KR100248646B1 - Process for producing polyacetal copolymer - Google Patents

Abstract

The present invention copolymerizes trioxane as a main monomer using a nonvolatile protonic acid catalyst as a polymerization catalyst until the conversion rate is 60% or more (based on all monomers), and then unreacted monomers are evaporated from the polymerization system. By separating, removing and recovering the monomer, the remaining monomer content of the polymerization system is reduced to 5% by weight or less, and trioxane as the main monomer is copolymerized to economically obtain a polyacetal copolymer having excellent thermal stability and properties. It relates to a manufacturing method.

Description

Production method of polyacetal copolymer {PROCESS FOR PRODUCING POLYACETAL COPOLYMER}

The present invention relates to a method for producing a polyacetal copolymer. More specifically, the present invention is carried out in the late stage or the final stage of the polymerization after copolymerization of trioxane and copolymerizable comonomers as the main monomer in the presence of a specific nonvolatile protonic acid catalyst as polymerization catalyst. A method for economically preparing a polyacetal copolymer excellent in properties such as thermal stability by a simple procedure of efficiently and economically removing unreacted monomers from a polymerization system and recovering them for reuse.

As a process for preparing polyacetal copolymers, cationic polymerization reactions using cyclic ethers or cyclic formals having adjacent carbon atoms as trioxanes and comonomers as main monomers are known. As cationic active catalysts used in the polymerization in this case, Lewis acids, in particular boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, phosphorus fluoride, bismuth fluoride, and antimony fluoride Halides of boron, tin, titanium, phosphorus, and antimony, and these compounds as complexes or salts thereof; Protonic acids such as perfluoroalkyl sulfonic acid and perchloric acid; Esters of protonic acid, especially perchloric acid and lower aliphatic alcohols such as perchloric acid tert-butyl ester; Protonic anhydrides, especially mixed anhydrides of perchloric acid and lower aliphatic carboxylic acids such as acetyl perchlorate; Or trimethyl oxonium hexafluorophosphate, triphenylmethylhexafluoroarsenate, acetyl tetrafluoroborate, acetyl hexafluorophosphate, and acetyl hexafluoroarsenate are proposed.

Among the catalytically active catalysts mentioned above, organic compounds such as boron trifluoride or ether and coordination compounds of boron trifluoride are most widely used on a commercial scale as catalysts for polymerization with trioxane as the main monomer.

Regardless of the catalyst used, it is extremely difficult to quickly obtain a polymerization yield close to 100% because the rate of polymerization suddenly greatly decreases in the later stages of the polymerization. The polymerization takes quite a long time and is therefore inefficient. In the later stages of the polymerization, the catalyst rather predominantly plays a role in promoting the decomposition of the resulting polymer, leading not only to reducing the molecular weight but also to lowering properties such as thermal stability. If the amount of polymerization catalyst is increased, the overall rate of polymerization is also increased. However, this increase is not necessarily a suitable means for the whole process of the polymerization, since increased amounts of catalysts rather severely deteriorate the properties of the resulting crude polymer and require complex stabilization treatments in later stages.

Therefore, the preparation of polyacetal copolymers generally stops the polymerization reaction at a relatively low conversion rate by adding a solution containing a catalyst deactivator to the polymerization system, and washes off unreacted monomers remaining in the polymerization system, Recovering this monomer in a purified form, and reusing the recovered monomers. Since unreacted monomers washed in the process are recovered in the form of a solution containing monomers at relatively low concentrations, their reuse requires the use of complex processes for separation and purification and the consumption of energy. If unreacted monomers are not recovered, unreacted monomers are completely wasted. In any case, unreacted monomers are economically burdensome.

Recognizing the true level of prior art mentioned above, the inventors of the present application have sought to economically produce very stable (particularly thermally) polyacetal copolymers by obtaining a high quality crude polymer and ultimately by a simple method, in particular polymerization. The catalyst was selected to enable the economic recovery of unreacted monomers suitable for reuse and ultimately produce a polyacetal polymer that combines quality and economic impact.

In the copolymerization reaction using trioxane as the main monomer, the late stage or terminating stage with conversion exceeding 60% shows a significant decrease in the rate of polymerization, so it is very important to obtain the yield of polymerization close to 100%. It takes a long time. At the end of the polymerization, the decomposition reaction becomes relatively very prevalent, causing quality problems such as lowering the molecular weight and greatly increasing the unstable polymer, requiring complex stabilization treatment. Due to this fact, the inventors of the present application sought to separate and recover unreacted trioxane and other monomers from the polymerization system by evaporation before the polymerization was completed and after the conversion reached a certain level. Separation and collection of the evaporated monomers is economically carried out, the collected evaporated monomers are reused directly or only through very simple purification treatments, and the qualitative damage of the polymer which may be caused by excessive decomposition at the end of the polymerization reaction is prevented. Recovery and reuse of unreacted monomers is simple and economical, compared to conventional methods of washing the polymerization system with a large amount of solvent and recovering the unreacted monomers in the form of solutions containing monomers at low concentrations. The expected effect on both quality and economics can be realized It demonstrated through experiment.

