Unsaturated polyester resin composition and preparation method thereof

Abstract

The present invention relates to an unsaturated polyester resin composition, comprising: a (meth) acrylate compound; and a polyester, wherein the polyester is formed by at least: a reagent a), comprising itaconic acid and / or itaconic anhydride; a reagent b), comprising maleic acid, maleic anhydride and / or fumaric acid; a reagent c), comprising dicyclopentadiene (DCPD); and a reagent d), comprising at least one difunctional alcohol or polyfunctional alcohol, preferably at least one diol; wherein the combined weight of the reagent a) (i.e. the combined weight of itaconic acid and / or itaconic anhydride) is at least 10 wt.%, preferably at least 20 wt.%, of the total weight of the diacids and anhydrides used in the unsaturated polyester resin composition. The present invention further relates to the use of the unsaturated polyester resin for structural parts and for gel coatings. The present invention also provides a method for preparing the unsaturated polyester resin composition.

Description

Technical Field

[0001] The present invention is in the field of unsaturated polyester resin compositions and methods for preparing these compositions. In particular, the present invention aims to provide low odor and low emission polyester resin compositions. Background Art

[0002] Unsaturated polyester resin compositions are used, inter alia, for the manufacture of composite parts and products, for example in open moulds. In addition to the resin composition, the composite parts and products usually also contain reinforcing fibres. For efficient production and satisfactory properties of the finished product, the resin composition must meet a number of requirements.

[0003] For example, the viscosity of the unsaturated polyester resin composition needs to be balanced so that the unsaturated polyester resin composition flows well when filling the spaces between the reinforcing fibers, but should not be so thin that the composition flows out again before curing.

[0004] The curing time of the unsaturated polyester resin composition needs to be adjusted so that there is enough processing time to combine the liquid unsaturated polyester resin composition and the reinforcing fibers in the mold, but once curing begins, it should not take too long to achieve sufficient stiffness to enable the product to be demoulded. A common method for evaluating whether the resin is cured enough for demoulding is to measure the hardness using a Barcol 934.1 test device according to ASTM-648. Preferably, the count on the scale should be greater than 10, more preferably it should be greater than 20.

[0005] In the finished product, the cured resin should be able to withstand the mechanical loads and temperatures expected during the product's service life. Therefore, the cured resin should have a sufficiently high heat deflection temperature (HDT).

[0006] Unsaturated polyester resin compositions with styrene as a reactive diluent can meet some of these requirements, but they release significant amounts of VOC emissions during processing. In addition, styrene has a carcinogenic, mutagenic or reprotoxic (CMR) classification, which means that adequate ventilation (and optionally ventilation air treatment) is required to avoid worker and environmental exposure to high concentrations of styrene. For this reason, there is a need for unsaturated polyester resin compositions with non-volatile reactive diluents, which preferably also have low odor and are preferably non-CMR. However, such existing unsaturated polyester resin compositions typically exhibit poor surface cure, and / or exhibit insufficient strength or temperature resistance.

[0007] Unsaturated polyester resin compositions are cured by free radical polymerization. Typically, free radical polymerization is strongly hindered by oxygen. For unsaturated polyester resin compositions applied in open molds, a known problem is that the air side of the resin is less cured. For resins with volatile reactive diluents such as styrene, physical drying leaves a polyester-rich layer on the surface that is (near) solid. This (near) solid layer forms a barrier to oxygen, allowing the resin below the surface to fully cure and form a surface that feels dry to the touch. For non-volatile diluents, solidification must come entirely from free radical polymerization, which is strongly hindered by oxygen at the surface exposed to air. Typically, the surface of the resin with non-volatile reactive diluents is still liquid or sticky one day after the start of curing. In other cases, poor surface cure can result in a soft surface.

[0008] In US20040220340A1, a styrene-free resin composition made by combining unsaturated polyester and urethane (meth) acrylate is described. The document claims that in order to obtain sufficient performance, the unsaturated polyester resin needs to be mixed with (meth) acrylate hydroxyl ester and urethane (meth) acrylate. These resins will have a high concentration of hydroxyl groups, which will lead to significant water absorption, which is unfavorable to material integrity or hydrolysis resistance. In addition, the production of these resins is relatively complicated. The claimed resin composition requires the synthesis of two different resins according to different procedures and their combination. If two resins are produced in the same reactor, an intermediate cleaning step is required. Alternatively, a separate reactor dedicated to different resin types is required. In both cases, separate mixing tanks are required for both resin types. Both procedures are much more complicated than the production of standard unsaturated polyester resins, both for the required equipment and process planning and logistics. Higher complexity leads to higher costs and increases the chance of production errors. Therefore, a resin composition that can be produced in a single batch in one reactor is highly preferred.

[0009] US20150018479 describes the use of diallyltrimethylolpropane methacrylate as a diluent to improve surface curing. Although this solution provides reasonable curing, it has another disadvantage. In open mold applications, curing is usually initiated by peroxides, which require accelerator activation. The most used accelerator is cobalt octoate. Cobalt and other oxidizing driers catalyze the oxidation of the allyl ether groups of diallyltrimethylolpropane methacrylate, resulting in the formation of acrolein. Since acrolein is volatile, highly toxic and carcinogenic, this is a very unwelcome side reaction. It is known that this reaction usually occurs with cobalt and oxidizing driers. Therefore, in open mold applications, it is preferred to avoid the use of allyl ether groups in combination with cobalt or other transition metals.

[0010] UV curable resins are usually made from low volatility acrylate or methacrylate diluents. In such resins, poor surface curing is a well-known problem. Progress in Organic Coatings 77 (2014) p1789-1798 lists different additives that can improve surface curing. However, all described additives have problems such as poor stability, toxicity, poor odor, yellowing and poor usability of unsaturated polyester resins. These additives seem to be unsuitable for use in unsaturated polyesters for open mold applications, because open mold applications require storage stability and safe use.

[0011] Another way to improve surface cure is to post-cure the unsaturated polyester resin composition at elevated temperatures, such as 60-80°C. However, such post-curing is energy intensive, increases cycle times, and requires special equipment. These disadvantages are most pronounced for large objects.

[0012] Preferably, the cured resin should be able to withstand the forces and temperatures expected in the application. The minimum values ​​may vary greatly for various applications. However, for construction purposes, the following minimum requirements are generally set. The HDT of the resin is preferably at least 55°C, and more preferably at least 60°C. The elongation at break is preferably at least 1.5%, more preferably at least 2.0%, and most preferably at least 2.5%. The modulus of the resin is at least 2.0 GPa, preferably at least 2.5 GPa, more preferably at least 3.0 GPa, and most preferably at least 3.5 GPa. The tensile strength should preferably be at least 30, preferably at least 40, more preferably at least 50 MPa, and most preferably at least 60 MPa. Summary of the invention

[0013] The present invention provides a resin composition that solves one or more of the above problems. Preferred embodiments of the present invention also solve one or more of the above problems.

