CN114369189B - Dehalogenation agent and method for preparing toluene diisocyanate and toluene diisocyanate trimer - Google Patents
Dehalogenation agent and method for preparing toluene diisocyanate and toluene diisocyanate trimer Download PDFInfo
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Abstract
The invention discloses a dehalogenation agent and a method for preparing toluene diisocyanate and toluene diisocyanate trimer. The dehalogenation agent is prepared by copolymerizing isothiocyanate containing double bond groups and other comonomers containing double bonds; or the polymer resin is prepared by copolymerizing the mono-thiocyanate containing double bond groups and other comonomers containing double bonds and then carrying out graft copolymerization with the polymer resin. In the dehalogenation agent, the content of isothiocyanate groups is 1-30wt%. By using the dehalogenation agent to treat toluene diisocyanate raw materials containing N-methylphenyl acyl chloride, dichloroimine and chlorobromotoluene diisocyanate, toluene diisocyanate with reduced content of halogenated organic impurities can be obtained, and toluene diisocyanate trimer with lower color can be prepared.
Description
Technical Field
The invention relates to the field of isocyanate, in particular to a dehalogenation agent, a method for refining Toluene Diisocyanate (TDI) and a method for preparing low-color-number toluene diisocyanate trimer.
Background
The preparation of toluene diisocyanate-based polyisocyanurates (TDI trimers) is known, and is commonly used as a curing agent in the fields of coatings, adhesives and the like, and has wide application. The general preparation is carried out by trimerizing a mixture of 2,4-TDI and 2,6-TDI, which is commercially available on a large scale, in a suitable organic solvent, catalyzed by amines comprising dialkylamino groups, such as phenol catalysts (mannich bases), triethylamine and/or triethylenediamine, until almost complete conversion, and then deactivating the catalyst by adding acidic reactive substances or by reaction with alkylating agents. Many specialized publications and patents describe the production process of this product in detail, such as patent CN107868226A, CN102212182B, CN103242254A, CN105026454A, CN105131247A, CN105131249A, CN105315433A, CN105754070A, CN105801794A, CN104892880B, CN 102816293B.
For reasons of health and environmental impact, preference is nowadays given to the type of monomer-lean trimer product as product. These products are prepared by distillative separation of the excess monomer after completion of the trimerization reaction, or by reaction of the excess monomer by addition of monofunctional alcohols, or by controlling the trimerization reaction at a correspondingly high conversion until the monomer is substantially converted to the higher oligomeric isocyanurate. By the first method, while TDI trimer is obtained, the distilled excess monomer contains more impurities and lower 2, 4-toluene diisocyanate, the impurity composition mainly comprises chlorine-containing substances, bromine-containing substances or chlorine-containing substances and bromine-containing substances which do not participate in the trimerization reaction, and the impurity content is far higher than the impurity content in toluene diisocyanate raw materials. Part of the production process can recycle distilled monomers, mix the distilled monomers with raw material toluene diisocyanate in a certain proportion, then continue to carry out trimerization reaction, and ensure that the trimerization reaction obtains high conversion rate by increasing the catalyst dosage.
However, the polyisocyanurates of the prior art prepared in this way have the fundamental disadvantage that their properties, in particular NCO content and color, are greatly influenced by the quality of the toluene isocyanate starting material, which in turn leads to a large variation in the catalyst usage. There is no lack of attempts to provide TDI grades that can be used to prepare lighter colored and more stable aromatic polyisocyanates to aging with increased catalyst consumption and thus discoloration of the polyisocyanates and paints prepared therewith. A process is described, for example, in EP1413571a, wherein a product fraction having a TDI content of at least 99.5% and less than 200 ppm by weight of solvent and/or chlorinated aromatic hydrocarbons, less than 100ppm by weight of hydrolyzable chlorine and less than 40 ppm by weight of acid is obtained by pre-concentrating a TDI crude solution to a solvent content of <20% and then fractionating in a divided wall distillation column. In US6900348 it is described that a lighter colour of diphenylmethane-diisocyanate can be obtained by using phosgene having a bromine content of <50 ppm. EP0816333a claims a process for reducing TDI colour by treating the crude solution with hydrogen before separating off the solvent.