The inventors of the present invention have experimented and studied these concepts at various angles, and since the standard boron trifluoride type catalysts that have been widely used up to now are inherently volatile, the vapor formed when the unreacted monomers evaporate at the end of the polymerization reaction. Accompanying the catalyst, it was found that the unreacted monomers in the evaporation and collection lines again polymerized and quickly blocked the lines, consequently hindering the evaporation and collection of the unreacted monomers. They continued various studies on this problem and found that the monomers evaporated during the evaporation and collection process by the use of specially selected specific nonvolatile catalysts do not accompany the catalyst, so that unreacted monomers can be easily evaporated and collected. It was also confirmed that this catalyst is characterized by having the ability to inhibit the formation of formate groups (-OCH = O) that make up the labile ends of the polymers formed. As a result, they completed the present invention.

Specifically, the present invention relates to a process for preparing polyacetal copolymers by copolymerizing cyclic ethers or cyclic formals having one or more carbon-carbon bonds as trioxane as the main monomer and comonomers, the polymerization of which Polymerize the monomer until it is converted to 60% or more (based on the total amount of monomers) using a nonvolatile protonic acid catalyst as a reaction catalyst, and then polymerize by separating and recovering the evaporated monomer from the polymerization system by evaporating the unreacted monomer. The amount of monomer remaining in the reaction system can be lowered to less than 5% by weight (based on the amount of polymer).

That is, the present invention uses a nonvolatile protonic acid catalyst as a polymerization catalyst and copolymerizes trioxane as a main monomer with a comonomer of cyclic ether or cyclic formal (each having one or more carbon-carbon bonds) to 60%. After reaching a degree of polymerization (based on the total amount of monomers) or higher, the unreacted monomers are then evaporated to separate, remove and recover them from the polymerization system to reduce the monomer content remaining in the polymerization system to 5 wt% or less (based on the polymer). It relates to a method for producing a polyacetal copolymer, comprising the step.

The present invention is now described in detail below.

As is apparent from the above description, the method of the present invention for the copolymerization of trioxane is characterized by the use of a nonvolatile protonic acid catalyst. Non-volatile protonic acids used advantageously in the present invention include, for example, heteropoly acids or acid salts thereof and isopoly acid or basic salts thereof.

The term "heteropolyacid" as used herein generally refers to a polyacid formed by dehydration condensation of different kinds of oxygen acids. Heteropolyacids contain mononuclear or multinuclear complex ions having a particular hetero element in their center and allow the condensed acid groups to condense by sharing an oxygen atom. Heteronuclear condensate acids of this kind can generally be represented by the following general formula (1):

_{H x [M m · M '} n O ℓ] · yH 2 O

Where

M represents a central element formed of one or both of P and Si,

M 'represents one or more coordination elements selected from W, Mo, and V,

l is 10 to 100,

m is 1 to 10,

n is 6 to 40,

x is an integer of 1 or more,

y is 0-50.

Particularly efficient heteropolyacids as polymerization catalysts of the present invention are those in which the central element (M) is formed of one or more elements selected from P and Si, and the coordination element (M ') is selected from W, Mo, and V (particularly preferably W and Has a composition of formula (1) formed from one or more elements selected from Mo).

In addition, acid salts of the composition of formula (1) in which hydrogen atoms, that is, H _x are partially substituted by various metal elements, can be used as the catalyst of the present invention.

Specific examples of the heteropolyacids of the present application include phosphomolybdic acid, phosphotungstic acid, phosphomolybdo tungstic acid, phosphomolybido dovanadinic acid, phosphomolybdo tungstovanadine acid, phospho tungstovanadine acid, Silico tungstic acid, silico molybdate, silico molybdodo tungstic acid, and silicomolybdo tungstovavanic acid. Among the heteropolyacids recited above, silicomolybdic acid, silicotungstic acid, phosphomolybdic acid, and phosphotungstic acid are particularly advantageous. Heteropolyacids are generally known in forms such as α ₀ type, β _II type, and β _IV type. In view of the polymerization activity, α ₀ type and β _IV type are preferred, and α ₀ type is particularly preferred.

Isopolyacids for the nonvolatile protonic acid catalysts of the invention are alternatively referred to as homonuclear condensate acids or homopolyacids. It is a polymeric inorganic oxygen acid formed from a condensate of inorganic oxygen acids containing one pentavalent or hexavalent metal component, as represented by the following formula (2) or (3):

^{_{xM I 2 O · pM V 2}} O 5 · yH 2 O

_{^{xM I 2 O · pM VI O}} 3 · yH 2 O

Where

M ^I represents a hydrogen atom,

M ^V represents V, Nb, or Ta (each belongs to group V in the periodic table of elements),

M ^VI represents Cr, Mo, W, or U (each belongs to group VI in the periodic table of elements),

p represents an integer of 1 or more,

x represents an integer of 1 or more,

y represents a number from 0 to 50.

