terminal alkene groups.

A ¹³C MR spectrum was obtained to further reveal the structural features of CUA (FIG. 5 A). The chemical shifts around 173 ppm were attributed to the carboxyl carbons. The characteristic peaks of carbon atoms on double bonds were identified at 138-142 ppm and 111- 115 ppm. The chemical shifts at 72-75 ppm and 67-70 ppm were attributed to the ester carbons (C12, 12') and hydroxyl carbons (C19¹, C25), respectively. The chemical shifts at 51-53 ppm were attributed to the two ring-bridging ether carbons (CI 9, C20), showing the existence of a branched structure in the CUA system. The chemical shifts of the double bond carbons of ECP and UA are at different positions. Therefore, the corresponding molar ratio of double bonds I and II was estimated to be 1 :0.8, based on the area ratio of the integrated peaks around 142 ppm (C15, C15^* and C26) and 139 ppm (C2, C2'). If the CUA system contains totally branched structures, the corresponding molar ratio between double bonds I and II should be higher than 1 :0.5. Therefore, the resulting molar ratio of 1 :0.8 indicated that in addition to the branched structures, a linear structure also existed:

CUA Linear Component

As a result, CUA appears to be a multicomponent system containing both branched and linear monomers with an estimated molar ratio of 1 :3, based on the molar ratio of double bonds I and II discussed above.

A reaction pathway was proposed to describe the CUA preparation process (FIG. 1). The competitive nucleophilic attack of hydroxyl against 10-undecenoic acid upon the oxonium ion played a key role in achieving a branched structure with ether-bridged cyclohexyl rings. The unique structure contributed significantly to the increase of glass transition temperature of the plant oil-based epoxy, as will discussed below.

Two significant component areas (A and B) were distinguished in GC chromatogram. A mass signal of m/z=124 was identified in the corresponding mass spectra, suggesting the existence of ECP segment (ECP Mw= 124). Characteristic mass signals (such as m/z=55, 83 and 96) were attributed to the UA component, which were also identified in the corresponding mass spectra. These characteristic mass peaks confirmed that CUA was composed of UA and ECP segments. Compared to A components, the relative ECP mass intensity (m/z=124) was stronger in B components, suggesting the higher content of ECP segment in B components. Besides, B components appeared at a longer retention time, indicating the higher molecular weight compared to A components. Considering the branched structure analyzed in the NMR spectra, it was inferred that the peaks appeared during the longer retention times (35-38 min) were attributed to the branched components, while the peaks appeared during the shorter retention times (24-27 min) were attributed to the linear components.

The stereoisomerism of ECP was the key reason that led to the isomers in CUA product.

The stereo specific reactions of UA-ECP can be illustrated by the transition state model proposed by John C. Leffingwell, etc., as shown in FIG. 6. For cis-epoxide, nucleophilic reagent attacks upon the positive charge part of the carbon atom from the bottom direction (FIG. 6a), and a cis- substituted structure formed. For trans-epoxide, nucleophilic reagent attacks upon the positive charge part of the carbon atom from the top direction (FIG. 6b), and a trans-substituted structure formed. Because ECP used in this work is a mixture of isomers, based on the transition states, the cis-ECP would be attacked by UA anion from the bottom direction, resulting in a cis-isomer, and correspondingly, the trans-isomers were derived from the trans-ECP. The NFH group would act as a second nucleophile involving the CNA against UA anion, which led to more complicated isomers with branched structures (see FIG. 7).

Synthesis of Linear Epoxy Precursor -MCUA Monomer

FIG. 3B shows the time evolution of FTIR spectra for the UA/MECP system (stoichiometric coefficient equal to one) at a reaction temperature of 80 °C. Similar to the UA/ECP system, the bands centered at 2678 cm^"1 (stretching O-H of carboxylic acid dimer) decreased and the bands centered at 3454 cm^"1 (stretching O-H of hydroxyl group) increased, as reaction time increased. This result confirmed the nucleophilic attack of UA upon the epoxide ring of MECP and formation of hydroxyl groups. However, different from UA/ECP system, the epoxy groups centered at 840 cm^"1 are still notable after 48 hours reaction, indicating that MECP had not been fully consumed during the reaction. The chemical structure of MECP is very similar to that of ECP, except that the individual hydrogen atoms on the cycloaliphatic ring and the double bond are respectively substituted by methyl groups. However, this minor structure change resulted in different FTIR results, indicating distinct reaction pathways in UA/MECP and UA/ECP systems. The chemical shifts derived from carboxyl carbon and double bond carbons of MCUA are similar to those in the CUA ¹³C NMR spectrum (FIG. 5B). However, the observed chemical shifts around 50 ppm in CUA were attributed to the two ring-bridging ether carbons disappeared in MCUA, indicating the lack of ether-bridged cyclohexyl structure in MCUA system (i.e. the lack of branched structures). The distinct chemical structures of MCUA and CUA were ascribed to the methyl substituent on the cycloaliphatic ring, which influenced the attack of the nucleophile upon the oxonium ion, stereochemically. Compared to the hydrogen atom in ECP, the bulky methyl group on the cycloaliphatic ring hindered the nucleophile attacking oxonium ion. Therefore, the nucleophilic attack by hydroxyl was sterically blocked, making it difficult to form the ether-bridged cyclohexyl structure. Compared to the hydroxyl group, the 10-undecenoic acid anion was more capable of realizing the nucleophilic attack upon the oxonium ion due to the electronic effect. Thus, the hydroxyl group could not achieve a further nucleophilic attack upon cycloaliphatic epoxide, resulting only in a linear-structured alkene monomer as in the reaction pathway shown in FIG. 2.

Epoxidation of Precursors CUA and MCUA, and Viscosities

CUA and MCUA were further epoxidized using m-chloroperoxybenzoic acid (m-CPB A), resulting in bio-epoxy monomers, termed ECUA and EMCUA, as shown in FIG. 8. ¹³C MR spectra were collected to identify the chemical structures of ECUA and EMCUA (FIG. 9):

ECUA l

ECUA 2

EMCUA

The disappearance of chemical shifts (100-150 ppm) due to double bonds and the appearance of new peaks at 45-60 cm due to carbon atoms on the epoxides confirmed the successful epoxidation. Compared with the carbon atom C15 (a= 55 ppm) in ECUA, the chemical shift of CI 5 in EMCUA moved to a higher position (a= 59 ppm), due to a lower shielding effect of the methyl group.