Patent CN105026454a proposes a method for improving TDI purity by special pretreatment of p-Toluenediamine (TDA). EP1864969a discloses a process for preparing lighter colored TDI wherein the TDA used in the phosgenation reaction comprises less than 0.1 wt.% alkylated cyclic ketone based on 100 wt.% TDA. A method of treating the amine used with solids comprising lewis acid and/or bronsted acid centres prior to reaction with phosgene is described in US5872278A, EP0866057 a. The isocyanate obtained then has a lighter colour than the isocyanate prepared with untreated amine.
Patent CN109704992A shows a toluene diisocyanate purifying process, which adopts inorganic nanometer layered hydrated aluminum magnesium hydroxide with superhigh temperature dewatering structure as adsorbent, and the inorganic nanometer layered hydrated aluminum magnesium hydroxide and high acidity TDI are mixed at 20-180 deg.c for 5-60min to obtain the mixture of low acidity TDI and adsorbent. The patent can only adsorb hydrogen chloride, reduce the content of hydrogen chloride in TDI products, and can not produce adsorption effect on halogenated organic compounds in TDI, thereby reducing the content of the halogenated organic compounds. The basic metal adsorbent under acidic conditions, thereby producing free metal ions, is present in the TDI product, resulting in an increase in its activity, which affects downstream applications.
In the presently disclosed processes or techniques, while TDI grades having higher purity and lighter color can be prepared by these relatively very complex processes, in these prior art techniques low hydrolysis chlorine, low acid products are obtained in part by further or enhanced rectification, and impurities in TDI are controlled in part by controlling the purity of the starting materials such as TDA, phosgene, etc. However, in the isocyanate production process, the control of the raw materials has a certain influence on the generation of impurities, but the generation of halogenated compounds cannot be prevented.
Disclosure of Invention
The invention aims to provide a dehalogenation agent, which is used for adsorbing halogenated impurities in existing low-quality toluene diisocyanate products by adopting a chemical adsorption method, so that high-purity TDI with low halogenated impurities can be prepared, and TDI prepared by the method is used as a raw material to prepare a TDI trimer with low color number.
This object is achieved in a method described in more detail below.
Toluene diisocyanate containing <15 ppm by weight of hydrogen chloride and/or < 5ppm by weight of N-methylphenyl acyl chloride and/or <100 ppm by weight of dichloroimine and/or <20 ppm by weight of mono-and/or dihalo-toluene isocyanate, preferably <10 ppm by weight of hydrogen chloride and/or <2 ppm by weight of N-methylphenyl acyl chloride and/or <70 ppm by weight of dichloroimine and/or <2 ppm by weight of dihalo-toluene isocyanate.
The dihalogenated toluene isocyanate is selected from one or more of the following compounds:
a dehalogenation agent is a polymer containing isothiocyanate groups.
As one scheme, the dehalogenation agent is prepared by copolymerizing isothiocyanate containing double bond groups and other comonomers containing double bonds, or is prepared by graft copolymerizing thiocyanate containing double bond groups and other comonomers containing double bonds with high polymer resin.
The isothiocyanate having a double bond group has the formula R-n=c=s, wherein R may be CH 2 ＝CH-(CH 2 ) m -、(CH 2 ＝C-CH 3 )-(C 6 H 4 ) x -(CH 2 ) n -(CH 3 ) z -、
(CH 2 ＝CH)-(C 6 H 4 ) y -(CH 2 ) p -、CH 3 -(CH 2 ) h -CH＝C-(CH 3 )-(CH 2 ) b -(C＝O)-N＝C＝S、CH 3 -(CH 2 ) h -CH＝C-(CH 3 )-(CH 2 ) e -(C 6 H 4 ) f Unsaturated alkyl groups or aromatic alkyl groups containing double bonds such as- (c=o) -n=c=s; the values of m are preferably from 4 to 10, such as 4, 5, 6, 7, 8, 9, 10, the values of n are preferably from 0 to 10, such as 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, the values of x are preferably from 1 to 5, such as 1, 2, 3, 4, 5, the values of y are preferably from 1 to 5, such as 1, 2, 3, 4, 5, z are preferably from 0 to 10, such as 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, the values of p are preferably from 0 to 10, such as 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, the values of h are preferably from 1 to 5, such as 1, 2, 3, 4, 5, the values of b are preferably from 1 to 5, such as 1, 2, 3, 4, 5,e are preferably from 0 to 5, such as 0, 1, 2, 3, 4, 5, the values of f are preferably from 1 to 3, such as 1.