[0014] An object of the present invention is to provide a curable resin composition which can be improved in VOC emissions while maintaining sufficient performance in terms of curing and mechanical properties of cured objects.

[0015] Another object of the present invention is to provide styrene-free or low styrene unsaturated polyester resin compositions having low VOC or hazardous air pollutant (HAP) emissions, particularly when these resin compositions are used in open mold applications.

[0016] Another object of the present invention is to provide an unsaturated polyester resin composition having a sufficiently fast curing time. Preferably, the hardness of the product should be greater than 10, more preferably greater than 20, as read on the scale of the device using a Barcol 934.1 test device according to ASTM-648. Once sufficient hardness is reached, the finished part can be removed from the mold. Preferably, the required hardness is reached after 24 hours, more preferably after 16 hours, still more preferably after 4 hours and most preferably after 2 hours, preferably depending on the required demoulding time.

[0017] Another object of the present invention is to provide an unsaturated polyester resin composition which provides a non-stick surface within 24 hours after the start of curing, preferably on the surface in contact with the mold and on the surface in contact with the atmosphere when an open mold is used.

[0018] Another object of the present invention is to provide an unsaturated polyester resin composition having a sufficiently high HDT; preferably the HDT is at least 55°C and more preferably at least 60°C.

[0019] Another object of the present invention is to provide an unsaturated polyester resin composition useful as a structural resin and a gel coat resin.

[0020] Another object of the present invention is to provide an unsaturated polyester resin composition having no CMR marker.

[0021] These and other objects, features and advantages of the present invention will become apparent from the following detailed description.

[0022] One aspect of the present invention provides an unsaturated polyester resin composition, comprising:

[0023] - a (meth)acrylate compound, and optionally an itaconate compound; and,

[0024] - a polyester formed from at least:

[0025] - Reagent a) comprising itaconic acid and / or itaconic anhydride;

[0026] - reagent b) comprising maleic acid, maleic anhydride and / or fumaric acid;

[0027] - a reagent c) comprising dicyclopentadiene (DCPD); and,

[0028] - reagent d) comprising at least one difunctional alcohol or polyfunctional alcohol;

[0029] The combined weight of reagent a) is at least 10 wt.%, preferably at least 20 wt.%, of the total weight of the diacid and anhydride used in the unsaturated polyester resin composition.

[0030] In some embodiments, prior to forming the polyester, a reaction mixture is formed from reagent b), reagent c), and optionally reagent a). In embodiments where the reaction mixture is formed from reagent b) and reagent c), the polyester will be formed from the resulting reaction mixture with reagent a) and reagent d). In embodiments where the reaction mixture is formed from reagent b), reagent c), and reagent a), the polyester will be formed from the resulting reaction mixture with reagent d).

[0031] In some embodiments, the weight of volatile organic compounds (VOC) is less than 10 wt.% of the total weight of the unsaturated polyester resin composition; preferably less than 5 wt.%, even more preferably less than 2 wt.%, and even more preferably less than 1 wt.%. In some embodiments, the combined weight of styrene, α-methylstyrene, vinyltoluene and / or methyl methacrylate is less than 10 wt.% of the total weight of the unsaturated polyester resin composition; preferably less than 5 wt.%, even more preferably less than 2 wt.%, and even more preferably less than 1 wt.%. Preferably, the vapor pressure of the diluent is lower than 100 Pa (at 20° C.), more preferably lower than 10 Pa (at 20° C.).

[0032] In some embodiments, the weight of the (meth)acrylate compound is at least 5 to at most 95 wt.% of the total weight of the unsaturated polyester resin composition; preferably 10 to 70 wt.%, more preferably 20 to 60 wt.%, most preferably 30 to 50 wt.%, for example 40 wt.%. In view of the significant difference in skin sensitization properties, methacrylate is preferred over acrylate.

[0033] In some embodiments, the (meth)acrylate compound is used as a diluent, preferably a reactive diluent, in the unsaturated polyester resin composition.

[0034] In some embodiments, the unsaturated polyester resin composition comprises an itaconate compound, preferably a dialkyl itaconate, more preferably dimethyl itaconate (DMI).

[0035] In some embodiments, the unsaturated polyester resin composition comprises dimethyl itaconate or another itaconate monomer, preferably as a diluent, more preferably as a reactive diluent. The itaconate monomer can be used alone or in combination with a methacrylate and / or acrylate diluent.

[0036] In some embodiments, the combined weight of itaconate compounds and (meth)acrylate compounds is at least 5 to up to 95 wt.% of the total weight of the unsaturated polyester resin composition; preferably 10 to 70 wt.%, more preferably 20 to 60 wt.%, most preferably 30 to 50 wt.%, for example 40 wt.%. Any ratio between itaconate and (meth)acrylate compounds can be used, but preferably at least 1 / 4 of the weight of the diluent is (meth)acrylate compounds, more preferably at least 1 / 3 of the weight of the diluent is (meth)acrylate compounds, and most preferably at least 1 / 2 of the weight of the diluent is (meth)acrylate compounds.

[0037] In some embodiments, the added weight of DCPD is at least 10 wt. % based on the total weight of the polyester.

[0038] In some embodiments, the unsaturated polyester resin composition comprises a transition metal salt or a transition metal complex. In some embodiments, the unsaturated polyester resin composition comprises a cobalt salt or a cobalt polymer.

[0039] In some embodiments, the unsaturated polyester resin composition comprises a photoinitiator. In some embodiments, the unsaturated polyester resin composition comprises an inorganic filler.

[0040] A further aspect of the present invention provides the use of an unsaturated polyester resin composition or an embodiment thereof as described herein as a building material for a structural component, preferably in an open mold. Another aspect of the present invention provides the use of a resin or an embodiment thereof as described herein as a gel coating formulation or a coating formulation, preferably in an open mold.

[0041] In yet another aspect, the present invention provides a method for preparing an unsaturated polyester resin composition, preferably an unsaturated polyester resin composition according to an embodiment of the present invention, the method comprising the steps of:

[0042] - A polyester formed from at least:

[0043] - Reagent a) comprising itaconic acid and / or itaconic anhydride;

[0044] - reagent b) comprising maleic acid, maleic anhydride and / or fumaric acid;

[0045] - a reagent c) comprising dicyclopentadiene (DCPD); and,

[0046] - reagent d) comprising at least one difunctional alcohol or polyfunctional alcohol;

[0047] - mixing the obtained polyester with a (meth)acrylate compound and optionally with an itaconate compound, thereby obtaining an unsaturated polyester resin composition;

[0048] The combined weight of reagent a) is at least 10 wt.%, preferably at least 20 wt.%, of the total weight of diacid and anhydride used in the unsaturated polyester resin composition.