Isopolyacids are treated with ion exchange resins with a solution of isopolyacid salts such as isopolymolybdate, isopolytungstate, or isopolyvanadate, corresponding to formula (2) or (3) mentioned above. Protonic acid prepared by any of a variety of methods, including methods comprising, and methods comprising concentrating this solution, adding inorganic acids to the concentrated solution, and ether extracting the resulting mixture. Forms of acid salts produced by partial substitution of protons (M ^I : hydrogen) by various metal elements can also be used as the catalyst of the present invention. In particular, the isopoly acid or the acid salt thereof of the formula (3) is preferred.

Specific examples of isopoly acids include isopoly tungstic acid such as paratungstic acid and metatungstic acid, isopoly molybdic acid such as paramolybdic acid and metamolybdic acid, and metapoly vanadic acid and isopoly vanadic acid. . Of the isopoly acids, isopoly tungstic acid is particularly preferred.

Preferably, in order to allow the reaction to proceed uniformly, the above-mentioned nonvolatile protonic acid catalyst is added to the monomer by diluting with a solvent which shows no adverse effect in the polymerization reaction. As diluents, ethers such as n-butyl ether, which are inert organic solvents capable of dissolving the aforementioned protonic acid catalyst, can be used. The diluent need not be limited to these ethers only. As described in detail below, linear acetals (eg methylal) and alcohols (eg methanol) which can be used as chain transfer agents for the control of molecular weight can also be used as diluents. Diluents can be used without causing any significant problems because they are effectively used in very small amounts based on the amount of monomers. As described in detail below, the diluent may be added with the comonomer to the polymerization system while pre-dissolving in some or all of the comonomer. This method is preferred in that it does not contain another solvent that may be needed in other methods, but the comonomer containing diluent is cooled completely and maintained at the lowest possible temperature, i. It is advantageous to avoid homopolymerization before addition and mixing.

Since the protonic acid catalyst described above has very high polymerization activity, it shows the expected effect even in extremely small amounts. This amount is generally in the range from 0.1 to 50 ppm, preferably from 0.5 to 20 ppm, and particularly preferably from 0.5 to 10 ppm (based on the total amount of monomers to be polymerized).

The present invention performs the polymerization of monomers using the above-mentioned nonvolatile protonic acid catalyst until the conversion reaches a level of at least 60% of the total amount of monomers fed.

As the main monomer for the polymerization, the present invention uses trioxane, which is a cyclic trimer of formaldehyde.

Comonomers used in the present invention are cyclic ethers or cyclic formals having at least one carbon-carbon bond. It may be any known comonomer previously used to copolymerize with trioxane.

Specific examples of cyclic ethers or cyclic formals include 1,3-dioxolane, diethylene glycol formal, 1,4-butane diol formal, 1,3-dioxane, ethylene oxide, propylene oxide, and epichlorohexyl Cyclic compounds, such as a drone, are mentioned. Cyclic ethers or cyclic formals with unsaturated-bonding groups can also be used. Comonomers that allow copolymers to form branched or cross-linked molecular structures, such as butane diol diglycidyl ether and butane diol dimethylidene glyceryl ether, having two or more cyclic ether groups or cyclic formal groups Compounds such as ren-diglycidyl ether or diformal can be used. Depending on the purpose of the copolymerization reaction, two or more such comonomers may be used in the form of a mixture.

Specific examples of comonomers particularly advantageously used herein include cyclic ethers or cyclic formals such as 1,3-dioxolane, diethylene glycol formal, 1,4-butane diol formal, and ethylene oxide. have.

The amount of comonomer used in the present invention is in the range of 0.1 to 20 mol% (based on the amount of trioxane), preferably 0.2 to 10 mol%. If the amount of comonomer is too small, the unstable terminal portion will increase and the stability will be lowered. Conversely, if the amount of comonomer is excessively large, the comonomer formed will increase in ductility and lead to a decrease in melting point. Some or all of the comonomers may be used simultaneously as diluents for protonic acid catalysts as described above.

The process of polymerization according to the present invention allows the incorporation of any known chain transfer agents, such as low molecular weight linear acetals, alcohols, and esters, such as methylal, into the polymerization system to control the degree of polymerization, depending on the purpose of manufacture. This chain transfer agent can be used simultaneously as the diluent for the protonic acid catalyst mentioned above. The polymerization system is preferably in a state where substantially no impurities such as formic acid and water having active hydrogen are present. Acceptable amounts of such impurities are each 30 ppm or less, preferably 20 ppm or less, and particularly preferably 10 ppm or less.