As a preferred embodiment, R-n=c=s according to the invention is selected from one or more of the following compounds:
the polymer resin can be prepared by copolymerization or graft polymerization of polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polyethylene polystyrene copolymer, polypropylene polystyrene copolymer and other polymer resins.
As a preferred embodiment, the method for preparing the dehalogenation agent according to the present invention comprises the steps of:
(1) Isothiocyanates having double bond groups are mixed with other comonomers containing double bonds (including but not limited to styrene, etc.), and copolymerized in the presence of initiators and/or catalysts to form polymers having a relative molecular weight of 300-3000;
(2) And (3) carrying out graft copolymerization on the polymer obtained in the step (1) and the high-molecular resin at high temperature to obtain a polymer with a relative molecular weight of 10000-1000000, washing and precipitating with an organic solvent, and removing the polymer with a molecular weight of less than 300.
As another preferred embodiment, the method for preparing the dehalogenation agent according to the present invention may also employ the following steps: isothiocyanates having double bond groups are mixed with other comonomers containing double bonds, including but not limited to styrene, and copolymerized in the presence of an initiator and/or catalyst to form polymers of relative molecular weight 10000-1000000.
In the dehalogenation agent, the content of isothiocyanate groups is 1-30wt%.
As a preferred embodiment, the dehalogenation agent includes, but is not limited to, the following structures:
the organic solvent in the step (2) of the present invention contains one or more of toluene, acetone, etc.
A process for preparing toluene diisocyanate according to the present invention comprising the steps of: the p-toluene diisocyanate raw material is refined by using the dehalogenation agent.
Toluene diisocyanate feedstocks described herein include, but are not limited to, TDI65, TDI80, TDI100, and other toluene diisocyanate-containing feedstocks such as toluene diisocyanate monomers distilled from the preparation of TDI trimers using thin film evaporation processes.
As one scheme, the toluene diisocyanate raw material comprises 30-99.5% of 2, 4-toluene diisocyanate, preferably 65-99.5% of hydrogen chloride, 1-15 ppm of N-methylphenyl acyl chloride, 5-10ppm of dichloroimine, 20-100ppm of monohalogenated and/or dihalogenated toluene isocyanate and 10-30ppm of monohalogenated toluene diisocyanate.
As a preferred embodiment, the method for preparing toluene diisocyanate according to the present invention comprises the steps of:
adding dehalogenation agent into toluene diisocyanate raw material at 40-120deg.C, wherein the addition amount of dehalogenation agent is 5-30wt% of toluene diisocyanate raw material to be refined, and stirring for 5-120min.
As another preferred embodiment, the method for preparing toluene diisocyanate according to the present invention comprises the steps of: filling dehalogenation agent into an adsorption tower with a filling height of 1m-5m, controlling the temperature of the adsorption tower at 40-120 ℃, and keeping the toluene diisocyanate to be refined in the adsorption tower for 20-120 min.
After refining by dehalogenation agent, the content of N-methylphenyl acyl chloride, dichlorine and chloro-bromo toluene isocyanate in the toluene diisocyanate obtained by the invention is greatly reduced.
A process for preparing a toluene diisocyanate trimer comprising the steps of: by trimerizing the toluene diisocyanate according to the present invention at a temperature of 40 to 120 ℃ in the presence of a diluent and a catalyst.
In the method for preparing toluene diisocyanate trimer according to the present invention, the reaction is carried out until almost complete conversion; almost complete conversion means that the TDI used is converted up to a residual monomer content of < 0.5% by weight, based on polyisocyanate plus diluent; the catalyst is then deactivated by addition of an acidic reactive species or by reaction with an alkylating agent.
The diluent of the present invention is used in an amount of 20 to 80wt% based on the total mass of all material added.
The diluent is one or more selected from ethyl acetate, butyl acetate, toluene, xylene, cyclohexanone, methyl ethyl ketone, propylene glycol methyl ether acetate and triethyl phosphate.
In the method for preparing toluene diisocyanate trimer according to the present invention, the catalyst is selected from the group consisting of phenol catalysts, amine catalysts such as triethylene diamine and triethylamine, and organic phosphine catalysts.