[0049] In some embodiments, the method includes the step of forming a reaction mixture from reagent b), reagent c) and optionally reagent a) prior to forming the polyester. In embodiments where the reaction mixture is formed from reagent b) and reagent c), the polyester will be formed from the resulting reaction mixture with reagent a) and reagent d). In embodiments where the reaction mixture is formed from reagent b), reagent c) and reagent a), the polyester will be formed from the resulting reaction mixture and reagent d).

[0050] Preferred embodiments of the resins described herein are also preferred embodiments of the uses and methods, and vice versa. DETAILED DESCRIPTION

[0051] As used herein hereinafter, the singular form "a", "an" and "the" include the singular and the plural, unless the context clearly indicates otherwise.

[0052] The terms "comprise", "comprises" used below are synonymous with "including", "include", "contain", "contains", and are inclusive or open-ended, and do not exclude other unmentioned components, elements or method steps. When the description refers to a product or method "comprising" specific features, components or steps, this refers to the possibility that other features, components or steps may also be present, but it may also refer to an embodiment that only includes the listed features, components or steps.

[0053] Numerical values ​​recited in numerical ranges include all values ​​and fractions within those ranges, as well as the recited endpoints.

[0054] The term "about" when used in reference to a measurable value (e.g., a parameter, an amount, a time period, etc.) is intended to include variations of the specified value of + / -10% or less, preferably + / -5% or less, more preferably + / -1% or less, as long as these variations are applicable to the invention disclosed herein. It should be understood that the value referred to by the term "about" itself is also disclosed.

[0055] All references cited in this specification are hereby deemed to be incorporated by reference in their entirety.

[0056] Unless otherwise defined, all terms disclosed in the present invention, including technical and scientific terms, have the meanings commonly given to them by those skilled in the art. For further guidance, definitions are included to further explain the terms used in the description of the present invention.

[0057] The present invention generally provides unsaturated polyester resin compositions that are improved in surface curing properties. The resin compositions of the present invention can exhibit effective curing in thin laminates, particularly at ambient temperature in an air atmosphere. In addition, the present invention generally provides unsaturated polyester resins that have a good balance in tensile strength, elongation at break, HDT, surface hardness, processing characteristics, and ease of production.

[0058] Furthermore, the present invention provides styrene-free or low styrene unsaturated polyester resin compositions which can have low emissions from VOCs or hazardous air pollutants (HAPs), especially when these resin compositions are used in open air, such as open mold applications.

[0059] One aspect of the present invention provides an unsaturated polyester resin composition, comprising:

[0060] - (meth)acrylate compounds; and

[0061] - a polyester formed from at least:

[0062] - Reagent a) comprising itaconic acid and / or itaconic anhydride;

[0063] - reagent b) comprising maleic acid, maleic anhydride and / or fumaric acid;

[0064] - a reagent c) comprising dicyclopentadiene (DCPD); and,

[0065] - reagent d) comprising at least one difunctional alcohol or polyfunctional alcohol, preferably at least one diol;

[0066] The combined weight of reagent a) (ie the combined weight of itaconic acid and / or itaconic anhydride) is at least 10 wt.%, preferably at least 20 wt.%, of the total weight of diacids and anhydrides used in the unsaturated polyester resin composition.

[0067] The presence of DCPD residue (DCPD-residue, DCPD residue) in unsaturated polyester is beneficial to surface curing. DCPD also contributes to the surface curing of the resin composition with (meth) acrylate compound as reactive diluent, but, compared with the resin composition rich in styrene, it is not effective enough to fully compensate for the poor starting position of the resin composition with non-volatile reactive diluent. Although the resin surface may feel dry to the touch after 24 hours, the top layer is still under-cured and remains soft. Unexpectedly, it is found that incorporating itaconic acid residue (itaconic residue, itaconic acid residue, itaconic acid residue) and maleic acid residue (maleic residue, maleic acid residue, maleic acid residue) or fumaric acid residue (fumaric residue, fumaric acid residue, fumaric acid residue) in DCPD-polyester resin provides a synergistic effect, thereby significantly improving the hardness of the resin surface.

[0068] Furthermore, the polyester is found to contribute to the viscosity of the uncured resin composition and, after curing, it imparts to the cured resin good mechanical properties, heat distortion temperature and low water absorption. The above properties also depend to a large extent on the choice of reactive diluent, but it has been found that the polyester used in the present invention provides a better compromise between the above properties compared to conventional polyester backbones in the same reactive diluent.

[0069] The term "combined weight of itaconic acid and itaconic anhydride" refers to the sum of the weight of all itaconic acid (if used) and all itaconic anhydride (if used) used to form the unsaturated polyester resin composition.

[0070] In some embodiments, a reaction mixture is formed from reagent b), reagent c), and optionally reagent a) prior to forming the polyester.

[0071] In various embodiments, it should be noted that even in the case where the reaction mixture is formed from only reagents b) and c), the polyester is formed from all four reagents a), b), c) and d). If the reaction mixture is formed from only two of the three reagents b) and c), then reagents a) and d) are added to the reaction mixture to form the polyester.

[0072] In some embodiments, the reaction mixture is formed by:

[0073] - reagent b) and reagent c); or,

[0074] - reagent a), reagent b) and reagent c).

[0075] In some embodiments, the reaction mixture is formed in the presence of water, particularly when the reagents comprise anhydrides.

[0076] In some embodiments, the anhydride present in reagent a) and / or reagent b) is hydrolyzed prior to forming the reaction mixture. Preferably, water is added to the reagent comprising the anhydride and the reagent is heated.

[0077] In some embodiments, during the formation of the polyester, it is preferred to remove water by distillation.

[0078] The following resin combinations containing compounds containing (meth)acrylates and / or itaconates as diluents are examples of the present invention: (i) an unsaturated polyester resin containing itaconic acid residues, maleic acid residues and DCPD residues; (ii) an unsaturated polyester resin containing itaconic acid residues, fumaric acid residues and DCPD residues.

[0079] The preparation of DCPD-maleate polyesters is known to those skilled in the art. However, in the formation, the method of the present invention differs from standard practice in that itaconic acid is added in the DCPD addition step or in the polycondensation step. In some embodiments, the added weight of DCPD is at least 10 wt.% of the total weight of the polyester.

[0080] In some embodiments, a preferred method comprises heating a mixture of maleic anhydride, water, and optionally itaconic acid to about 130-140°C, during which time the maleic anhydride reacts with water to form maleic acid. A clear solution is preferably formed, although a well-flowing slurry with solid itaconic acid is also acceptable. DCPD is added to the mixture, producing an exothermic reaction. The rate of addition of DCPD is preferably controlled so that the temperature does not rise above 150°C, or preferably not above 140°C, to avoid dangerous decomposition reactions. In an alternative procedure, DCPD is part of the starting mixture, and water or maleic anhydride is added at a controlled rate. After the addition of the acid, water, and DCPD, the mixture needs to be reacted at 130-150°C for another hour or more to obtain sufficient conversion.

