HK1073853B - Ytterbium(iii) acetylacetonate as a catalyst for the preparation of aliphatic oligocarbonate polyols - Google Patents

Description

Use of ytterbium (III) acetylacetonate as catalyst for the production of aliphatic oligocarbonate polyols

Technical Field

The invention relates to the use of ytterbium (III) acetylacetonate as a catalyst for producing aliphatic oligocarbonate polyols by transesterification between organic carbonates and aliphatic polyols, to the polyols produced using said catalyst and to the prepolymers produced from said polyols.

Background

Oligocarbonate polyols are important starting materials for the preparation of, for example, plastics, coatings and adhesives. They are reacted with, for example, isocyanates, epoxides, (cyclo) esters, acids or anhydrides (DE-A1955902). In general, these oligocarbonate polyols can be prepared from aliphatic polyols by reaction with phosgene (for example DE-A1595446), with bischlorocarbonates (for example DE-A857948), with diaryl carbonates (for example DE-A1012557), with cyclic carbonates (for example DE-A2523352) or dialkyl carbonates (for example WO 2003/2630).

It is known that in the reaction of aryl esters, such as diphenyl carbonate, with aliphatic polyols, such as 1, 6-hexanediol, satisfactory conversion can be achieved only by removing liberated alcohol compounds, such as phenol, during the shift in the reaction equilibrium (for example EP-A0533275). However, if alkyl carbonates are used (e.g.dimethyl carbonate), it is generally necessary to use transesterification catalysts, for example alkali or alkaline earth metals and their oxides, alkoxides, carbonates, borates or salts of organic acids (e.g.WO 2003/2630).

Furthermore, preference is given to using tin or organotin compounds such as bis (tributyltin) oxide, dibutyltin laurate or alternatively dibutyltin oxide (DE-A2523352) and also titanium compounds such as titanium tetrabutoxide, titanium tetraisopropoxide or titanium dioxide (for example EP-B0343572 and WO 2003/2630).

However, the transesterification catalysts known from the prior art for the preparation of aliphatic oligocarbonate polyols by reaction of alkyl carbonates with aliphatic polyols have certain disadvantages.

Recently, organotin compounds have been recognized as potential carcinogens for humans. Thus, organotin compounds are regarded as undesirable constituents, whereas previously preferred catalyst compounds such as bis (tributyltin) oxide, dibutyltin oxide or dibutyltin laurate remain in the two-stage product of the oligocarbonate polyol. If a strong base is used, for example alkali metals, alkaline earth metals or alkoxides thereof, an additional process step is required after the oligomerization reaction is complete to neutralize the product. On the other hand, if a Ti compound is used as the catalyst, the resulting product undergoes an undesirable discoloration (yellowing) during storage due to the presence of Ti (iii) compounds, possibly forming complexes with Ti (iv) compounds and/or titanium.

In addition to the above-mentioned undesirable discoloration behavior, the titanium-containing catalysts have a high activity towards compounds containing isocyanate groups when oligocarbonates having hydroxyl end groups are further reacted as starting materials in the preparation of polyurethanes. This property is even more pronounced when the titanium-catalyzed oligocarbonate polyol is reacted with an aromatic (poly) isocyanate at elevated temperatures, an example of which occurs, for example, in the preparation of thermoplastic elastomers or Thermoplastic Polyurethanes (TPU). This undesirable property even leads to a reduction in the pot life or reaction time of the reaction mixture to such an extent that, owing to the use of titanium-containing oligocarbonate polyols, such oligocarbonate polyols are no longer suitable for these applications. In order to avoid this disadvantageous property, the transesterification catalyst present in the product should be deactivated as far as possible in at least one additional production step after the end of the synthesis.

EP-B1091993 teaches that inactivation can be carried out by addition of phosphoric acid, whereas US-A4891421 suggests that inactivation is carried out by hydrolysis of the titanium compound, a corresponding amount of water being added to the product and removed again from the product by distillation after the inactivation has ended.

