HK1168119B - Method for producing carbodiimides - Google Patents

Description

The present invention relates to a process for the production of carbodiimides.

The present invention also relates to carbodiimides with a high molecular weight and/or low polydispersity and the use of carbodiimides of the invention, inter alia, as stabilizers against the hydrolytic degradation of ester group-containing compounds and as net-workers and chain extenders in plastics.

Organic carbodiimides are known and are used, for example, as a stabilizer against the hydrolytic degradation of ester-containing compounds, e.g. from polyaddition and polycondensation products, such as polyurethanes. Carbodiimides can be produced by commonly known processes, e.g. by the action of catalysts on mono- or polyisocyanates under carbon dioxide decomposition.

Such carbodiimides, their manufacture and use as stabilizers against the hydrolytic cleavage of polyester-based plastics are described e.g. in US-A 5597942, US-A 5733959 and US-A 5 210 170.

DE 10 2004 041 605 A1 describes a structurally specific carbodiimide and the method of its production. In the concrete examples, the production is done without solvent, i.e. in substance. The carbodiimide production is carried out in the presence of catalysts (in particular in the presence of methyl-2,5-dihydrophospholene-1-oxides and/or 1-methyl-2,3-dihydrophospholene-1-oxides). The catalysts can then be removed from the polycarbodiimide by distillation. The resulting (still containing isocyanate groups) polycarbodiimides are then converted to further acrylate (final functionalisation).

US-A 6 498 225 concerns block copolymers which include, inter alia, a carbodiamide building block. The carbodiamides are produced in the presence of basic catalysts at elevated temperatures by decomposition of carbon dioxide.

EP 0 965 582 A reveals specific carbodiimides based on 1,3-bis- ((1-methyl-1-isocyanate-ethyl) benzole containing 12 to 40% by weight of ethylene oxide units.

EP 0 940 389 A describes structurally specific carbodiimides which contain urethane groups and/or urea groups in addition to the carbodiimide function, where the carbodiimide structures are bound to non-aromatic hydrocarbon atoms. It also describes a method for the production of these carbodiimides and mixtures containing these carbodiimides. The production of the carbodiimides takes place in the absence or presence of organic solvents. In the examples, the synthesis is solvent-free, i.e. in substance.

EP 1 125 956 A concerns structurally specific carbodiimides which furthermore contain urea groups and/or sulphonic acid groups and/or sulfonate groups. These carbodiimides are produced by transformation of 1,3-bis- ((1-methyl-1-isocyanatoethyl) benzole with at least one amino sulfonic acid and/or at least one amino sulfonate in the presence of conventional catalysts, preferably in solvents. Once the desired content of NCO groups has been reached, polycarbodiimide formation is interrupted and the catalysts are deactivated or deactivated. In the examples, polycarbodiimide is used as an eductid, which is obtained according to US 5A 597 942; a detailed representation of the carbodiimide is not provided in the examples.

EP 0 792 897 A reveals specific aromatic polycarbodiimides and their production in the conventional way by means of phosphorus-containing catalysts. The production is done in a solvent. An isocyanate can be added to cap the end of the carbodiimide at the beginning, middle or end of the reaction to produce the carbodiimide. At the end of the reaction, the reaction mixture is put into a solvent in which the carbodiimide is insoluble so that it can be separated and separated from the monomer and the catalyst.

US 5,750,636 describes the production of polycarbodiimides in a solvent using conventional catalysts.

EP 0 686 626 A concerns special hydrophilic carbodiimides.

EP 0 628 541 A describes structurally specific carbodiimides or oligocarbodiimides with terminal isocyanate, urea and/or urethane groups. The production of carbodiimides can be carried out in the presence or absence of solvents.

The state of the art thus provides a basis for the production of carbodiimides, which can be carried out either in the substance or in the presence of solvents.

The carbodiimides obtained by these condensation processes in solution or substance have the disadvantage of relatively low molecular weights.

The state of the art carbodiimides also have a polydispersity that is too high.

The present invention is therefore intended to provide a method for the production of carbodiimides which produces carbodiimides which preferably have higher molecular weights than the carbodiimides obtained by the conventional methods.