[0081] Preferably, the initial mixture to which DCPD is added comprises maleic acid, water and itaconic acid.

[0082] More preferably, the ratio of maleic acid to itaconic acid is between 1 :4 and 2: 1. Most preferably, the ratio is between 1 :2 and 1.5:1.

[0083] Alternatively, DCPD-maleate is first prepared using standard procedures and then itaconic acid is added, wherein the ratio between maleic acid and itaconic acid is between 1:4 and 2: 1. Most preferably, the ratio is between 1:2 and 1.5:1.

[0084] In some embodiments, the next step is a polycondensation step, for which diol and / or glycol (ethylene glycol) are added, and optionally additional itaconic acid or other diacids or anhydrides. For the polycondensation process, various methods are known in the art.

[0085] In some embodiments, all reactants are heated together to 150-250° C., and then water is removed, preferably by distillation, and the polymer is formed.

[0086] In some embodiments, the method includes flushing the mixture with an inert gas such as nitrogen during the polycondensation process, and / or reducing the pressure in the reactor. This allows for more efficient water removal.

[0087] In some embodiments, toluene is added to enhance the removal of water by azeotropic distillation. The process can be carried out at lower temperatures, such as 100-120° C., to promote polycondensation with thermally unstable components. Other inert solvents that form azeotropes with water can also be used.

[0088] In some embodiments, the combined amount of DCPD and hydroxyl groups should be nearly equal to the amount of acid groups on a molar basis. Nearly equal means that the amount of DCPD + hydroxyl groups is 80-120%, preferably 110-90%, and most preferably 110-100% of the amount of acid groups.

[0089] In some embodiments, for smooth processing of the unsaturated polyester resin, the viscosity at 23° C. should preferably be 100-2000 mPa.s, more preferably 150-1000 mPa.s, and most preferably 200-600 mPa.s. In certain embodiments, rheological additives for producing thixotropy are used.

[0090] In some embodiments, to initiate curing, methods known in the art may be used. This may include peroxide accelerator systems, UV-curing, thermal initiators and / or electron beams. A more specific example is a combination of MEKP peroxide with cobalt and / or other accelerators and BPO-amine initiators.

[0091] In some embodiments, polycondensation is enhanced by the addition of a catalyst.

[0092] In some embodiments, the polycondensation is stopped before reaching full conversion. A common method for determining conversion is to measure the acid value according to ISO 2114-2000. In some embodiments, the acid value of the unsaturated polyester resin preferably ranges from 10 to 100 mg KOH / g resin, more preferably from 15 to 60 mg KOH / g resin, and most preferably from 20 to 50 mg KOH / g resin.

[0093] In some embodiments, in addition to the diacids listed above, other diacids may be included in the resin composition. Typical examples of suitable diacids and anhydrides may include fumaric acid, citraconic acid, citraconic anhydride, mesaconic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, tetrahydrophthalic acid, phthalic acid, phthalic anhydride, terephthalic acid and isophthalic acid. Diacids not explicitly mentioned may also be used; the composition of the present invention is by no means limited to the listed diacids for guidance of those skilled in the art. In addition, monoacids, triacids and higher acids may also be included in the composition. Typical examples of suitable monoacids may include (meth) acrylic acid, lactic acid, benzoic acid, etc.

[0094] In some embodiments, difunctional alcohols or polyfunctional alcohols are used for the polymerization process. Preferably, diols are used, such as, for example, 1,2-propylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propylene glycol, dipropylene glycol, tripropylene glycol, neopentyl glycol, 2-methyl-1,3-propanediol, isosorbide, 2,3-butylene glycol, butyl ethyl propanediol, hydrogenated bisphenol-A or ethoxylated / propoxylated bisphenol A. In some embodiments, in addition to difunctional or polyfunctional alcohols, monohydric alcohols, such as 2-ethylhexanol or benzyl alcohol, and polyhydric alcohols, such as glycerol or trimethylolpropane, can also be used. In some embodiments, other monohydric alcohols, dihydric alcohols and polyhydric alcohols can also be used.

[0095] In some embodiments, the polyester may be made from a single diol or from a combination of diols and / or monools and polyols.

[0096] In some embodiments, an inhibitor to prevent free radical polymerization may be added during the polycondensation process. For example, an unsaturated polyester resin may be prepared in the presence of hydroquinone, 2-methylhydroquinone, benzoquinone, 2-methylbenzoquinone or other substituted hydroquinones or quinones as an inhibitor.

[0097] In some embodiments, an esterification catalyst and / or an isomerization catalyst may be used during the polycondensation process.

[0098] In some embodiments, the non-volatile diluent is selected from the group of acrylates and the group of methacrylates. Of these two groups, methacrylates are preferred over acrylates because they are generally much stronger skin sensitizers and therefore require more worker protection.

[0099] In some embodiments, after preparing the DCPD-modified polyester, the polyester can be diluted in a reactive diluent. As a suitable diluent, all commercially available (meth)acrylates can be used. Examples of such (meth)acrylates can include hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), glycerol formal (meth)acrylate, butyl methacrylate, hexyl (meth)acrylate, tert-butyl methacrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate, tert-butyl cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, trimethylolpropane tri(meth)acrylate, PEG200 di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,3-butanediol di(meth)acrylate. Difunctional reactive diluents include 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, PEG400 di(meth)acrylate, triethylene glycol di(meth)acrylate, and / or tripropylene glycol di(meth)acrylate.

[0100] In some embodiments, in addition to (meth)acrylate, itaconate diluents such as dimethyl itaconate, diethyl itaconate, diisopropyl itaconate, di-n-propyl itaconate and dibutyl itaconate can also be used. Among these diluents, dimethyl itaconate is preferred. Preferably, itaconate diluents are used in combination with (meth)acrylate diluents. More preferably, itaconate diluents are used in combination with methacrylate diluents.

[0101] In some embodiments, the combined amount of (meth)acrylate and itaconate diluents is at least 5 to up to 95 wt.% of the total unsaturated polyester resin composition; preferably 10 to 70 wt.%, more preferably 20 to 60 wt.%, most preferably 30 to 50 wt.%, such as 40 wt.%. The preferred concentration of multifunctional (meth)acrylate in the present invention is at least 5 to up to 95 wt.% of the total unsaturated polyester resin composition; preferably 5 to 85 wt.%, more preferably 5 to 80 wt.%, even more preferably 5 to 75 wt.%, even more preferably 5 to 70 wt.%, even more preferably 5 to 65 wt.%, even more preferably 5 to 60 wt.%, more preferably 10 to 60 wt.%, even more preferably 20 to 60% wt.%, such as 20 wt.%, such as 25 wt.%, such as 30 wt.%, such as 35 wt.%, such as 40 wt.%, such as 45 wt.%, such as 50 wt.%, such as 55 wt.%. These amounts can refer to the total amount of a single reactive diluent or a combination of two or more reactive diluents.

