JPS63452B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving the stability of acetal polymers by converting their unstable terminal hydroxyl groups into highly stable groups, particularly in orthoesters or orthocarbonates. This invention relates to a method for improving the stability of acetal polymers by converting them into ether groups through treatment. Acetal polymers that can be treated in the process of this invention are polymers having a molecular weight greater than about 10,000 made by polymerizing aldehydes or copolymerizing one or more aldehydes with non-aldehyde monomers. These acetal polymers obtained from cyclic oligomers of aldehydes, such as trioxane and tetraoxane (oligomers of formaldehyde), by homopolymerization or copolymerization with non-aldehyde monomers, can also be treated by the process of the invention. It is known that acetal polymers obtained from polymerization and copolymerization methods contain at least one terminal hydroxyl group per polymer. The instability of these hydroxyl groups leads to gradual degradation of the polymer chains at the temperatures required for processing the polymer. It is therefore necessary to treat the polymer in order to convert the hydroxyl groups into other groups that are more thermally and chemically stable. In particular, their stability is conferred by converting hydroxyl groups into ether groups by reacting with orthoesters, dialkyl acetals, ketals and organic orthocarbonates. The known methods are carried out in a variety of ways, and in fact there are four basic methods summarized below. (1) bringing an end-capping agent (esterifying or etherifying agent) into contact with an acetal polymer dispersed in a liquid medium that is not a solvent for the polymer; The liquid medium can consist partially or entirely of an endcapper. (2) The end-capping agent is brought into contact with the acetal polymer dissolved in a liquid that is a solvent for the polymer, which solvent liquid can consist in part or in whole of the end-capping agent. (3) bringing the end-capping agent into contact with the acetal polymer dispersed in a mixture of two liquids consisting of a solvent and a non-solvent for the polymer;
These liquids shall be fully miscible at processing temperatures. (4) Bringing the endcapping agent in vapor state into contact with the acetal polymer in the form of fluidized solid particles. This type of method is known, for example, in US Pat. No. 2,998,409;
No. 2964500, No. 3192182 and No. 3875117, and British Patent No. 880737. The processes described therein are generally satisfactory in the sense that end-capped (esterified or etherified) products are obtained; however, the economics of the process, the yield and the properties of the end-capped polymers are uncertain. There will be a difference, and it may even be a considerable difference. One common feature of the methods described above is that they require relatively large amounts of endcapping agent and/or solvent or dispersion compared to the amount of polymer undergoing endcapping. Particularly in processes in which the reaction is carried out in the liquid phase, the weight ratio between liquid and acetal polymer is at least 3:1, and
It can even be up to 15:1. In each of the methods described above, special technical and chemical problems also arise depending on the particular system chosen for the reaction. For example, when the end-capping reaction is carried out in solution, there are considerable difficulties in precipitation of the end-capped acetal polymer. On the other hand, when the reaction is carried out in a fluidized bed method, large amounts of gas and/or steam are required and there are more difficulties in achieving homogeneous contact between the solid particles of the polymer and the endcapper. Furthermore, in all the methods described above, the presence of a large amount of liquid and endcapper ensures that both the liquid used to dissolve or disperse the polymer and the unreacted endcapper can be recovered as completely as possible. This requirement makes this method difficult to perform economically. In order to carry out the reaction with a small amount of end-capping agent in terms of ease, it is necessary to take into account that this end-capping agent will react with the aldehyde monomer formed by the degradation of the acetal polymer. be. For example, when polyformaldehyde is esterified, the formaldehyde monomers formed react with acetic anhydride, thus forming methylene-glycol acetate type by-products, which are difficult to separate and form acetal polymers. particularly by coloring the polymer. The object of the present invention is therefore a process for endcapping acetal