DE2418951A1 - METHOD FOR STABILIZING POLYACETALS HAVING TERMINAL HYDROXYL GROUPS BY REACTION WITH ORGANIC ISOCYANATES OR ISOTHIOCYANATES - Google Patents

Description

SOCIETA 'ITALIANA RESINE S.I.R. SIp.A. Milan, 11ali en

¹¹ Process for stabilizing polyacetals having terminal hydroxyl groups by reaction with organic isocyanates or isothiocyanates ^t;

Priority: April 20, 1973, Italy, No. 23 257-

The invention relates to an improved method of stabilization of polyacetals. In particular, the invention relates to an improved method for stabilizing terminal Polyacetals containing hydroxyl groups by reaction with organic isocyanates or isothiocyanates. Through this treatment v / ground the hydroxyl groups in urethane or thiourethane groups converted.

Polyacetals are understood here to mean polymers with a molecular weight of at least 10,000 which have been prepared by copolymerization of an aldehyde, copolymerization of various aldehydes or copolymerization of one or more aldehydes with other non-aldehydic monomers. Specific examples of polyacetals are those from _{formaldehyde and L} the cyclic oligomers of formaldehyde ε, v / ie trioxane xnxä

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Tetraox'ane, or from 5, "6-dihydro-1,2-pyran ~ 3-carboxyaldehyde (Dimers of acrolein) by homopolymerization or copolymerization polyacetals obtained with non-aldehyde monomers. The copolymers are obtained, for example, from the copolymerization of an aldehyde such as formaldehyde or a corresponding one cyclic oligomers, such as trioxane, with various monomers, e.g. cyclic ethers, such as ethylene oxide, 1,3-dioxolane and EpI-chlorohydrin. The polyacetals contain at least one hydroxyl group per macromolecule. The production of such polyacetals is for example in US Patents 2,678,994, 2,828,286 and 2,844,561.

DT-OS 2 263 606 describes a process for stabilizing polyacetals containing terminal hydroxyl groups !! described, in which preferably carboxylic acid anhydrides, isocyanates, isothiocyanates or orthoesters can be used to react with the hydroxyl groups.

The conversion of the hydroxyl groups in urethane or. Thiourethane groups using organic isocyanates or isothiocyanates has a very beneficial effect on the properties of the in this way stabilized polyacetals, because this makes it possible to ίεΐ, to bind sterically hindering groups to the ends of the macromolecules, which allow certain physical properties to influence the polymers favorably.

The presence of urethane or thiourethane groups in polymers with a high degree of crystallinity, such as the polyoxymethylene ^ plays an essential role, especially with regard to the formation of crystallization nuclei

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lize and solidify the polymers occur during processing to moldings.

It is known that polyacetals containing hydroxyl groups can be reacted with organic isocyanates or isothiocyanates by that these compounds with the solid polyacetal or suspended in a liquid reaction medium polyacetal treated. According to another known process, the reaction is carried out in a homogeneous phase in a solvent. The best results in terms of yield and thermal stability of the stabilized polyacetal obtained are obtained, when the process is carried out in homogeneous solution. If the process is carried out with the solid polyacetal or the in one liquid reaction medium carried out suspended polyacetal, the reaction rates are generally very high low and the terminal hydroxyl groups are only incompletely grounded converted into urethane or thiourethane groups. In these processes only low yields of products are achieved, whose thermal stability does not meet the practical requirements. Implementation in liquid more homogeneous Phase has the disadvantage that large amounts of solvent and isocyanate or isothiocyanate - if these are used as solvents serve - are required. In other words, the proportions of solvent to polyacetal or isocyanate or isothiocyanate to polyacetal must be very large. At low proportions, the solutions are so viscous that it is practically impossible to dissipate the noise generated during implementation. Furthermore, such highly viscous solutions are difficult to r: if ·· to. Hand lifting, e.g. difficult to pump. Finally brings

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the implementation in a homogeneous solution Problems with the precipitation of the stabilized polyacetals. The precipitated stabilized Polyacetal is obtained in sticky form, which makes the subsequent filtration more difficult. Furthermore, the bulk density of the precipitated stabilized polyacetal is usually so low that it causes serious problems in handling and storage appear. The process is due to the large amounts of solvent required or '. Isocyanate or isothiocyanate also uneconomical because of the large consumption of thermal energy, the high costs of chemicals and because of the unavoidable Losses that occur when the stabilized polyacetal is separated off and purified in the continuous process and the solvent or unreacted isocyanate or isothiocyanate is returned to the reaction zone.