Toluene diisocyanate trimers produced according to the present invention have an APHA color of <100 hassen, preferably <50 hassen, more preferably <30 hassen.
The toluene diisocyanate trimer prepared by the method can be used for preparing polyurethane paint, in particular to a two-component polyurethane paint.
The dehalogenation principle of the dehalogenation agent is as follows:
X＝Cl、Br、I。
the invention has the beneficial effects that: the dehalogenation agent can greatly reduce trace chlorinated organic substances, brominated substances and chlorinated brominated substances in toluene diisocyanate to obtain high-purity Toluene Diisocyanate (TDI), and TDI trimer with lower chromaticity can be obtained by taking the TDI as a raw material.
Detailed Description
In the examples which follow, all percentages are given by weight of the entire reaction system.
The NCO content was determined by titration according to DIN EN ISO 11909. Dynamic viscosity was measured according to DIN 3219 with DIN measuring block 125 at 23℃with a Reolab QC viscometer from Anton Paar company at a shear rate of 1 to 1600 1/s.
The residual monomer content was determined by gas chromatography according to DIN EN ISO 10283.
The solids content (non-volatile content) is measured in accordance with DIN 3251 under the test conditions described herein for isocyanates.
The impurity content is determined by a gas chromatography method, the structure and the peak-out time of the impurity are confirmed by a gas chromatography-mass spectrometer, and the content adopts a gas chromatography area normalization result.
The colour was measured at 23℃in 50mm disposable round cuvettes based on DIN EN 1557 using LICO 400 from the company HACH Lange.
Preparation of dehalogenation agent 1
5g of 3-isopropenyl-alpha, alpha-dimethylbenzyl-isothiocyanate and 20g of styrene are added into a 100ml three-necked flask, uniformly mixed, added with 0.025g of dicumyl peroxide as an initiator, stirred, dissolved, heated to 80 ℃ and reacted for 30min to obtain an oligomer containing-N=C=S groups and having a molecular weight of 2000, added with 30g of polypropylene (F401) particles, heated to 190 ℃ and subjected to melt grafting polymerization. Adding 100ml of toluene into the obtained product, heating to 90 ℃ to dissolve the toluene, filtering the solution while the solution is hot, pouring the filtrate into acetone to settle for 12 hours, repeatedly dissolving and settling for three times, and finally placing the precipitate (PP-styrene-isothiocyanate) obtained by filtering into a vacuum drying oven (90 ℃) to dry for 24 hours to obtain the purified grafted product PP-styrene-isothiocyanate. The structure is schematically as follows:
preparation of dehalogenation agent 2
50g of styrene and 0.05g of benzoyl peroxide are added into a 250ml four-neck flask, the mixture is uniformly mixed, the temperature is raised to 85 ℃, 10g of vinyl-methylphenyl-isothiocyanate is slowly added dropwise, and after the dropwise addition is finished, the temperature is kept for 3 hours, and the temperature is lowered, so that a solid substance is obtained. The solid matter is dissolved in toluene, filtered while the solid matter is hot, the filtrate is poured into acetone to be settled for 12 hours, the dissolution and the settlement are repeated for three times, and the purified polystyrene-isothiocyanate copolymer is obtained by filtering. The structure is schematically as follows:
example 1
The industrial toluene diisocyanate having 10ppm by weight of hydrogen chloride, 10ppm by weight of N-methylphenyl acyl chloride, 33 ppm by weight of dichloroimine and 26 ppm by weight of chlorobromotoluene diisocyanate was subjected to dehalogenation treatment by an adsorption column of dehalogenation agent 1 at 80℃for 120 minutes to obtain toluene diisocyanate having 10ppm by weight of hydrogen chloride, 1ppm by weight of N-methylphenyl acyl chloride, 7 ppm by weight of dichloroimine and 2 ppm by weight of chlorobromoisocyanate.
