CS203242B1 - Method for treatment of dimethylformamide for the production of linear polyurethans solutios and/or low-molecular compounds with polyurethan segments,containing hydroxyl,eventually isocyanate groups - Google Patents

Description

The invention relates to a process for the treatment of dimethylformamide for the production of solutions of linear polyurethanes and / or low molecular weight compounds with polyurethane segments containing hydroxyl or isocyanate groups. The term "linear polyurethanes" refers to polymers containing in the chain polyurethane and / or urea moieties and having a predominantly linear structure, but no substantially branched or spatially crosslinked structures relative to this linear structure, in particular no biuret and / or allophanate moieties. In addition, all or a substantial portion of the components or units are substantially bifunctional.

These elastomers include the so-called polyurethane, polyurea or polyurethane elastomers (hereinafter referred to as polyurethanes), produced by chain extension of the prepolymer with terminal isocyanate groups or by reaction of a higher molecular weight bifunctional compound and a low molecular weight bifunctional compound with diisocyanate under vigorous stirring at higher temperature. The components reported in the literature and the relative amounts of the individual components can be selected in a known manner according to the desired properties, but the amount of isocyanate used must be approximately equal to the sum of the total reactive hydrogen so that the products are free of isocyanate during storage.

For the preparation of these elastomers according to the known diisocyanate polyaddition process, hydroxyl-terminated polyesters, hydroxypolyalkyleoxides, hydroxypolyacetates or similar polymers with a hydroxyl-terminated group, diisocyanates and glycol chain extenders are predominantly used. hydroxyl-terminated polymers having a substantially linear structure and a molecular weight ranging from 500 to 10,000, preferably between 800 and 4000, are used as reactants for the production of polyurethanes. Compounds having a melting point below 60 ° C are preferably used.

The hydroxyl-terminated polyesters used are prepared by known methods, with or without a catalyst, by esterification of a dicarboxylic acid of the formula HOOC-R-COOH, in which R may be an alkylene radical of 2 to 8 carbon atoms or an aromatic radical (optionally only partially), glycols of formula HO- (CH _{2) x} -OH, wherein x has a value from 2 to 8. In addition, also is well suited diols with alkyl side chains (e.g., neopentyl glycol) and ether glycol (e.g., diethylene glycol). Usually, more than one mole of glycol per mole of dicarboxylic acid is used to ensure linearity in esterification.

Hydroxypolyalkylene oxides or polyethers are also substantially linear compounds containing terminal hydroxyl groups as well as ether linkages of low molecular weight components. The polyethers correspond essentially to the general formula HO [(CH ₂ ) _n O] _x H, wherein n is a number from 2 to 6 and x is an integer. Since the polyethers provide hydrolysis-resistant polyurethanes, they are preferably used when such polyurethanes are required. Polyacetates are made from aldehydes and excess polyhydric alcohols. The best known polyacetate is the reaction product of formaldehyde and ethyl glycol.

Further useful are other literature compounds such as lactone polyesters, mixed polymers with ester, ether, acetate or urethane groups, high molecular weight carboxyl, amine or mercapto terminated compounds.

The chain-extending compounds typically belong to the following classes of compounds: glycols, glycol ethers, hydroxyalkyl ethers of hydroquinone, aromatics and cycloallates with hydroxy groups, and other compounds reported in the chain-extending literature.

As the diisocyanate components, all of the organic diisocyanates known from the literature can be used for the production of polyurethanes. Examples of useful diisocyanates are aliphatic such as tetramethylene diisocyanate, hexamethylene diisocyanate, decamethylene diisocyanate, aromatic such as toluylene-2,4-diisocyanate, toluylene-2,6-diisocyanate, technical mixtures of diisocyanate, 4,4'-diphenylmethane diisocyanate, 4'-diisocyanate, m- and p-phenylenediisocyanate, p-xylenediisocyanate, naphthylene-1,5-diisocyanate, tetrahydronaphthylene-1,5-diisocyanate, diphenyl-4,4'-diisocyanate, 3,3'-dimethyldiphenyl-4, 4'-diisocyanate as well as other alkyl, alkoxy or halo-substituted derivatives, cycloaliphatic. such as dicyclohexyl methane diisocyanate, n-ethylcyclohexyldiisocyanate, 2,2,4-trimethylhexyldiisocyanate, and mixtures of these diisocyanates.