Low viscosity of epoxy resin is preferred in the UV-curing process to achieve good flowability and faster wetting on the substrate. Although addition of diluents can reduce viscosity, from an eco-friendly viewpoint synthesis of epoxy resin with low viscosity is preferable. The viscosities of epoxy monomers diglycidyl ether of bisphenol-A (DGEBA), ECUA, and EMCUA, as a function of shear rate were evaluated (FIG. 10). Compared with DGEBA, the complex viscosities of ECUA and EMCUA were considerably lower and, consequently, more desirable for UV-curing. The viscosity of EMCUA was lower than ECUA when shear rate was above 20 rad/s, which was attributed to the higher amount of linear structures in the EMCUA monomer compared to ECUA.

UV Polymerization and Transparency

The curing characteristics of epoxy monomers under ultraviolet light were evaluated using PCA-DSC (FIG. 11). Apparent exothermic peaks were observed for all the samples, indicating effective epoxy curing occurred under UV radiation. The exothermic peak times of EMCUA and ECUA were shorter than that of DGEBA (FIG. 11 and Table 1), indicating EMCUA and ECUA possessed higher reactivity than DGEBA during UV curing. This feature was attributed to the built-in hydroxyl groups in the ECUA and EMCUA systems. Compared with the bulky epoxide, the steric requirement for the attack of hydroxyl upon the oxonium ion is considerably less, and a faster reaction by hydroxyl attack occurred. Therefore, an accelerated curing behavior was observed in the network formation process. Epoxidized soybean oil (ESO) possessed the slowest curing speed and lowest exothermic enthalpy. The bulky fatty acid ester chains hindered the propagation of epoxides during the ESO curing. Table 1. Exotherm parameters of epoxy monomers in the UV-curing process.

Sample DGEBA ESO ECUA EMCUA

Exothermic peak (min) 0.98 1.21 0.88 0.82

Onset of leveling off 6.49 10.79 7.86 6.12

(min)

Exothermic enthalpy (J/g) 312.7 263.1 336.1 332.9

The appearance of UV-cured films is crucial for exterior coating applications. The built-in hydroxyl groups in bio-epoxy synthesized here not only accelerated the curing speed, but also suppressed the "orange skin" effect on the cured film surface (FIG. 12a). An "orange skin" mark was found on the surface of P-DGEBA film (marked by circle), while smooth surfaces were achieved for the P-ECUA and P-EMCUA systems. The origin of surface drawbacks such as "orange skin" is complicated. One possible reason is the internal stresses generated during the polymerization. For the DGEBA system, the chain propagation continued through the nucleophilic attack of the epoxy ring upon the growing oxiranium ion chain end; however, for ECUA and EMCUA, the participation of hydroxyl groups in the nucleophilic attack led to a termination of the growing oxonium ion chain and transfer into a new chain. The chain transfer mechanism caused by the hydroxyl group accounted for the notable improvement in film appearance. No obvious differences in the light transmittance of P-ECUA and P-EMCUA were observed in the visible range (380-700 nm) (FIG. 12b). Compared to the yellowing color of P- DGEBA, the bio-epoxies exhibited a clear and colorless appearance, with a higher light transmission throughout the visible wavelength range.

Dynamic Mechanical Properties and Internal Structures

The dynamic mechanical properties of UV-cured epoxy resins are shown in FIG. 13 A. P- ESO had the lowest glass transition temperature of 18 °C. The newly developed epoxy resins showed a remarkable increase in T_g. The T_g of P-ECUA reached 142 °C and was closer to that of P-DGEBA, which was higher than the previous reported T_g of plant oil-based epoxy resins. The variation of storage modulus (Ε') with temperature was another criteria reflecting the epoxy resin heat resistance and network feature. Using the E ' value in a rubbery state, the crosslink density (z^'e) based on the theory of rubber elasticity can be calculated according to equation below: _ E

K ^~ 3RT ₍₁₎

where R is the gas constant, T is the absolute temperature, and E' is corresponding plateau storage modulus at T_g +70 °C. Crosslink density (¾) for each sample is shown as an inset in FIG. 13 A. P-ECUA had a higher and moduli £ ' in a rubbery state than that of P-DGEBA, corresponding to a higher heat resistance. The T_g of P-EMCUA was higher than that of P-ESO; however, P-EMCUA had a lower storage modulus in the rubbery state and lower crosslink density. These distinct dynamic properties are closely related to their respective photo- polymerized network structures. Scheme 4 shows a typical UV-curing process for epoxy monomers from initiation to chain propagation. Different from DGEBA and ESO curing, a significant chain transfer effect (Propagation 2 in FIG. 14) caused by the nucleophilic attack of hydroxyl groups in ECUA and EMCUA should be considered. As a result, in addition to the crosslink structures built via the ring-opening polymerization of epoxides (Propagation 1 in FIG. 14), the hydroxyl groups were also involved in the construction of crosslinks through the chain transfer mechanism. Due to this chain transfer effect, more types of crosslink structures would be expected in P-ECUA and P-EMCUA networks.

The networks of P-DGEBA and P-ESO are created by two types of crosslink structures: chain segments derived from the ring-opening of oxiranes (type I, circled by ellipse shadow), and chain segments derived from the DGEBA backbone or ESO fatty acid section (type II, circled by rectangle shadow) (FIG. 13C). Due to the presence of hydroxyl groups, the connection of hydroxyl and epoxides resulted in a third type of crosslink (type III, circled by square shadow) in P-ECUA and P-EMCUA. The ether-bridged cyclohexyl structure formed in preparation of CUA lead to a fourth type crosslink (type IV, circled by round shadow) in P-ECUA. All samples contained a type I crosslink structure, in which the chain length between cross-links was very short, resulting in a more rigid property. The lowest T_g of P-ESO was mainly attributed to the flexible fatty acid chain segments (type II). Although the undecenoic acid chains in P-EMCUA are also flexible, the more rigid cycloaliphatic ring enhanced the chain stiffness. Moreover, the type III crosslink structure, derived from the chain transfer effect of hydroxyl groups, also increased the number of crosslink sites and enhanced chain stiffness. Therefore, P-EMCUA had an evidently increased T_g. In addition to the type III crosslink, the inherent type IV crosslink structure afforded P-ECUA additional stiffness, and remarkably increased T_g and storage modulus in the rubbery state: as shown in FIG. 139A and B, respectively. These results indicate an epoxy derived from plant oils can also obtain a high glass transition temperature when based on an appropriate rational design. By regulating the stoichiometric coefficient of UA and ECP to form more ether-bridged cyclohexyl structures, we believe a superior thermal resistant bio-epoxy with higher T_g > 142 °C can be obtained. P-DGEBA had the highest T_g compared to the bio- based epoxy resins, even although the crosslink density was lower. This result was due to the rigid benzyl groups existing in the type II crosslink structure.

