Asymmetric and Symmetric Monomer Mixtures of Esters of Itaconic Acid and the Corresponding Copolymers

Abstract

To provide a convenient esterification procedure for itaconic acid which can provide a mixture of asymmetric and symmetric esters of itaconic acid which can be advantageously utilized as reactive diluents for the curing of unsaturated polyesters as well as provide copolymers upon polymerization. The present invention relates to a monomer mixture containing asymmetric and symmetric esters of itaconic acid that can be used as reactive diluents, as well as copolymers resulting from the polymerization of such monomer mixtures, more specifically including the asymmetric monomers methylethyl itaconate (MEI) and ethylmethyl itaconate (EMI) and the symmetric monomers dimethyl itaconate (DMI) and diethyl itaconate (DEI).

Description

[Technical field]

[0001] Field The present invention relates to monomer mixtures containing asymmetric and symmetric esters of itaconic acid that can be used as reactive diluents, as well as copolymers resulting from the polymerization of such monomer mixtures, more specifically including the asymmetric monomers methylethylitaconate (MEI) and ethylmethylitaconate (EMI) and the symmetric monomers dimethylitaconate (DMI) and diethylitaconate (DEI). [Background technology]

[0002] background U.S. Patent No. 9,432,421 reports on the emulsion polymerization of esters of itaconic acid, specifically the polymerization of itaconic acid-containing ester functional groups, such as alkyl esters of itaconic acid, known as alkyl itaconates. Itaconic acid ester polymers having selected particle sizes and levels of molecular weight and tacticity and containing greater than 50% by weight of esters of itaconic acid are produced via emulsion polymerization.

[0003] US Pat. No. 8,227,560 reports methods and polymers based on vinyl type monomers containing pendant carboxylic acid and ester group functionalities, such as the polymerization of itaconic acid.

[0004] U.S. Patent No. 8,410,232 reports esters of itaconic acid suitable for polymerization in aqueous media in the presence of seed particles, which are shown to both absorb monomer and polymerize to the desired particle size. Summary of the Invention [Problem to be solved by the invention]

[0005] Thus, while efforts have focused on the formation of certain esters of itaconic acid, a need exists to provide a convenient esterification procedure for itaconic acid that can provide a mixture of asymmetric and symmetric esters of itaconic acid that can be advantageously utilized as reactive diluents for the curing of unsaturated polyesters as well as to provide copolymers upon polymerization. [Means for solving the problem]

[0006] overview The general structure: [ka] and wherein MEI and EMI are present in an amount of from 50.0% (wt.) to 98.0% (wt.), DMI and DEI are present in an amount of from 50.0% (wt.) to 2.0% (wt.), and the total amount of monomers present does not exceed 100.0% (wt.).

[0007] The structure: [ka] Random copolymers of esters of itaconic acid comprising: repeat units "a" and "b" are present in an amount equal to or greater than 50.0% (wt.) and equal to or greater than 98.0% (wt.); repeat units "c" and "d" are present at a level between 50.0% (wt.) and 2.0% (wt.); and the sum of repeat units "a", "b", "c", and "d" does not exceed 100.0% (wt.).

[0008] (a) providing an unsaturated polyester resin; and (b) providing a polyester resin having the general structure: [ka] 1. A method for curing an unsaturated polyester resin comprising: (a) providing a mixture comprising asymmetric and symmetric monomeric esters of itaconic acid comprising methyl ethyl itaconate (MEI), ethyl methyl itaconate (EMI), dimethyl itaconate (DMI), and diethyl itaconoate (DEI) having a molar ratio of 1:1; (b) providing a mixture comprising asymmetric and symmetric monomeric esters of itaconic acid comprising methyl ethyl itaconate (MEI), ethyl methyl itaconate (EMI), dimethyl itaconate (DMI), and diethyl itaconoate (DEI) having a molar ratio of 1:1; (c) curing the polyester resin. [Brief description of the drawings]

[0009] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] 1 is a proton NMR scan of the monomer mixture of Example 6. [Diagram 2] 1 is another proton NMR scan of the monomer mixture of Example 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As mentioned above, a preparation protocol is disclosed that provides asymmetric monomers of methyl ethyl itaconate (MEI) and ethyl methyl itaconate (EMI) along with symmetric monomers of dimethyl itaconate (DMI) and diethyl itaconate (DEI). Polymerization of such mixtures of MEI, EMI, DMI, and DEI produces copolymer resins that are particularly useful as reactive diluents for curing (e.g., crosslinking) unsaturated polyesters.