For its technical availability and for the characteristics of the resulting polyurethanes, 4,4‘-diphenylmethane diisocyanate and 2,4- (2,6) -toluylene diisocyanate are preferably used.

Polyurethanes are produced according to known methods, and production is predominantly continuous, by feeding the components simultaneously or sequentially through a metering pump to the mixing chamber and then discharging onto a strip guided by the heating chamber. Granulation is usually followed by storage at a higher temperature to ensure complete reaction between the hydroxyl and isocyanate groups.

as mentioned above, the molar ratios of the reactants are chosen such that the reaction product contains substantially no free hydroxyl or isocyanate groups.

The high molecular weight hydroxyl compounds, the low molecular weight hydroxyl compounds and the diisocyanates are reacted generally in a molar ratio of 1: 0 to 15, preferably 0.1 to 10: 1 to 16, preferably 1.1 to 11, so that the number of isocyanate equivalents corresponds to the number of hydroxyl equivalents. It follows from the reaction ratios of the reactants and the listed compounds or classes of compounds that numerous recipes are possible, and thus the formation of properties over a wide range is possible.

Furthermore, low molecular weight compounds containing hydroxyl or isocyanate groups with polyurethane segments can also be used for further solution reactions. The preparation of these compounds is usually carried out according to analogous synthesis principles. However, the reaction is carried out in such a way that no high molecular weight elastomers are formed, but only products of substantially low hydroxyl or isocyanate group-containing linear compounds are usually readily soluble, so that during storage the degradation reactions of the solutions are more pronounced during storage than dissolution.

In addition, there is, inter alia, the need to vary the concentration of polyurethane solutions which have not been produced by dissolving the rigid elastomers. but by extending the chains of the prepolymers with isocyanate groups with bifunctional chain extenders in the presence of a suitable solvent. Degradation reactions can occur during storage by impurities introduced in this process.

The preparation of polyurethanes in solution is described in the literature. According to the process data, precursors are prepared from polyols and diisocyanates by heating to about 60-120 ° C.

Depending on the reaction ratio used, the polyols are "preloaded" through urethane compounds (NCO / OH less than 2) or linked at the end of the chains with diisocyanates (NCO / OH = = 2). At a molar excess of diisocyanates of more than 100% (NCO / OH greater than 2), in addition to the prepolymer, free diisocyanate is also present. It is also possible to react the diisocyanate with a molar excess of polyol and to react the product with another diisocyanate before the chain extension itself. The polyols used for the preparation of the precursors usually have molecular weights of about 300 to 5000, preferably 500 to 3000. They are freed of water residues under vacuum (1.3 to 2 kPaj at a temperature of 100 to 135 ° C, or by azeotropic distillation. and / or cycloaliphatic diisocyanates, Arylene diisocyanates are preferred because they are more reactive than alkylene diisocyanates.

The high variability of the polyurethanes / polyureas is due not only to the large number of possible starting products - polyethers, polyesters or other linear hydroxyl-terminated polymers, but also to a number of possibilities for process control, in particular for chain elongation. For this, it is necessary to produce in the first stage precursors having terminal free NCO groups. These are bound after dissolution in the chain extension with suitable substances, the following compounds being suitable as chain extenders: alcohols, dlamines, amino acids, ureas, heterocyclic nitrogen bases, hydrezine and derivatives thereof, water. Dimethyl acetamide, dimstylacetamide, dimethyl sulfoxide, tetrahydrofuran and / or acetone, dioxane, benzene, toluene, methylethylketone, methylene chloride, chlorobenzene, ethyl acetate, etc. are preferably used as solvents in the chain-extending reaction.