polymers which does not have the disadvantages mentioned above. In particular, the present invention provides a method for etherifying the terminal hydroxyl groups of an acetal polymer by reacting the acetal polymer with an endcapping agent selected from orthoesters and orthocarbonates, which method is performed in the form of a powder. forming a homogeneous mixture of the acetal polymer and the endcapping agent in liquid form, the amount of the endcapping agent being less than the amount that would cause the polymer powder to lose its free-flowing properties; The reaction is carried out under stirring at a temperature of at least 70° C. until substantially complete, and the end-capped polymer is recovered from the reaction product. The basic point of the process of the invention is therefore to end-capped the acetal polymer in powder form with a liquid end-capping agent in an amount that does not change the properties of the physical state of the material, in particular the free rolling properties. It is about doing. In practice, this result can be achieved by using an amount of endcapping agent from 0.01 to 0.30 parts by weight per part by weight of acetal polymer, preferably from 0.02 to 0.15 parts by weight per part by weight of said acetal polymer. , the lower limit in each case being determined by the amount necessary to complete or substantially complete the endcapping reaction. Under these conditions, acetal polymers, especially
The acetal polymer in the form of a powder with a particle size of 20-500 μ does not substantially lose its free-flowing properties and can therefore be processed in a powder reactor equipped with a stirrer, and this Rapid heating of the mass below a preselected temperature for reaction can be achieved and homogeneous contact between the polymer and endcapper can be achieved. The production of a homogeneous mixture between powdered acetal polymer and endcapper can be carried out in various ways. For example, the polymer may be wetted with a liquid endcapper before being fed to the reactor or directly within the reactor. Furthermore, the end-capping agent is inert (non-reactive) under the reaction conditions.
It may be used in or dissolved in a low boiling diluent. According to a preferred embodiment, the polymer is first wetted with a solution of the endcapper in an organic solvent in such proportions as to achieve within the limits mentioned above. The solvent is then evaporated at a temperature below the end-capping temperature and the free-flowing powder thus obtained is processed in the manner described above. In particular, the reaction temperature is appropriately maintained within the range of 70 to 170°C. Preferred values are 80-165°C. The endcapping pressure should be such as to keep the endcapping agent in substantially liquid form at the selected reaction temperature. Pressure is generally maintained at a value equal to or greater than atmospheric pressure,
The most favorable value depends primarily on the volatility of the agent chosen for the endcapping reaction. It is generally preferred to use superpressure even with high boiling endcappers to substantially avoid loss of the endcapper by evaporation. The time for the endcapping reaction is between 5 and 90 minutes, with the most suitable time depending on the reaction temperature, the type of endcapping agent, the presence or absence of an endcapping catalyst to ensure completion or substantial completion of the reaction. , and the properties of the acetal polymer in each case. In the etherification reaction, the endcapping agent is an orthoester, usually an orthoester of an aliphatic or aromatic acid with an aliphatic, cycloaliphatic or aromatic alcohol, such as methyl or ethyl orthoformate, methyl or ethyl orthoacetate. and methyl or ethyl orthobenzoate, and orthocarbonates such as methyl or ethyl orthocarbonate. The etherification reaction is preferably carried out in the presence of Lewis acid type catalysts, examples of which include: (1) A strong or moderate strength organic acid with an acid dissociation constant, or primary acid dissociation constant, greater than 10 ^-5 . Examples of these acids are p-toluenesulfonic acid, acetic acid and oxalic acid. (2) Alkyl, cycloalkyl, and alkyl aromatic esters of strong or medium strength mineral acids. Examples of these esters are dimethyl and diethyl sulfate and dimethyl and diethyl hydrogen phosphate. (3) Alkyl, cycloalkyl, and alkyl aromatic esters of strong or medium strength organic acids.
Examples of these esters include methyl-p-toluenesulfonate. The amount of catalyst used in the etherification reaction varies over a wide range, generally for 1 part by weight of etherification agent.
