HK1100672B - Oligocarbonate polyols comprising terminal secondary hydroxyl groups - Google Patents

Description

Oligocarbonate polyols having terminal secondary hydroxyl groups

The invention relates to a method for producing aliphatic oligocarbonate polyols having terminal secondary hydroxyl groups by transesterification of organic carbonates with aliphatic polyols.

The oligocarbonate diols can in principle be prepared by reacting aliphatic polyols with phosgene, dichlorocarbonate, diaryl carbonate, cyclic carbonate or dialkyl carbonate. They are important precursors for the production of plastics, coatings and adhesives. For example, they are reacted with isocyanates, epoxides, (cyclo) esters, acids or anhydrides.

DE-A10130882 describes, for example, the preparation of aliphatic oligocarbonate diols by reacting dimethyl carbonate with aliphatic diols under pressure. The diols disclosed in this document are exclusively diols having primary hydroxyl functions, so that only aliphatic oligocarbonates having terminal primary hydroxyl groups are obtained.

Furthermore, DE-A10156896 discloses that, for the preparation of aliphatic oligocarbonate polyols by transesterification of organic carbonates, it is also possible to use polyols having secondary or tertiary hydroxyl groups. There is no description in this document about separate, stepwise addition of polyols having primary hydroxyl groups and polyols having secondary hydroxyl groups.

However, the preparation processes known from the prior art have the disadvantage that, when polyols having secondary hydroxyl functions are used, the transesterification with organic carbonates can only be carried out at low conversions, with the result that oligocarbonate polyols having an average molecular weight of more than 500 g/mol cannot be prepared or can only be obtained if very long transesterification times are acceptable. This preparation process is uneconomical due to the poor space-time yields (space-time yield) obtained.

On the other hand, oligocarbonate polyols having terminal secondary hydroxyl groups have attracted considerable interest as coreactants for highly reactive (poly) isocyanates, for example in the preparation of aromatic polyisocyanate prepolymers, or for controlling the urethanization reaction by means of different OH activities.

It was therefore an object of the present invention to provide an economically viable process for preparing aliphatic oligocarbonate polyols having terminal secondary hydroxyl groups.

This object is achieved by a multistage process as described hereinafter.

The invention provides a process for preparing aliphatic oligocarbonate polyols having secondary OH groups and a number-average molecular weight of > 500 g/mol, comprising the following steps:

A) firstly reacting an excess of organic carbonate with a polyol which contains only primary OH groups to prepare a polymer having an average OH group concentration of 0.3 mol% or less based on 1 mol of the reaction product thus obtained,

B) the cleavage products formed are removed simultaneously with the transesterification or else subsequently together with excess unreacted carbonate and, in a further step,

C) the polymer thus formed is reacted with an aliphatic polyol containing at least one secondary OH group per molecule to give a product having an average secondary OH group concentration of > 5 mol%, based on the sum of all OH groups present.

The polymer from stage A) preferably contains on average less than 0.2 mol%, more preferably less than or equal to 0.1 mol% and most preferably from 0 to 0.05 mol% of OH groups.

The oligocarbonate polyols obtained after step C) preferably have a secondary OH group content of > 5 mol%, more preferably > 30 mol% and most preferably from 60 to 95 mol%, based on the sum of all OH groups.

The number average molecular weight of the oligocarbonate polyols obtained after step C) is generally from 500 to 5000 g/mol, preferably from 500 to 3000 g/mol, more preferably from 750 to 2500 g/mol.

The oligocarbonate polyols obtained after step C) have an average OH functionality of > 1.80, preferably > 1.90, more preferably from 1.90 to 5.0.

The organic carbonates used in stage a) can be, for example, aryl carbonates, alkyl carbonates, alkylene carbonates or any mixtures thereof. Examples include diphenyl carbonate (DPC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate. Diphenyl carbonate, dimethyl carbonate and diethyl carbonate are preferably used. Particular preference is given to using diphenyl carbonate and dimethyl carbonate.