Two basic operating procedures have been established for combining the two reactants. The chain extender (equivalent amount) is introduced dissolved in the solvent and at the same time diluted and the undiluted feedstock is added gradually or rapidly or the pre-product solution is introduced in reverse or the dissolved chain extender is added immediately or slowly.

In some patents, multistage chain extensions of dissolved precedents are also claimed. In these processes, the chains of the prepolymers containing the isocyanate groups are not immediately extended, but the synthesis of the high molecular weight end state is achieved via intermediate stages containing the amine and isocyanate groups.

In contrast to the solvent-free polyurethane production, bifunctional compounds highly reactive to isocyanate can also be used for chain extension, since the dissolution of chain extenders and precursor products usually greatly reduces the reaction rate.

The polymer solutions can be used in a variety of application areas, such as for layering sheet materials, for the production of films and microporous products, fibers, paints, adhesives and, after solvent removal, for the production of moldings. KscmS of this, iyio raisins are suitable for impregnation.

For the technical use of similar solutions, it is essential that polyurethane solutions always have the same dynamic and intrinsic viscosities for the same dry matter (viscosity limit values and that they do not change when the polymers dissolve, making solid technology impossible and adaptation based on different products) Quality fluctuations can reduce the utility value of end products such as foils, fibers, coatings and impregnations in terms of strength, elongation and ermoplasticity, which may exhibit significant variations. such important properties as notch strength, flexural strength, flexibility, formability, abrasion resistance, hardness, aging resistance and other properties that determine the substantially useful properties of the polyurethane product.

The production of polyurethane solutions for these uses is widely described in the literature. According to the present teachings, polyurethanes, in particular polyurethane granules or chips, are usually dissolved at temperatures below 100 ° C in appropriate solvents, either granulating the granules at room temperature and then dissolving at elevated temperature with stirring, or adding the granules in batches to heated solvents. with stirring.

It is known that all polyurethane elastomers have only limited stability against hydrolytic effects. In addition, most of the impurities in the solvents, especially the organic bases, and of them the strongly low molecular weight organic bases, have a degrading effect on the polyurethanes during dissolution, so that depending on the no. it changes the polyurethanes so that there is also a noticeable change in characteristics due to more or less degraded products due to the uncontrolled release of bonds. This makes the use of these polyurethane solutions more difficult, or makes reproducibility of the application technology impossible, since the dissolution process requires heat and intensive mixing with shear forces, so that undesirable degradation is further promoted.

It has been reported in the literature that urethane, urea, allophanate and biuret groups are substantially more resistant to hydrolytic effects at 75 ^° C than ester groups which are already cleaved by 0.5 N methanolic sodium hydroxide solution or 0.5% methanolic acid solution. saline. In contrast to the torsion, the " fission agent equilibrium " is more pronounced at higher temperatures, so that the instability of urethane, urea, allophanate and biuret groups increases. Isocyanate adducts are cleavable amines to ureas at low temperatures. This so-called aminolysis leads in each case to degradation reactions and thus to a change in polyurethanes. Since the ester moiety is also particularly subject to aminolysis, amines in solvents are undesirable as they act at low concentrations and change the polyurethane during dissolution.

Substantial differences in polymer characteristics can already be expected in the production of solutions of varying concentrations, since during dissolution different amounts of impurities act on the polyurethane and thus the degradation or change of the polyurethane does not occur uniformly. It is further known that the solvents are refined or treated by one or more purification processes, such as distillation, also by treatment with the aromatic mono- or diisocyanate according to U.S. Pat. aut. Certificate No. 126 965, ion-exchange cleaning or treatment with dehydrating agents. These processes do not always lead to the desired result, since traces of impurities are very difficult to remove. Removing the last traces of impurities is technically and economically very demanding, so this is largely dispensed with, thus creating a solvent which does not meet all quality requirements, and the proportions of impurities may still fluctuate within certain limits.

It is also known to use sulfonyl laocyanates as dehydrating agents in liquid and pasty, optionally solvent, clear or pigmented polyurethane compositions. The use of sulfonyl isocyanates has the advantage that the adducts formed by the reaction do not precipitate. These sulfonyl isocyanates are not produced in large volumes and are therefore not available for technical use.