The polymerization reaction of the present invention can be carried out by the same apparatus and the same method as previously used for the known copolymerization of trioxane. The method may be batch or continuous in the form of a process. Processes using liquid monomers and forming polymers in the form of solid granules as a result of polymerization are generally used.

As the polymerization reaction apparatus of the present invention, a general reaction column capable of temperature control and equipped with a stirrer can be used for a polymerization reaction carried out batchwise, and simultaneously kneading, two-axis screw type continuous extrusion and mixing device, two-axis paddle type continuous A mixing device and a continuous polymerization device previously proposed for the copolymerization of trioxane can be used for the polymerization which is carried out continuously. Two or more kinds of polymerization reactors may be used in a mixed form.

Suitably, the polymerization temperature is in the range from 60 to 120 ° C, preferably 65 to 110 ° C.

The present invention evaporates the unreacted monomer remaining in the polymerization system in a step of reducing the decomposition reaction in which the rate of polymerization carried out by the method described above is relatively predominant, and the evaporated monomer is separated and removed from the polymerization system. Characterized in that. Separation of the unreacted monomers by evaporation mentioned above is carried out after the conversion of the polymerization reaches at least 60% (based on the total amount of monomers), preferably 70 to 90%, and particularly preferably 75 to 85%. .

If the separation of unreacted monomers is carried out at a stage where the conversion is excessively low, it gives a desirable effect on the quality of the product, while requiring excessively long time for recovery and reducing the yield of the resulting polymer. The same economic disadvantage will arise. If the separation of the unreacted monomer is carried out in a stage where the conversion is excessively high, the separation process itself is achieved in a short time and the yield of the resulting polymer is high, while a decomposition reaction is caused in a subsequent stage, adversely affecting the quality of the product. Will give.

From this point of view, the present invention properly performs separation of unreacted monomers after the conversion of the polymerization reaches a level within the range specified above. The level is appropriately selected within a range that satisfies the purpose of the polymerization reaction.

As described above, the present invention is characterized by evaporating unreacted monomers in the reaction system and removing the evaporated monomers therefrom. The monomer mixture of the present invention having trioxane as a main component shows high volatility at the polymerization temperature. Therefore, by connecting the reaction system to a reduced pressure inhaler, passing an inert carrier gas such as nitrogen gas through the reaction system, or using both methods together, unexpectedly simply evaporating unreacted monomers at certain stages of the polymerization reaction. It can be removed from the reaction system. The separation of the unreacted monomers by evaporation described above in the present invention is due to the use of nonvolatile protonic acid as the polymerization catalyst. When a volatile boron trifluoride type catalyst previously used in general is used herein, the monomer is polymerized in a line for evaporation and separation and the polymer thus produced is separated because the evaporated and separated monomer is accompanied by this catalyst. And blocking the line for recovery would result in penalties that hinder the smooth running of the operation. According to the process of the present invention, since the unreacted monomer is separated and collected in a vaporized state without containing an external substance such as a solvent, the monomer can be reused immediately after collection. This collected monomer can be prepared by very simple purification treatment for reuse. If this monomer is added to the process for purifying freshly fed trioxane, the energy required for its recovery and purification will be significantly reduced. Thus, the present method is disadvantageous of complex recovery and purification treatments, such as concentration, which requires enormous energy consumption, unlike conventional methods of separating and collecting unreacted monomers in the form of solutions containing monomers at low concentrations by washing. Avoiding this can make recovery and reuse very economical.

The present invention provides a polymerization reaction until the residual content of the unreacted monomer in the polymerization reaction reaches a level of 5 wt% or less (based on the amount of the polymer), preferably 3 wt% or less, and more preferably 2 wt% or less. Unreacted monomer is separated and removed from the system. Therefore, the final remaining monomer is only discarded as waste, so it is preferred that it is the minimum amount possible. Attempts to completely remove the remaining monomers require a long time and are rather uneconomical and lead to degradation of the polymer. It is not necessary to reduce this amount unduly, but rather it can stop reducing the amount at the appropriate level. The process of the present invention has the advantage of inhibiting the degradation of the polymer because latent heat of evaporation due to the evaporation of the monomer effectively suppresses the increase in temperature due to the accumulation of the heat of reaction in the polymer system and even causes the decrease in temperature.

The method of the present invention only needs to satisfy the basic construction conditions described above, and can be applied in various forms.

For example, using a continuous polymerization apparatus as mentioned above, setting the outlet of the apparatus under conditions such that the conversion rate reaches a certain level, and passing the reduced pressure, intake, or inert gas to or near the outlet. Placing the apparatus and consequently performing the evaporation and separation of the unreacted monomers; In two or more stages, the polymerization reaction is carried out in the polymerization stage of the preceding stage until a certain level of conversion is achieved using the polymerization apparatus, and then the reaction system is transferred to the polymerization stage in the subsequent stage, where the polymerization reaction is carried out. Further continuing, at the same time, evaporating and separating unreacted monomers; And methods of inactivating the catalyst in the presence of a catalyst-inactivating agent as described in detail herein below, as well as performing evaporation and removal of unreacted monomers. The methods can be used in combination as appropriate.