The primary aliphatic polyols used in stage A) are generally compounds having from 4 to 50 carbon atoms in the chain (branched and/or unbranched), and the chain may also be interrupted by further heteroatoms, such as oxygen (O), sulfur (S) or nitrogen (N). A) The OH functionality of these polyols used in (1) is from 2 to 8, more preferably from 2 to 4.

Examples of suitable aliphatic primary polyols are 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 7-heptanediol, 1, 12-dodecanediol, cyclohexanedimethanol, 3-methyl-1, 5-pentanediol, 2, 4-diethyl-1, 5-pentanediol, bis (2-hydroxyethyl) ether, bis (6-hydroxyhexyl) ether, dimer diol, trimethylolpropane, pentaerythritol, or short-chain polyether polyols having primary hydroxyl groups and a number average molecular weight of 700 g/mol or less, and mixtures thereof.

Furthermore, addition products or mixtures of the above-mentioned aliphatic primary polyols with lactones (cyclic esters) such as epsilon-caprolactone or valerolactone may be used.

The aliphatic polyols having at least one secondary hydroxyl group used in stage C) are generally compounds having from 4 to 50 carbon atoms in the chain (branched and/or unbranched) and the chain may also be interrupted by further heteroatoms such as oxygen (O), sulfur (S) or nitrogen (N). C) The OH functionality of these polyols used in (1) is preferably from 2 to 8, more preferably from 2 to 4.

Examples of these aliphatic polyols having at least one secondary hydroxyl group are 1, 2-propanediol, 1, 3-butanediol, 1, 2-pentanediol, 1, 3-pentanediol, 1, 4-pentanediol, 2, 3-pentanediol, 2, 4-pentanediol, 1, 2-hexanediol, 1, 3-hexanediol, 1, 4-hexanediol, 1, 5-hexanediol, 2, 3-hexanediol, 2, 4-hexanediol, 2, 5-hexanediol, 2, 4-trimethylpentane-1, 3-diol, 2-bis (4-hydroxycyclohexyl) propane, glucose, sorbitol, short chain polyether polyols having secondary hydroxyl groups and a number average molecular weight of 700 g/mol or less, and mixtures thereof.

In addition, all compounds known from the prior art which are capable of catalyzing transesterification reactions can be used in the process according to the invention. Particularly suitable for the process according to the invention are hydroxides, oxides, metal alkoxides, carbonates, organometallic compounds and complexes of metals of main groups I, II and IV of the Mendeleev's periodic Table of the elements and of transition groups II and IV, including rare earth metals, in particular compounds of titanium, zirconium, lead, tin, antimony, yttrium and ytterbium.

Examples include the catalysts LiOH, Li₂CO₃、K₂CO₃、Mg₅(OH)₂(CO₃)₄Titanium tetraalkoxide, dibutyltin dilaurate, dibutyltin oxide, bis (tributyltin) oxide, yttrium (III) acetylacetonate, and ytterbium (III) acetylacetonate.

In the case of using a transesterification catalyst, it is preferable to use Mg₅(OH)₂(CO₃)₄Titanium tetraalkoxide, dibutyltin dilaurate, yttrium (III) acetylacetonate, and ytterbium (III) acetylacetonate.

In the case of using a catalyst, the concentration of the catalyst is 0.01ppm to 1000ppm (metal content based on the oligocarbonate polyol of the present invention obtained), preferably 0.01ppm to 500ppm, more preferably 0.1ppm to 300 ppm.

The process according to the invention is generally carried out at a temperature of from 50 to 250 ℃, preferably from 100 to 200 ℃ and a pressure of from 0.01 to 10 bar (absolute), preferably from 0.05 to 6 bar (absolute).

Stage C) of the process according to the invention is carried out until the experimentally determined hydroxyl functionality reaches more than 90% of theory, preferably more than 95% of theory.

In order to accelerate the reaction in stage C), it is possible to add further transesterification catalysts and/or to carry out the reaction at pressures of < 1013 mbar (abs.).