[0102] Although low volatility diluents are preferred, in some embodiments, a small amount of volatile diluent may be present. The small amount is preferably less than 10.0% of the total formulation, more preferably less than 5.0%, even more preferably less than 2.0% and even more preferably less than 1.0%. Examples of volatile diluents are styrene, α-methylstyrene, vinyltoluene and methyl methacrylate. Therefore, in some embodiments, the amount of volatile organic compounds (VOC) is less than 10 wt.% of the total amount of the unsaturated polyester resin composition; preferably less than 5 wt.%, even more preferably less than 2 wt.%, and even more preferably less than 1 wt.%. More particularly, in some embodiments, the amount of styrene, α-methylstyrene, vinyltoluene and / or methyl methacrylate is less than 10 wt.% of the total amount of the unsaturated polyester resin composition; preferably less than 5 wt.%, even more preferably less than 2 wt.%, and even more preferably less than 1 wt.%.

[0103] In some embodiments, the unsaturated polyester resin composition may further comprise various additives, such as inhibitors, accelerators, promoters, fillers, pigments, dyes, UV-stabilizers, thixotropic agents, defoamers, photoinitiators and / or other additives. Suitable compounds may be found as further listed below.

[0104] In some embodiments, the unsaturated polyester resin composition may contain an accelerator. As accelerators, typical transition metal compounds are used, such as compounds of vanadium, iron, manganese, copper, nickel, molybdenum, tungsten, cobalt and chromium. Preferred transition metals are V, Cu, Co, Mn and Fe. The transition metal may be present in the form of a carboxylate, a polymer or a complex with a ligand. Examples of such complexes are Borchi OxyCure TM , 2700F and Nuodex DryCoat. The accelerator can be based on one transition metal or a combination of transition metals.

[0105] In some embodiments, the unsaturated polyester resin composition may include an accelerator. Examples of accelerators are acetylacetone, N,N-dimethylacetoacetamide, N,N-diethylacetoacetamide, acetyl esters, and aromatic amines (such as N,N-dimethylaniline, N,N-diethylaniline, toluidine and dimethylbenzene such as N,N-diisopropyl alcohol-p-toluidine; N,N-dimethyl-p-toluidine; N,N-bis(2-hydroxyethyl)xylbenzene and -toluidine). In addition, alkali and alkaline salts may be added.

[0106] In some embodiments, the unsaturated polyester resin composition may further comprise a free radical inhibitor. These free radical inhibitors are preferably selected from the group consisting of phenolic compounds, benzoquinone, hydroquinone, catechol, stable free radicals and / or phenothiazines. The amount of the free radical inhibitor that can be added can vary within a fairly wide range and can be selected as a first indication of the gel time that is desired to be achieved.

[0107] Suitable examples of free radical inhibitors that can be used in embodiments of the unsaturated polyester resin composition are, for example, 2-methoxyphenol, 4-methoxyphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butylphenol, 2,4,6-trimethylphenol, 2,4,6-tris-dimethylaminomethylphenol, 4,4'-thio-bis(3-methyl-6-tert-butylphenol), 4,4'-isopropylphenol, 2,4-di-tert-butylphenol, 6,6'-di-tert-butyl-2,2'-methylenedi-p-cresol, hydroquinone, 2-methylhydroquinone, 2-tert-butylhydroquinone, 2,5-di-tert-butylhydroquinone, 2,6-di-tert-butylhydroquinone, 2,6-dimethylhydroquinone, 2,3,5-trimethylhydroquinone, catechol, 4-tert-butylcatechol, 4,6-di-tert-butylcatechol, benzoquinone, 2,3,5,6-tetrachloro-1, 4-benzoquinone, methyl benzoquinone, 2,6-dimethylbenzoquinone, naphthoquinone, 1-oxy-2,2,6,6-tetramethylpiperidine, 1-oxy-2,2,6,6-tetramethylpiperidin-4-ol (a compound also known as TEMPOL), 1-oxy-2,2,6,6-tetramethylpiperidin-4-one (a compound also known as TEMPON), 1-oxy-2,2,6,6-tetramethyl-4-carboxy-piperidine (a compound also known as 4-carboxy-TEMPO), 1-oxy-2,2,5,5-tetramethylpyrrolidine, 1-oxy-2,2,5,5-tetramethyl-3-carboxypyrrolidine (also known as 3-carboxy-PROXYL), galvinoxyl, aluminum-N-nitrosophenylhydroxylamine, diethylhydroxylamine, phenothiazine, and / or a derivative or combination of any of these compounds.

[0108] In some embodiments, the amount of the free radical inhibitor in the unsaturated polyester resin composition ranges from 0.0001 to 10.0% by weight relative to the total amount of the unsaturated polyester and the reactive diluent present in the unsaturated polyester resin composition. More preferably, the amount of the inhibitor in the unsaturated polyester resin composition ranges from 0.001 to 1.0% by weight. Depending on the type of inhibitor selected, a person skilled in the art can easily assess what amount thereof will lead to good results according to the present invention.

[0109] The present invention further relates to a process for free-radical curing of an unsaturated polyester resin composition according to the invention, wherein curing is effected by adding and activating an initiator to the resin composition as described above. Preferably, curing is carried out at a temperature in the range of -20 to +200° C., preferably in the range of -20 to +100° C., and most preferably in the range of -10 to +60° C. (so-called cold curing).

[0110] In some embodiments, the initiator can be a photoinitiator, a thermal initiator, or a redox initiator, and / or combinations thereof.

[0111] As referred to herein, a photoinitiator is capable of initiating curing upon irradiation. Photoinitiation is understood as curing using irradiation with light of a suitable wavelength (photoirradiation). This is also referred to as photocuring.

[0112] In some embodiments, a sensitizer may be added to a photoinitiator to form a photoinitiating system.

[0113] In some embodiments, mixtures of photoinitiators may be used, optionally in combination with one or more sensitizers.

[0114] In some embodiments, the photoinitiator system can be selected from a large group of photoinitiator systems known to the skilled person. A large number of suitable photoinitiator systems can be found in, for example, "Chemistry and Technology of UV and EB Formulations", 2nd Edition, by K. Dietliker and JV Crivello (SITA Technology, London; 1998), Volume 3, which is incorporated herein by reference.

[0115] In some embodiments, the thermal initiator can be selected from azo compounds, such as azoisobutyronitrile (AIBN), CC unstable compounds, such as benzopinacol, peroxides, and mixtures thereof. In some embodiments, the thermal initiator is preferably an organic peroxide, or a combination of two or more organic peroxides.

[0116] In some embodiments, the redox initiator is preferably an organic peroxide in combination with at least one of the above-mentioned co-initiators. Examples of suitable peroxides are, for example, hydroperoxides, peroxycarbonates (of the formula -OC(O)OO-), peroxyesters (of the formula -C(O)OO-), diacyl peroxides (of the formula -C(O)OOC(O)-), dialkyl peroxides (of the formula -OO-), and the like.