150g of this toluene diisocyanate was placed in advance with 143.25g of butyl acetate in a 500ml double-jacketed, ground vessel purged with nitrogen. The reaction mixture was heated to the desired reaction temperature of 75 ℃. 0.5% by mass of 2,4, 6-tris (dimethylaminomethyl) phenol based on toluene diisocyanate was intermittently added as a catalyst which was diluted to a concentration of 10% by weight in advance with butyl acetate as a solvent. After the trimerization reaction is significantly started, the addition of the catalyst is interrupted to safely output the released reaction heat. The slow addition of catalyst continues as the desired reaction temperature is again reached. After about 5 hours, 7.5g of the total catalyst solution were metered in and stirring was continued for 12 hours while maintaining a reaction temperature of 75℃until the desired NCO content was reached. To safely stop the trimerization reaction, 1.15 times mole benzoyl chloride based on the NCO molar content was added to the reaction mixture. After 1.30g was added, the reaction product was stirred at 80℃for a further 1 hour. The polyisocyanates containing solvent and isocyanurate groups obtained in this way have the following characteristic values:
NCO content = 8.06 wt%
Viscosity=1240mpa×s@23° c
Residual monomer content = 0.08 wt%
Solids=51.1 wt.%
APHA color = 15 halsen.
Example 2
In analogy to example 1, toluene diisocyanate having 10ppm by weight of hydrogen chloride, 5ppm by weight of N-methylphenyl acyl chloride, 8ppm by weight of dichloroimine and 5ppm by weight of chlorobromotoluene isocyanate was obtained by using the same toluene diisocyanate as in example 1 as a starting material and adjusting the temperature of the adsorption column to 40℃and the residence time to 110 minutes. To carry out the reaction. The reaction procedure and the order of addition were the same as in example 1. The polyisocyanates containing solvent and isocyanurate groups thus obtained have the following characteristic values:
NCO content=7.85 wt%
Viscosity = 1196pa x s@23 deg.c
Residual monomer content = 0.12 wt%
Solids=52.1 wt%
APHA color = 25 halsen.
Example 3
The reaction was carried out in analogy to example 1, starting from the same toluene diisocyanate as in example 1 and having an adsorption column temperature of 40℃and a residence time of 60min, obtaining toluene diisocyanate having 10ppm by weight of hydrogen chloride, 8ppm by weight of N-methylphenyl acyl chloride, and 14ppm by weight of dichloroimine, and 11ppm by weight of chlorobromotoluene isocyanate. The reaction procedure and the order of addition were the same as in example 1. The polyisocyanates containing solvent and isocyanurate groups thus obtained have the following characteristic values:
NCO content = 8.03 wt%
Viscosity = 12720mpa @ s @23 °c
Residual monomer content = 0.19 wt%
Solids=51.3 wt.%
APHA color=61 halsen.
Example 4
In analogy to example 1, using the same toluene diisocyanate as in example 1 as a starting material, the adsorption column was replaced with a stirred tank, a polypropylene resin of dehalogenation agent was added based on the weight of the toluene diisocyanate product to be treated, and the reaction tank temperature was 40℃and the stirring time was 30 minutes, to obtain toluene diisocyanate having 10ppm by weight of hydrogen chloride, 8ppm by weight of N-methylphenyl chloride, and 13 ppm by weight of dichloroimine, and 9 ppm by weight of chlorobromotoluene isocyanate. To carry out the reaction. The reaction procedure and the order of addition were the same as in example 1. The polyisocyanates containing solvent and isocyanurate groups thus obtained have the following characteristic values:
NCO content = 8.01 wt%
Viscosity = 1235mpa x s @23 °c
Residual monomer content = 0.16 wt%
Solids=51.7 wt%
APHA color = 53 halsen.
Example 5
In analogy to example 1, using the same toluene diisocyanate as in example 1 as a starting material, the adsorption column was replaced with a stirred tank, dehalogenation agent 2 was added based on the weight of the toluene diisocyanate product to be treated, and the reaction tank was stirred at 40℃for 120min to obtain toluene diisocyanate having 10ppm by weight of hydrogen chloride, 1ppm by weight of N-methylphenyl chloride, 5ppm by weight of dichloroimine, and 2 ppm by weight of chlorobromotoluene isocyanate. To carry out the reaction. The reaction procedure and the order of addition were the same as in example 1. The polyisocyanates containing solvent and isocyanurate groups thus obtained have the following characteristic values:
NCO content=7.97 wt%
Viscosity=1290mpa×s@23° c
Residual monomer content = 0.14 wt%
Solids=51.2 wt.%
APHA color = 13 halsen.