The present invention is also intended to provide a method for the production of carbodiimides which produces carbodiimides which preferably have lower polydispersities than the carbodiimides obtained by the conventional methods.

The present invention is also intended to provide a method for the production of carbodiimides which would obtain carbodiimides which preferably have higher molecular weights than the carbodiimides obtained by the conventional methods and which would obtain carbodiimides which preferably have lower polydispersities than the carbodiimides obtained by the conventional methods.

The present invention is also intended to provide a method for the production of carbodiimides which would preferably allow the carbodiimides to have low residues of isocyanate, in particular, the residual content of isocyanate in the carbodiimide should be less than 1.5% by weight relative to the carbodiimide.

Finally, the method of the invention is expected to have an overall response time comparable to conventional methods at a comparable turnover of about 95%.

This problem is solved by preservation according to the invention for the production of compounds containing at least one carbodiamide group.

The process of the invention is characterised by the implementation of at least one isocyanate-containing parent compound or derivative thereof, the process of the invention being carried out in at least two steps.

In particular, the method of the invention uses at least one isocyanate-containing parent compound in the presence of a catalyst in a two-step process. (1) in step (1) first subjected to a first polymerisation into substance, resulting in a first polymerisation product; and (2) in step (2) the first polymerisation product from step (1) subjected to a second polymerisation in solution.

The second step of the process preferably does not add any additional catalyst.

In the second step of the process, the solvent is preferably added without previous cooling.

According to the invention, it has been shown that a combination process for the production of carbodiimides, which includes both polymerization in substance (process step 1) and polymerization in solution (process step 2) solves the tasks defined above. In particular, the carbodiimides obtained by the process according to the invention have higher molecular masses and lower polydispersity compared to the carbodiimides obtained either by a process in substance only or by a process in solution only.

In addition, the method of the invention can be used to obtain carbodiimides with a residual isocyanate content of preferably less than 2,00 weight by weight, preferably less than 1,5% by weight, and in particular preferably less than 1,00 weight by weight, and specially less than 0,75% by weight.

The total reaction time to be used for the method of the invention is within the range of conventional methods known from the state of the art.

For the purposes of the present invention, a conventional process for the production of carbodiimide is a process in which an isocyanate-containing compound is converted to a carbodiimide in the presence of a catalyst and by decomposition of carbon dioxide, and the process is carried out exclusively in either substance or exclusively in solution.

The following describes, without limiting the present invention, particular features of the process according to the invention: The solvent to be added to perform polymerization in solution (i.e. step 2) is generally added at an isocyanate turnover of 40 to 60%, preferably 45 to 55%, in particular at about 50%. The process according to the invention is carried out in the second step of the process up to an NCO content of the compounds containing at least one carbodiimide group, preferably not more than 2,00%, preferably not more than 1,5%, preferably not more than 1,00%, and in particular not more than 0,75%.

In particular, the isocyanate-containing compound is selected from the group consisting of cyclohexylisocyanate, isophorondiisocyanate (IPDI), hexamethylenediisocyanate (HDI), 2-methylpentadiisocyanate (MPDI), methylbis-methyl (MDIPI); 2,2,4-trimethylhexamethylenediisocyanate/2,4,4-trimethylhexamethylenediisocyanate (DITM), norboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriboriborib

For the purpose of the present invention, the isocyanate-containing compound is specifically selected from the group consisting of isophorondiisocyanate (IPDI), tetramethylxylylendiisocyanate (TMXDI), dicyclohexylmethyldiisocyanate (H12MDI) and 1,3,5-triisopropyl-2,4-diisocyanate benzene (TRIDI).

For the purposes of the present invention, the isocyanate-containing compound is further preferred 1,3,5-triisopropyl-2,4-diisocyanate benzene (TRIDI).

Furthermore, it is possible for the present invention to use a derivative of the parent compound containing isocyanate, in particular, derivatives selected from the group consisting of isocyanurates, urediones, allophanates and/or biuret.

The condensation reaction of the compound containing at least one isocyanate generally requires a catalyst.