The use of betaine salts to stabilize the viscosity of polyurethane solutions is known. Betaine salts, however, are added after dissolution or after the polvadition process in addition to prevent polymer changes during storage.

It is apparent from the West German disclosure that numerous polyurethane solutions produced by dissolving solid polymers in solvent or by polymerization in solution readily adversely change during storage and must therefore be processed within a relatively short time after manufacture. According to the disclosure, warm polyurethane solutions can be obtained by adding small amounts of a stabilizing organic compound containing carboxyl groups to the polyurethane solutions, while the unstabilized polyurethane solution is readily degraded, stored under the same conditions. The stabilization described is limited to post-stabilization of the solutions. The change in polymer during dissolution due to impurities contained in the solvent is disregarded so that only the polyurethanes already altered during dissolution are stabilized.

In the process already proposed for the treatment of dimethylformamide as solvent for polyurethane / polyurea synthesis, the idea of the invention is to block the low molecular weight isocyanate-active impurities by means of isocyanates or diisocyanates in order to avoid side reactions during the process.

The purpose of the invention is to preserve the characteristics of the predominantly linear polyurethanes and / or low molecular weight compounds with polyurethane segments containing hydroxyl or isocyanate groups in the solvent treatment.

The invention is based on the task of changing solvents in such a way that it cannot induce or stimulate degradation reactions of linear polyurethanes and / or low molecular weight compounds with polyurethane segments containing hydroxyl or isocyanate groups.

According to the invention, dimethylformamide for the preparation of solutions of linear polyurethanes and / or low molecular weight compounds with polyurethane segments containing hydroxyl or isocyanate groups is treated by treating the diphenylformamide with 50 to 100% by weight of methyl iodide, benzoyl chloride or perchloric acid. %, relative to the reacting impurities, leaving the resulting soluble reaction products in the solvent, in contrast, the insoluble reaction products can be filtered off or also left in the solvent.

The impurities in the solvent can be allowed to react completely. However, the reaction must then proceed until the impurities in question are no longer detectable.

Surprisingly, it has been found that it is usually sufficient to substantially reduce the content of impurities and that there is no need to focus on complete reaction, since the traces of impurities remaining thus in the solvent do not adversely affect the dissolution result. In addition, it has been found that the polyurethane solution produced with the untreated solvent has different characteristics than the solution of the same concentration made with the pretreated solvent, even if the impurities of the untreated solvent are in a range where their adverse effects can no longer be practically talked about. In other words, by pretreating the solvent, its character is noticeably changed to such an extent that it is possible to produce polyurethane solutions from granulates with properties other than that which can be prepared with a pure but untreated solvent.

By using such pretreated solvents to dissolve high molecular weight and low molecular weight, especially linear polyurethanes, it is guaranteed that the degradation reaction is suppressed due to hydrolysis, aminolysis and other degradation reactions to such an extent that the polyurethane does not change or change insignificantly in its characteristics. , which could be attributed to a change in the properties of polyurethane.

It has been found that the dynamic viscosity of the resulting polyurethane solution depends on the content of impurities present in the solvent. In addition, changes occur at the viscosity limit number. By correcting dimethylformamide with isocyanate, quaternary, neutralizing or acylating compounds, the impurities causing degradation of the polyurethane are reacted, so that after dissolution of the polyurethane granulates the highest values for dynamic viscosity and the limit viscosity number and the range of polyurethane properties are retained. A polyurethane elastomer having the following characteristics was used to produce the polyurethane solutions mentioned in the examples:

Test method

Hardness: Shore A 80 ± 5 TGL 14 365 Tensile strength: N / mm ² 35.0 TGL 53 504 Tear strength: % 700 DIN 53 504 Impact elasticity: % 400 TGL 24 415 Resistance to tearing: N / cm 500 DIN 53 515 Abrasion resistance: mm ³ 50 DIN 53 516 Residual deformation by pressure: % 15 Dec DIN 53 517 Density: g / cm ³ 1,22 TGL 14 370 Bulk weight: g / dm ³ 500 - The examples below serve closer Example 2

The percentages given are percentages by weight.