It can be varied by 0.001 to 0.02 parts by weight. The catalyst can be added at any time before the start of the etherification reaction. According to a preferred embodiment, it is added together with the etherification agent into a solution of the etherification agent in a solvent (or diluent). When using the end-capping agent in the form of a solution in a solvent, the former is present in an amount of 0.05 to 0.50 parts by weight per part by weight of acetal polymer, so as to easily achieve homogeneous mixing of the polymer and the end-capping agent. It is convenient to use. The solution of endcapper can be added to the powdered polymer before or after it is introduced into the reactor. In each case, it is preferred that the solvent (or diluent) be completely or substantially completely removed prior to initiation of the endcapping reaction in order to impart the aforementioned free-flowing properties to the acetal polymer. This removal is advantageously carried out by evaporation at low temperatures, in each case below the end-capping temperature. During this evaporation, care should be taken to avoid removing the endcapper. Evaporation is preferably carried out under reduced pressure and the solvent (or diluent) thus recovered can be recycled without further purification. Preferred solvents and diluents for endcappers generally consist of low boiling aliphatic, cycloaliphatic and aromatic hydrocarbons, such as linear or branched pentane, hexane or heptane, cyclohexane and benzene. Halogenated lower aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride are also useful for this purpose. Finally, aliphatic ethers such as diethyl ether, aliphatic esters such as methyl and ethyl formate and methyl and ethyl acetate, and aliphatic ketones such as acetone can also be used. As mentioned above, the basic features of the method of the present invention are:
The purpose is to carry out the reaction using a reaction system consisting of a free-flowing powder containing the endcapper in liquid form. There are no particularly strict regulations on other physical properties of the polymer powder, but for this method,
This is particularly important in terms of the selection of the ratio between the acetal polymer and the end-capping agent and the selection of the method of adding the end-capping agent to the polymer. In both cases, the important properties are the apparent density of the powder and its particle size distribution. For example, as the apparent density (generally within the range of 0.05 to 0.8 g/ml) and particle size increase, the ratio between endcapper and acetal polymer must be progressively decreased within the above-mentioned range. Regardless of the method chosen, the resulting end-capped acetal polymer has the same physical properties as the polymer that was subjected to the end-capping reaction. The process of the invention makes it possible to achieve intimate mixing between the acetal polymer and its end-capping agent, thus resulting in high reaction yields and yields of end-capping polymers with the desired properties of stability and coloration. bring. Additionally, the use of significantly reduced amounts of endcapper provides economic benefits for subsequent process steps. In fact, unreacted endcapper can be immediately recovered from the acetal polymer by applying reduced pressure after the reaction is complete or by washing with a solvent. Furthermore, according to one embodiment made possible by the low amount of end-capping agent present at the end of the reaction, it is possible to wash the end-capped polymer directly with water, making it economical. ,however,
Other cleaning agents can also be used. In such a case, neutralization and removal of by-products, catalyst residues or other additives from the final product is facilitated. Particularly in accordance with this example, the reaction mixture can be discharged into water to form an aqueous suspension of polymer, and the polymer can then be recovered and dried. It is generally preferred to use a basic aqueous (or organic) liquid so that any acid residues present can be easily neutralized and removed from the etherified polymer. The basic substance is preferably present in the liquid in an amount of 0.01 to 10% by weight, such as an alkali metal hydroxide, an alkali metal salt of a weak organic acid or an inorganic acid,
It may be selected from ammonia and aliphatic amines and cycloaliphatic amines. In either case, the final recovered polymer has the desired properties of thermal stability and color. Example 1 The endcapping reaction was carried out in a 130 capacity steel reactor equipped with a stirrer with suitable equipment for mixing the powders. The reactor was equipped with an upper charge valve and a lower discharge valve, and its upper end was connected to a vacuum pump by a tube with an exchanger and a distillate collector interposed therebetween. Devices for controlling the pressure allow the reaction to be carried out in an inert atmosphere at the desired pressure. A spray placed at the top of the reactor allows the liquid to be mixed in in finely dispersed form. Finally, the reactor is equipped with a jacket for heating and cooling. After blowing nitrogen, 50 kg of crude polyoxymethylene (polyoxymethylene glycol) obtained by polymerizing pure frame monomer formaldehyde in an inert liquid (heptane) using an anionic initiator was placed in the reactor. Ta. This polymer has an intrinsic viscosity ηe1.59
dl/g. In each example, the intrinsic viscosity is 0.5% (wt/vol) of the polymer in p-chlorophenol containing 2% α-pinene.