[0011] The structure of the four monomer mixture of MEI, EMI, DMI, and DEI is as follows: [ka] As an example,

[0012] Preferably, the blend of asymmetric monomers above is one in which MEI and EMI are present in the four-monomer mixture in an amount of 50.0% (wt.) to 98.0% (wt.), although the amount of MEI and EMI can vary. More preferably, the asymmetric monomers MEI and EMI in the four-monomer mixture are present in an amount of 50.0% (wt.) to 90.0% (wt.), or 50.0% (wt.) to 80.0% (wt.), 50.0% (wt.) to 70.0% (wt.), or 50.0% (wt.) to 60.0% (wt.), with the remainder to 100% being made up of DMI and DEI, as described below.

[0013] Moreover, preferably, there is at least a minimum of 10.0% (wt.) MEI, with the remainder being EMI, or there is at least a minimum of 10.0% (wt.) EMI, with the remainder being MEI. For example, there may be preferably at least 10.0% (wt.) MEI and 40.0% to 88.0% (wt.) EMI. Or, there may be preferably 10.0% (wt.) EMI and 40.0% to 88.0% (wt.) MEI.

[0014] As alluded to above, the levels of the two symmetric monomers DMI and DEI in the four monomer mixture are such that they in combination are preferably present at a level of from 50.0% (wt.) to 2.0% (wt.), or from 50.0% (wt.) to 10.0% (wt), or from 50.0% (wt.) to 20.0% (wt.), or from 50.0% (wt.) to 30.0% (wt.), or from 50.0% (wt.) to 40.0% (wt.), with the total amount of the four monomers present not exceeding 100.0% by weight. For example, if there is 50.0%-60.0% (wt.) MEI and EMI in combination, the corresponding amounts of DMI and DEI in the combination can be 50.0%-40.0%, and if a mixture of 55.0% (wt.) MEI and EMI is selected, a mixture of 45.0% (wt.) DMI and DEI can be selected.

[0015] Additionally, for any of the above-mentioned levels of the two symmetric monomers DMI and DEI, each is preferably present in equal amounts. For example, when the two symmetric monomers DMI and DEI are present in a four-monomer mixture at a combined level of 50.0% (wt.), they are each individually preferably present at a level of 25.0% (wt.).

[0016] It has also been observed that the four monomer mixtures herein tend to be produced with certain impurities. Specifically, the impurities are non-reactive molecules, such as those having the following structure: [ka] (wherein R is independently either a methyl group or an ethyl group). Other impurities include the methyl or ethyl ester of mesaconic acid having the structure: [ka] (wherein R is again independently either a methyl group or an ethyl group). Thus, the level of impurities of methyl or ethyl ester of mesaconic acid and / or methyl or ethyl ester of citraconic acid is preferably maintained at a level of 0-10.0% (wt.), or 0-5.0% (wt.), or 0-2.5% (wt.), or 0-1.0% (wt.) in the mixture of four monomers described herein.

[0017] Polymerization of the above referenced four monomer mixture produces the following repeat unit: [ka] It is now noteworthy that it is possible to form random copolymers of esters of itaconic acid having

[0018] In the foregoing, the copolymer composition preferably tracks the monomer feed composition, i.e., the asymmetric repeat units "a" and "b" are preferably present in an amount of 50.0 wt.% or greater and represent poly(methyl ethyl itaconate) (PMEI) and poly(ethyl methyl itaconate) (PEMI), respectively. More preferably, repeat units "a" and "b" are present in the random copolymer at a level of 50.0% (wt.) or more up to 98.0% (wt.), or 50.0% (wt.) to 90.0% (wt.), or 50.0% (wt.) to 80.0% (wt.), or 50.0% (wt.) to 70.0% (wt.), or 50.0% (wt.) to 60.0% (wt.), with the individual amounts of PMEI and PEMI being variable so long as, in combination, the PMEI and PEMI composition falls within the indicated weight percentage ranges of the random copolymer composition. Even more preferably, at least a minimum of 10.0% (wt.) PMEI is present in the random copolymer, or at least a minimum of 10.0% (wt.) PEMI is present in the random copolymer.