In addition, the typical reaction temperature is 150 ℃ to 230 ℃, and the reaction temperature is unlikely to be lowered by using the existing catalyst, mainly to avoid the formation of by-products such as ether or vinyl groups, which may be generated at high temperature. These undesirable end groups correspond to chain terminators for the subsequent polymerization. For example, in the reaction of polyurethanes with polyfunctional (poly) isocyanates, they can reduce the network density and thus the product properties (e.g., solvent or acid resistance).

In addition, the oligocarbonate polyols prepared using catalysts known from the prior art have a high content of ether groups (e.g.methyl ether, hexyl ether, etc.). However, these ether groups in the oligocarbonate polyols lead, for example, to unsatisfactory hot air resistance of the thermoplastic elastomers based on such oligocarbonate polyols, since the ether compounds in the materials decompose under these conditions, leading to material degradation.

Disclosure of Invention

Summary of The Invention

It is an object of the present invention to provide suitable catalysts for the transesterification of organic carbonates, in particular dialkyl carbonates, with aliphatic polyols to prepare aliphatic oligocarbonate polyols, which catalysts do not have the disadvantageous properties described above.

Ytterbium (III) acetylacetonate has now been found to be such a class of catalysts.

Detailed Description

In the process of the invention, ytterbium (III) acetylacetonate is used as transesterification catalyst for the preparation of aliphatic oligocarbonate polyols having a number-average molecular weight value of 500-5000g/mol from aliphatic polyols and organic carbonates. The aliphatic oligocarbonate polyols obtained are particularly suitable for the preparation of isocyanate-terminated prepolymers and polyurethanes.

In the process of the invention, the catalyst can be used either in solid form or in solution, for example in an educt.

According to the invention, the catalyst is used in a concentration of 0.01 to 10000ppm, preferably 0.1 to 5000ppm, most preferably 0.1 to 1000ppm, based on the total mass of the educts used.

The reaction temperature during the transesterification reaction is 40 to 250 deg.C, preferably 60 to 230 deg.C, and most preferably 80 to 210 deg.C.

The transesterification reaction may be carried out at atmospheric pressure or at 10 deg.C^-3-10³Reduced pressure or elevated pressure of bar.

Any known, in particular those readily available, aryl, alkyl, alkylene carbonate may be used as the organic carbonate in the process of the present invention. Examples of specific carbonates suitable for use in the present invention include: diphenyl carbonate (DPC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate, and the like.

Preferably, diphenyl carbonate, dimethyl carbonate or diethyl carbonate is used. Most preferably diphenyl carbonate or dimethyl carbonate is used.

Aliphatic alcohols having 2 to 100C atoms with an OH functionality of 2 or more (primary, secondary or tertiary), linear, cyclic, branched, unbranched, saturated or unsaturated, can be used as reaction partners for organic carbonates. Specific examples of suitable aliphatic alcohols include ethylene glycol, 1, 3-propanediol, 1, 3-butanediol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 2-ethylhexanediol, 3-methyl-1, 5-pentanediol, cyclohexanedimethanol, trimethylolpropane, pentaerythritol, dimer diol, diethylene glycol, and the like.

Likewise, polyols may also be used in the practice of the present invention. Suitable polyols include those which are obtained by ring-opening reaction of lactones or epoxides with aliphatic alcohols having an OH functionality of > 2 (primary, secondary or tertiary) (linear, cyclic, branched, unbranched, saturated or unsaturated), for example products obtained by addition reaction of epsilon-caprolactone with 1, 6-hexanediol or epsilon-caprolactone with trimethylolpropane, and mixtures thereof.

Finally, mixtures of the various polyols mentioned above may also be used as educts.

Aliphatic or cycloaliphatic branched or unbranched primary or secondary alcohols with OH functions ≧ 2 are preferred. Particularly preferred are aliphatic branched or unbranched primary polyols having an OH function of 2 or more.

If a catalyst according to the invention is used, the step of finally deactivating the transesterification catalyst, for example by adding a chelating agent such as phosphoric acid, dibutyl phosphate, oxalic acid or the like, or a precipitating agent such as water, can be dispensed with. The ytterbium-comprising oligocarbonate polyols obtained are suitable subsequently, without further treatment, for example as starting materials for the preparation of polyurethanes.