[0117] The present invention further relates to a cured object or structural part prepared from the unsaturated polyester resin composition as described above by curing with an initiator as described above.

[0118] In some embodiments, surface curing is performed in the open air, such as for open mold applications.

[0119] As used herein, "structural resins" or "structural resin compositions" are capable of providing structural components suitable for application for construction purposes. Preferably such resin compositions are non-aqueous systems. Preferably, they may contain up to 5% by weight of water, mainly from reactions during the resin preparation process. As referred to herein, "structural components" are considered to have a thickness of at least 0.5 mm and to have suitable mechanical properties after curing. End segments to which the resin composition according to the invention may be applied are, for example, automotive parts, boats, chemical anchoring, roofing, buildings, containers, relining, pipes, tanks, flooring, windmill blades.

[0120] The present invention further relates to a gel coat formulation prepared from the unsaturated polyester resin composition as described above.The gel coat may be applied in an open mould.

[0121] A further aspect of the present invention provides the use of the unsaturated polyester resin composition described herein or embodiments thereof for producing a structural part in an open mold.

[0122] A further aspect of the present invention provides a structural part produced using the unsaturated polyester resin composition described herein or embodiments thereof, preferably produced in an open mold.

[0123] A further aspect of the present invention provides use of the unsaturated polyester resin composition described herein or embodiments thereof for preparing a gel coat formulation.

[0124] A further aspect of the present invention provides the use of the unsaturated polyester resin composition described herein or embodiments thereof for applying a gel coat in an open mould.

[0125] A further aspect of the present invention provides a gel coat formulation comprising the unsaturated polyester resin composition described herein or an embodiment thereof, preferably for application in an open mould.

[0126] A further aspect of the present invention provides a method for preparing an unsaturated polyester resin composition, preferably an unsaturated polyester resin composition according to the embodiments described herein, comprising the steps of:

[0127] - A polyester formed from at least:

[0128] - Reagent a) comprising itaconic acid and / or itaconic anhydride;

[0129] - reagent b) comprising maleic acid, maleic anhydride and / or fumaric acid;

[0130] - a reagent c) comprising dicyclopentadiene (DCPD); and,

[0131] - reagent d) comprising at least one difunctional alcohol or polyfunctional alcohol;

[0132] - mixing the obtained polyester with a (meth)acrylate compound and optionally with an itaconate compound to provide an unsaturated polyester resin composition;

[0133] The combined weight of reagent a) is at least 10 wt.%, preferably at least 20 wt.%, of the total weight of diacids and anhydrides used in the unsaturated polyester resin composition.

[0134] In some embodiments, the method includes the step of forming a reaction mixture from reagent b), reagent c), and optionally reagent a) prior to forming the polyester. In embodiments where the reaction mixture is formed from reagent b) and reagent c), the polyester will be formed from the resulting reaction mixture with reagent a) and reagent d). In embodiments where the reaction mixture is formed from reagent b), reagent c), and reagent a), the polyester will be formed from the resulting reaction mixture with reagent d).

[0135] In some embodiments, water is added to reagent a) and / or b), especially when reagent a) or b) comprises an anhydride.

[0136] In some embodiments, the unsaturated polyester resin composition may include any suitable compound listed as an embodiment of the unsaturated polyester resin composition above.

[0137] In some embodiments, the reaction mixture may include an inhibitor.

[0138] In some embodiments, the reaction mixture can be formed in the absence of reagent a) and reagent a) is added together with reagent d) to form the polyester. Also in these embodiments, the combined weight of itaconic acid and itaconic anhydride is at least 10 wt.%, preferably at least 20 wt.%, of the total weight of the diacid and anhydride used in the unsaturated polyester resin composition.

[0139] In some embodiments, reagent c) is added to reagent a) and / or b) to form a reaction mixture, and if reagent a) and / or b) comprises an anhydride, reagent a) and / or reagent b) is preferably hydrolyzed prior to adding reagent c). This allows control of the reaction and control of the heat generated during the reaction.

[0140] In some embodiments, reagent a) and / or reagent b) are added to reagent c) to form a reaction mixture, and if reagent a) and / or reagent b) comprise an anhydride, reagent a) and / or reagent b) are preferably hydrolyzed prior to addition to reagent c). This approach provides resins with similar chemical and physical properties, but this approach is less preferred because it is less safe.

[0141] In some embodiments, reagent a) and / or reagent b) are hydrolyzed prior to forming the reaction mixture by heating to a temperature of at least 130°C to at most 140°C, preferably 135°C, in the presence of water.

[0142] In some embodiments, the one or more glycols are, for example, propylene glycol, neopentyl glycol, and / or diethylene glycol.

[0143] In some embodiments, the structural unit formed according to the above method may be:

[0144]

[0145] The present invention will be further illustrated by the following non-limiting examples.

[0146] Example

[0147] Methods used

[0148] To test the mechanical properties and HDT of the cured resin, samples were prepared as follows: A mold was made of two glass plates with wax and a 4 mm thick rubber spacer. The resin to be tested was thoroughly mixed with 0.1% Byk 555 (air release agent), 1.0% accelerator NL-49P (Nouryon) and 1.5% Butanoc M-50, degassed, and poured into the mold. After 24 hours, the cured resin was demoulded and post-cured at 80° C. for 24 hours.

[0149] Tensile properties were measured according to ISO 527-2.

[0150] Heat distortion temperature (HDT) was measured according to ISO 75-A.

[0151] Experiment 1: Preparation of DCPD-Polyester A (Example 1)

[0152] Main chain A was prepared according to the following procedure:

[0153] In a vessel equipped with a packed column, a temperature measuring device and an inert gas inlet, a mixture of maleic anhydride (10.0 mol), itaconic acid (10.0 mol), water (10 mol) and an inhibitor is heated to 135-140°C. DCPD (8.0 mol) is added to the mixture at a controlled rate to avoid a temperature increase due to the exothermic reaction; the addition takes about 30 minutes. Under these conditions, DCPD reacts with the acid groups of maleic acid and itaconic acid to form DCPD-maleate and DCPD-itaconate. After the addition of DCPD is complete, the mixture is placed at 135-140°C for one hour, followed by the addition of neopentyl glycol (13.0 mol) and propylene glycol (4.0 mol). The mixture is heated to a temperature of 140°C, followed by the temperature being raised to 190°C over two and a half hours. The mixture is maintained at a temperature between 190-200°C until the distillation of water stops. The packed column is removed and the mixture is kept under reduced pressure (about 100 mbar) until the acid number reaches a value of about 30-35 mg KOH / g resin.The vacuum is then released with an inert gas and the mixture is cooled.