Mechanical Properties

Compared with P-DGEBA, P-ECUA demonstrates superior mechanical properties with higher tensile strength and elongation at break (FIG. 15), which is ascribed to its unique network structure. As discussed above, the network of P-ECUA is constructed by four types of crosslink structures: the inherent crosslink structure (type IV), the subsequently formed crosslink structures (types I and III) with a rigid skeleton and high crosslink density, and the crosslink structure (type II) derived from the flexible undecenoic acid chain and conferring a certain toughness. The tensile strength of P-EMCUA is lower than that of P-DGEBA: however, this strength is still acceptable in non- structural applications. Moreover, P-EMCUA exhibits an interesting ductile feature. The inset in FIG. 15A shows that the P-EMCUA film was integral without cracking and the nail was firmly stuck after penetrating the film. The methyl group on the cycloaliphatic ring hindered the nucleophilic attack of the hydroxyl group and the formation of the secondary ester crosslink structure (type IV). Consequently, the resulting network constructed by EMCUA has lower crosslink density and longer chain segments compared with ECU A, leading to more extensible and ductile networks.

A comprehensive performance comparison of epoxy resins is shown in FIG. 16. Relative to commercial DGEBA, the UV-cured epoxy resins derived from 10-undecenoic acid showed outstanding performance across a range of properties. P-ECUA with well-balanced features of processability, appearance, renewability, heat resistance, and mechanical properties is a promising renewable alternative to some bisphenol A-based epoxies.

Materials and Methods

Materials. 10-undecenoic acid (UA, 98%), 4-ethenyl-7-oxabicyclo[4.1.0]heptanes (ECP,

98%, aka 4-vinyl-l-cyclohexene 1,2-epoxide, mixture of isomers), and (+)-limonene 1,2-epoxide (MECP, 98%) were purchased from Sigma-Aldrich (USA). Diglycidyl ether of bisphenol A (DGEBA) with epoxy equivalent weight of 175 g moHwas obtained from Dow Chemical Company. M-chloroperoxybenzoic acid (m-CPBA, 70-75%) was purchased from Acros Organics. The epoxidized soybean oil (ESO, VIKOFLEX® 7170) was provided by Arkemalnc, and cationic initiator (PC-2506,[4-(2-hydroxyl-l-tetradecyloxy)-phenyl], phenyliodoniumhexafluorantimonate) was kindly provided by Polyset Inc.

Synthesis of UA-ECP Epoxy Precursor CUA. UA (100.0 g) and ECP (67.4 g) were charged into a 250 mL round-bottomed flask equipped with a reflux condenser, and the mixture was stirred with a magnetic bar at 80 °C for 48 h and transferred to a 2000 mL separating funnel. 400 mL hexane and 800 mL sodium carbonate solution (10 wt %) were then added to separate the residual UA from the product. Hexane solvent was then removed and collected through high vacuum rotary evaporation at 60 °C, and a colorless CUA liquid with a yield rate of 82 % (relative to pure ECP) was obtained. NMR spectra were performed as: ¾ NMR (CDCh, δ ppm) 5.72 (s, 5H), 4.92 (s, 10H), 4.80 (m, 2H), 4.67 (m, 2H), 3.77 (m, 1H), 3.65 (m, 1H), 2.74 (m, 2H), 2.37 (m, 2H), 2.24 (s, 4H), 1.97 (s, 4H), 1.83 (m, 2H), 1.55 (s, 4H), 1.28 (s, 37H); ¹³C NMR (600 MHz, CDCh): δ = 173.5 (2C), 142.0 (3C), 138.8 (2C), 173.5 (2C), 1 14.1 (2C), 1 13.9 (3C), 74.0-72.9 (2C), 68.7-67.4 (2C), 52.8.0-51.3 ppm (2C).

Synthesis of UA-MECP Epoxy Precursor MCUA. The synthesis and purification procedures of MCUA were the same as that of CUA, and a colorless liquid with a yield rate of 70% (relative to pure MECP) was obtained. NMR spectra were performed as: ¾ NMR (CDCh, ( ppm) 5.76 (s, 2H), 4.92 (s, 4H), 4.78 (m, 1H), 4.67 (s, 4H), 4.04 (s, 2H), 2.25 (m, 4H), 1.99 (m, 4H), 1.86 (m, 2H), 1.67 (s, 4H), 1.57 (m, 4H), 1.49 (s, 2H), 1.25 (s, 30H), 1.13 (s, 2H). ¹³C NMR (600 MHz, CDCh): S= 172.7 (1C), 148.8 (1C), 139.0 (1C), 1 14.1 (1C), 108.8 (1C), 82.4-75.2 (1C), 70.3-69.7 ppm (1C).

Synthesis of UA-ECP Epoxy ECUA. CUA (50.0 g), m-CPBA (163 g) and 300 mL dichloromethane were charged into a 1000 mL round-bottomed flask with a reflux condenser and a magnetic stirrer. The reactants were mixed at 0 °C for 3 h and then kept at 25 °C for 48 h. 600 ml ethyl ether was added into the mixture after removing dichloromethane by vacuum rotary evaporator. Then 300 mL sodium sulfite solution (10 wt %), 500 mL saturated sodium bicarbonate solution and 500mL saturated sodium chloride solution were subsequently used to wash the product. Ethyl ether and residual water in organic layer were then removed and collected by vacuum rotary evaporator, and finally a clear and colorless ECUA liquid was obtained with a yield rate of 84% with respect to the CUA. NMR spectra were performed as: ¾ NMR (CDCh, δ ppm) 4.81 (m, 2H), 4.68 (m, 2H), 3.81 (m, 2H), 2.81 (m, 3H), 2.72 (m, 2H), 2.65 (s, 5H), 2.46 (m, 3H), 2.37 (m, 2H), 2.22 (m, 4H), 1.77 (m, 2H), 1.48 (m, 4H), 1.21 (s, 45H); ¹³C NMR (600 MHz, CDCh): δ = 172.7 (2C), 72.6-71.1 (2C), 67.5-66.1 (2C), 55.7-55.2 (5C), 52.2 (2C), 46.9 (2C), 46.2-45.8 ppm (3C).

Synthesis of UA-MECP Epoxy EMCUA. The synthesis and purification procedures of EMCUA were the same as that of ECUA, and a clear and colorless liquid with a yield rate of 91% (relative to the MCUA) was obtained. NMR spectra were performed as: ¾ NMR (CDCh, ( ppm) 4.71 (m, 1H), 3.96 (m, 1H), 2.80 (m, 2H), 2.64 (m, 2H), 2.53 (m, 2H), 2.44 (m, 2H), 2.36 (m, 2H), 2.17 (m, 4H), 1.58 (m, 2H), 1.51 (m, 4H), 1.42 (s, 34H), 1.15 (s, 2H), 1.04 (s, 2H);¹³C NMR (600 MHz, CDCh): δ = 172.7 (1C), 82.0-74.5 (2C), 69.6 (1C), 59.1 (1C), 53.2 (1C), 52.2 (1C), 47.0 ppm (1C).