In order to effectively carry out the evaporation and separation of the unreacted monomers in the present invention, it is preferable that the polymers to which the unreacted monomers are to be treated are pulverized to form new surfaces. Preferably, for this purpose, the polymerization apparatus used is either a device capable of pulverizing the polymer particles in the latter part to form a new surface or a device capable of performing a grinding treatment on the polymer prior to evaporation of the unreacted monomer. Is provided. Alternatively, the polymerization apparatus may be provided with a mechanism capable of grinding and stirring the polymer so that the polymerization apparatus may be operated to perform evaporation and removal simultaneously with the grinding and surface regeneration. From this point of view, preferably, the polymers to which the unreacted monomers are to be treated are pulverized so that polymer particles having a diameter of 3 mm or less are at least 90% of all polymer particles in order to smoothly evaporate and remove the unreacted monomers.

A catalyst-inactivator is added thereto to deactivate the catalyst contained in the product of the polymerization in which the evaporated unreacted monomer has been removed. The catalyst is deactivated using a small amount of deactivator by the method described in detail below. The product containing the deactivated catalyst need not be cleaned, but can be directly heat treated. As a result, a polyacetal copolymer having high thermal stability is obtained.

A process for deactivating a catalyst, contemplated by the present invention, involves exposing the copolymerization product to basic gas or a small amount of this product (e.g., up to 7 wt% (based on the amount of polymer), preferably up to 5 wt% Is combined with a solution containing a basic compound and then mixed.

Specific examples of the basic gas efficiently used in the deactivation treatment of the present invention include ammonia and / or amine compounds. Since the amine compound used in this case is in contact with the formed crude polymer in gaseous form, it is preferable to have a low molecular weight and a low boiling point. Suitably, the boiling point is 150 degrees C or less. More specifically, the formula R ₁ NH ₂ · R ₁ R ₂ NH and R ₁ R ₂ R ₃ N, wherein R ₁ , R ₂ , and R ₃ are independently 4 or less, preferably 2 or less An alkyl group having an atom of carbon or an alcohol group) is a preferred example. An amine compound having a relatively high boiling point can be used diluted with a carrier gas as described in detail below so that the crude polymer can be contacted in gaseous form.

Specific examples of the amine compounds described above include methyl amine, dimethyl amine, trimethyl amine, ethyl amine, diethyl amine, triethyl amine, butyl amine, dibutyl amine, tributyl amine and the corresponding alcohol amines such as tri Methanol amine). Among them, methyl amine, dimethyl amine and trimethyl amine are particularly preferred.

The above-mentioned basic gas may be used in the form of a gas alone, or in the form of a mixed gas diluted with a carrier gas, for contact with the formed polymer. Although not specifically defined, the carrier gas is preferably an inert gas. Nitrogen gas or other organic gases are exemplified.

The method of contacting the basic gas with the formed crude polymer does not need to be particularly limited and may be performed by any method capable of bringing the basic gas into full contact with the formed copolymer particles. For example, a method comprising allowing the crude polymer to be thoroughly stirred and mixed in an atmosphere of basic gas, a method comprising blowing the basic gas back into the stream of the crude copolymer, or particles adjacent to the crude polymer bed. Methods may be used that include circulating between them.

The basic gas used in the present invention needs an amount sufficient to inactivate the catalyst by neutralization. Preference is given to at least 10 moles per mole of catalyst used.

As a diluent, the present invention uses various basic compounds in the form of solutions or dispersions containing only small amounts of the compound. The basic compound needs an amount sufficient to completely deactivate the catalyst by neutralization. Preferably, the deactivator is added in the form of a deactivator solution with the deactivator dissolved or dispersed in water or an organic solvent.

In this case, the amount of inactivating agent solution added is in the range of 0.3 to 7% by weight (based on the amount of crude polymer formed), preferably 0.5 to 5% by weight. In spite of the addition in small amounts, the deactivator solution, when sufficiently stirred and mixed with the crude polymer, results in complete deactivation of the catalyst and, consequently, makes available the properties of the polymerization catalyst used.

The deactivator used efficiently in the process can be any known basic substance. Specific examples of inactivating agents include ammonia, various amine compounds, or oxides, hydroxides, organic acid salts, or inorganic acid salts of alkali or alkaline earth metals, and trivalent phosphorus compounds. This deactivator can be used advantageously alone or in the form of a mixture of two or more.

Amine compounds that can be used efficiently herein include primary, secondary, and 3 such as methyl amine, dimethyl amine, trimethyl amine, ethyl amine, diethyl amine, triethyl amine, butyl amine, dibutyl amine, and tributyl amine. Primary aliphatic amines and aromatic amines, and their corresponding alcohol amines such as triethanol amines, and aniline, diphenyl amines, heterocyclic amines, and hindered amines such as piperidine derivatives.