The invention also provides oligocarbonate diols having a number average molecular weight value of 500-5000g/mol, which are prepared by transesterification of organic carbonates with aliphatic polyols in the presence of ytterbium (III) acetylacetonate, and NCO-terminated prepolymers prepared from oligocarbonate diols by reaction with a stoichiometric excess of organic (poly) isocyanates.

The ether group content of such oligocarbonate diols prepared in the presence of ytterbium (III) acetylacetonate is lower than that of oligocarbonate diols prepared using catalysts of the prior art. This directly affects the properties of the NCO-terminated prepolymers produced therefrom. These prepolymers have better storage stability than prepolymers prepared using prior art oligocarbonate diols. In addition, the thermoplastic elastomers prepared from these oligocarbonate diols also have a higher hot air resistance.

It has furthermore been found that ytterbium compounds, in particular ytterbium (III) acetylacetonate, are also advantageous for catalyzing further esterification reactions or transesterification reactions, for example for the preparation of polyesters or polyacrylates. The catalyst may be present in the product in the further reaction, since it does not adversely affect the reaction of the polyol and polyisocyanate.

Detailed Description

Example 1

Dimethyl carbonate (3.06g) and 1-hexanol (6.94g) in a molar ratio of 1: 2 were kept at constant amounts (5.7X 10 g) each time^-6mol) (see Table 1) were mixed together in a 20ml rolled flange glass vessel with degassingThe natural rubber septum of the mouth is closed. If the catalyst used is in the form of a solid aggregate at room temperature, it is first dissolved in an educt. The reaction mixture was heated to 80 ℃ with stirring for 6 hours. After cooling to room temperature, the product spectrum is analyzed by gas chromatography, optionally in combination with mass spectrometric detection. The content of reaction products, i.e.methyl-or dihexyl carbonate, is quantified by integrating the corresponding gas chromatograms and can be used as a criterion for evaluating the activity of the transesterification catalyst used. The results of these activity assays are shown in Table 1.

TABLE 1

Catalyst used and reaction product content

Serial number	Catalyst and process for preparing same	Content of methyl hexyl carbonate [% by area ]	Content of dihexyl carbonate (area%)	Total content [% by area ]
					1	Without catalyst	4.0	0.1	4.1
2	Dibutyl tin oxide	5.1	0.2	5.3
					3	Dibutyl tin laurate	3.4	0.1	3.5
4	Bis (tributyltin) oxide	3.7	0.0	3.7
					5	Titanium tetraisopropoxide	1.9	0.0	1.9
6	Magnesium carbonate	2.1	0.1	2.2
					7	Ytterbium acetylacetonate (III)	23.5	5.3	28.8

Example 2

Dimethyl carbonate (4.15g) and 1, 6-hexanediol (5.85 g) were metered in constant amounts (5.7X 10 each time)^-6mol) of catalyst (see Table 2) were mixed in a 20ml glass-rolled vesselSealed with a natural rubber septum with an exhaust port. The molar ratio of dimethyl carbonate to 1, 6-hexanediol is chosen such that an aliphatic oligocarbonate diol with an average molar mass of 2000g/mol is obtained at the end of the reaction. If the catalyst used is in the form of a solid aggregate at room temperature, it is first dissolved in an educt. The reaction mixture was heated to 80 ℃ with stirring for 6 hours. After cooling to room temperature, the contents of the reaction products of interest (e.g.monoesters, diesters, oligocarbonate polyols) are first determined by means of gas chromatography and mass spectrometry and then quantified by integrating the corresponding gas chromatograms, and these product contents can be used as a criterion for evaluating the activity of the transesterification catalysts used. The results of these activity assays are shown in table 2.

