The present invention relates to an unsaturated polyester resin composition comprising an unsaturated polyester (a), a reactive diluent (b) and a transition metal compound (c).

The present invention further also relates to objects and structural parts prepared from such unsaturated polyester resin compositions by curing with a peroxide. The present invention finally also relates to methods of peroxide curing of unsaturated polyester resin compositions.

As meant herein, objects and structural parts are considered to have a thickness of at least 0,5 mm and appropriate mechanical properties. The term "objects and structural parts" as meant herein also includes cured resin compositions as are used in the field of chemical anchoring, construction, roofing, flooring, windmill blades, containers, tanks, pipes, automotive parts, boats, etc.

Unsaturated polyester resin compositions, especially those comprising styrene as reactive diluent, are well known in the art. For example, in [R. A. T. M. van Benthem, L. J. Evers, J. Mattheij, A. Hofland, L. J. Molhoek, A. J. de Koning, J. F. G. A. Jansen and M. van Duin, "Handbook of Polymer Reaction Engineering", eds. T. Meyer, J. Keurentjes, chapter 16, pages 869-871] unsaturated polyesters in styrene are described and more particularly, it is stated that in general the ethylenically unsaturated carbons in unsaturated polyesters are based on maleic or fumaric building blocks. Moreover in general these compositions are pre-accelerated with a transition metal compound like a cobalt salt and can be efficiently cured with a peroxide. In this handbook styrene is used as the reactive diluent.

Although styrene is a very effective reactive diluent, i.e. has a high copolymerization ability and a good cutting power, it has also several drawbacks. For instance styrene has an undesirable odour. More importantly styrene is considered to be a potentially carcinogenic substance (see for instance Chemical & Engineering News, vol. 89, no. 25, page 1 1 , eds. W.G. Schulz, S.L. Cai, http://www.cen-online.org) which is even more hindering since styrene is volatile.

Styrene-free unsaturated polyester resin compositions are known. For instance W097/44399 describes a powder coating composition in which the unsaturated polyester could be based on maleic, fumaric, itaconic, citraconic or mesaconic acid building blocks, although only examples using fumaric building blocks are given. Although these compositions are styrene free, they are employed as powder coatings, i.e. they are solids and consequently not suitable for construction purposes. This is exemplified by the fact that for many construction applications the cured objects are obtained by processes such as vacuum infusion, SMC/BMC, vacuum-assisted resin transfer moulding in which processes solids cannot be used but liquid resin compositions are required.

Consequently, there is still a need for unsaturated polyester resin compositions suitable for construction purposes in which styrene can be partially or completely replaced with another reactive diluent while such new resin composition still has a low viscosity (similar or lower compared to the styrene equivalent), and the reactive diluent has a low odour, is less volatile than styrene (i.e. it should have a higher boiling point) and has a good reactivity (similar or faster compared to styrene) with unsaturated polyester.

Therefore, the object of the present invention is to provide a reactive diluent for unsaturated polyester resins with less odour and being less volatile than styrene, with a sufficient copolymerization ability (reactivity) with the unsaturated polyester resin and with a good cutting power in unsaturated polyester resin compositions and which can result in good curing efficiency (as demonstrated by short gel time, short peak time and/or high peak temperature).

This object has surprisingly been achieved in that the composition comprises an unsaturated polyester (a1) comprising building blocks according to formula (

and, as monomer copolymerizable with said unsaturated polyester (a1), a monomer (b1) according to formula (2)

whereby n= 0-3; and R ₂ each individually represent H, C C ₂ o alkyl, C ₃ -C ₂₀ cycloalkyl, C ₆ -C ₂ o aryl, C ₇ -C ₂ o alkylaryl or C ₇ -C ₂₀ arylalkyl; X = O, S or NR ₃ whereby R ₃ = H, C C ₂ o alkyl, C ₃ -C ₂₀ cycloalkyl, C ₆ -C ₂₀ aryl, C ₇ -C ₂₀ alkylaryl, C ₇ -C ₂₀ arylalkyl, part of a polymer chain or attached to a polymer chain,

and at least one transition metal compound (c) selected from the group consisting of cobalt, copper, manganese, iron salts and complexes.