In a first design of the process of the invention, the catalyst is at least one catalyst containing phosphorus; furthermore, the catalyst may be selected from the group consisting of phospholes, phosphoenoxides, phospholidines and phosphoenoxides; the catalyst used for the implementation of the parent compound containing at least one isocyanate is further preferentially selected from the group consisting of methyl-2,5-dihydrophospholene-1-oxide (CAS [930-38-1]), 1-methyl-2,3-dihydrophospholene-1-oxide (CAS [7-72-8-45]) and mixtures thereof (CAS [15-63-86]).

In a second design of the process of the invention, the catalyst is a base, preferably selected from the group consisting of alkali hydroxides, e.g. KOH or NaOH; alcohols, e.g. potassium tertiary butylate, potassium methylate and sodium methylate.

In the present invention, the catalyst content in the first design is preferably 0.001 to 1.00 weight percent, preferably 0.001 to 0.50 weight percent, and preferably 0.001 to 0.02 weight percent, each with respect to at least one isocyanate-containing compound.

In the present invention, the second design has a catalyst content of preferably 0.01 to 2.00 weight percent, preferably 0.05 to 1.00 weight percent, and preferably 0.1 to 0.50 weight percent, each with respect to at least one isocyanate-containing compound.

In the process step (2) of the process of the invention, i.e. during polymerisation in solution, a solvent is used, preferably selected from the group consisting of benzene; alkylbenzols, in particular and preferably toluene, o-xylol, m-xylol, p-xylol, diisoproypbenzols and/or triisopropylbenzols; acetone; isobutylmethylketone; tetrahydrofuran; hexane; benzene; dioxane; N-methylpyrrolidone; dimethylformamide and/or dimethylacetamide.

In general, in step (2) solvents are added in the range of 0.5 to 80% by weight, preferably 1 to 50% by weight, and in particular 2 to 20% by weight, in relation to the amount of monomer used in step (1).

The reaction rate can be adjusted in the usual way by selecting the reaction conditions, e.g. reaction temperature, catalyst type and quantity and reaction time. The most simple way of tracking the reaction is to determine the NCO content. Other parameters, e.g. viscosity increase, colour depth or CO2 development, can also be used to track and control the reaction.

As regards the temperatures at which the carbodiamide formation is carried out, it is preferable that step (1) be carried out at a temperature between 50 and 220 °C, further between 100 and 200 °C, and particularly between 140 and 190 °C.

The corresponding temperature at which the carbodiid formation takes place can be reached by means of a temperature ramp. The term temperature ramp is understood in the present invention to mean that the temperature at which the carbodiid formation takes place is reached not immediately but by slow heating.

The temperature ramp may be, for example, 1 to 10 °C/30 minutes.

The test procedure (2) is carried out at a temperature preferably between 50 and 220 °C, further preferably between 100 and 200 °C, and particularly preferably between 140 and 190 °C.

In a further embodiment of the present invention, the implementation of the compound containing at least one isocyanate is performed in the presence of a protective gas atmosphere, whereby either only the first step of the implementation into substance or the second step of the implementation into solution can be performed in the presence of a protective gas atmosphere.

In a preferred embodiment, however, both steps are performed in the presence of a protective gas, preferably argon, nitrogen or any mixture of these gases.

When the reaction mixture has the desired content of NCO groups, the formation of polycarbodiamide is usually stopped. To this end, the catalysts can be distilled at reduced pressure or deactivated by the addition of a deactivator, such as phosphorus trichloride, in the case of phosphorus-containing catalysts.

In a further development of the present invention, the method according to the invention thus comprises, after the process step (2), a process step (3), in which at least one catalyst distillate is removed from the carbodiamide compound and/or at least one catalyst is deactivated by the addition of a deactivator, such as phosphorus trichloride.

If necessary, the reaction mixture shall also be treated as follows (procedure 3.3), with the possibility of separation or deactivation of the catalyst as described in steps 3.1 and/or 3.2 above before treatment.

For this purpose, additional solvent may be added to the reaction mixture obtained from step (2) depending on the amount of solvent already added in step (2) or, alternatively, if sufficient solvent has already been added in step (2), no further solvent may be added.

If a solvent is added to the treatment after step 2, it may be the same solvent used in the solvent polymerisation in step 2 and described above.