It has surprisingly been found that it is possible to remove the unstable terminal hydroxyl groups of the polyacetals by reaction the polyacetals in suspension in a liquid reaction medium with organic isocyanates or isothiocyanates in To transfer urethane or thiourethane groups, while at the same time high conversion rates and an almost complete conversion can be achieved and the formed stabilized Let polyacetals easily separate from the reaction mixture.

The invention thus relates to a method for stabilizing terminal hydroxyl groups containing polyacetals ^ by reaction with organic isocyanates or isothiocyanates, characterized in that the isocyanate or irothiocyanate

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Cyanate at temperatures of about 50 to 200 ⁰ C with the polyacetal to react, which is suspended in a liquid reaction medium under the process conditions, the reaction medium of at least one of the components of the ■ reaction mixture inert, the polymer does not dissolve and under the process conditions liquid nonsolvent and at least one solvent which dissolves the polymer and the isocyanate or isothiocyanate, is inert to the constituents of the reaction mixture and is liquid under the process conditions, and wherein the solvent and the nonsolvent are completely miscible under the reaction conditions, but at temperatures which are significantly below the reaction temperature, are not or only partially miscible.

Specific examples of those used in the process of the invention organic isocyanates or isothiocyanates are listed below:

Aliphatic monoisocyanates and monoisothiocyanates in the alkyl radical Contain 2 to 20 carbon atoms. The hydrogen atoms of the alkyl radicals can be partially or completely through Halogen atoms, especially chlorine atoms, may be substituted. The alkyl radicals can also have one or more heteroatoms, such as oxygen atoms, contain. Specific examples are ethyl, propyl and octadecyl isocyanate, 2-methoxyethyl isocyanate, 2-ethoxypropyl isocyanate, Methyl isothiocyanate, tert-butyl isothiocyanate and n-dodecyl isothiocyanate.

Cycloaliphatic monoisocyanates and monoisothiocyanates can also be used used, such as cyclohexyl and methoxycyclohexyl

isocyanate and cyclohexyl isothiocyanate,
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aromatic monoisocyanates and. Monoisothiocyanates, such as phenyl, ο-, m- and p-tolyl-, 1- and 2-naphthyl- and p-chlorophenyl isocyanate,

Urethane group-containing monoisocyanates, for example have been obtained by reacting 1 mole of a diisocyanate with 1 mole of methanol,

Thiourethane groups containing monoisothiocyanates, for example by reacting 1 mole of a diisothiocyanate with 1 mole

Methanol have been obtained,

aliphatic diisocyanates and diisothiocyanates _s such as 1,4-tetramethylene and 1,6-hexamethylene diisocyanate and _1,6-f Hexamethylendiisοthiοcyanat

cycloaliphatic diisocyanates and diisothiocyanates such as cyclohexane diisocyanate and cyclohexane diisothiocyanate, aromatic diisocyanates and diisothiocyanates, such as p-phenylene diisocyanate, 2,4- and 2,6-tolylene diisocyanate, 4,4-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate and the corresponding Diisothiocyanates, as well as aliphatic, cycloaliphatic and aromatic triisocyanates, such as 4,4 *, 4 "-triphenylmethane triisocyanate.

The organic isocyanates, in particular the aromatic and aliphatic diisocyanates, such as 2,4- and 2,6-tolylene diisocyanate, are preferred and mixtures thereof and 1,6-hexanemethylene diisocyanate. All of the organic isocyanates and isothiocyanates mentioned are commercial products.

The solvents used in the process according to the invention are compounds which are liquid under the process conditions and the polyacetal can ions at the reaction temperature at which the blocking of the hydroxyl groups in the polyacetal takes place.

Solvents preferred for the purposes of the invention are N-substituted carboxamides, such as dimethylformamide and dimethylacetamide, and aromatic nitro compounds, such as nitrobenzene _f um3

Sulfoxides such as dimethyl sulfoxide. Dimethylformamide is special L preferred. -J

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r · π

The solvent used in the process of the invention must be compared to the polyacetal, the nonsolvent and the Isocyanate or isothiocyanate must be inert. The isocyanate or isothiocyanate must also be in the solvent under the process conditions be soluble. The non-solvent used in the process of the invention is a compound listed under is liquid under the process conditions and the polyacetal does not dissolve or only partially dissolves under the process conditions. That · Non-solvents must be inert towards the solvent, the isocyanate or isothiocyanate and the polyacetal. Specific examples of nonsolvents are saturated straight or branched aliphatic hydrocarbons, cycloaliphatic hydrocarbons and alkyl aromatic hydrocarbons, with one or more unbranched or branched alkyl radicals with at least 6 carbon atoms. Preferred Examples are unbranched paraffins with 6 to 20 carbon atoms and the alkylbenzenes with 8 to 20 carbon atoms in the alkyl radical.