[0019] The symmetric repeat units "c" and "d", representing poly(dimethyl itaconate) (PDMI) and poly(diethyl itaconate) (PDEI), in combination, are preferably present in the random copolymer at a level of 50.0% (wt.) to 2.0% (wt.), or 50.0% (wt.) to 10.0% (wt.), or 50.0% (wt.) to 20.0% (wt.), or 50.0% (wt.) to 30.0% (wt.), or 50.0% (wt.) to 40.0% (wt.), with the sum of the repeat units "a", "b", "c", and "d" not exceeding 100.0% (wt.). More preferably, the random copolymer contains 1.0% to 25.0% (wt.) PDMI and 1.0% to 25.0% (wt.) PDEI.

[0020] As alluded to above, it is contemplated that the random copolymers herein produced from the above-referenced four-component monomer compositions have utility as reactive diluents for curing (e.g., crosslinking) unsaturated polyester resins. References to unsaturated polyester resins may be understood as references to polyester chains containing one or more sites of residual unsaturation, i.e., -C=C-type linkages, preferably between ester linkages, examples of which are illustrated below (where R can be an alkyl or aromatic group, and "n" is the variable number of repeat units). References to curing herein are understood herein as utilizing the four-component monomer composition to aid in crosslinking one or more selected polymer chains. Typically, such curing may be accomplished by free radical polymerization, and preferably an organic peroxide, such as methyl ethyl ketone peroxide, may be utilized.

[0021] The unsaturated polyester resins utilized herein may preferably have a number average molecular weight (Mn) in the range of 1,000 to 100,000, or 1,000 to 50,000, or 1,000 to 25,000. [ka]

[0022] In this regard, it is worth noting that, although the monomer DMI itself is generally unstable, the four-component monomer composition herein containing DMI does not exhibit the storage instability of pure DMI. Furthermore, DMI reportedly has a glass transition temperature (Tg) of about 100°C when polymerized into homopolymer form. Meanwhile, the homopolymer of DEI reportedly has a Tg of approximately 56°C, which is relatively low for a suitable diluent and may adversely affect the mechanical performance vs. temperature in the final cured polyester resin. The polymerization forms a random copolymer of the four-component monomer composition herein, again avoiding the problem of using unstable DMI and allowing a Tg of greater than 56°C to be achieved, providing a more effective reactive diluent for crosslinking unsaturated polyester resins. More specifically, it is contemplated that the random copolymer formed from the four-component monomer composition herein can be easily configured to provide a Tg value preferably within the range of 75°C to 85°C. That is, the use of the random copolymers disclosed herein as reactive diluents for unsaturated polyester laminating resins is contemplated to provide a relatively stable monomer mixture derived from itaconic acid, improved mechanical performance versus temperature for the cured unsaturated polyester resins, especially when such resins are fiber-filled.

[0023] Additionally, it is contemplated herein that the four-component monomer compositions herein derived from itaconic acid may be combined with conventional reactive diluents for unsaturated polyester resins, such as vinyl-type monomers (e.g., styrene, α-methylstyrene, acrylates, methyl methacrylate, methacrylates, and / or vinyl toluene). For example, the four-component monomer compositions herein may themselves be combined and diluted with one or more of the vinyl-type monomers described herein, where the level of the vinyl-type monomer may be present at a level of up to 50.0% (wt.) of the monomeric composition. EXAMPLES

[0024] Working Example Example 1: 112.8 gr itaconic anhydride, 0.49 gr MEHQ were added to a round bottom flask reactor equipped with a magnetic stirrer and a Dean-Stark condenser. Heat was set to 90°C with an electric mantle. Upon melting itaconic anhydride, 106.7 gr ethanol and 2.7 gr MSA were added slowly. Heat was then set to 120C and 22.5 gr methanol was added. Heat was then set to 140C and 25 gr methanol was added. Heat was then set to 150C and 17 gr methanol was added. The resulting product was a dark amber solution. Acid titration gave an acid value of 127 mg KOH / g. The resulting solution was washed twice with 200 gr 16% sodium carbonate solution. After a carbonate solution wash to remove any acidic monomers, the resulting mixture was analyzed by high pressure liquid chromatography (HPLC).

[0025] [Table 1]

[0026] Example 2: 56.02 gr of itaconic anhydride, 0.005 gr of MEHQ were added to a round bottom flask reactor equipped with a magnetic stirrer and a Dean-Stark condenser. The heat was set to 90C with an electric mantle until the anhydride was melted. 24.6 gr of ethanol was added gradually. Then the heat was set to 120C. 8 gr of methanol and 0.6 gr of MSA were added. The temperature was then increased to 140C followed by the addition of 8 gr of methanol. The temperature was then increased to 150C followed by the addition of 5 gr of methanol. The resulting solution was washed twice with 100 gr of 15% sodium carbonate solution. After the carbonate solution wash to remove any acidic monomers, the analysis of the resulting mixture was carried out by high pressure liquid chromatography (HPLC).