Specific examples of alkali metal or alkaline earth metal compounds include oxides, hydroxides, carbonates, bicarbonates, phosphates, borates, silicates and other inorganic weak acid salts, acetates, oxalates, formates, benzoates, terephthalates of alkali or alkaline earth metal compounds. , Isophthalates, phthalates, fatty acid salts and other organic acid salts, and alkoxides and phenoxylates such as methoxides, ethoxides, n-butoxides, secondary-butoxides, tert-butoxydes Can be mentioned. Among the alkali metal or alkaline earth metal compounds mentioned above, hydroxides, carbonates, and fatty acid salts are particularly preferably used. Specific examples of the alkali metal or alkaline earth metal include lithium, sodium, potassium, cesium, magnesium, calcium, strontium, and barium. Among the alkali metals and alkaline earth metals mentioned above, lithium, sodium, potassium, magnesium, and calcium are particularly preferably used. More specifically, calcium hydroxide, magnesium hydroxide, sodium carbonate, calcium acetate, calcium stearate, and calcium hydroxystearate are more advantageous.

As a solvent for the preparation of the inactivating agent, water or an organic solvent is used. Specific examples of the organic solvent include alcohols such as methanol and ethanol; Ketones such as ethyl ketone and acetone; Aromatic compounds such as benzene, toluene, and xylene; And saturated hydrocarbons such as cyclohexane, n-hexane, and n-heptane. An aqueous solution of such an organic solvent is particularly preferably used.

The method used to add the deactivator solution to the crude polymer is not particularly limited. It is preferred to spray this solution, which is efficiently dispersed and in contact with the crude polymer, or mixed thoroughly with the crude polymer by stirring.

When a solution containing a basic gas or a basic compound in a small amount is added to the crude polymer formed as a catalyst-inactivator to deactivate the catalyst in the polymer, the crude polymer is preferably in the form of fine particles. In this connection, it is preferable that the apparatus for the polymerization reaction can completely grind the bulky polymer. Alternatively, the product resulting from the polymerization can be separately milled by the milling apparatus before adding the deactivator. Alternatively, grinding and stirring may be performed simultaneously in the presence of an inactivating agent.

During the inactivation treatment, the crude polymer preferably has a particle size distribution in which at least 90% of the total particles have a diameter of 3 mm or less, preferably 2 mm or less, and more preferably 1 mm or less.

The temperature of the deactivation treatment is in the range of 0 to 140 ° C, preferably 20 to 120 ° C.

In the present invention, the crude polymer added with the catalyst-inactivator can be immediately heat treated for dissolution.

The heat treatment is preferably carried out in the presence of a stabilizer. Stabilizers should generally be added at a freely selectable time point after the polymerization and before heat treatment. Stabilizers may be added simultaneously with the above-mentioned deactivating agents or during the heat treatment. In a preferred embodiment, the heat treatment is carried out in the presence of a small amount (eg 0.1 to 7% by weight) of water. This preferred embodiment is carried out automatically when the deactivator is used in the form of an aqueous solution.

Stabilizers used as important components herein can be any known material, such as, for example, various hindered phenolic antioxidants. Advantageously, various nitrogen-containing compounds, metal oxides, or fatty acid salts are used with this stabilizer.

Specific examples of hindered phenolic antioxidants include 2,6-di-t-butyl-4-methyl phenol, triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) Propionate], 1,6-hexane diol-bis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], tetrakis [3- (3,5-di -t-butyl-4-hydroxyphenyl) propionate] methane, N, N'-hexa-methylenebis (3,5-di-t-butyl-4-hydroxyhydrocinnamid), 2-t- Butyl-6- (3'-t-butyl-5'-methyl-2'-hydroxybenzyl) -4-methylphenyl acrylate, and 3,9-bis [2-{(3-t-butyl-4- Hydroxy-5-methylphenyl) propionyloxy} -1,1'-dimethylethyl] -2,4,8,10- tetraoxaspiro [5,5] -undecane. In addition, the hindered phenolic antioxidants described above may be present during the copolymerization reaction by partial or all addition to the monomer or comonomer in advance.

Specific examples of nitrogen-containing compounds include dicyandiamide, melamine or derivatives thereof, urea or derivatives thereof, benzotriazole type compounds, piperidine type compounds (hindered amines), various polyamides or copolymers thereof (e.g. nylon 6 , 12, 6/12, 6/66/610, and 6/66/610, 12).

The metal oxide is preferably an oxide of an alkaline earth metal. Specific examples of the metal fatty acid salts include calcium salts or magnesium salts of higher fatty acids.

The stabilizers listed above each have their own various actions. Preferably, two or more stabilizers are selected together to meet the relevant goals.