TABLE 2

Catalyst used and reaction product content

Serial number	Catalyst and process for preparing same	Reaction product content [% by area ]
			1	Without catalyst	4.8
2	Dibutyl tin oxide	8.3
			3	Dibutyl tin laurate	3.3
4	Bis (tributyltin) oxide	3.9
			5	Titanium tetraisopropoxide	1.6
6	Magnesium carbonate	4.5
			7	Ytterbium acetylacetonate (III)	37.6

Example 3

Preparation of aliphatic oligocarbonate diols using ytterbium (III) acetylacetonate

1759g of 1, 6-hexanediol and 0.02g of ytterbium (III) acetylacetonate are charged into a 5 l pressure reactor equipped with a distillation head, stirrer and receiver. The contents were heated to 160 ℃ under a nitrogen pressure of 2 bar. 1245.5g of dimethyl carbonate were then added over 3h, while the pressure was increased to 3.9 bar. The reaction temperature was then raised to 185 ℃ and the reaction mixture was stirred for 1 h. Finally, 1245.5g of dimethyl carbonate were added in the course of 3 hours, while the pressure was increased to 7.5 bar. After the addition was complete, stirring was continued for a further 2h, the pressure being increased to 8.2 bar. The passage to the distillation head and to the receiver is always open during the entire transesterification reaction, so that methanol in the form of a mixture with dimethyl carbonate can be distilled off. Finally, the reaction mixture was depressurized to standard pressure over 15min, the temperature was lowered to 150 ℃ and the distillation was continued at this temperature for a further 1 h. In order to remove the excess dimethyl carbonate and methanol and also to deblock (activate) the terminal OH groups, the pressure was subsequently reduced to 10 mbar. After 2 hours, the reaction temperature was finally raised to 180 ℃ over 1 hour and maintained for a further 4 hours. The obtained oligocarbonate diol had an OH value of 5 mgKOH/g.

The reaction batch was vented, 185g of 1, 6-hexanediol were added, and the batch was heated to 180 ℃ at standard pressure for 6 hours. The pressure was then reduced to 10mbar and the temperature was 180 ℃ for 6 hours.

After degassing the reaction batch and cooling to room temperature, a colorless, waxy oligocarbonate diol having the following characteristic values is obtained: m_n2000 g/mol; OH value is 56.5 mgKOH/g; content of methyl ether: < 0.1 wt.%; viscosity: at 75 ℃ is2800mPas。

Example 4 (comparative)

Aliphatic oligocarbonate diols are prepared using catalysts known in the art.

1759g l, 6-hexanediol and 0.02g of titanium tetraisopropoxide were charged to a 5 l pressure reactor equipped with a distillation head, stirrer and receiver. The contents were heated to 160 ℃ under a nitrogen pressure of 2 bar. 622.75g of dimethyl carbonate were then added over 1 hour, the pressure being increased to 3.9 bar. The reaction temperature was subsequently raised to 180 ℃ and 622.75g of dimethyl carbonate were added in the course of 1 hour. Finally, 1245.5g of dimethyl carbonate were added at 185 ℃ over 2 hours, and the reaction pressure was increased to 7.5 bar. After the addition was complete, stirring was continued at this temperature for a further 1 hour. The passage to the distillation head and to the receiver is always open during the entire transesterification reaction, so that methanol in the form of a mixture with dimethyl carbonate can be distilled off. Finally, the reaction mixture was depressurized to standard pressure over 15 minutes, the temperature was lowered to 160 ℃ and the distillation was continued at this temperature for a further 1 hour. In order to remove excess methanol and dimethyl carbonate and also to deblock (activate) the terminal OH groups, the pressure was subsequently reduced to 15 mbar. After a further distillation time of 4 hours under these conditions, the reaction batch was vented. The obtained oligocarbonate diol had an OH value of 116 mgKOH/g. 60g of dimethyl carbonate are then added to the reaction batch, which is heated to 185 ℃ under a pressure of 2.6bar for 6 hours.

The pressure was then reduced to 15mbar and the temperature 185 ℃ for 8 hours. After degassing and treatment of the reaction product with 0.04g of dibutyl phosphate as catalyst deactivator, the reaction batch was cooled to room temperature to give colorless, waxy oligocarbonate diols having the following characteristic values: m_n2000 g/mol; OH value 56.5mg KOH/g; content of methyl ether: 3.8 wt.%; viscosity: 2600mPas at 75 ℃.