[0027] [Table 2]

[0028] Example 3: 56.12 gr Itaconic anhydride, 0.0062 gr MEHQ were added to a round bottom flask reactor equipped with a magnetic stirrer and a Dean-Stark condenser. Heat was set to 90C with an electric mantle until the anhydride was melted. 16.5 gr Methanol was added slowly and held for 90 minutes. 24.08 gr Ethanol and 0.623 gr MSA were added. Heat was then set to 120C and then 140C. 10 gr Ethanol was added. The temperature was held at 140C until boiling stopped. Analysis of the resulting mixture was carried out by high pressure liquid chromatography (HPLC) after removing any acidic monomers with a carbonate solution wash.

[0029] [Table 3]

[0030] Example 4: 28.17 gr itaconic anhydride, 0.0035 gr MEHQ were added to a round bottom flask reactor equipped with a magnetic stirrer and a Dean-Stark condenser. Heat was set to 90C with an electric mantle until the anhydride was melted. 5.75 gr ethanol and 4 gr methanol were added slowly and held for 60 minutes. Heat was then set to 120C. 3 gr ethanol, 2.1 gr methanol, and 0.6 gr MSA were added. Temperature was then increased to 130C. Analysis of the resulting mixture was carried out by high pressure liquid chromatography (HPLC) after removing any acidic monomers with a carbonate solution wash.

[0031] [Table 4]

[0032] Example 5 - Polymerization: 2.194 gr of the alkyl itaconate mixture from Example 3 was mixed with 0.054 gr of azobisisobutyronitrile (AIBN) in a sealed glass vial and then heated to 60C for 18 hours. The resulting polymer was a clear glass. Molecular weight analysis by GPC provides a number average molecular weight of 9,453 g / mole and a weight average molecular weight of 16,970 g / mole.

[0033] Example 6: In a round bottom flask reactor equipped with a magnetic stirrer, Dean-Stark condenser, 1133.68 gr itaconic acid, 0.770 gr MEHQ, 9 gr methylsulfonic acid, 280.54 gr methanol, and 402.5 gr ethanol were added. Heat was set at 100C with an electric mantle for 2 hours. Heat was then increased to 120C for 1 hour and 30 minutes. 70 gr anhydrous methanol was then added dropwise over 25 minutes. A vacuum of 630 torr was then applied for 15 minutes. Another 65 gr methanol and 65 gr ethanol were then added dropwise under atmospheric conditions for 2 hours, followed by a vacuum of 600 torr for 15 minutes. Another 50 gr methanol and 50 gr ethanol were then added dropwise under atmospheric conditions, followed by a vacuum of 600 torr for 20 minutes. The resulting solution was washed twice with 100 gr 15% sodium carbonate solution at 80C. 100.17 gr of the resulting solution was fractionated by vacuum distillation using a 20 cm packed column equipped with ceramic Rashid rings mixed with 1 mm glass beads. The intermediate fraction was collected at 85-88 torr and column top temperatures of 106.6°C to 109.7°C. HPLC analysis of this intermediate fraction yielded the following composition:

[0034] [Table 5]

[0035] NMR analysis of the intermediate fraction was also performed. Proton NMR in Figure 1 revealed the essential absence of citraconate and mesaconate esters by the absence of peaks between 5.75 ppm and 6.3 ppm and between 6.35 and 7.0 ppm, respectively. "Essentially absent" means that there is no peak area greater than 1% relative to the area of ​​the adjacent peaks between 6.3 and 6.35 ppm representing vinylic protons. The same NMR spectrum in Figure 2 reveals a set of peaks between 5.65 and 5.75 ppm with a structure of four very tight doublets. The chemical shifts correspond to the vinylic protons at the edge of the nearest carbonyl. The four peaks are proportional to the relative amounts of dimethyl itaconate, methyl ethyl itaconate, ethyl methyl itaconate, and diethyl itaconate.

[0036] Performance Test Method Acid value This method provides a standard characterization of the amount of residual acid in an ester or polyester. This method is most suitable for non-aqueous materials.

[0037] Solvent Preparation: Prepare the solvent by mixing 2 parts toluene and 1 part absolute ethanol. Add 3 drops of phenolphthalein indicator (1% in ethanol) to the solvent mix.