If desired, the polymerization system at this stage may contain various other additives such as, for example, fillers such as glass fibers, crystallization promoters (seeds), and anti-sticking agents.

The temperature of the heat treatment of the present invention is in the range between the melting point of the formed copolymer and 250 ° C., preferably between the melting point and 230 ° C. If the temperature exceeds 250 ° C., there will be a disadvantage that the polymer is degraded by decomposition. The apparatus for the heat treatment is not particularly limited, but should only be capable of kneading the molten polymer and releasing the trapped gas. Specific examples of heat-treatment devices include single or multi-axis continuous extrusion kneading devices equipped with one or more outlets and co-dough.

In the present invention, the polymerization catalyst is completely inactivated and separated together with the volatile components through the separation by the decomposition of the unstable end portion of the crude copolymer by the inactivating agent incorporated in the polymerization system and by the heat treatment. Removal of the unstable end portion is facilitated, resulting in a pellet of stable polyacetal copolymer. For this purpose, it is of course preferred that the outlet utilizes reduced pressure in order to ensure that the components released are inspired.

Example

The invention will now be described in detail below with reference to the working examples. Naturally, the present invention is not limited to this embodiment. In the working examples and the comparative examples, the physical size determined by the term specified below and the method described below is used.

% Or ppm: Always expressed by weight.

Conversion rate: determined by washing the sample product of the polymerization with an inactivating agent solution, drying the washed sample polymer, and calculating the percentage ratio of the weight of the dried sample polymer to the total weight of monomers fed.

Residual monomer content: determined by washing the sample product with a specific inactivating agent solution, analyzing the wash by gas chromatography to determine its monomer content, and calculating the% ratio of weight of monomer to weight of crude polymer. .

Melt index (MI): Melt index (g / 10 min) as determined at 190 ° C. This is considered as a specific value corresponding to molecular weight. The size of MI decreases proportionally with increasing molecular weight. The crude polymer resulting from the polymerization is measured in the presence of a stabilizer and the pellet produced from melt extrusion is measured in its unreacted form.

Alkaline Degradation Rate (Existent Amount of Unstable Portion): 1 g of crushed crude copolymer flakes or copolymer pellets is placed in 100 mL of 50% aqueous methanol solution containing 0.5% ammonium hydroxide and the sample solution is 180 ° C. for 45 minutes in a closed container. After heating with, the resulting solution is quantitatively determined to determine the amount of formaldehyde dissolved in the solution and to determine the ratio of the amount of formaldehyde to the weight of the polymer.

Weight loss rate by heating: 5 g of crude polymer flakes (containing powder stabilizer) or copolymer pellets are heated in air at 230 ° C. for 45 minutes and then determined by calculating the weight loss rate.

Examples 1-8 and Comparative Examples 1 and 2:

In a closed autoclave equipped with a jacket capable of passing the heating medium and stirring blades capable of providing mixing and grinding movements, trioxane containing 3.5% of various comonomers in Table 1 is added, stirred and put into the jacket The various catalysts (dibutyl ether solution) of Table 1 were added in the amounts of Table 1 while allowing the internal temperature of about 70 ° C. to be maintained by passing hot water at 70 ° C. to allow polymerization.

When the conversion reached a level of 60% or more (value determined by preliminary testing under the same conditions introduced in Table 1), the unreacted monomer was discharged (covered with a jacket and formed at 100 ° C.) by a vacuum inhaler or on top of the autoclave. Separated from the reaction system by passing through a nitrogen stream. The evaporated unreacted monomer was collected by condensation. The collected monomers showed substantially no polymer formation. After a certain time (see Table 1), a 1% aqueous ammonia solution was added to the reaction system to stop the polymerization from proceeding, and the reaction system was washed. The unreacted monomer content of the reaction system was analyzed and the yield of the polymerization reaction and the properties of the resulting polymer were examined. The results are shown in Table 1 below.

The polymerization was carried out by the procedure described above using boron trifluoride (dibutyl etherate) instead as catalyst for the purpose of comparison. When an attempt was made to separate the monomers by evaporation, at the same time, polymers formed extensively in the outlet and collection device, hindering the smooth collection of unreacted monomers (see Comparative Example 1).

For comparison (see Comparative Example 2 in Table 1), when the polymerization described above is continued uninterrupted for the evaporation and recovery of unreacted monomers, the resulting crude polymer contains a large amount of unreacted monomers, resulting in inferior properties. Found.

The catalyst used in the working examples was as shown below:

Heteropoly Acid (HPA)

HPA-1: Phosphomolybdic Acid

HPA-2: Silicotungstic Acid

HPA-3: phosphotungstic acid

Isopoly acid (IPA)

IPA-1: Paratungstic Acid

IPA-2: Metatungstic Acid

Example 9:

About 10% of the monomer collected in Example 2 was added to the freshly supplied monomer and the polymerization was carried out according to the procedure of Example 2. In this example, the conversion was 78% (see: Conversion obtained in Example 2 was 84% (using newly supplied monomer)) and the recovered unreacted monomer could be reused in substantially unmodified form. .