It has surprisingly been found that when the resin composition comprises an unsaturated polyester resin comprising building blocks according to formula (1), styrene can be partially or even completely replaced with a compound according to formula (2) while the reactivity of the compound according to formula (2) with the unsaturated polyester resin comprising building blocks according to formula (1) remains on the same level or may even be improved. It also has been surprisingly found that the monomer (b1) has a similar cutting power compared to styrene in compositions comprising unsaturated polyester resins comprising building blocks according to formula (1) thereby enabeling the formulation of very low viscous resins which are very suitable for all kinds of applications in which vacuum infusion is used. It has furthermore surprisingly been found that the resin compositions according to the invention can be efficiently cured with a peroxide. An additional advantage of a resin composition according to the invention is that, when performing the curing in air, the cure is similar to the cure with styrene and may outperform alternatives like

methacrylates. Furthermore an additional advantage of using compounds according to formula (2) is that they can be prepared from biobased raw materials.

Compounds according to formula (2) can be obtained commercially from for example TCI Europe and can be prepared with the method as described for example by Gary M. Ksander, John E. McMurry, and Mark Johnson, "A Method for the Synthesis of Unsaturated Carbonyl Compounds" in J. Org. Chem. 1977, vol. 42, issue 7, pages 1 180-1 185, or by Mitsuru Ueda and Masami Takahasi, "Radical-Initiated Homo- and Copolymerization of a-Methylene-y-Butyrolactone" in J. Pol. Sci. A 1982, vol. 20, p. 2819-2828.

Preferably, n is 1 or 2. More preferably, n is 1. X is preferably O.

Preferably, Ri and R ₂ each individually represent H or CH ₃ . More preferably, Ri and R ₂ are both H or Ri is H and R ₂ is CH ₃ . In a preferred embodiment of the invention, the composition comprises a compound (b1) according to formula (3)

whereby is H or CH ₃ .

The amount of compound (b1) relative to the total amount of unsaturated polyester (compounds (a)) and monomer copolymerizable with (a) (compounds (b)) is preferably at least 1 wt.%, more preferably at least 5 wt.%, even more preferably at least 10 wt.% and even more preferably at least 25 wt.%. The amount of compound (b1) relative to the total amount of compounds (a) and (b) is preferably at most 99 wt.%, more preferably at most 95 wt.%, more preferably at most 90 wt.%, even more preferably at most 70 wt.% and even more preferably at most 65 wt.%. Preferably, the amount of compound (b1) relative to the total amount of compounds (a) and (b) is from 1 to 95 wt.%, and more preferably from 25 to 65 wt.%.

The composition optionally may further comprise another (than compound with formula (2)) ethylenically unsaturated compound (b2) with a number- average molecular weight M _n of at most 300 g/mol. Non-limiting examples are hydroxyethylmethacrylate, hydroxypropylmethacrylate, methyl methacrylate, ethyl methacrylate and laurylmethacrylate or mixtures thereof.

Besides these monomers also solvents may be present in the resin composition. In general the composition comprises less than 5% water as solvent.

An unsaturated polyester is an unsaturated polyester comprising unsaturated diacid building blocks and diol building blocks, and is prepared by the polycondensation of at least one diacid and at least one diol and in which a least a part of the diacids is an unsaturated diacid. According to the invention, at least a part of the unsaturated diacid building blocks are building blocks according to formula (1)