The amount of organic carbonate or corresponding polyol used in stage A) depends on the desired number-average molecular weight (M) of the oligocarbonate polyol to be prepared_n)。

It is important that the organic carbonate in A) is always in excess, based on the primary OH groups present in the polyol, so that even after stage A) a substantially OH-free polymer having the abovementioned OH group content is obtained. In general, the organic carbonates are present in an excess of 5 to 100 mol%, preferably in an excess of 10 to 50 mol%, based on the stoichiometric amount required for preparing the theoretical OH-functional compound.

In stage A) of the process according to the invention, the transesterification of the aliphatic primary polyol with the organic carbonate can also be carried out stepwise, i.e.the organic carbonate is added stepwise to the aliphatic primary polyol, with by-products being removed between stepwise additions, if appropriate at a pressure of less than 1 bar (absolute). It is likewise possible to meter the organic carbonate continuously while continuously removing the by-products.

In general, the reaction time of stage A) is from 5 to 100 hours, preferably from 10 to 80 hours. In general, the reaction time of stage C) is from 1 to 50 hours, preferably from 5 to 25 hours.

The oligocarbonate polyols obtained by the process according to the invention are particularly suitable for producing coatings, dispersions, adhesives and sealants.

In principle, such coatings, dispersions, adhesives and sealants can be applied to all known substrates and cured.

Examples

By reaction of the corresponding products¹The calculation of the integral of the H NMR spectrum determines the content of terminal secondary hydroxyl groups in the oligocarbonate diol, as well as the hydroxyl functionality. In all cases, the target compound used as a benchmark is the ideal structure resulting from the chosen stoichiometry. First, the number average molecular weight (M) of a specific product was calculated from the integral of proton resonance of the repeating unit in the molecule_n). This object is achieved by signals from the methylene groups of the diols used, the CH groups of the oligocarbonate diols₂The methylene end groups of the-OH groups are used for normalization. Likewise, the proportion of non-hydroxyl-functional end groups (essentially methyl ester groups and methyl ether groups) is determined by integration of the corresponding signals and normalization to the methylene end groups. The sum of the molecular weight of the desired oligocarbonate diol and the molecular weight of the terminal non-hydroxyl functional groups (chain terminators) is the total molecular weight. The proportion of chain terminators in the entire compound is accordingly calculated in mol%. The actual functionality to be determined constitutes the difference between the theoretical maximum functionality and the chain terminator content. The proportion of terminal secondary hydroxyl groups is determined in a similar manner.

The hydroxyl number (OHN) was determined in accordance with DIN 53240-2.

Calculating the number average molecular weight (M) from the relationship between the hydroxyl number and the functionality_n)。

The viscosity was determined according to DIN EN ISO 3219 with a VISKOLA LC-3/ISO rotational viscometer from Physika, Germany.

Example 1:

295.9 g of 1, 6-hexanediol were heated to 120 ℃ in a multi-necked flask with stirrer and reflux condenser and dehydrated at 2 mbar for 2 hours. The oil bath was then cooled to 110 ℃ under nitrogen, 0.08 g of ytterbium (III) acetylacetonate were added and 363.9 g of dimethyl carbonate were metered in over 20 minutes. After the addition was complete, the reaction mixture was held at reflux for 24 hours.

The reaction mixture is then subjected to distillation during which methanol by-product is removed as well as traces of dimethyl carbonate. The distillation was first carried out at 150 ℃ for 4 hours and then continued at 180 ℃ for 4 hours. The temperature was then lowered to 130 ℃ and the pressure was reduced to < 20 mbar. In addition, in this case, a nitrogen stream (2 l/h) was passed through the reaction mixture. Finally, the temperature was increased from 130 ℃ to 180 ℃ provided that the top temperature did not exceed 60 ℃. The reaction mixture was held at this temperature for 6 hours. The hydroxyl number (OHN) determined thereafter was 18.8 mg KOH/g, indicating that the hydroxyl group concentration in the oligocarbonate was still too high. An additional 100 g of dimethyl carbonate were then added at the oil bath temperature of 120 c and the mixture was held at reflux for 2 hours. Then, the by-product and excess dimethyl carbonate were distilled at 150 ℃ for 2 hours. Finally, the temperature was raised to 180 ℃ over 6 hours and maintained at this temperature for 1 hour.