UV Polymerization. Cationic photo-initiator (PC-2506, 3wt%) was added into DGEBA, ESO, ECUA and EMCUA, respectively. The mixture was mixed homogenously with the aid of a Vortex mixer and sonicator, then coated onto a 15.24 cm x25.4cm glass plate with a film casting knife (model 4302, BYK-Gardner USA) set at 160 μπι wet thickness. The resin containing photo-initiator was cured with a Fusion 300S UV system (300 W/inch power, D bulb, UVA radiation dose 1.7-1.8J/cm²) equipped with a LC6B benchtop conveyor at conveyor speed of 213 cm/min. The corresponding cured resins were named as uv-DGEBA, uv-ESO, uv-ECUA and uv- EMCUA, respectively.

Characterizations.

Fourier transform infrared (FTIR) measurements were done with a Perkin-Elmer Frontier FT-IR/NIR spectrometer. Spectra acquisitions were based on 32 scans with data spacing of 2.0 cm^"1. 2D-FTIR spectra were performed and calculated by 2Dshige (Shigeaki Morita, Kwansei- Gakuin University, 2004e2005). ¾ NMR were performed using a Bruker 300 MHz spectrometer at room temperature. ¾-¾ COSY spectra were obtained with 128 increments and four scans for each increment.¹³C NMR spectra were recorded using a Bruker 600 MHz spectrometer at room temperature. Deuterated chloroform (CDCh) was used as solvent for NMR tests.

The contents of epoxy precursors CUA and MCUA were determined by gas chromatography (GC) using a Shimadzu GC-2010 plus GC system (Shimadzu, Columbia, MD) equipped with a flame ionization detector (FID). Helium was used as the carrier gas at a flow rate of 1.5 ml/min. The injector and column temperatures were ramped from 80 °C to 300 °C at 7 °C/min with the detector temperature held at 380 °C. Rheological behaviors were measured using a Bohlin CVOR150 rheometer (Malvern Instruments, Southborough, MA) with a parallel plate (PP20, 20-mm plate diameter and 500-μιη gap). Frequency sweep was conducted at 25 °C with a strain of 0.5 % and an angular frequency range of 0.1-30 rad/s. The photocalorimetric measurements of resins were performed with a TA Q200 DSC coupled to a photocalorimeter accessory (PCA, OmniCure S2000, TA instruments) equipped with a high-pressure 200-W mercury lamp. The UV wavelength was adjusted to 320-500 nm using a cut-off filter, and a light intensity of 100 mW/cm² was used. Approximately 10 mg of each resin was accurately weighed in an open aluminum pan, and an empty aluminum pan was used as reference. The sample was equilibrated at 25 °C for 0.5 min without UV, then UV-irradiated for 20 min under a nitrogen atmosphere. Light transmittances were measured by UV spectrometer (Hewlett-Packard 8453) with 0.16 mm thickness for specimens. Dynamic mechanical analysis (DMA) was performed with a DMA (Q800 New Castle, DE) using a tension mode. A 5μπι amplitude was applied to guarantee the measurement was within the linear viscoelastic region. Samples were heated from - 50 °C to 270 °C using a heating rate of 3 °C/min and frequency of lHz. Tensile strength and elongation at break were measured according to ASTM D882-12 using a tensile tester (TT-1100, Chemlnstruments, Fairfield, OH) with a specimen dimension of 40 χ 8 x 0.16 mm and a grip separation rate of 2.54 cm min^"1. Five specimens were tested for each sample to obtain an average.

Conclusions

A unique bio-alkene with ether-bridged cyclohexyl structures and built-in hydroxyl groups was obtained through a one-step solvent-free nucleophilic substitution reaction. The ether-bridged cycloaliphatic rings provided stiffer chain segments and cross-link sites, while the long aliphatic chains derived from UA provided flexibility. As an ideal structure for an epoxy precursor, it achieved a good balance between stiffness and flexibility. In addition, the built-in hydroxyl group offered higher UV-curing reactivity and the possibility for further modification. The resulting bio-epoxy resin ECUA exhibited higher T_g of 142 °C compared to reported values, and good potential in heat resistance suggesting the poor heat resistance of plant oil-based epoxy can be overcome provided the appropriate structure is generated. Compared with commercial epoxy DGEBA, ECUA demonstrated superior performance across a range of properties including lower viscosity, higher reactivity, better appearance and more robust mechanical properties. The fully biorenewable epoxy EMCUA from the linear structured precursor, MCUA, exhibited an intriguing ductile behavior. The results achieved show that it is possible to design and generate plant oil derived epoxy materials with high T_g, or good ductility, using renewable undecenoic acid feedstock rather than petro-based bisphenol A.

EXAMPLE 2

Fatty acid chain combined with cycloaliphatic rings via Amberlyst-15: a promising structure for a high bio-content epoxy design

Example 1 described a high-performance bio-based epoxy ECUA via the CNA (competitive nucleophilic attack) strategy utilizing 10-undecenoic acid (UA) and 4-ethenyl-7- oxabicyclo[4.1.0]heptanes (ECP) as building blocks. The major contribution of the CNA is to generate a branched structure in the ECUA system that demonstrated high glass transition and high mechanical strength. To prove our hypothesis of the CNA strategy, we also used limonene oxide (MECP) with a methyl group, with the hope that the methyl group would hinder the CNA route to produce a linear structure. As a result, the epoxy (EMCUA) derived from UA and MECP showed lower glass transition and lower mechanical strength compared to the epoxy (ECUA) derived from UA and ECP, because there is no branched structure in the EMCUA system. However, limonene oxide (MECP), a monocyclic terpene derivate from an abundant citrus peels, possesses a rigid six-membered-ring and a terminal C=C bond. Combining with fatty acid chain, a potential epoxy building block is achieved herein with improved mechanical strength and thermal resistance as well as low viscosity when a branched structure is achieved.

Inspired by the branch-structured CUA in Example 1, this work describes a new strategy to obtain a high-performance epoxy using fatty acid and terpene as building blocks. The linear precursor (MCUA) from the reaction of UA and limonene oxide (MECP) as a base platform and Amberlyst-15, an inexpensive and reusable granule as a heterogeneous catalyst (Dow Chemical Company), to achieve an efficient graft of ECP onto the MCUA monomers under mild reaction conditions. The resultant epoxy precursor, named MCCA, has a novel ether-bridged cycloaliphatic structure (FIG. 1 (a)).