The carbodiamide is then removed preferably by the addition of a polar solvent such as acetone, ethyl acetate, ethanol or methanol.

This treatment (variant 3.3) is particularly preferable.

A further processing is to directly remove the solvent from the polymerisation product from step (2) and to prepare the resulting residue as the final product.

The preferred carbodiimides of the invention are those with a content of catalysts for the formation of carbodiimides of less than 25 ppm in the final product, i.e. after processing.

The molecular weight of the carbodiimides obtained in accordance with the invention is higher than the molecular weight of corresponding carbodiimides obtained by pure substance polymerisation or pure polymerisation in solution, as illustrated by the examples described below.

The physical, mechanical and rheological properties of carbodiimides are determined by polymorphism (the ratio of weight to number). This ratio is also known as polydisperity D and is a measure of the width of a molten mass distribution. The greater the polydisperity, the wider the molten mass distribution. The molecular weights were determined preferably by gel permeation chromatography in tetrahydrofuran at 40 °C against polystyrene as standard.

The carbodiimides produced by the method of the invention are characterised by a polydispersity of less than 2,5, preferably less than 2,25, especially preferably less than 2,00, especially between 1,6 and 1,8.

The carbodiimides obtained by the method of the invention have a molecular weight Mw of 20000 to 40000 g/mol, preferably 25000 to 35000 g/mol, and preferably 26000 to 34000 g/mol. The carbodiimides obtained by the method of the invention can also be finalized. The corresponding finalizations are described in the EC 10 2004 041 605 A1, whose disclosure is included by reference in the present invention by reference.

After complete carbodiimidification, the free terminal isocyanate groups of the carbodiimide and/or oligomeric polycarbodiimide can be completely or partially saturated in the carbodiimides produced by the method of the invention, thus blocking or reducing the free terminal isocyanate groups of the carbodiimide and/or oligomeric polycarbodiimide with C-H or N-H reactive hydrogen bonds, or with aliphatic, cycloalphalic and/or araliphic amines, such alcohols and/or alkoxypolyoxyalkyl alcohols. A favourable embodiment allows for the complete removal of the isocyanate groups by adding the aliphatic, cycloalphalic or araliphic amyl, alkoxyl and/or alkoxyl hydroxyl groups in order to reduce the concentration of the non-alphactic, hydroxycarbodiol group, and, if necessary, by removing the N-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH-OH

Another preferred method is to prepare the (poly) carbodiamides of the invention with partially or fully saturated isocyanate groups by first converting up to 50% by weight, preferably up to 23% by weight, of the isocyanate groups with at least one aliphatic, cycloaliphatic or araliphic amine, alcohol and/or alkoxypolyoxyalkyl alcohol, and then condensing the free isocyanate groups in the presence of catalysts by carbon dioxide decomposition to carbodiamides and/or oligomeric polycarbodiamides.

In particular, the monocarbodiimides and/or oligomeric polycarbodiimides produced by the method of the invention are excellent acceptors for carboxyl compounds and are therefore preferably used as stabilizers against the hydrolytic degradation of compounds containing ester groups, e.g. polymers containing ester groups, e.g. polycondensation products such as thermoplastic polyester such as polyethylene and butyl terephthalate, polyethylene esters, polyamide, polyesteramides, polycaprolactones and unsaturated polyester resins and polyester resins such as block copolymers polyethylene or butyl carbodiamide and polyurethane and polyurethane polyurethanes. These are known as polyurethane or polyurethane-based products, and are generally used in the manufacture of polyester resins or polyethylene esters. These are known as good expansion products and are used in the manufacture of polyurethane or polyurethane-based compounds, and their properties are described in the standard formulations and packaging, as well as their structure and composition.

In particular, the carbodiimides produced in accordance with the invention are used for the production of plastic films, in particular PET (polyethylene terephthalate) films, TPU (thermoplastic polyurethane) films and PLA (polylactic acid) films.

The present invention is explained in more detail by the following examples without being limiting.