[0038] Sample preparation: Weigh 0.2 g of sample into the titration beaker, add 40 g of solvent and mix until completely dissolved. Add 3 drops of phenolphthalein indicator (1% in ethanol) to the sample.

[0039] Titrate the sample: Place titration beaker with magnetic stir bar on stir plate and stir at medium speed. Fill burette with 0.1 M KOH in ethanol and position burette above test solution. Begin titration by adding titrant at a rate of approximately 1 mL / min while stirring, stopping for at least 10 seconds when sample turns pink and record the volume of titrant used (V1).

[0040] Titration of blank sample: Perform the titration method with blank solvent and record the titration volume (V2).

[0041] Calculations and reporting of all determination methods: Acid value (AV) calculation

number

[0042] Molecular weight determination Molecular weights were determined using gel permeation chromatography (GPC). First, the eluent (HPLC grade tetrahydrofuran - THF) is passed through three VISCOTEK GPC columns (LT4000L, T2000, and LT5000L) for approximately 1 hour to equilibrate the GPC. A refractive index detector (RID) is used to measure the signal concentration. The RID is purged 20 minutes before starting the sample analysis. The instrument conditions used are as follows: eluent: HPLC grade THF with in-line degasser, flow rate: 1.0 mL / min, runtime: 45 min, injection volume: 100 μL, aspirate / dispense speed: 200 μL / min, RID optics temperature: 40° C., auto purge: 1 min, column temperature: 35° C.

[0043] Prepare a 1 wt.% polymer solution using the GPC elution solution as the solvent. Filter this solution into a 2 mL HPLC vial with a 0.2 μM syringe-tip filter and then crimp closed. Place the vial in the GPC autosampler and start the chromatographic run. A molecular weight calibration was performed using nine polystyrene standards with molecular weights ranging from 589 g / mol to 1,800,000 g / mol. A third-order polynomial correlation between peak elution times and molecular weights was created using the nine standards. This calibration function is used to evaluate each unknown sample.

[0044] Determination of monomer composition The compositions were determined using high performance liquid chromatography (HPLC). The reference elution times of itaconic acid, dimethyl itaconate, and diethyl itaconate were determined by using pure monomers. HPLC was performed in isocratic mode through a reversed-phase C18 column with an eluent composition of 80% 0.1 wt.% phosphoric acid aqueous solution and 20% acetonitrile. Signal concentration was measured using a UV detector at 210 nm. The instrument conditions used were: flow rate: 1.0 mL / min, run time: 14 min, injection volume: 100 μL, column temperature: 23° C. Sample preparation included dilution to about 1% in acetonitrile and filtration with a 0.2 μM syringe-tip filter into a 2 mL HPLC vial, then crimped shut. The table below shows the typical retention times of the reference itaconates and their assignment to the two novel asymmetric esters. Retention may vary slightly over time, but the relative order of the peaks and their relative spacing remain essentially the same.

[0045] [Table 6]

[0046] Proton NMR analysis The sample was dissolved in CDCl3 and transferred to a 5 mm NMR tube. It was then analyzed by proton ( 1Samples were analyzed on a Bruker BioSpin Avance NEO 500MHz NMR spectrometer equipped with a broadband iProbe model probe tuned to 1H. Sample temperature was adjusted to 25C. One-dimensional single pulse experiments were performed with a 30 degree excitation pulse (zg30) for a total of 16 scans with receiver gain automatically adjusted by the TopSpin acquisition software. The relaxation delay was set to 1 second, the acquisition time was 3.3 seconds, the FID acquisition size was 32K data points, and the spectral width was set to 10,000Hz. Following acquisition, data were imported into Mnova NMR processing software. After Fourier transformation, processed data contained 64K data points (1 level of zero filling) and a 0.3Hz exponential multiplier (line broadening) and third order Bernstein polynomial baselight correction were applied.

[0047] The above description of several embodiments has been presented for purposes of illustration and is not intended to be exhaustive or to limit the scope of the claims to the precise and / or preferred features, as various modifications are possible in light of the disclosure herein.

Claims

1. The general structure: 【Chemistry 1】 and wherein MEI and EMI are present in an amount of from 50.0% (wt.) to 98.0% (wt.), DMI and DEI are present in an amount of from 50.0% (wt.) to 2.0% (wt.), and the total amount of monomers present does not exceed 100.0% (wt.).

2. 2. The mixture of claim 1, wherein MEI and EMI are present in an amount of from 50.0% (wt.) to 90.0% (wt.) and DMI and DEI are present at a level of from 50.0% (wt.) to 10.0% (wt.).