MCCA Component 1

MCCA Component 2

MCCA Component 3

MCCA Component 4

The corresponding epoxy EMCCA can be cross-linked in seconds via UV-radiation to achieve a highly transparent colorless film (transmittance -90%) with bio-content of about 80 wt% and tensile strength of abou

EMCCA Component 1

EMCCA Component 2

EMCCA Component 3

EMCCA Component 4

Compared to the previously reported ECUA (transmittance -90%, bio-content -54 wt %, tensile strength -48 MPa), this newly developed epoxy keeps the optical transparency while demonstrating higher bio-content and tensile strength. Clearly, it is an attractive strategy to obtain a colorless epoxy resin with high tensile strength and bio-content in seconds from fatty acid and terpene system, without the aid of a hardener and time-consuming heating process. Besides, EMCCA showed a better thermal resistance (T_g =90°C) compared to the previously reported EMCUA (T_g = 50°C), [28] and the viscosity is 2.7 Pa s, about 50% lower than the commercial DGEGA (5.3 Pa s). The work herein shows a promising candidate for bio-based epoxies and provides a direction to design high bio-content epoxies with desirable properties (e.g., low viscosity, high strength, thermal resistance, and transparency) via a rational combination of plant oil and terpene derived building blocks.

The specific procedure for MCCA synthesis is described in FIG. 18. MCUA was prepared following the same methods as described in Example 1 above. The synthetic pathway of MCCA (FIG. 17(a)) shows the reaction characteristics, in which the oxirane ring on ECP was activated by the Amberlyst-15 (SN1 route, FIG. 18) and then the hydroxyl group on MCUA attacked upon the positive charge part of the carbon atom on the oxirane ring (SN2 route, FIG. 18) to accomplish the graft of ECP onto MCUA. In the process, the ring opening between ECPs was effectively avoided via the selective catalysis of Amberlyst-15 (see FIG. 19). The grafting efficiency of ECP onto MCUA was indicated by the ratio of intensity change (Ιο-Γ) to the initial intensity To of epoxy signals (stretching C-O-C of epoxy group centered at 811 cm^"1 in FTIR spectrum). As FIG. 20(a) shows, the grafting efficiency was very low at room temperature; while increasing temperature to 60 °C could significantly improve the grafting efficiency; higher Amberlyst-15 loading further shortens the reaction time and a high degree of ECP grafting on MCUA ((h-I) /Iox 100%=93.4%) was accomplished within 24 hours.

The MCCA system is a combination of MCCA and MCUA monomers, and the chemical structural features were revealed by ¹H- MR spectra (FIG. 20(d). The stereoisomerism of cycloaliphatic rings led to the stereospecific reactions of nucleophile upon oxonium, which caused the complication of the nucleophilic attack and the existence of isomers in the product, as discussed in Example 1. For clarification, only typical chemical structures are demonstrated in FIG. 20(b). The graft of ECP ring onto MCUA can be distinguished via the comparison of ¾-¾ COSY spectra of MCUA and MCCA (FIG. 20(c) and (d)). For MCUA, the correlated peaks ((f 1=1.85 ppm, f2=4.82 ppm) and (f 1=1.71 ppm, f2=4.82 ppm)) are attributed to the coupling of proton 27with the vicinity proton on hydroxyl group and the protons on limonene oxide ring, respectively. Compared to MCUA, in addition to these two correlated peaks, another correlated peak (f 1=1.63 ppm, f2=4.82 ppm) can be found in the ¾-¾ COSY spectra of MCCA (detail of the chemical shifts were shown in the corresponding ¹H- MR spectra). This peak can be attributed to the coupling of protons connected by hydroxyl or ether group with the vicinity protons on ECP or limonene oxide ring. Similarly, compared to the single correlated peak (f 1 =1.71 ppm, f2=4.06 ppm, the coupling of proton connected with ester group with the vicinity protons on limonene oxide ring) for MCUA, the occurrence of multiple correlated peaks ((fl=1.72 ppm, f2=4.10 ppm) and (fl=1.78 ppm, f2=4.10 ppm)) for MCCA can be attributed to the graft of ECP ring, by which the chemical environment around the ester-connected proton was changed, leading to the complicated multiple correlated peaks. Coupling areas discussed above are illustrated as the shadow regions shown in FIG. 20(b).

Epoxidation of MCCA was conducted using m-chloroperoxybenzoic acid (m-CPB A) at room temperature (FIG. 17(b) and related 1H-NMR and mass spectra are presented in FIG. 21). The resultant product EMCCA is a clear liquid and can be easily cured via ultraviolet radiation to achieve a colorless, highly transparent film (FIG. 22). Compared to the previously reported EMCUA, the grafting of ECP on the MCUA resulted in a slight increase in viscosity (FIG. 23(a)). Even though, the viscosity of EMCCA (2.7 Pa s at 25°C) is about 50% lower than the commercial DGEGA (5.3 Pa s at 25°C). The UV-cured film from this newly developed epoxy monomer (EMCCA) demonstrated an impressive mechanical enhancement: tensile strength was doubled with a value higher than 60 MPa (FIG. 23(b)) via a few seconds of UV radiation, without the aid of hardeners and further heating treatment. Remarkable increase in thermal resistance (e.g., Tg shifting from 50 °C of the UV-cured EMCUA to 90 °C of the UV-cured EMCCA) was also observed (FIG. 23(c)). These significant improvements are attributed to the unique chemical structure of EMCCA. As FIG. 17(b) shows, 10-undecenoic acid segment composed the flexible moiety of EMCCA, which is built up by an aliphatic chain with 11 carbon atoms, sharing the transfer of applied stress and external deformation. The rigid moiety of EMCCA is composed of cycloaliphatic rings from citrus oil and ECP, in which the rings are bridged by ether group. In addition, like the epoxy rings, the hydroxyl group attached to the cycloaliphatic ring is also capable of taking part in the ring-opening reaction of oxiranes, contributing to the cross-linking sites in the network formation process. Compared to the EMCUA linear structure, the branched structure imparts EMCCA a higher potential in the enhancement of epoxy resin. Key features of the resultant epoxy networks are illustrated in FIG. 23(e). The network of UV-cured EMCUA is created by three type crosslinked structures: chain segments derived from the ring-opening of oxiranes (type I, highlighted by ellipse shadow); chain segments derived from the EMCUA backbone (type II, highlighted by rectangle shadow); and chain segments derived from the connection of hydroxyl and epoxides (type III, highlighted by square shadow). Compared to the EMCUA network, the intrinsic ether-bridged cyclohexyl in the EMCCA network leads to the fourth type of crosslinking (type IV, highlighted by round shadow in FIG. 23(e)). This crosslink is composed of two rigid ether-bridged cyclohexyl rings, which remarkably increase the chain stiffness and sustaine the stress applied to the network, and that contributes to the high tensile strength compared to the EMCUA network (increased from 32 MPa to 64 MPa, FIG. 23(b)). Creep curves further confirms the distinct network structures of UV-cured EMCUA and EMCCA. As FIG. 23(d) shows, EMCCA network shows a sharper slope in the initial stage of the creep curve. Since initial slope is related to the elastic response of polymers, for EMCCA network, the sharper slope meant a faster elastic response to stress and shorter average molecular chains between cross-links compared to that of EMCUA network. Higher amount of cross-links in EMCCA network effectively sustains the applied stress and retards the network deformation, and in the recovery stage (95 min -155 min), contrary to the slow recovery process of EMCUA network, an instant restoration is accomplished.