The same polyurethane granulate was dissolved within 2.5 hours at 80 ° C with stirring to a 15 ° / other dimethylformamide polyurethane solution with a different impurity content:

Example 1 water 0.01%

The polyurethane granulate was dissolved in formic acid 2. 10 ^-3 % methylformamide over 2.5 hours at 80 ° C dimethylamine 0.51% with stirring to 15% solution. methanol 10 ^-4 %

The dimethylformamide used for the dissolution contained the following impurities ?:

water 0.01% following dynamic viscosity ožity formic acid 2: 10 ~ ³ % dimethylamine 9. IO- ³ % 3960 mPa. with at 8.28 s ^_1 methanol <10- ⁴ % 3820 mPa. with * 20.7 O 3600 mPa. with at 41.4 S ¹ 3260 mPa. with at 82.8 S ' ¹ Polyurethane solution exhibited in vis- limit number 1.25 ml / g followed by Example 3 Dynamic viscosity:

9660 mPa. s at 5 s “ ¹

7000 mPa.s at 12.5 s ¹ 6880 mPa. s at 25 s ^-1 6160 mPa. s at 50 s “ ¹

The resulting polyurethane solution showed

20% polyurethane solutions were prepared from the polyurethane granulate within 2.5 hours (solution A) and within 6 hours (solution B) at 80 ° C with stirring. The dimethylformamide used for the dissolution contained the following impurities:

A B

water 0.01% 0.01 % formic acid 2.IO ' ³ % 2.IO- ³ % dimethylamine 0.054% 0.50 % methanol <IO ⁴ % <IO ⁴ % Polyurethane solutions had viscosity- 0.99 ml / g (solution R) of the solution pouring cynunnc : ké limit value of 1.03 ml / g (solution A 1 and viscosity: AND (B) 24,700 mPa. s at 5 s “ ¹ 11,960 mPa.s at 8.28 sec ^-1 22,000 mPa.s at 12.5 s ^-1 10,880 mPa. s at 20.7 s ^-1 20,300 mPa. s at 25 s ^_1 10 130 mPa, s at 41,4 s “ ¹ 16,600 mPa. s at 50 s ^_1 Example 4 ve 10% solutions at 80 ° C with stirring whit- within 4 hours. Dimethylformamide used as The polyurethane granules were prepared the solvent contained the following impurities: A B C

water formic acid 0.02% 2.IO ' ³ % 0.02% 2.IO “ ³ % 0.02% 2.IO ' ³ % dimethylamine 8.5. IO ' ³ % 0.5% 0.051% methanol IO ⁴ % 10-4 o / _o IO “ ⁴ o / ₀

The polyurethane solutions produced exhibited C 1.18 ml / g at viscosity limit numbers

A 1.23 ml / g of the following dynamic viscosity:

B 0.69 ml / g

AND (B) C 1465 mPa. with at 8.56 S ¹ 390 mPa. with at 10 s ^-1 665 mPa. with at 8.56 S ¹ 1440 mPa. with at 21.4 s ^-1 430 mPa. with at 47.5 s ^_1 745 mPa. with at 21.4 s ^_1 1280 mPa. with at 42.8 S ^_1 400 mPa. with at 95 s ^_1 680 mPa. with at 42.8 S ¹ 1240 mPa. with at 85.6 S ¹ 395 mPa. with at 190 S ' ¹ 680 mPa. with At 85.6 S ^_1

Example 1 a d 5 Example 1 a d 6

The polyurethane granulate is dissolved in pre-treated dimethylformamide to a 10% and 15% solution at 80 ° C with stirring. The correction of dimethylformamide is described in Example 6. After a dissolution time of 4 hours, the major portion was still not dissolved, but was in the swollen state. In comparative experiments of Examples 1 and 4 (solution Aj, it was found that the polyurethane granulate had already dissolved after 2.5 and 4 hours respectively. Thus, the impurity contents in the solvent already lead to chemical degradation of the polyurethane. found at 10% viscosity 3010 mPa · s at 8.28 s ^-1 for 15% viscosity 18,300 mPa · s at 5 s ^1. The solution was filtered prior to measurement because it contained small amounts of gel After 22 hours of dissolution (no fractions) gel) the following values of the viscosity were measured:

10% solution (viscosity limit number 1.35 ml / g)

1310 mPa. s at 8.28 s ^_1

1310 mPa. s at 20, ‘7 s ~ t

1370 mPa. s at 82,8 s ”i 15% solution (viscosity limit number 1,45 ml / g)

9560 mPa. s at 8.28 s ^_1

8350 mPa. s at 20.7 s

7460 mPa. s at 41.4 s ^_1

6600 mPa. s at 82.8 s “ ¹

From the values it is apparent that the thermal degradation of the polyurethane occurred due to the long dissolution time. Thus, when using dimethylformamide so treated, the dissolution times must not be prolonged excessively, but the residual amounts of undissolved polyurethane must be filtered to prevent changes in polyurethane due to thermal degradation.

20% solutions could not be prepared in 22 hours using treated dimethylformamide. The solutions still contained many gel fractions (about 20% based on the polyurethane used,

2000 g of dimethylformamide containing

0.01% water

0.0019% formic acid

0.00085% dimethylamine

0.0001% of methanol is reacted with 2.4 g of 4,4‘-diphenylmethylene diisocyanate at 80 ° C for 4 hours with stirring. After this period, no isocyanate is detectable.

Example 7

2000 g of dimethylformamide having the same impurity content as described in Example 6 was reacted with 10.6 g of a 50% solution of 4,4'-diphenylmethane diisocyanate blocked half-methanol at 80 ^° C with stirring. After this time no isocyanate can be detected.

Dissolution of the polyurethane granulate to a 10% solution at 80 ° C with stirring results in a solution having a dynamic viscosity of 3000 mPa. at 25 s ¹ and a viscosity limit number of 1.42 ml / g.

Example 8

1.60 g of 70% perchloric acid is added to 1000 g of dimethylformamide containing 0.05 θ / o dimethylamine (the total sum of amines is expressed as dimethylamine). Upon dissolution of the polyurethane granulate to 10 (% solution at 80 ° C with stirring) solution having a dynamic viscosity of 3040 mPa · s at 10.7 s ^-1 and a viscosity limit number of 1.48 ml / g.

Example 9

To 1000 g of dimethylformamide containing 0.005 dimethylamine (total sum of amines expressed as dimethylamine) was added 315 mg of methyl iodide.

The 10% polyurethane solution prepared using dimethylformamide so treated had a dynamic viscosity of 3120 mPa. s at 20.7 s ^-1 and a viscosity limit value of 1.49 ml / g / g.

Example 10

156 mg of benzoyl chloride was added to 100 g of dimethylformamide containing 0.005% dimethylamide (total sum of amines expressed as dimethylamine). A 10% polyurethane solution prepared with dimethylformamide so treated has a dynamic viscosity of 3080 mPa. s at 20.7 s ¹ and a viscosity limit number of 1.48 ml / g.

The calculation of the viscosity limit numbers was made from the equation lU Irel as t _L orel -, C t _L = flow time (mean) of polyurethane solution c, t _c = solvent flow time, c = 0.5 g PUR / 100 ml of solution.

The dynamic viscosity was measured with a RN viscometer from Prufgerátewerk Medingen (NDR).

Claims (1)

SUBJECT Process for treating dimethylformamide for the production of solutions of linear polyurethanes and / or low molecular weight compounds with polyurethane segments containing hydroxyl or isocyanate groups, characterized in that dimethyiformamide is treated with 50 to 100% by weight of methyl iodide, benzoyl chloride or perchloric acid. %, based on the reacting impurities, leaving the resulting soluble reaction products in a solvent and insoluble reaction products being filtered off or also left in the solvent.