According to an essential feature of the method according to the invention, the solvent and the nonsolvent are in the Complete temperature range in which the hydroxyl groups react with the isocyanates or isothiocyanates mixable with each other. However, they are not or only partially miscible at temperatures which are significantly lower than the reaction temperature e.g. at room temperature (20 to 25 ° C).

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The weight ratio of solvent to nonsolvent can be in a relatively wide range. It is preferably 0.05 ·: 1 to 1: 1, depending on the miscibility of the two compounds at the different temperatures.

The weight ratio of polyacetal to the liquid reaction medium, i.e. the mixture of solvent, nonsolvent and isocyanate or isothiocyanate, can also be combined in one relatively wide range. Preferably, weight ratios of 1: 0.5 to 1:10 are used, as the case may be the crystallization properties, the bulk density and the suspensibility of the polyacetal.

The concentration of the isocyanate or isothiocyanate in the reaction medium depends on the nature of the compounds used and is normally 0.2 to 3.0 percent by weight, based on the solvent.

The inventive method v / ill generally in a range of 50 to 200 ⁰ C. The best results are obtained at temperatures of 120 to 180 ⁰ C. If the reaction temperature is above the boiling point of the reaction mixture, the reaction must be carried out under pressure so that it proceeds in the liquid phase. The reaction is generally carried out for 1 to 60 minutes. The process conditions are preferably chosen so that the reaction proceeds quickly and the residence times are correspondingly short.

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The reasons why surprisingly much better results can be achieved when the conversion of the hydroxyl groups of the polyacetals is carried out according to the process according to the invention are not exactly known. It is believed that the simultaneous use of solvent and non-solvent means for the polyacetal under the particular process conditions according to the invention, the selective dissolution of that part of the macromolecule to which the hydroxyl groups are attached which are subjected to the reaction with the isocyanate or isothiocyanate. The rapid and complete implementation of the hydroxyl groups is believed to be due to the selective dissolution of this part of the macromolecule. The remaining part of the macromolecule, i.e. the larger part of the macromolecule which contains the crystalline part of the macromolecule, is due to the presence of the nonsolvent is not resolved.

The immiscibility of the solvent with the nonsolvent at temperatures below the reaction temperature is advantageous for various reasons. For example after the reaction has ended and after the stabilized polyacetal obtained has been separated off from the reaction mixture, the solvent separated from the nonsolvent by simply cooling. It has been found experimentally that after cooling, a phase consisting of the solvent is obtained, almost all of the impurities occurring during the stabilization reaction and contains by-products. That way, only the solvent needs to be cleaned before going back into the Reaction vessel is returned. The nonsolvent can be placed in the reaction vessel without or after only simple treatment

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be recycled, which is particularly advantageous when you consider that the nonsolvent is usually in the reaction medium is in excess.

The examples illustrate the invention. In Examples 1 to 6, a 5 liter steel reactor is used with an anchor stirrer, a thermometer, a reflux condenser and a pressure control valve is equipped. Implementation is preferred carried out under a protective gas such as nitrogen. The reactor is surrounded by a heating jacket through which a hot liquid is passed as a heat transfer medium heated in a thermostat. A siphon tube reaching close to the bottom of the reactor allows, by using a low pressure to remove the reaction mixture from the reactor and through a pipe directly to a steel filter with a diameter of 30 cm, which is surrounded by a heating jacket. The steel filter contains a steel mesh and is against the atmosphere is completely closed off so that the protective gas cannot escape. It also has a steel disc, which can be pressed against the steel mesh and is used to squeeze out the filtered moist stabilized polyacetal. That The filtrate is collected in a 5 liter glass vessel.

example 1

The reactor described above is thoroughly purged with nitrogen. Then 1800 g of dimethylformamide, 18.0 g of 2,4-tolylene diisocyanate and 150 g of polyoxymethylene diol added to the reactor with stirring. The polyoxymethylene diol was obtained by copolymerizing trioxane at 1.5 percent by weight Ethylene oxide using a cationic polymer

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sation initiator produced. The inherent viscosity of the polyoxymethylene diol used is 1.80, measured in p-chlorophenol containing 2 percent by weight of a-pinene at 60.degree. The reactor contents are hot through 175 ⁰ C oil circulating through the jacket, heated. The internal pressure is adjusted to such a value that the temperature of the reaction mixture is 160.degree. The polyacetal melts at this temperature. The resulting highly viscous solution is heated an additional 10 minutes at 16O ⁰ C and cooled thereto. The stabilized polyacetal precipitates and a suspension which is difficult to stir is obtained. The suspension is passed through a slight overpressure onto the steel filter, where the polymer is pressed out with the steel disc provided for this purpose. 1420 g of liquid are collected in the glass vessel. The remaining on the Stahlfilte.r pulverulent stabilized polyacetal is thoroughly washed with acetone and then dried in a vacuum oven at 6O ⁰ C. Yield 133.5g.