3. 2. The mixture of claim 1, wherein the MEI and EMI are present in an amount of from 50.0% (wt.) to 80.0% (wt.) and the DMI and EMI are present at a level of from 50.0% (wt.) to 20.0% (wt.).

4. 2. The mixture of claim 1, wherein the MEI and EMI are present in an amount of from 50.0% (wt.) to 70.0% (wt.) and the DMI and EMI are present at a level of from 50.0% (wt.) to 30.0% (wt.).

5. 2. The mixture of claim 1, wherein the MEI and EMI are present in an amount of from 50.0% (wt.) to 60.0% (wt.) and the DMI and EMI are present at a level of from 50.0% (wt.) to 40.0% (wt.).

6. The mixture has the following structure: 【Chemistry 2】 wherein R is independently either a methyl group or an ethyl group.

2. The mixture of claim 1, optionally comprising a methyl or ethyl ester of mesaconic acid having the formula:

7. The mixture has the following structure: 【Chemistry 3】 wherein R is independently either a methyl group or an ethyl group.

2. The mixture of claim 1, optionally comprising a methyl or ethyl ester of citraconic acid having the formula:

8. 10. The mixture of claim 1 further comprising a vinyl-type monomer.

9. The following structure: 【Chemistry 4】 wherein repeat units "a" and "b" are present in an amount of from 50.0% (wt.) to 98.0% (wt.), repeat units "c" and "d" are present at a level of from 50.0% (wt.) to 2.0% (wt.), and the sum of repeat units "a", "b", "c", and "d" does not exceed 100.0% (wt.).

10. 10. The random copolymer of claim 9, wherein repeat units "a" and "b" are present in an amount of from 50.0% (wt.) to 90.0% (wt.) and repeat units "c" and "d" are present at a level of from 50.0% (wt.) to 10.0% (wt.).

11. 10. The random copolymer of claim 9, wherein repeat units "a" and "b" are present in an amount of from 50.0% (wt.) to 80.0% (wt.) and repeat units "c" and "d" are present at a level of from 50.0% (wt.) to 20.0% (wt.).

12. 10. The random copolymer of claim 9, wherein repeat units "a" and "b" are present in an amount of from 50.0% (wt.) to 70.0% (wt.) and repeat units "c" and "d" are present at a level of from 50.0% (wt.) to 30.0% (wt.).

13. 10. The random copolymer of claim 9, wherein repeat units "a" and "b" are present in an amount of 50.0% (wt.) to 60.0% (wt.) and repeat units "c" and "d" are present in an amount of 50.0% (wt.) to 40.0% (wt.).

14. a. providing an unsaturated polyester resin; b. A compound having the following general structure: 【Chemistry 5】 providing a mixture comprising asymmetric and symmetric monomeric esters of itaconic acid, including methyl ethyl itaconate (MEI), ethyl methyl itaconate (EMI), dimethyl itaconate (DMI), and diethyl itaconoate (DEI), having the formula: provided that MEI and EMI are present in an amount of 50.0% (wt.) or more and up to 98.0% (wt.), DMI and DEI are present in an amount of 50.0% (wt.) to 2.0% (wt.), and the total amount of monomers present does not exceed 100.0% (wt.); c. curing the polyester resin; 2. A method for curing an unsaturated polyester resin comprising:

15. 15. The method of claim 14, wherein the MEI and EMI are present in an amount of 50.0% (wt.) to 90.0% (wt.) and the DMI and DEI are present at a level of 50.0% (wt.) to 10.0% (wt.).

16. 15. The method of claim 14, wherein the MEI and EMI are present in an amount of 50.0% (wt.) to 80.0% (wt.) and the DMI and EMI are present at a level of 50.0% (wt.) to 20.0% (wt.).

17. 15. The method of claim 14, wherein the MEI and EMI are present in an amount of 50.0% (wt.) to 70.0% (wt.) and the DMI and EMI are present at a level of 50.0% (wt.) to 30.0% (wt.).

18. 15. The method of claim 14, wherein the MEI and EMI are present in an amount of 50.0% (wt.) to 60.0% (wt.) and the DMI and EMI are present at a level of 50.0% (wt.) to 40.0% (wt.).

19. The method of claim 14 further comprising a vinyl type monomer.

20. 20. The method of claim 19, wherein the vinyl type monomer is selected from the group consisting of styrene, alpha-methylstyrene, acrylates, methyl methacrylates, methacrylates, and vinyl toluene.

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