ΛΛΛΛΛΛΛ/ (1) Besides the unsaturated diacid building block according to formula (1) also other unsaturated diacid building blocks may be present such as for instance fumaric, maleic, citraconic and mesaconic building blocks. Besides the unsaturated diacid building blocks also saturated diacid building blocks may be present such as for example succinic, adipic, ortho-phthalic, iso-phthalic, tere-phthalic, cyclohexane dicarboxylic building blocks. In the resin composition according to the invention, the molar amount of building blocks according to formula (1) relative to the total molar amount of diacid building blocks is preferably from 10% to 100% , more preferably from 30% to 95% and even more preferably from 50% to 90%. In the resin composition according to the invention, the molar amount of building blocks according to formula (1) relative to the total molar amount of α,β-unsaturated diacid building blocks is preferably from 40% to 90%. The diol building block can be any type of diol building block. Non limiting examples are for instance ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, ethoxylated bisphenol A, neopentyl glycol, 1 ,3-propane diol, 1 ,4- butane diol, polymeric diols like poly-THF, polyethylene glycol. For controlling the molecular weight it is also possible that mono-ols and mono acids are employed in the synthesis of unsaturated polyesters comprising building blocks according to formula (1). Similarly when branching is required it is also possible that triols or even tetrols and triacids or tetracids are employed in the synthesis of unsaturated polyesters comprising building blocks according to formula (1).

The total amount of unsaturated polyester (compound (a)) relative to the total amount of unsaturated polyester (compounds (a)) and monomer

copolymerizable with (a) (compounds (b)) is preferably from 20 to 80 wt.%, more preferably from 25 to 75 wt.%, even more preferably from 30 to 70 wt.% and most preferably from 35 to 65 wt.%.

The acid value of the unsaturated polyester comprising building blocks according to formula (1) can vary widely and is in general between 20 and 160 mg KOH/g primary resin. Preferably the unsaturated polyester comprising building blocks according to formula (1) has an acid value in the range of from 40 to 150 mg KOH/g of resin, more preferably in the range of from 45 to 100 mg KOH/g of resin. As used herein, the acid value of the resin is determined titrimetrically according to ISO 21 14-2000.

Preferably the number-average molecular weight M _n of the unsaturated polyester comprising building blocks according to formula 1 is in the range of from 500 to 10000 g/mol, preferably from 700 to 5000 g/mol and more preferably from 900 to 3000 g/mol. As used herein, the number-average molecular weight M _n of the unsaturated polyester is determined using gel permeation chromatography according to ISO 13885-1 using polystyrene standards.

For clarity purposes the term primary resin is introduced. With primary resin or primary resin system is meant the mixture of unsaturated polyester comprising building blocks according to formula (1) (a1), the monomers (b1) according to formula (2) and, in case present, other unsaturated polyester resins and vinyl ester resins (a2) and other ethylenically unsaturated compounds (b2) with a number-average molecular weight M _n of at most 300 g/mol.

The resin composition according to the invention comprises a transition metal compound (c), dissolved in the mixture of unsaturated polyesters (a) and monomers (b) copolymerizable with the unsaturated polyesters, and selected from the group consisting of cobalt salts, cobalt complexes, copper salts, copper complexes, manganese salts, manganese complexes, iron salts, iron complexes and any mixtures thereof. Preferably, the resin composition comprises a transition metal compound (c) selected from the group consisting of cobalt carboxylate, copper carboxylate, iron carboxylate, manganese carboxylate, cobalt acetylacetonate, copper acetylacetonate, iron acetylacetonate, manganese acetylacetonate, iron halide and any mixtures thereof. A preferred iron halide is iron chloride. More preferably the transition metal compound (c) is a cobalt carboxylate, a copper carboxylate, an iron carboxylate, a manganese carboxylate, a cobalt acetylacetonate, a copper acetylacetonate, an iron acetylacetonate, a manganese acetylacetonate, or an iron halide or any mixture thereof. More preferably, in view of curing efficiency, the resin composition comprises a transition metal compound (c) selected from the group consisting of Co, Cu, Mn salts and complexes and any mixture thereof.The carboxylate is preferably a C C ₃₀ carboxylate and more preferably a Ci-Ci ₆ carboxylate.

The Co salt is preferably a Co ²⁺ and/or a Co ³⁺ salt. The Co complex is preferably a Co ²⁺ and/or a Co ³⁺ complex. The Cu salt is preferably a Cu ⁺ and/or a Cu ²⁺ salt. The Cu complex is preferably a Cu ⁺ and/or a Cu ²⁺ complex. The Mn salt is preferably a Mn ²⁺ and/or a Mn ³⁺ salt. The Mn complex is preferably a Mn ²⁺ and/or a Mn ³⁺ complex. The Fe salt is preferably a Fe ²⁺ and/or a Fe ³⁺ salt. The Fe complex is preferably a Fe ²⁺ and/or a Fe ³⁺ complex.