Measured in solution at 60°C. Furthermore, the polymer was a powder having the following properties. Apparent Density 0.67g/ml Particle Size Distribution >177μ 58.3% 177-60μ 36.7% After starting the stirrer, a solution consisting of 2.0Kg trimethyl orthoformate and 2.0g boron trifluoride etherate was added into the reactor. Sprayed. After stirring for 10 minutes, the mixture was heated to 1 atm gauge pressure.
It was brought to 105°C and left at these conditions for the next 30 minutes, then cooled at 50°C for 15 minutes at an absolute pressure of 0.02 atmospheres. The etherified polymer containing less than 0.1% by weight of residual orthoether was discharged into an aqueous solution (200) containing 1% by weight of ammonia. at 70-80℃
After stirring for 20 minutes, the suspension was centrifuged and the polymer was thoroughly washed with water and dried under reduced pressure at 80°C. 49.6 kg of etherified polyoxymethylene was thus recovered, on which the following measurements were carried out. Intrinsic viscosity: ηe Apparent density: γ〓 Viscosity: Thermal aging at 220°C in a nitrogen atmosphere: K This latter measurement, carried out on a ₂₂₀ thermobalance, shows that the polymer The decomposition rate in weight percent is shown. Alkaline stable fraction: 1 part by weight of ASF polymer in dimethylformamide
Heat in 10 parts by weight of a solution of 0.5% by weight tributylamine at 160° C. for 30 minutes. The percentage (wt%) of the polymer recovered after treatment represents the alkaline stable fraction. The following measurements were performed on this final fraction. Intrinsic viscosity: ηe (ASF) Thermal deterioration: K ₂₂₀ (ASF) The measurement results are shown in column P-1 in Table 1 below. Example 2 A crude polyoxymethylene obtained in the same manner as in Example 1 and having the following properties was etherified. ηe = 2.15 dl/g γ = 0.27 g/ml Particle size >177μ 14.3% 177-60μ 37.1% <60μ 48.6% The reaction was carried out under strictly anhydrous conditions and 95 parts by weight of petroleum ether (boiling point 40-60 °C) ), 20Kg of polymer in a liquid containing 7.5 parts by weight of triethyl orthoformate and 0.15 parts by weight of diethyl sulfate.
was dispersed. After centrifugation, the polymer was placed into the reactor under stirring. The wet polymer is Polymer 1
It contained 0.30 parts by weight of liquid per part by weight. The temperature of the device is 40 in 20 minutes at an absolute pressure of 0.4 atm.
It was set to ℃. The solvent content in the polymer was reduced to a value of less than 0.2% by weight. At this point the device is set to a 0.7 atm gauge,
It was then heated at 145°C for 30 minutes. After this time had elapsed, the reaction mixture was rapidly discharged into an aqueous solution (200) containing 1% by weight of sodium carbonate. The suspension was kept under stirring at 80° C. for 20 minutes and then centrifuged. After washing completely with water until the washing water became neutral, the polymer was dried at 80° C. under reduced pressure. Thus, 19.92 kg of etherified polyoxymethylene was recovered. Regarding this, the measurements shown in Example 1 were carried out. The results of these measurements are shown in Table 1.