The following properties of the stabilized polyacetal (POM-1) are determined:

Intrinsic viscosity (? 7 _Ω ), bulk density Cy) and thermal degradation in

e ex

Nitrogen atmosphere at 2 20 ° C (K ₂₂₀ ). The rate of decomposition in percent by weight of the polymer per minute during the first 30 minutes is determined using a thermobalance. The results are summarized in Table I. Table I also shows the properties of the -Aungang polymer to be stabilized.

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Example 2

The reactor described above is charged according to Example 1 with 1800 g of dimethylformamide, 18.0 g of 2,4-tolylene diisocyanate and 450 g of the polyoxymethylene diol used in Example 1. Through heated to 175 ⁰ C oil in the heating jacket of the reactor is heated. The internal pressure is adjusted to such a value that the temperature of the reaction mixture is 160.degree. At this temperature the polymer solution is highly viscous. kos, which makes the heat exchange more difficult. The reaction mixture is heated to 160 ° C. for a further 10 minutes and then cooled. The stabilized polyacetal precipitates here. The polymer suspension obtained cannot be stirred and is difficult to apply to the steel filter, the mother liquor being used several times. The stabilized polymer remaining on the steel filter is washed thoroughly with acetone and then dried in a vacuum oven at 60.degree. Yield 391 »5 g. The properties of the stabilized polymer (POM-2) obtained are summarized in Table I.

Example 3

The reactor described above is charged according to Example 1 with 1800 g of n-dodecane, 18.0 g of 2,4-tolylene diisocyanate and 450 g of polyoxymethylene diol. The compounds used in Examples 1 and 2 are used as the polyacetal and isocyanate. Through heated to 175 ⁰ C oil in the heating jacket of the reactor with the internal temperature is set by pressure control at 160 ° C is heated. The very liquid suspension is heated to 160 ° C. for a further 10 minutes and then cooled. the

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The polymer suspension obtained is passed onto the steel filter and quickly filtered off. What is left on the steel filter stabilized. The polymer is washed with acetone and then dried in a vacuum oven at 60 ° C. Yield 382.5g. The properties of the stabilized polymer (POM-3) obtained are summarized in Table I.

Example 4

The reactor described above is charged according to Example 1 with 1350 g of n-dodecane, 450 g of dimethylformamide, 4.50 g of 2,4-tolylene diisocyanate and 450 g of the polyoxyraethylene diol used in Example 1. By heated at 170 ⁰ C in the oil 'heating jacket of the reactor is heated. The internal temperature is set to 160 ° C. by regulating the pressure. The reaction mixture is heated to 160 ° C. for a further 10 minutes and then cooled. The polymer suspension obtained is applied to the steel filter by a slight excess pressure and quickly filtered off. A liquid is collected in the glass vessel, which separates into two layers at room temperature, an upper paraffin layer and a lower solvent layer. The stabilized polymer granulate remaining on the filter is washed thoroughly with acetone and then dried ^{at 60 ° C. in a vacuum oven.} Yield 411.7g. The properties of the stabilized polymer obtained (POM-4) are summarized in Table I.

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Table I.
Polymer yield, ~ _e γ _α K ₂₂₀

Starting polymer - 1.80 0.60 2.020

POM-1 89.0 1.78 0.25 0.030

POM-2 87.0 1.81 0.35 0.035

POM-3 x 85.0 1.83 0.60 0.060

POM-4 91.5 1.81 \ 0.65 0.020

Example 5

The reactor is charged with 900 g of n-dodecylbenzene, 900 g of dimethyl sulfoxide, 4.50 g of 1,6-hexamethylene diisocyanate and 450 g of polyoxymethylene diol. The polyoxymethylene diol was prepared by polymerizing pure monomeric B'ormaldehyde in heptane using an anionic polymerization initiator. The inherent viscosity of the polyoxymethylene diol used is 1.61, measured at 60 ° C. in p-chlorophenol containing 2 percent by weight of oe-pinene. By circulation of hot oil in the heating jacket of the reactor is heated until the internal temperature is 155 ⁰ C. The liquid suspension thus obtained is heated to this temperature for a further 15 minutes and then cooled. The polymer suspension can easily be directed onto the steel filter by means of a slight overpressure. The stabilized polymer which has been filtered off is pressed out.