The total amount of Co, Cu, Mn and Fe compounds in the resin composition according to the invention is preferably such that the total amount of Co, Cu, Mn and Fe in mmol per kg of primary resin is preferably from 0.001 to 30, more preferably from 0.01 to 30 and even more preferably from 0.1 to 20.

The resin composition may comprise a co-accelerator. Depending on the transition metal choice, the person skilled in the art will be able to choose an appropriate co-accelerator to obtain the desired curing characteristics. For example, in case a Co compound is used as transition metal compound, the co-accelerator is preferably an amine and/or a 1 ,3-dioxo compound. In case a Cu compound is used as transition metal compound, the co-accelerator is preferably an amine, acetoacetamide, a K salt, an imidazole and/or a gallate or mixtures thereof. In case a Mn compound is used as transition metal compound, the co-accelerator is preferably a 1 ,3-dioxo compound, a thiol and/or a K or Li salt or mixtures thereof. In case a Fe compound is used as transition metal compound, the co-accelerator is preferably a 1 ,3-dioxo compound and/or a thiol preferably in combination with an alkali metal salt. Non-limiting examples of 1 ,3-dioxo compounds are acetyl acetone, acetoacetates and

acetoacetamides.The amount of co accelerator can vary within wide ranges and is preferably more than 0.01 wt.% and less than 10 wt.% preferably more than 0.1 wt.% and less than 5 wt.% (relative to primary resin).

In one embodiment of the invention, the resin composition comprises a Co compound as transition metal compound and optionally a co-accelerator. The co- accelerator is preferably an amine and/or a 1 ,3-dioxo compound. In another embodiment of the invention, the resin composition comprises a Cu compound as transition metal compound and the resin composition preferably further comprises a co- accelerator preferably selected from an amine, an acetoacetamide, a K salt, an imidazole and/or a gallate or mixtures thereof. In still another embodiment of the invention, the resin composition comprises a Mn compound as transition metal compound and the resin composition preferably further comprises a co-accelerator preferably selected from a 1 ,3-dioxo compound, a thiol and/or a K or Li salt or mixtures thereof. In still another embodiment of the invention, the resin composition comprises a Fe compound as transition metal compound and the resin composition preferably further comprises a co-accelerator, the co-accelerator is preferably a 1 ,3-dioxo compound and/or a thiol preferably in combination with an alkali metal salt.

The resin composition preferably further comprises a radical inhibitor. These radical inhibitors are preferably chosen from the group of phenolic compounds, benzoquinones, hydroquinones, catechols, stable radicals and/or phenothiazines. The amount of radical inhibitor that can be added may vary within rather wide ranges, and may be chosen as a first indication of the gel time as is desired to be achieved.

Suitable examples of radical inhibitors that can be used in the resin compositions according to the invention are, for instance, 2-methoxyphenol,

4-methoxyphenol, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butylphenol,

2,4,6-trimethyl-phenol, 2,4,6-tris-dimethylaminomethyl phenol,

4,4'-thio-bis(3-methyl-6-t-butylphenol), 4,4'-isopropylidene diphenol,

2,4-di-t-butylphenol, 6,6'-di-t-butyl-2,2'-methylene di-p-cresol, hydroquinone,

2-methylhydroquinone, 2-t-butylhydroquinone, 2,5-di-t-butylhydroquinone,

2,6-di-t-butylhydroquinone, 2,6-dimethylhydroquinone , 2,3,5-trimethylhydroquinone, catechol, 4-t-butylcatechol, 4,6-di-t-butylcatechol, benzoquinone,