Comparative example 1
In the case of using toluene diisocyanate grades having 10ppm by weight of hydrogen chloride and 10ppm by weight of N-methylphenyl acyl chloride and 33 ppm by weight of dichloroimine and 26 ppm by weight of chlorobromoisocyanate, the solvent and isocyanurate group-containing polyisocyanates thus obtained have the following characteristic values, analogously to example 1:
NCO content=9.33 wt%
Viscosity=1150mpa×s@23° c
Residual monomer content = 0.21 wt%
Solids=51.3 wt.%
APHA-color value=140 halsen.
Comparative example 2
An industrially produced toluene diisocyanate having a hydrogen chloride content of 10ppm by weight, an N-methylphenyl acyl chloride content of 10ppm by weight, a dichloroimine content of 30ppm by weight, a chlorotoluene diisocyanate content of 5ppm by weight and a chlorotromotoluene diisocyanate content of 20 ppm by weight was treated by passing through an adsorption column of a highly transparent polystyrene resin (trade name GPPS GP-525) produced by Jiangsu Baulong Co., ltd., residence time of 120 minutes, temperature of 80℃and toluene diisocyanate having a composition of 10ppm by weight of hydrogen chloride, 10ppm by weight of N-methylphenyl acyl chloride, and 30ppm by weight of dichloroimine, 25 ppm by weight of chlorotromotoluene isocyanate was obtained. Using this toluene diisocyanate as a starting material, similar to the embodiment of the trimer in example 1, a solvent-and isocyanurate-group-containing polyisocyanate was obtained having the following characteristic values:
NCO content=9.31 wt%
Viscosity = 1147mpa @ s @23 °c
Residual monomer content = 0.18 wt%
Solids=51.5 wt.%
APHA color = 143 halsen.
This comparative example shows that the treatment with the polymer p-toluene diisocyanate product without supporting the dehalogenating agent does not change the impurity content in the toluene diisocyanate product before and after the treatment, and the color number of the polyisocyanate product prepared from the same as a raw material is not improved.
The results from the comparative examples and examples show that TDI trimer polyisocyanate products prepared with toluene diisocyanate prepared according to the process of the present invention from examples 1 and 2 have lower color.
Claims (7)
1. A dehalogenation agent, the preparation method comprising the steps of: mixing isothiocyanate with double bond group and other comonomer with double bond, and copolymerizing in the presence of initiator and/or catalyst to form polymer with relative molecular weight of 10000-1000000; alternatively, the method comprises the following steps: (1) Mixing isothiocyanate with double bond group and other comonomer containing double bond, and copolymerizing in the presence of initiator and/or catalyst to form polymer with relative molecular weight of 300-3000; (2) Performing graft copolymerization on the polymer obtained in the step (1) and the high-molecular resin at high temperature to obtain a polymer with a relative molecular weight of 10000-1000000, washing and precipitating with an organic solvent, and removing the polymer with a molecular weight of less than 300;
the isothiocyanate having a double bond group is selected from one or more of the following compounds:
the other comonomer containing double bonds is styrene.
2. The dehalogenation agent according to claim 1, wherein said polymer resin is polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, and polyethylene polystyrene copolymer or polypropylene polystyrene copolymer.
3. The dehalogenation agent according to claim 1, wherein the dehalogenation agent has the structural formula:
in the dehalogenation agent, the content of isothiocyanate groups is 1-30wt%.
4. A method for preparing toluene diisocyanate, comprising the steps of: the raw material of the p-toluene diisocyanate is refined by using the dehalogenation agent according to any one of claims 1 to 3, and the obtained toluene diisocyanate has 10ppm of hydrogen chloride, 1 to 8ppm of N-methylphenyl acyl chloride, 7 to 14ppm of dichloroimine and 2 to 11ppm of bromotoluene isocyanate.
5. A method for preparing toluene diisocyanate trimer, comprising the steps of: a process for the trimerization of toluene diisocyanate obtained by the process of claim 4, said toluene diisocyanate trimer having an APHA color of <100 hassen, at a temperature of 40 to 120 ℃ in the presence of a diluent and a catalyst.
6. The process of claim 5, wherein the toluene diisocyanate trimer has an APHA color number of <50 hassen.
7. The method of claim 6, wherein the toluene diisocyanate trimer has an APHA color number of <30 hassen.
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