Since fatty acid was used as the building block of EMCCA, two conventional epoxy monomers are shown in FIG. 24 for the performance comparison. EMCCA (FIG. 24, #3) demonstrated superior properties over other monomers in terms of viscosity, heat resistance and tensile strength. For monomer #1 in FIG. 24, the lack of rigid structures limited its improvement in heat resistance and mechanical strength. Though the rigid sucrose moiety was introduced into monomer #2 in Table 1, the reinforcement is limited because of the lower reactivity of internal oxiranes occurring in the network-curing process (FIG. 25). More rational design was achieved for EMCCA (FIG. 24, #3) through the introduction of rigid moiety (cycloaliphatic rings) and terminal oxiranes (higher reactivity). Compared to the counterparts, EMCCA demonstrates lower viscosity, higher thermal resistance and tensile strength even without the aid of a hardener. Considering most hardeners are petrochemicals, this hardener-free epoxy resin obviously increased the bio-based content. EMCCA combined the advantages of building blocks derived from terpene (rigid structure) and plant oil (low viscosity) resources. As FIG. 26 shows, the various building block members in terpene and plant oil families provide a variety of possible combinations of these two family members for the design of high bio-content epoxies as demonstrated in this work. Promising epoxy candidates can be expected via selecting appropriate members and combining them through rational chemical strategies, a. Monomer 1 was cured with an equivalent of hardener; monomer 2 was cured with 0.4 equivalent of hardener; EMCCA (monomer 3) was cured without hardener and was cured with 0.4 equivalent of hardener for the comparison with monomer 2. b. viscosity was determined at room temperature.

By combining fatty acid chain with cycloaliphatic rings, a promising epoxy with high bio-content was achieved, which demonstrated high strength and transparency, low viscosity, as well as fast curing reactivity. The fatty acid chain renders the epoxy low viscosity, while the cycloaliphatic ring from monocyclic terpene renders the epoxy rigid moiety. Using catalyst Amberlyst-15, an ECP ring was effectively connected with a terpene ring to form an ether- bridged cycloaliphatic structure, which plays a key role in the remarkable mechanical and thermal properties of the epoxy network. A combination of plant oil and terpene- derivatives for the epoxy design appear to be an attractive direction to overcome the traditional deficiencies of bio-based epoxies (e.g., high viscosity, or low mechanical strength, or relatively low bio- content), and, hence, to further advance the sustainable development of bio-based epoxy materials.

Experimental Section

Materials. 10-undecenoic acid (UA, 98%), 4-ethenyl-7-oxabicyclo[4.1.0]heptanes (ECP, 98%), (+)-limonene 1,2-epoxide (MECP, 98%), 4-methyl hexahydrophthalic anhydride (98%) and 4(5)-methylimidazole (98%) were purchased from Sigma-Aldrich (USA). Amberlyst-15 dry hydrogen form (particle size < 300 μπι, capacity 4.7meq/g by dry weight) was obtained from Dow Chemical Company. M-chloroperoxybenzoic acid (m-CPBA, 70-75%) was purchased from Acros Organics. Cationic initiator (PC-2506,[4-(2-hydroxyl-l-tetradecyloxy)-phenyl], phenyliodonium hexafluorantimonate) was kindly provided by Polyset Inc.

Synthesis of Epoxy Precursor CUA. UA (100.0 g) and ECP (67.4 g) were charged into a 250 mL round-bottomed flask equipped with a reflux condenser, and the mixture was stirred with a magnetic bar at 80 °C for 48 h and transferred to a 2000 mL separating funnel. 400 mL hexane and 800 mL sodium carbonate solution (10 wt %) were then added to separate the residual UA from the product. Hexane solvent was then removed and collected through high vacuum rotary evaporation at 60 °C, and a colorless CUA liquid with a yield rate of 82 % (relative to pure ECP) was obtained.

Synthesis of Epoxy Precursor MCUA. The synthesis and purification procedures of MCUA were the same as that of CUA, and a colorless liquid with a yield rate of 70% (relative to pure MECP) was obtained.

Synthesis of Epoxy ECUA. CUA (50.0 g), m-CPBA (163 g) and 300 mL dichloromethane were charged into a 1000 mL round-bottomed flask with a reflux condenser and a magnetic stirrer. The reactants were mixed at 0 °C for 3 h and then kept at 25 °C for 48 h. 600 ml ethyl ether was added into the mixture after removing dichloromethane by vacuum rotary evaporator. Then 300 mL sodium sulfite solution (10 wt %), 500 mL saturated sodium bicarbonate solution and 500mL saturated sodium chloride solution were subsequently used to wash the product. Ethyl ether and residual water in organic layer were then removed and collected by vacuum rotary evaporator, and finally a clear and colorless ECUA liquid was obtained with a yield rate of 84% with respect to the CUA.

Synthesis of Epoxy EMCUA. The synthesis and purification procedures of EMCUA were the same as that of ECUA, and a clear and colorless liquid with a yield rate of 91% (relative to the MCUA) was obtained.

Synthesis of Epoxy Precursor MCCA. MCUA (10.0 g) and ECP (2.5 g) were charged into a 20mL glass vial. Different amounts of solid catalyst Amberlyst-15 (1.2 g or 1.6 g ) was then added and the mixture was stirred with a magnetic bar at a given temperature. Two temperatures of 25 °C and 60°Cwere selected and the experiment was stopped after 48 h. Amberlyst-15 was deposited on the bottom and the clear liquid product can be transferred easily.

Synthesis of Epoxy EMCCA. MCCA (10.0 g), m-CPBA (20.0 g) and 40 mL dichloromethane were charged into a 150 mL round-bottomed flask with a reflux condenser and a magnetic stirrer. The reactants were mixed at 0 °C for 3 h and then kept at 25 °C for 48 h. 90 ml ethyl ether was added into the mixture after removing dichloromethane by vacuum rotary evaporator. Then 90 mL sodium sulfite solution (10 wt %), 90 mL saturated sodium bicarbonate solution and 90mL saturated sodium chloride solution were subsequently used to wash the product. Ethyl ether and residual water in organic layer were then removed and collected by vacuum rotary evaporator, and finally a clear EMCCA liquid was obtained with a yield rate of 93% with respect to the MCCA. FIG. 18.