The ether content of the oligocarbonate diol obtained in example 3 is significantly lower than that of the oligocarbonate diol obtained in example 4. This directly affects the hot air resistance of the thermoplastic elastomers prepared from these polyols.

Example 5

A polyurethane prepolymer was prepared using the aliphatic oligocarbonate diol obtained in example 3 as a starting material.

To a 250ml three-necked flask equipped with a stirrer and a reflux condenser was added 50.24g of diphenylmethane-4, 4' -diisocyanate at 80 ℃ and then, under a nitrogen atmosphere, 99.76g of the aliphatic oligocarbonate diol from example 3 heated to 80 ℃ (equivalent ratio of isocyanate to polyol: 1.00: 0.25) was slowly added. After the addition was complete, the flask contents were stirred for 30 min.

A liquid, highly viscous polyurethane prepolymer having the following characteristic values was obtained: NCO content: 8.50 wt.%: viscosity: 6560mPas at 70 ℃.

The prepolymer was stored at 80 ℃ for a further 72h and then checked for viscosity and NCO content.

After storage, the liquid product had the following characteristic data: NCO content: 8.40 wt.%; viscosity: 6980mPas (corresponding to a 6.4% increase in viscosity) at 70 ℃.

Example 6 (comparative)

A polyurethane prepolymer was prepared using the aliphatic oligocarbonate diol obtained in example 4 as a starting material.

To a 250ml three-necked flask equipped with a stirrer and a reflux condenser was added 50.24g of diphenylmethane 4, 4' -diisocyanate at 80 ℃ and then, under a nitrogen atmosphere, 99.76g of the aliphatic oligocarbonate diol from example 4 heated to 80 ℃ (equivalent ratio of isocyanate to polyol: 1.00: 0.25) was slowly added. After the addition was complete, the flask contents were stirred for 30 min.

A liquid, highly viscous polyurethane prepolymer having the following characteristic values was obtained: NCO content: 8.5 wt.%; viscosity: 5700mPas at 70 ℃.

The prepolymer was stored at 80 ℃ for a further 72 hours and then the viscosity and NCO content were determined. After storage, the product is obtained in solid form (gel).

From the viscosity comparison results of examples 5 and 6, it is evident that the viscosity of the prepolymer obtained from example 6 increases significantly during storage so as to turn into a gel-like state, whereas the viscosity in example 5 increases by 6.4%, well below the critical limit of 20%.

It is therefore clear that the aliphatic oligocarbonate polyols prepared using the catalyst ytterbium (III) acetylacetonate according to the invention have a significantly reduced and thus more advantageous activity in the reaction with (poly) isocyanates to give (poly) urethanes compared with those prepared with the aid of the catalysts known from the prior art, even if these known catalysts are "deactivated".

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (7)

1. A process for preparing aliphatic oligocarbonate polyols having a number-average molecular weight of 500-5000g/mol, which comprises reacting aliphatic polyols with organic carbonates in the presence of ytterbium (III) acetylacetonate as transesterification catalyst.

2. The method according to claim 1, wherein the organic carbonate is dimethyl carbonate, diethyl carbonate, diphenyl carbonate, or any combination thereof.

3. The process according to claim 1, wherein the organic carbonate is dimethyl carbonate.

4. The process of claim 1 wherein the aliphatic polyol is the addition reaction product of (a) an aliphatic diol and (b) a lactone or epoxide.

5. The process according to claim 1, wherein the aliphatic polyol is 1, 6-hexanediol, a ring-opening product of 1, 6-hexanediol and epsilon-caprolactone, or a mixture thereof.

6. The process according to claim 1, wherein the concentration of the catalyst is from 0.01 to 10000ppm, based on the total mass of the educts used.

7. The process according to claim 1, wherein the methyl ether content in the aliphatic oligocarbonate polyol is less than or equal to 0.2 wt.%.