[0154] Experiment 2: Preparation of DCPD-Polyester B (Comparative Example 1)

[0155] Main chain B was prepared according to the following procedure:

[0156] In a container equipped with a packed column, a temperature measuring device and an inert gas inlet, a mixture of maleic anhydride (20.0 mol), water (10 mol) and an inhibitor is heated to 135-140°C. DCPD (8.0 mol) is added to the mixture at a controlled rate to avoid temperature rise due to the exothermic reaction, and the addition takes about 30 minutes. Under these conditions, DCPD reacts with the acid group of maleic acid to form DCPD-maleate. After the DCPD addition is completed, the mixture is placed at 135-140°C for one hour, followed by the addition of neopentyl glycol (13.0 mol) and propylene glycol (4.0 mol). The mixture is heated to a temperature of 140°C, and then the temperature is raised to 190°C within two and a half hours. The mixture is maintained at a temperature between 190-200°C until the distillation of water stops. The packed column is removed and the mixture is maintained under reduced pressure (about 100 mbar) until the acid value reaches a value of about 30-35 mg KOH / g resin. The vacuum is then released with an inert gas, and the mixture is cooled.

[0157] Experiment 3: Preparation of benzyl alcohol-polyester C (Comparative Example 2)

[0158] Main chain C was prepared according to the following procedure:

[0159] In a vessel equipped with a packed column, a temperature measuring device and an inert gas inlet, a mixture of maleic anhydride (10.0 mol), itaconic acid (10 mol) and an inhibitor is heated to 135-140° C. Benzyl alcohol (8.0 mol) is added to the mixture and allowed to react for about 1 hour. Subsequently, neopentyl glycol (13.0 mol) and propylene glycol (4.0 mol) are added. The mixture is heated to a temperature of 140° C. and then the temperature is raised to 190° C. in two and a half hours. The mixture is maintained at a temperature between 190-200° C. until the distillation of water stops. The packed column is removed and the mixture is maintained under reduced pressure (about 100 mbar) until the acid value reaches a value of about 30-35 mg KOH / g resin. The vacuum is then released with an inert gas and the mixture is cooled.

[0160] Experiment 4: Preparation of DCPD-polyester D (Example 2)

[0161] Main chain D was prepared according to the following procedure:

[0162] In a vessel equipped with a packed column, a temperature measuring device and an inert gas inlet, a mixture of maleic anhydride (8.0 mol), itaconic acid (12.0 mol), water (10 mol) and an inhibitor is heated to 135-140°C. DCPD (8.0 mol) is added to the mixture at a controlled rate to avoid a temperature increase due to the exothermic reaction; the addition takes about 30 minutes. Under these conditions, DCPD reacts with the acid groups of maleic acid and itaconic acid to form DCPD-maleate and DCP-itaconate. After the addition of DCPD is complete, the mixture is placed at 135-140°C for one hour, followed by the addition of neopentyl glycol (8.8 mol) and propylene glycol (8.8 mol). The mixture is heated to a temperature of 140°C, followed by the temperature being raised to 190°C over two and a half hours. The mixture is maintained at a temperature between 190-200°C until the distillation of water stops. The packed column is removed and the mixture is kept under reduced pressure (about 100 mbar) until the acid number reaches a value of about 30-35 mg KOH / g resin.The vacuum is then released with an inert gas and the mixture is cooled.

[0163] Experiment 5: Preparation of DCPD-Polyester E (Example 3)

[0164] Main chain E was prepared according to the following procedure:

[0165] In a vessel equipped with a packed column, a temperature measuring device and an inert gas inlet, a mixture of maleic anhydride (4.0 mol), itaconic acid (16.0 mol), water (10 mol) and an inhibitor is heated to 135-140°C. DCPD (12.0 mol) is added to the mixture at a controlled rate to avoid a temperature increase due to the exothermic reaction; the addition takes about 30 minutes. Under these conditions, DCPD reacts with the acid groups of maleic acid and itaconic acid to form DCPD-maleate and DCP-itaconate. After the addition of DCPD is complete, the mixture is placed at 135-140°C for one hour, followed by the addition of neopentyl glycol (12.0 mol) and diethylene glycol (4.0 mol). The mixture is heated to a temperature of 140°C, followed by the temperature being raised to 190°C over two and a half hours. The mixture is maintained at a temperature between 190-200°C until the distillation of water stops. Remove the packed column and keep the mixture under reduced pressure (about 100 mbar) until the acid number reaches a value of about 30-35 mg KOH / g resin. Then release the vacuum with an inert gas and cool the mixture. This experiment shows that a large amount of excess DCPD can be used compared to the amount of maleic acid.

[0166] Experiment 6 (Comparative Example 3)

[0167] In a vessel equipped with a packed column, a temperature measuring device and an inert gas inlet, an attempt was made to heat a mixture of itaconic acid, inhibitor and water to 135-140°C. With equimolar amounts of itaconic acid and water, the mixture remained solid and could not be stirred effectively. By increasing the amount of water, a suspension could be made that could be stirred, but in this case the water began to boil at <110°C. Thus, the conditions required for safe addition of DCPD could not be achieved when starting with just itaconic acid, inhibitor and water.

[0168] Experiment 7 (Comparative Example 4)

[0169] In a vessel equipped with a packed column, a temperature measuring device and an inlet for an inert gas, a mixture of 5 mol of itaconic acid, 1 mol of neopentyl glycol, 1 mol of diethylene glycol, an inhibitor and water is heated to 135-140°C. To this suspension, 3 mol of DCPD are added over a period of about 40 minutes. Unlike the experiment with the presence of maleic acid, no exothermic reaction is now observed. After the addition is complete, the mixture is kept at 135-140°C for a further two hours. Unlike the experiment with the presence of maleic acid, the mixture remains turbid and after stopping stirring the mixture separates into two layers, one of which is a layer of unreacted DCPD, and the experiment is stopped. This experiment shows that the presence of maleic acid is required for the successful addition of DCPD to itaconic acid.

[0170] Experiment 8

[0171] The backbones from experiments 1-3 were diluted in a combination of triethylene glycol dimethacrylate (TRGDMA) and dimethyl itaconate (DMI). To cure these resins, they were mixed with 0.3% cobalt octoate solution (10% Co), 0.1% copper naphthenate solution (8% Cu), 0.5% NN-diethylacetoacetamide and 2.0% Butanox LPT-IN. These formulations were poured into an open metal mold to form a layer with a thickness of about 4 mm. After 24 hours, the stickiness of the surface was evaluated by touch and the Barcol hardness was determined. The results are shown in Table 1. After 24 hours, the resin with backbone A alone was fully cured.