Film preparation. Cationic photo-initiator (PC-2506, 3wt%) was added into EMCCA.

The mixture was mixed homogenously with the aid of a Vortex mixer and sonicator, then coated onto a 6 inch x 10 inch glass plate with a film casting knife (model 4302, BYK-Gardner USA) set at 160 μπι wet thickness. The resin containing photo-initiator was cured with a Fusion 300S UV system (300 W/inch power, D bulb, UVA radiation dose 1.7-1.8J/cm²) equipped with a LC6B bench top conveyor at conveyor speed of 213 cm/min. The corresponding cured film was named as uv-EMCCA. Similarly, the UV cured film from EMCUA was name as uv-EMCUA.

Equipment and Characterizations. Fourier transform infrared (FTIR) measurements were done with a Perkin-Elmer Frontier FT-IR/NIR spectrometer. Spectra acquisitions were based on 32 scans with data spacing of 2.0 cm^"1. ¾ MR were performed using a Bruker 300 MHz spectrometer at room temperature. ¾-¾ COSY spectra were obtained with 128 increments and four scans for each increment. The positive-ion electro-spray ionization time-of-flight (ESI-TOF) mass spectra were acquired by injecting the sample (solubilized in acetonitrile) into the ESI-TOF mass spectrometer (Q-Tof-2™, Micromass Ltd.). Rheological behaviors were measured using a Bohlin CVOR150 rheometer (Malvern Instruments, Southborough, MA) with a parallel plate (PP20, 20-mm plate diameter and 500-μιη gap). The photocalorimetric measurements of resins were performed with a TA Q200 DSC coupled to a photocalorimeter accessory (PCA, OmniCure S2000, TA instruments) equipped with a high-pressure 200-W mercury lamp. The UV wavelength was adjusted to 320-500 nm using a cut-off filter, and a light intensity of 100 mW/cm² was used. Approximately 10 mg of each resin was accurately weighed in an open aluminum pan, and an empty aluminum pan was used as reference. The sample was equilibrated at 25 °C for 0.5 min without UV, then UV-irradiated for 20 min under a nitrogen atmosphere. Light transmittances were measured by UV spectrometer (Hewlett-Packard 8453) with 0.16 mm thickness for specimens. Dynamic mechanical analysis (DMA) was performed with a DMA (Q800 New Castle, DE) using a tension mode. A 5μπι amplitude was applied to guarantee the measurement was within the linear viscoelastic region. Samples were heated from 0 °C to 120 °C using a heating rate of 3 °C/min and frequency of lHz. Creep behavior measurements was also carried out on DMA (Q800 New Castle, DE). For creep measurement, samples were soaked in a testing chamber for 5min at 25 °C to ensure temperature balance. Rectangular samples with 16 mm length, 8 mm width, and 0.16 mm thickness were stretched by fixed stresses in order to realize a 2 - 4% strain. Stress was maintained for 90 min and then released in order to record strain recovery in the subsequent time. Tensile strength and elongation at break were measured according to ASTM D882-12 using a tensile tester (TT-1100, Chemlnstruments, Fairfield, OH) with a specimen dimension of 40 χ 8 x 0.16 mm and a grip separation rate of 2.54 cm min^"1.

The mechanisms of nucleophilic substitution of epoxides are illustrated in section 8.6 in Organic Chemistry With a Biological Emphasis by Tim Soderberg, which explains that the acid- catalyzed epoxide ring-opening reaction is as a hybrid, or cross, between an SN2 and SNl mechanism. See FIG. 28. The oxygen is first protonated yielding a good leaving group (step 1). Then the carbon-oxygen bond begins to break (step 2) and positive charge begins to build up on the more substituted carbon. Unlike in an SNl reaction, the nucleophile attacks the electrophilic carbon (step 3) before a complete carbocation intermediate has a chance to form. The attack takes place preferentially from the backside (like in an SN2 reaction) because the carbon-oxygen bond is still to some degree in place, and the oxygen blocks attack from the front side. In our system, the epoxy ring of ECP was first protonated (SN1 route) by the Amberlyst- 15. Then the hydroxyl group on MCUA attacked the electrophilic carbonon epoxy ring to realize a ring opening (SN2 route), and a graft of ECP on MCUA was achieved.

For the graft of cycloaliphatic ring on MCUA, MECP is a "greener" building block compared to ECP because of the fully bio-based component from citrus oil. However, as FIG. 27(a) shows, solid catalyst Amberlyst-15 is dissolvable in MECP, and consequently the product cannot be separated from the catalyst easily through a simple filtration. Distinct from the case in MECP, Amberlyst-15 is insoluble in ECP (FIG. 27 (b)) and can be easily removed from the system; thereby ECP was selected as the cycloaliphatic ring for grafting onto MCUA in this work, under the following reaction conditions.

We selected 4-ethenyl-7-oxabicyclo[4.1.0] heptanes (ECP) as a model chemical to testify whether the introduction of catalyst Amberlyst-15 could accelerate the ring opening of ECP or not. As shown in FIG. 19, after 48h reaction at 80°C, the characteristic peak of epoxy ring (811 cm^"1) was unchanged. This indicates that Amberlyst-15 cannot accelerate the ring-opening reaction of ECPs, and there was no ring-opening reaction between ECPs undergoing a heating at 80°C for 48h.

The electrospray ionization (ESI) mass spectra (positive-ion mode) of EMCUA and EMCCA were determined. The theoretical molar mass of EMCUA is 368, and the ion peak was seen on the graph at m/z 407.2 is speculated to be the ion adduct of EMCUA plus CFbCN (molar mass= 408), i.e., [EMCUA+ CH3CN]⁺. Correspondingly, the ion peak at m/z 391.2 is speculated to be the ion that lost one oxygen atom from [EMCUA+ CH3CN]⁺.

Compared to the mass spectrum of EMCUA, in addition to the characteristic peaks at m/z 391.2 and 407.2, an ion peak at m/z 503.3 appears in the EMCCA mass spectrum. The theoretical molar mass of EMCCA is 508, therefore the peak at m/z 503.3 is speculated to be the fragmented EMCCA ion. The stereoisomerism of cycloaliphatic epoxide was the key reason that led to the isomers in MCUA and MCCA products. For cis-epoxide, nucleophilic reagent attacks upon the positive charge part of the carbon atom from the bottom direction, and a cis-substituted structure formed. For trans-epoxide, nucleophilic reagent attacks upon the positive charge part of the carbon atom from the top direction, and a trans-substituted structure formed. Because ECP used in this work is a mixture of isomers, based on the transition states, the cis-ECP would be attacked by OH group from the bottom direction, resulting in a cis-isomer, and correspondingly, the trans-isomers were derived from the trans-ECP.