Examples of implementations:

A total of four processes were carried out to produce carbodiimides:

Test a): Polymerization of the substance

In a 500 ml heated nitrogen-filled planing flask, 306 g of triisopropylbenzyldiisocyanate is introduced under nitrogen and heated to 140 °C. After adding 19 mg of 1-methylphosphorenoxide, the reaction mixture is heated to 180 °C within 5 hours, at which temperature it is allowed to react for 43 hours, achieving an NCO content of 2,1% (equivalent to 93% of turnover).

The test chemical is used to determine the concentration of the test chemical in the test medium.

In a 500 ml heated plunger flask filled with nitrogen, 420 g of a 50% solution of triisopropylbenzoldisocyanate in diisopropylbenzol is introduced under nitrogen and heated to 140 °C. After adding 0,005% MPO (12 mg) relative to the isocyanate, the reaction mixture is heated to 180 °C within 5 hours, at which temperature the reaction is allowed to continue for 43 hours, achieving an NCO content of 3,4% (corresponding to 77 % of turnover).

Test c): Combination method

In a 500 ml heated nitrogen-filled planing flask, 420 g of triisopropylbenzyldiisocyanate is introduced under nitrogen and heated to 140 °C. After adding 24 mg of 1-methylphospholenoxide, the reaction mixture is heated to 180 °C within 5 hours. After 3 hours at this temperature, 48 g of diisopropylbenzene is added. Then react for another 40 hours at 180 °C to obtain an NCO content of 1,1% (corresponding to 96 % turnover).

The following is the evaluation:

Since the isocyanate content per gram of substance is determined, the isocyanate gel agers shown in Figure 1 already take into account the different solvent levels for better comparability.

The decrease in NCO content shows that polymerization in a 50% solution is the slowest reaction (comparison: solution polymerization).

In the other two cases, the first eight hours are spent in substance polymerization, and the greater decrease in the reaction rate is apparent after about 15 hours; see Figure 1.

The NCO course over a reaction time of 15 to 48 hours is shown in Figure 1, where the curve for (1) the decrease in NCO content for the combination process of the invention (square) shows. (2) the transformation into substance (square) and (3) the transformation into solution (triangle) are used for comparison.

This shows that the process of the invention is faster than the conventional processes of substance or pure solvent polymerization.

In Figure 2 the elution diagrams (measured in THF against polystyrene as standard) of the process variants of the carbodiimidifications in substance (comparison, dashed line (2)), in solution (comparison, dotted line (3)) and in the combination method of the invention (dashed line (1)) are shown.

The solvent signal has been cut off.

A comparison of the curves shows that in the combination process of the invention the maximum is reached at an elution volume of about 17.4 mL, whereas in the substance process two peaks are reached at higher elution volumes (17.8 mL and 18.6 mL). This observation is also reflected in the achieved weight median mould masses. For example, the weight median mould mass in the substance polymerization is 13800 g/mol, while in solution only a weight median mould mass of 4600 g/mol is achieved. This combination process of the invention yields after the same time a weight median of 28900 g/mol, which is about twice as large as that of the substance polymerization. The two weight median mould masses that are used for the polymerisation of the two tables are shown, as well as the two optical mass median mass, which can be used for the distribution of the three tables. The two optical mass median mould masses are confirmed by the two molybdenum mass variations shown in the method, as well as the two optical mass median mass variations shown in the three tables.

Zeit [h]	Substanz (Vergleich)	Lösung (Vergleich)	Kombination (erfindungsgemäß)
0	100,00%	100,00%	100,00%
2	86,70%	92,11%	92,18%
4	68,78%	84,69%	81,29%
6	59,52%	79,73%	63,27%
8	46,53%	71,29%	52,38%
24	17,93%	44,76%	14,02%
32	12,82%	37,01%	8,23%
48	7,21%	22,79%	4,12%

Substanz (Vergleich)	4900	13800	2,78
Lösungsmittel (Vergleich)	1500	4600	2,99
Kombination (erfindungsgemäß.)	13300	28900	2,18

Test d): Combination method (as described in the invention)

In a 500 ml heated plunger flask filled with nitrogen, 420 g of triisopropylbenzyldiisocyanate is introduced under nitrogen and heated to 140 °C. After adding 26 mg of 1-methylphospholenoxide, the reaction mixture is heated to 180 °C within 5 hours. After 1.5 hours at this temperature, 45 g of diisopropylbenzene is added. Then react for another 40 hours at 180 °C to obtain an NCO content of 0,8% (corresponding to 97% of the turnover).