[0172] Table 1

[0173] I II III Main Chain A 55％ Main chain B 55％ Main Chain C 55％ TRGDMA 22.5％ 22.5％ 22.5％ DMI 22.5％ 22.5％ 22.5％ 24h watch face No stickiness No stickiness Strong viscosity Barcol 934.1 20 0 0

[0174] Experiment 9

[0175] The DCPD-polyesters from experiments 1-5 were diluted using different combinations of different methacrylate compounds with dimethyl itaconate as diluents. The viscosity of these resins was measured and then the resins were cured using 1.0% accelerator NL-49P and 1.5% ButanoxM-50 (both from Nouryon) and post-cured at 80°C for 24 hours. The HDT and tensile properties of these resins were then measured. The results in Table 2 show that the resins according to the present invention (main chains A, D and E) show sufficient viscosity, HDT and tensile properties. The resin using comparative main chain B has a high viscosity and too low HDT. The resin using comparative main chain C has an even lower HDT and a low modulus. These trends between the main chains were observed with all tested diluent combinations.

[0176] Table 2

[0177]

Claims

1. An unsaturated polyester resin composition comprising: - (meth)acrylate compounds; and, - a polyester formed from at least: - Reagent a) comprising itaconic acid and / or itaconic anhydride; - reagent b) comprising maleic acid, maleic anhydride and / or fumaric acid; - a reagent c) comprising dicyclopentadiene; and, - reagent d) comprising at least one difunctional alcohol or polyfunctional alcohol; in, The combined weight of the reagents a) is at least 20 wt. % of the total weight of the diacids and anhydrides used in the unsaturated polyester resin composition.

2. The unsaturated polyester resin composition according to claim 1, wherein Prior to forming the polyester, a reaction mixture is formed from reagent b), reagent c) and optionally reagent a).

3. The unsaturated polyester resin composition according to claim 1 or claim 2, wherein The weight of volatile organic compounds is less than 10 wt. % of the total weight of the unsaturated polyester resin composition.

4. The unsaturated polyester resin composition according to claim 3, wherein The weight of volatile organic compounds is less than 5 wt. % of the total weight of the unsaturated polyester resin composition.

5. The unsaturated polyester resin composition according to claim 3, wherein The weight of volatile organic compounds is less than 2 wt. % of the total weight of the unsaturated polyester resin composition.

6. The unsaturated polyester resin composition according to claim 3, wherein The weight of volatile organic compounds is less than 1 wt. % of the total weight of the unsaturated polyester resin composition.

7. The unsaturated polyester resin composition according to any one of claims 1 to 6, wherein The combined weight of styrene, α-methylstyrene, vinyltoluene and / or methyl methacrylate is less than 10 wt.% of the total weight of the unsaturated polyester resin composition.

8. The unsaturated polyester resin composition according to claim 7, wherein The combined weight of styrene, α-methylstyrene, vinyltoluene and / or methyl methacrylate is less than 5 wt.% of the total weight of the unsaturated polyester resin composition.

9. The unsaturated polyester resin composition according to claim 7, wherein The combined weight of styrene, α-methylstyrene, vinyltoluene and / or methyl methacrylate is less than 2 wt.% of the total weight of the unsaturated polyester resin composition.

10. The unsaturated polyester resin composition according to claim 7, wherein The combined weight of styrene, α-methylstyrene, vinyltoluene and / or methyl methacrylate is less than 1 wt.% of the total weight of the unsaturated polyester resin composition.

11. The unsaturated polyester resin composition according to any one of claims 1 to 6, wherein The weight of the (meth)acrylate compound is at least 5 wt.% to at most 95 wt.% of the total weight of the unsaturated polyester resin composition.

12. The unsaturated polyester resin composition according to claim 11, wherein The weight of the (meth)acrylate compound is 10 wt. % to 70 wt. % of the total weight of the unsaturated polyester resin composition.

13. The unsaturated polyester resin composition according to claim 11, wherein The weight of the (meth)acrylate compound is 20 wt.% to 60 wt.% of the total weight of the unsaturated polyester resin composition.

14. The unsaturated polyester resin composition according to claim 11, wherein The weight of the (meth)acrylate compound is 30 wt. % to 50 wt. % of the total weight of the unsaturated polyester resin composition.

15. The unsaturated polyester resin composition according to claim 11, wherein The weight of the (meth)acrylate compound is 40 wt.% of the total weight of the unsaturated polyester resin composition. 16 . The unsaturated polyester resin composition according to claim 1 , further comprising an itaconate compound.

17. The unsaturated polyester resin composition according to claim 16, further comprising a dialkyl itaconate.

18. The unsaturated polyester resin composition according to claim 16, further comprising dimethyl itaconate.

19. The unsaturated polyester resin composition according to claim 16, wherein The combined weight of the (meth)acrylate compound and the itaconate compound is at least 5 wt.% to at most 95 wt.% of the total weight of the unsaturated polyester resin composition.

20. The unsaturated polyester resin composition according to claim 16, wherein The combined weight of the (meth)acrylate compound and the itaconate compound is 10 wt.% to 70 wt.% of the total weight of the unsaturated polyester resin composition.

21. The unsaturated polyester resin composition according to claim 16, wherein The combined weight of the (meth)acrylate compound and the itaconate compound is 20 wt.% to 60 wt.% of the total weight of the unsaturated polyester resin composition.

22. The unsaturated polyester resin composition according to claim 16, wherein The combined weight of the (meth)acrylate compound and the itaconate compound is 30 wt.% to 50 wt.% of the total weight of the unsaturated polyester resin composition.

23. The unsaturated polyester resin composition according to claim 16, wherein The combined weight of the (meth)acrylate compound and the itaconate compound is 40 wt.% of the total weight of the unsaturated polyester resin composition.

24. The unsaturated polyester resin composition according to any one of claims 1 to 6, wherein The added weight of dicyclopentadiene is at least 10 wt. % based on the total weight of the polyester.

25. The unsaturated polyester resin composition according to any one of claims 1 to 6, further comprising a transition metal salt or a transition metal complex.

26. The unsaturated polyester resin composition according to any one of claims 1 to 6, further comprising a cobalt salt or a cobalt polymer.

27. Use of the unsaturated polyester resin composition according to any one of claims 1 to 9 as a building material for structural parts.

28. Use of the unsaturated polyester resin composition according to any one of claims 1 to 9 as a coating formulation.

29. Use of the unsaturated polyester resin composition according to any one of claims 1 to 9 as a gel coating formulation.

30. Use according to any one of claims 27 to 29 in an open mould.

31. A method for preparing an unsaturated polyester resin composition according to any one of claims 1 to 9, the method comprising the following steps: - A polyester formed from at least: - Reagent a) comprising itaconic acid and / or itaconic anhydride; - reagent b) comprising maleic acid, maleic anhydride and / or fumaric acid; - a reagent c) comprising dicyclopentadiene; and, - reagent d) comprising at least one difunctional alcohol or polyfunctional alcohol; - mixing the obtained polyester with a (meth)acrylate compound to obtain the unsaturated polyester resin composition; Wherein, the combined weight of the reagent a) is at least 20 wt.% of the total weight of the diacid and anhydride used in the unsaturated polyester resin composition.

32. The process according to claim 31, comprising the step of forming a reaction mixture from reagent b), reagent c) and optionally reagent a) prior to forming the polyester.

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