It is shown in column 2. Example 3 In the reactor of Example 1 under strictly anhydrous conditions
50Kg of crude polyoxymethylene with an intrinsic viscosity of 1.47dl/g was charged. After starting stirring, a liquid consisting of 7.5 Kg of triethyl orthoformate and 102.5 g of diethyl sulfate was sprayed from the top of the reactor. After stirring for 15 minutes at ambient temperature, the temperature was brought to 150° C. at a pressure of 1 atm gauge and the mixture was left under these conditions for 30 minutes. Then heat the device to 100℃ for 15 minutes.
and at the same time reduce the pressure to approximately 0.02 atm (absolute pressure)
It was lowered to . The drug was collected in a condenser placed downstream of the exchanger. The polymer was then released into an aqueous solution (200) containing 1.5% by weight ammonia. After stirring at 80-90°C for about 30 minutes, the suspension was centrifuged, the polymer was washed with water until the water became neutral, and it was dried under reduced pressure at 80°C. Thus, 49.6 kg of etherified polyoxymethylene was recovered. The properties of this product are shown in column P-3 in Table 1. Example 4 A crude polyoxymethylene obtained in the same manner as in Example 1 and having the following properties was etherified. ηe=1.84dl/g γ=0.19g/ml The reaction was carried out under strictly anhydrous conditions, 15Kg of polymer was mixed with 80 parts by weight of anhydrous cyclohexane, 20 parts by weight of isoamyl orthoformate and 0.40 parts by weight. of boron trifluoride etherified with diethyl ether. After centrifugation, the polymer was placed into a reactor under stirring. The powder contained 0.31 parts by weight of liquid for 1 part by weight of polymer. The temperature of the device was increased to 40℃ in 20 minutes at an absolute pressure of 0.6 atm.
The cyclohexane content of the polymer was thus reduced to less than 0.1% by weight. The device was then brought to a pressure of 1 atm gauge for 60 minutes.
Heated at 155°C. At the end of this time, the mixture is cooled to room temperature and
Transferred onto a filter strip, which was washed countercurrently with cyclohexane. Cyclohexane was used in an amount of 200% by weight based on the polymer. The released polymer had an orthoester content below analytically detectable levels (≦500 ppm). The polymer was then dissolved at the boiling point in cyclohexane containing 3% by weight of triethylamine (1:1 by weight).
4) was suspended for 2 hours. After centrifugation and further solvent washing, the polymer was dried at 80°C under reduced pressure. Thus, 14.25 kg of etherified polyoxymethylene was recovered, and the measurement results thereof are shown in column P-4 of Table 1 below. 【table】

Claims (1)

[Scope of Claims] 1. A method for etherifying the terminal hydroxyl groups of an acetal polymer by reacting the acetal polymer with an end-capping agent selected from orthoesters and orthocarbonates, comprising: an acetal polymer in powder form and a liquid; forming a homogeneous mixture of endcapping agents in the form of , said acetal polymer having an apparent density of 0.05 to 0.8 g/ml, and
It is in the form of granules having a size of 20 to 500μ, and the above terminal capping agent is added per part by weight of the acetal polymer.
In an amount of 0.01 to 0.30 parts by weight, but less than the amount that would cause the polymer powder to lose its free-flowing properties, the mixture was heated at a temperature of 70 to 170°C and at a temperature such that the endcapper remained in substantially liquid form. A method characterized in that the reaction is carried out under pressure and stirring for 5 to 90 minutes, and the end-capped polymer is recovered from the reaction product. 2. The method according to claim 1, wherein the terminal blocking agent is used in an amount of 0.02 to 0.15 parts by weight per 1 part by weight of the acetal polymer. 3 A patent for forming such a homogeneous mixture by mixing an endcapping agent and a polymer in the form of a solution in an inert (non-reactive) diluent and removing said diluent at a temperature below the endcapping temperature. A method according to claim 1 or 2. 4 The end capping agent is methyl and ethyl orthoformate, ethyl and methyl orthoacetate,
and ethyl and methyl orthocarbonate. 5. The method according to claim 4, wherein the end-blocking reaction is carried out in the presence of an etherification catalyst selected from Lewis acids.