In experiment d) the NCO content before solvent addition is 15,4% and the NCN content built up to 8,75%

After the 48-hour reaction time, the NCO content is still 0.8%, with the NCN level having increased to 12.9% (solvent still present in the sample).

Figure 3 shows the chromatogram of the sample after 48 hours of reaction time. The signal at about 29 mL is from the solvent. The numerical and weight mean molecular weights with and without solvent signal and the resulting polydispersities can be found in Table 3.

Auswertung:			D
mit Lösungsmittel	3300	29600	9,08
ohne Lösungsmittel	13500	30900	2,29

Processing of the first:

Distillation at 180 °C under vacuum for four hours removed most of the solvent.

After distillation, the NCO content remains at 0,6%, whereas the NCN content has increased to 13,6% (residual solvent is still present in the sample).

Figure 4 shows the gel permeation chromatogram of the sample after 52 hours reaction time ((48 hours reaction time and four hours distillation of the solvent). The signal at about 29 mL is from the solvent and is significantly reduced compared to the sample before distillation.

Auswertung:	Mn [g/mol]	Mw [g/mol]	D
mit Lösungsmittel	8500	31800	3,76
ohne Lösungsmittel	15100	32100	2,13

The following is added to the list of products:

The resulting product is prepared as a 54% toluene solution at 85 °C after 48 hours of reaction time, slowly added to 1.4 times the acetone, and the resulting product filtered, washed and dried. Other

	Mn [g/mol]	Mw [g/mol]	D
Versuch d Fällung 1	19370	34170	1,76

Claims (8)

1. Process for preparing compounds which comprise at least one carbodiimide group by at least reacting at least one isocyanate-containing starting compound or a derivative thereof in two stages in the presence of a catalyst, characterized in that they

   (1) are subjected first to a first polymerization in bulk, to give a first polymerization product; and

   (2) the first polymerization product, originating from process step (1), is subjected to a second polymerization in solution.
2. Process according to Claim 1, characterized in that the first polymerization in process step (1) is carried out to an isocyanate conversion of 40% to 60%.
3. Process according to either of Claims 1 and 2, characterized in that the isocyanate-containing compound is selected from the group consisting of cyclohexyl isocyanate, isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), 2-methylpentane diisocyanate (MPDI), methylenebis(2,6-diisopropylphenyl isocyanate) (MDIPI); 2,2,4-trimethylhexamethylene diisocyanate/2,4,4-trimethylhexamethylene diisocyanate (TMDI), norbornane diisocyanate (NBDI), methylenediphenyl diisocyanate (MDI), diisocyanatomethylbenzene, and also the 2,4- and the 2,6-isomer and technical mixtures of both isomers (TDI), tetramethylxylylene diisocyanate (TMXDI), 1,3-bis(1-methyl-1-isocyanatoethyl)benzene, 1,3,5-triisopropyl-2,4-diisocyanatobenzene (TRIDI) and/or dicyclohexylmethyl diisocyanate (H12MDI).
4. Process according to any of Claims 1 to 3, characterized in that the derivative of the isocyanate-containing starting compound is a derivative selected from the group consisting of isocyanurates, uretdiones, allophanates and/or biurets.
5. Process according to any of Claims 1 to 4, characterized in that process step (1) is carried out at a temperature between 50 to 220°C.
6. Process according to Claim 5, characterized in that the temperature defined in Claim 5 is achieved by means of a temperature ramp.
7. Process according to any of Claims 1 to 6, characterized in that process step (2) is carried out at a temperature between 50 to 220°C.
8. Process according to any of Claims 1 to 7, characterized in that the solvent used in process step (2) is selected from the group consisting of benzene, alkylbenzene, more particularly toluene, o-xylene, m-xylene, p-xylene, diisopropylbenzene and/or triisopropylbenzene; acetone; isobutyl methyl ketone; tetrahydrofuran; hexane; benzine; dioxane; N-methylpyrrolidone; dimethylformamide and/or dimethylacetamide.