A liquid is obtained as the filtrate, which is at room temperature separates into two layers, an upper hydrocarbon layer and a lower solvent layer. The stabilized polymer granulate obtained is washed thoroughly with acetone and then dried in a vacuum oven at 60 ° C. Yield 414.5g. The properties of the obtained stabilized j

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Polymer (ΡΟΜ-5) are summarized in Table II. In table II the properties of the starting polymer are also given.

Example 6

The reactor is filled with 562.5 g of n-dodecylbenzene, 562.5 g of dimethyl sulfoxide, 5.62 g of phenyl isothiocyanate and 450 g of the polyoxymethylene diol used in Example 5 are charged. Through circulation The reactor is heated by hot oil in the heating jacket until the internal temperature is 162 ° C. The liquid suspension obtained is heated to this temperature for another 5 minutes and then cooled. The polymer suspension can can be easily placed on the steel filter. The stabilized polymer which has been filtered off is pressed out. The filtrate falls a liquid that separates into two layers at room temperature, an upper hydrocarbon layer and a lower one Solvent layer. The stabilized polymer granulate obtained is washed thoroughly with acetone and then in dried in a vacuum oven at 60 ° C. Yield 408.6g. The properties of the stabilized polymer obtained (POM-6) are summarized in Table II.

Table II

Polymer Yield,
Wt% ' ¹ Ie 0.48 ^K 220 Starting polymer - 1.61 0.56 3.00 POM-5 92.1 1.63 0.51 0.02 POM-6 90.8 1.60 0.03

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Claims (9)

Claims I (ΐ /. A process for stabilizing terminal hydroxyl groups containing polyacetals by reaction with organic isocyanates or isothiocyanates, characterized in that the isocyanate or isothiocyanate is brought ^{to reaction at temperatures of about 50 to 200 0} C with the polyacetal, which in a The reaction medium is suspended under the process conditions, the reaction medium being composed of at least one compound which is inert towards the constituents of the reaction mixture, does not dissolve the polymer and is liquid under the process conditions (nonsolvent) and of at least one which dissolves the polymer and the isocyanate or isothiocyanate, respectively Components of the reaction mixture inert, under the process conditions liquid compound (solvent), and wherein the solvent and the nonsolvent completely miscible under the reaction conditions, but at temperatures that are substantially below the reaction are not miscible or only partially miscible. 2. The method according to claim 1, characterized in that there is at least one organic isocyanate or isothiocyanate Compound with one or more isocyanate or isothiocyanate groups from the group of the aliphatic monoisocyanates and Monoisothiocyanates, cycloaliphatic monoisocyanates and monoisothiocyanates, aromatic monoisocyanates and monoisothiocyanates, Monoisocyanates and monoisothiocyanates containing urethane or thiourethane groups, aliphatic diisocyanates and di-L 409844/0820 - 17 - 2A18951 ^π isothiocyanates, cycloaliphatic diisocyanates and diisothiocyanates, aromatic diisocyanates and diisothiocyanates and aliphatic, cycloaliphatic and aromatic triisocyanates used. 3. The method according to claim 1, characterized in that the solvent used is compounds from the group of substituted Amides, especially dimethylformamide and dimethylacetamide, of aromatic nitro compounds, especially nitrobenzene, and which uses sulfoxides, especially dimethyl sulfoxide. 4. The method according to claim 1, characterized in that compounds from the group of saturated unbranched or branched hydrocarbons are used as nonsolvents, cycloaliphatic hydrocarbons and alky! aromatic Hydrocarbons with at least 6 carbon atoms in the unbranched or branched alkyl moiety is used. 5. The method according to claim 1, characterized in that the solvent and the nonsolvent are used in a weight ratio of 0.05: 1 to 1: 1. 6. The method according to claim 1, characterized in that the polyacetal and the liquid reaction medium are used in a weight ratio of 1: 0.5 to 1:10. 7. The method according to claim 1, characterized in that the organic isocyanate or isothiocyanate in an amount of 0.2 to 3.0 percent by weight, based on the solvent, a 409844/0820 puts. 8. The method of claim 1 to 7, characterized in that one carries out the reaction at temperatures of 120 to 180 ⁰ C. 9. The method according to claim 1 to 8, characterized in that the reaction is carried out for 1 to 60 minutes. J .409844 / 0820