Film preparation procedure: Cationic photo-initiator (PC-2506, 3wt%) was added into EMCCA. The mixture was mixed homogenously with the aid of a Vortex mixer and sonicator, then coated onto a 6 inch x 10 inch glass plate with a film casting knife (model 4302, BYK- Gardner USA) set at 160 μπι wet thickness. The resin containing photo-initiator was cured with a Fusion 300S UV system (300 W/inch power, D bulb, UVA radiation dose 1.7-1.8J/cm²) equipped with a LC6B bench top conveyor at conveyor speed of 213 cm/min. The corresponding cured film was named as uv-EMCCA. Similarly, the UV cured film from EMCUA was name as uv-EMCUA.

The exothermic peaks shown in Figure S8a indicate epoxy curing via the ring-opening reaction. Compared to ESO, EMCUA demonstrates a shorter peak time of 0.82 min, suggesting the higher reactivity of EMCUA than that of ESO. Epoxy ring opening and chain propagation process is discussed in Example 1. Compared to the bulky epoxy ring, the steric requirement for the attack of hydroxyl upon the oxonium ion is relatively less, and a faster reaction by hydroxyl attack was expected.

Claims

CLAIMS:

1. An epoxy resin comprising at least one biobased epoxy compound, said biobased epoxy compound comprising an eth -bridged cycloaliphatic ring structure:

where, each of Ra' and Rb' are selected from the group consisting of -H, branched and unbranched alkyl groups, fatty acid moieties, substituted or unsubstituted aliphatic cyclic rings, substituted or unsubstituted aromatic moieties, epoxy moieties, and combinations thereof, with the proviso that at least one of Ra' and Rb' each comprise an epoxy moiety.

2. The epoxy resin of claim 1, wherein at least one Rb' is a fatty acid moiety.

3. The epoxy resin of claim 2, wherein said fatty acid moiety further comprise an epoxy moiety.

4. The epoxy resin of claim 1, wherein said compound is a branched compound selected from the group consisting of:

where n is 1 to 21, and any one of the cycloaliphatic rings in the foregoing structures may be substituted or unsubstituted.

5. The epoxy resin of claim 1, further comprising a linear biobased epoxy compound selected from the group consis ing of:

where n is 1 to 21, and any one of the cycloaliphatic rings in the foregoing linear structures may be substituted or unsubstituted.

6. The epoxy resin of claim 5, said resin consisting essentially of said biobased epoxy compounds.

7. The epoxy resin of claim 1, comprising said biobased epoxy compound homogenously mixed with a catalyst and optional solvent system.

8. The epoxy resin of claim 7, wherein said catalyst is a cationic photoinitiator selected from the group consisting of iodonium antimonate salts and alpha hydroxyketones.

9. The epoxy resin of claim 8, wherein said resin has a viscosity of less than 5 Pa s.

10. An article comprising:

a substrate having a surface; and

a layer of a biobased adhesive, coating, or film adjacent said substrate surface, wherein said layer is formed from an epoxy resin according to any one of claims 1-9.

11. The article of claim 10, wherein said layer is a cured layer, said cured layer having a % light transmittance of at least about 80% at a wavelength of between 300-325 nm when cured at a thickness of about 150-μπι.

12. The article of claim 10, wherein said layer is a cured layer having a glass transition temperature of from about 130°C to about 160°C.

13. The article of claim 10, wherein said layer has a tensile strength of at least about 40 MPa, wherein said epoxy resin is substantially free of any hardeners.

14. The article of claim 10, wherein said layer is a cured layer that is substantially insoluble in organic solvents and water.

15. The article of claim 10, said article being selected from the group consisting of: solar cell, semiconductors, organic light-emitting diodes and displays, tape, paper, electrodes, wound dressings, and screen protectors for electronic displays.

16. A method of forming a biobased adhesive, coating, or film, said method comprising: providing an epoxy resin according to any one of claims 1-9;

applying said epoxy resin to a substrate; and

exposing said epoxy resin to activating radiation to yield a cured biobased adhesive, coating, or film on said substrate.

17. The method of claim 16, wherein said epoxy resin is substantially free of any solvents.

18. The method of claim 16, wherein said activating radiation is UV-light.

19. A method of forming a biobased epoxy precursor compound, said method comprising: reacting an alicyclic oxirane compound with a biobased unsaturated fatty acid or a biobased compound comprising an unsaturated fatty acid moiety under conditions to yield a biobased epoxy precursor compound, said precursor compound comprising an ethe -bridged cycloaliphatic ring structure:

where, each of Ra and Rb are selected from the group consisting of -H, branched and unbranched alkyl groups, branched and unbranched alkenes, unsaturated fatty acid moieties, substituted or unsubstituted aliphatic cyclic rings, substituted or unsubstituted aromatic moieties, and combinations thereof, with the proviso that at least one of R_a and Rb each comprise an alkene.

20. The method of claim 19, wherein said alicyclic oxirane compound is a cyclic epoxide with at least one unsaturated substitution.

21. The method of claim 20, wherein said alicyclic oxirane compound is a substituted or 1,2- epoxy-4-vinylcyclohexane or 3,4-epoxy-l-cyclohexene.

22. The method of claim 19, wherein said fatty acid or fatty acid moiety is a medium chain fatty acid with an aliphatic chain length of 3 to 24 carbons.

23. The method of claim 19, wherein said fatty acid or fatty acid moiety comprises a terminal alkene.

24. The method of claim 19, wherein said fatty acid or fatty acid moiety is 10-undecenoic acid, 8-nonenoic acid, or 7-octenoic acid.

25. The method of claim 19, wherein said reacting comprising mixing said alicyclic oxirane compound and said biobased unsaturated fatty acid or biobased compound comprising an unsaturated fatty acid moiety at a temperature of from about 20°C to about 160°C for a time period of from about 30 minutes to about 72 hours.

26. The method of claim 19, wherein said reacting is carried out without a catalyst.

27. The method of claim 19, wherein said reacting is carried out with an acidic reusable ion exchange resin.

28. The method of claim 19, wherein said precursor compound is selected from the group consisting of:

where n is 1 to 21, and any one of the cycloaliphatic rings in the foregoing structures may be substituted or unsubstituted.

29. The method of claim 28, wherein said reacting further yields a linear biobased epoxy precursor compound selected from the group consisting of:

where n is 1 to 21, and any one of the cycloaliphatic rings in the foregoing structures may be substituted or unsubstituted.