2,3,5,6-tetrachloro-1 ,4-benzoquinone, methylbenzoquinone,

2,6-dimethylbenzoquinone, napthoquinone, 1 -oxyl-2,2,6,6-tetramethylpiperidine, 1-oxyl-2,2,6,6-tetramethylpiperidine-4-ol (a compound also referred to as TEMPOL), 1-oxyl-2,2,6,6-tetramethylpiperidine-4-one (a compound also referred to as TEMPON), 1-oxyl-2,2,6,6-tetramethyl-4-carboxyl-piperidine (a compound also referred to as 4-carboxy-TEMPO), 1-oxyl-2,2,5,5-tetramethylpyrrolidine,

1-oxyl-2,2,5,5-tetramethyl-3-carboxylpyrrolidine (also called 3-carboxy-PROXYL), galvinoxyl, aluminium-N-nitrosophenyl hydroxylamine, diethylhydroxylamine, phenothiazine and/or derivatives or combinations of any of these compounds.

Advantageously, the amount of radical inhibitor in the resin composition according to the invention (relative to the total amount of resin composition) is in the range of from 0.0001 to 10 % by weight. More preferably, the amount of inhibitor in the resin composition is in the range of from 0.001 to 1 % by weight. The skilled man quite easily can assess, in dependence of the type of inhibitor selected, which amount thereof leads to good results according to the invention.

The unsaturated polyester resin composition according to the invention may further comprise (in)organic filler. The amount of organic and inorganic filler relative to the amount of primary resin can vary within wide ranges and is preferably from 10 to 90 wt.%. Preferably, the composition comprises fibre as inorganic filler.

The unsaturated polyester resin composition according to the invention may further comprise a low profile additive for those applications in which the surface quality is important like for instance SMC and BMC type applications. The amount of low profile additive relative to the primary resin can vary within wide ranges and it is preferably from 20 to 70 wt.%.

The present invention further relates to a process for radically curing a resin composition according to the invention whereby the curing is effected in the presence of a radical initiating system. Preferably, the radical initiating system uses peroxides. More preferably, peroxides are selected from the group consisting of hydroperoxides, perketals, peresters, percarbonates and mixtures thereof. The amount of peroxide relative to the primary resin is preferably from 0.01 to 30 wt.%, more preferably from 0.05-20 wt.% and even more preferably from 0.1-15 wt.%.

Preferably the peroxide is added to the primary resin optionally comprising additives fillers inhibitors etc. Preferably the process for radically curing the resin composition as described above comprises adding the peroxide to a composition comprising at least compounds (a) and (b) and the transition metal compound (c).

The curing is effected preferably at a temperature in the range of from -20 to +150 °C, more preferably in the range of from -20 to +100 °C and even more preferably in the range of from -20 to + 40 °C.

The present invention further relates to a multicomponent system comprising an unsaturated polyester (a1) comprising building blocks according to formula (1) νΛΛΛΛΛΛ V

and, as monomer copolymerizable with said unsaturated polyester (a1), a monomer (b1) according to formula (2)

whereby n= 0-3; and R ₂ each individually represent H, C C ₂ o alkyl, C ₃ -C ₂₀ cycloalkyl, C ₆ -C ₂ o aryl, C ₇ -C ₂₀ alkylaryl or C ₇ -C ₂₀ arylalkyl; X = O, S or NR ₃ whereby R ₃ = H, C C ₂ o alkyl, C ₃ -C ₂₀ cycloalkyl, C ₆ -C ₂ o aryl, C ₇ -C ₂₀ alkylaryl, C ₇ -C ₂₀ arylalkyl, part of a polymer chain or attached to a polymer chain;

at least one transition metal compound (c) selected from the group consisting of cobalt, copper, manganese, iron salts and complexes and

a peroxide (d) selected from the group consisting of hydroperoxides, perketals, peresters, percarbonates and mixtures thereof.

Preferred compounds (a), (b) and (c) as well as the amounts are as described above. The system may further comprise additional compounds in amounts as described above.