The resulting oligocarbonates have a hydroxyl number of 0 and therefore a hydroxyl group concentration of < 0.05 mol%.

To the oligocarbonate obtained 48.5 g of 1, 3-butanediol were added and the mixture was stirred at 180 ℃ for 8 hours, during which time methanol was removed as a by-product from the reaction mixture. This gives a waxy oligocarbonate diol having the following characteristic data:

hydroxyl Number (OHN): 53.0 mg KOH/g

M_n: 2100 g/mol

Hydroxyl functionality: 1.97

Content of terminal secondary hydroxyl group: 75 mol%

Viscosity: 3500mPas at 75 ℃ C

Comparative example

314.5 g of 1, 3-butanediol are heated to 120 ℃ in a multi-necked flask with stirrer and reflux condenser and dehydrated at 20 mbar for 2 hours. The oil bath was then cooled to 110 ℃ under nitrogen, 0.08 g of ytterbium (III) acetylacetonate were added and 444.5 g of dimethyl carbonate were metered in over the course of 20 minutes. After the addition was complete, the reaction mixture was held at reflux for 24 hours.

The reaction mixture is then subjected to distillation during which methanol by-product is removed as well as traces of dimethyl carbonate. The distillation was first carried out at 150 ℃ for 4 hours and then continued at 180 ℃ for 4 hours. The temperature was then lowered to 130 ℃ and the pressure was reduced to < 20 mbar. In addition, in this case, a nitrogen stream (2 l/h) was passed through the reaction mixture. Finally, the temperature was increased from 130 ℃ to 180 ℃ provided that the top temperature did not exceed 60 ℃. The reaction mixture was held at this temperature for 6 hours. The hydroxyl number (OHN) determined thereafter was 348.5 mg KOH/g, indicating that virtually no polymer degradation had occurred. In addition, corresponding¹H NMR shows a high proportion of by-products contaminating the product, which is therefore not suitable for further reaction with, for example, (polyisocyanates).

Claims (8)

1. A process for preparing aliphatic oligocarbonate polyols having secondary OH groups and a number average molecular weight of > 500 g/mol, which comprises the steps of:

A) firstly reacting an excess of organic carbonate with a polyol which contains only primary OH groups to prepare a polymer having an average OH group concentration of not more than 0.3 mol%, based on 1 mol of the reaction product thus obtained,

B) the cleavage products formed are removed simultaneously with the transesterification or else subsequently together with excess unreacted carbonate and, in a further step,

C) reacting the polymer thus formed with an aliphatic polyol containing at least one secondary OH group per molecule to give a product having an average secondary OH group concentration of > 5 mol%, based on the sum of all OH groups present,

wherein the catalyst used in the method is an yttrium compound and/or an ytterbium compound.

2. The process for preparing aliphatic oligocarbonate polyols according to claim 1, wherein the polymer from stage A) contains on average from 0 to 0.05 mol% of OH groups.

3. The process for preparing aliphatic oligocarbonate polyols according to claim 1 or 2, wherein the oligocarbonate polyol obtained after step C) has a secondary OH group content of from 60 to 95 mol%, based on the sum of all OH groups.

4. The method of claim 1, wherein the catalyst is yttrium acetylacetonate and/or ytterbium acetylacetonate.

5. Aliphatic oligocarbonate polyols obtainable by a process according to any one of claims 1 to 4.

6. The aliphatic oligocarbonate polyol according to claim 5, having an average OH functionality of from 1.90 to 5.0.

7. The aliphatic oligocarbonate polyol according to claim 5 or 6, having a number average molecular weight of from 750 to 2500 g/mol.

8. Coatings, dispersions, adhesives and/or sealants prepared using the aliphatic oligocarbonate polyols according to any of claims 5 to 7.