The use of the multicomponent system according to the invention requires mixing of at least the compounds (a), (b) and (c) together with the peroxide (d) selected from the group consisting of hydroperoxides, perketals, peresters, percarbonates and mixtures thereof to obtain a cured network. As used herein, multicomponent systems means a system with at least two spatially separated components whereby the peroxide is present in one component that does not comprise radical copolymerizable compounds including compounds (a) and (b) in order to prevent premature radical copolymerization of the compounds (a) and (b) prior to the use of the multicomponent system to obtain the cured network. At the moment that the radical copolymerization of the compounds (a) and (b) is desired, at least a peroxide as described above is added to this composition. Preferably, said adding is done by mixing the peroxide into the composition comprising compounds (a) and (b). The multicomponent system according to the invention comprises at least two components.

In one embodiment, the multicomponent system comprises at least three components I, II and III, whereby component I consists of a composition comprising compounds (a) and (b), component II consists of a composition comprising compound (c) and component III comprises the peroxide (d).

In another embodiment, the system comprises at least two components I and II, whereby component I consists of a composition comprising compounds (a), (b) and (c) and component II comprises the peroxide.

The present invention further relates to a two component system consisting of a first component I and a second component II, the first component I is a resin composition as defined above and the second component II comprises a peroxide selected from the group consisting of hydroperoxides, perketals, peresters, percarbonates and mixtures thereof. Very suitable examples of hydroperoxides are tert-butyl

hydroperoxide and cumene hydroperoxide. Preferred perketals are the addition products of hydrogen peroxide with a ketone. Very suitable examples of such perketals are methyl ethyl keton peroxide and acetylacetonperoxide. A very suitable example of perester is tert-butyl perbenzoate. A very suitable example of percarbonate is for instance tert-butyl peroxy ethylhexylcarbonate. The skilled man quite easily can assess, in dependence of the type of transition metal compound selected, which peroxide leads to good results according to the invention. The peroxide is preferably a hydroperoxide, a perester and/or a perketal as these peroxides have a higher thermal stability than percarbonates.

The present invention further relates to cured objects obtained by curing the resin composition according to the invention with a peroxide or obtained by the process according to the invention or obtained by mixing the compounds of the multicomponent system as described above.

The present invention further relates to the use of such a cured structural part in automotive, boats, chemical anchoring, roofing, construction, containers, relining, pipes, tanks, flooring or windmill blades.

The invention is now demonstrated by means of a series of examples and comparative examples. All examples are supportive of the scope of claims. The invention, however, is not restricted to the specific embodiments as shown in the examples.

Gel timer experiments

In some of the examples and comparative experiments presented hereinafter, it is mentioned that curing was monitored by means of standard gel time equipment. This is intended to mean that both the gel time (T _ge i or T25->35°c) and peak time (Tpea _k or T ₂ 5-> _P ea _k ) and peak temperature were determined by exotherm

measurements according to the method of DIN 16945 when curing the resin with the peroxides as indicated in the examples and comparative examples. The equipment used therefore was a Soform gel timer, with a Peakpro software package and National Instruments hardware; the waterbath and thermostat used were respectively Haake W26, and Haake DL30. Preparation of unsaturated polyester resin (1) with itaconate building blocks

An unsaturated polyester was prepared by polycondensation of 198.5 parts of itaconic acid, 450.1 parts of phthalic anhydride, 351.4 parts of 1 ,3-propanediol. The starting compounds were charged into a reactor equipped with condenser, stirrer, a temperature control system and an inlet for nitrogen. Under a gentle flow of nitrogen, the reaction mixture was heated up and maintained at a temperature of 170-200°C. The acid value dropped slowly and at the end of the process vacuum was applied to help stripping the water from the reaction mixture to reach the targeted acid value. An acid value of 45.5 was reached. At the end of the polycondensation, 26 ppm hydroquinone and 84 ppm methyl hydroquinone were added. Gel permeation chromatography showed that the resin had a number-average molecular weight M _n of 1055 g/mol and a polydispersity of 1.9 (column calibrated relative to polystyrene standards). Preparation of unsaturated polyester resin (2) with fumarate building blocks

An unsaturated polyester was prepared by polycondensation of 105 parts of maleic anhydride, 314 parts of phthalic anhydride, 244 parts of 1 ,2- propanediol. The starting compounds were charged into a reactor equipped with condenser, stirrer, a temperature control system and an inlet for nitrogen. Under a gentle flow of nitrogen, the reaction mixture was heated up and maintained at a temperature of 170-200°C. The acid value dropped slowly and at the end of the process vacuum was applied to help stripping the water from the reaction mixture to reach the targeted acid value. An acid value of 52 was reached. At the end of the polycondensation, 26 ppm hydroquinone and 84 ppm methyl hydroquinone were added. Gel permeation chromatography showed that the resin had a number-average molecular weight M _n of 1214 g/mol and a polydispersity of 2.02 (column calibrated relative to polystyrene standards).

Example 1 and comparative experiment A

To 24 g of each the unsaturated polyester (1) and (2), 16 g of MBL were added and mixed. Next, 200 mg of accelerator NL-49-P (a 1 % Co solution, Akzo Nobel) and 400 mg of Butanox M50 were added and the curing was monitored in a standard gel timer equipment. Furthermore, 12 g of the mixture were poured into an aluminum dish for the determination of Barcol hardness of a 4 mm casting before and after postcure over night at 80°C. Table 1

Although in both Example 1 and Comp A, an exotherm and a curing process was observed, only the small casting of Example 1 achieved a good hardness of the surface (Barcol). The casting of Comparative Experiment A gave a very brittle material of which no hardness could be determined.

Both, example 1 and Comp A were analyzed by IR. In Comp A, no crosslinking, i.e. copolymerization of fumarate unsaturations and MBL could be found, but the analysis indicated the homopolymerization of MBL. In Example 1 , a copolymerization of itaconate unsaturations and MBL leading to formation of a crosslinked network was observed. As a result, a non-brittle casting with good surface hardness was formed exclusively with the unsaturated polyester composition according to the invention. Example 2 and comparative experiments B1-B5

To 24 g of the itaconic acid containing unsaturated polyester (1) and

16 g of various monomers was added 200 mg NL-49-P (a 1 % Co solution, Akzo

Nobel). Of these mixtures the viscosity was determined (Brookfield CAP 1000, 25°C,

750 rpm, cone 4 and 6). To these mixtures 400 mg Butanox M50 (a perketal, Akzo Nobel) was added. 12 g of the mixture was poured into an aluminum dish for the determination of Barcol hardness of a 4 mm casting after postcure over night at 80°C.

Furthermore of 25 g the curing was monitored in the standard gel timer equipment.

Barcol hardness was measured according to ASTM D 2583. The results are shown in table 2. Table 2

MBL=a-methylene butyrolactone

Sty=styrene

BMA= butylmethacrylate

LMA= lauryl methacrylate

HPMA= 2-hydroxypropyl methacrylate

MMA= methyl methacrylate

This example and the comparative experiments clearly show that the reactive diluents according to formula (2) are well suited to be used in itaconate polyesters. Example 2 exhibits a very good cutting power (indicated by the low viscosity) similar to styrene (Comp B1). Furthermore, the reactive diluent MBL has a low volatility (indicated by the high boiling point). In contrast to all other alternative reactive diluents (Comp B2 to B5), the curing in example 2 is very efficient, it is even much more efficient as compared to styrene (indicated by the higher peak temperature and the shorter gel time and peak time). It exhibits a surprisingly good through curing (indicated by Barcol hardness at the bottom of the cup) and furthermore a good curing in air (indicated by hardness at the top of the casting) was obtained.

Example 3-5 and comparative experiments C1-C4

100 g of the itaconic acid containing unsaturated polyester (1) were diluted in 66.67 g of MBL to give a resin. To 30 g of this resin was added 150 mg of various metal solutions (see table 3) and optionally further additives as co-accelerators (obtained from Aldrich). Next to these mixtures 300 mg peroxide (see table 3) was added. The curing of 25 g of this mixture was monitored in the standard gel timer equipment. The results are shown in table 3. Table 3

These examples combined with the comparative experiments demonstrate that curing can be effected by using the transition metal compounds claimed. ln example 4 and 5, co- accelerators were added to the formulation. However, when adding these additives in comparative experiments C1 to C4 in which a Zr, Zn, Ca or K is present, no cure is observed.