Examples 10-15 and Comparative Examples 3 and 4:

Continuous mixing reaction comprising two partially overlapping circular cross sections and a jacket equipped with a jacket for passing a heating (cooling) medium on the outer surface and two rotary shafts each positioned longitudinally with a plurality of stirring and propulsion paddles. The apparatus was continuously fed trioxane containing 2.5% 1,3-dioxolane as comonomer and 700 ppm methylal as molecular weight modifier through one end of the reaction apparatus, while the various catalysts of The various amounts of Table 2 (based on the total amount of monomers) were calculated as the total amount and added continuously to the feed vessel, and the copolymerization reaction was carried out while keeping the jacket at 70 ° C. by passing hot water and rotating the two rotating shafts at a fixed speed. . The catalyst was prepared in the form of a solution in 1,3-dioxolane (about 1% on a trioxane basis) and added to the polymerization system while maintaining at about 0 ° C.

Subsequently, the reaction product coming from the outlet of the polymerization reactor (shown to have a median conversion in Table 2 below) was introduced into a second continuous mixing unit (covered with a jacket and kept at 100 ° C.) and filled with nitrogen, while the second Unreacted monomer was evaporated by vacuum inhalation by the outlet (100 ° C.) provided in the apparatus. Evaporated unreacted monomer was separated from the reaction system and led to a condenser and collected in the condenser. The collection went smoothly. The collected monomers showed substantially no polymer formation. The extracted product from the reactor was taken and analyzed for residual monomer content.

The reaction product from the second evaporator was then passed through a mill to grind (at least 90% of the particles in a particle size distribution with a diameter of 2 mm or less), while at the same time the various basic gases or various basic The compound solution was added and then stirred at 80 ° C. for 30 minutes. Then the resulting mixture and 0.5% tetrakis- [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, 0.1% as stabilizer added thereto Melamine and 0.03% magnesium oxide were stirred and mixed together for 5 minutes. The resulting blend was placed in a biaxial extrusion apparatus equipped with an outlet, melted and mixed at a temperature of 210 ° C, and extruded under a vacuum of 5 mmHg at the outlet to produce pellets. The pellets were dried and tested for polymer quality. The results are shown in Table 2 below.

Polymerization Condition Unreacted monomer Deactivator Quality of extruded pellets Catalyst (A) Amount (ppm; based on total monomer) % Conversion Remaining monomer (%; based on total monomer) Kinds Amount (%; based on total monomers) MI (g / 10 min) Alkali decomposition rate (%) % Weight reduction due to heating Example 10 HPA-1 3 81 One Ammonia gas 0.1 5.8 0.32 0.29 Example 11 HPA-1 3 81 One Methylamine gas 0.5 6.0 0.34 0.32 Example 12 HPA-1 3 81 One 10% aqueous ammonia solution 1.0 5.7 0.32 0.28 Example 13 HPA-1 3 81 One 5% triethyl amine aqueous solution 1.0 6.0 0.35 0.32 Example 14 HPA-1 3 81 One 0.1% calcium hydroxide aqueous solution 3.0 6.2 0.36 0.31 Example 15 IPA-1 4 76 2 10% aqueous ammonia solution 1.0 6.4 0.35 0.32 Comparative Example 3 HPA-1 3 81 Not retrieved (10 <) 10% aqueous ammonia solution 1.0 Extrusion is impossible due to excess residual monomer Comparative Example 4 BF ₃ 40 80 Unrecoverable (10 <) 10% aqueous ammonia solution 1.0

As is evident from the description given above and the examples cited above, the production process according to the invention can economically produce polyacetal copolymers which are excellent in properties such as thermal stability by simple procedures when compared with conventional methods. To be.

Claims (20)

In the presence of a non-volatile protonic acid catalyst as a polymerization catalyst, trioxane, the main monomer, is copolymerized with a cyclic ether or cyclic formal, which is a comonomer having one or more carbon-carbon bonds, at a temperature of 60 to 120 ° C. to 60% (total After reaching a degree of polymerization of monomer) or higher, the unreacted monomers are then evaporated to separate, remove and recover them from the polymerization system, thereby reducing the residual monomer content of the polymerization system to 5% by weight or less (polymer basis), and then the catalyst. -Adding a deactivator, the method of producing a polyacetal copolymer. The method of claim 1, Wherein the nonvolatile protonic acid catalyst is one or more catalysts selected from heteropolyacids, acid salts thereof, isopolyacids, and acid salts thereof. The method of claim 2, Heteropoly acid and acid salts thereof are represented by the following general formula (1): Formula 1 _{H x [M m · M '} n O ℓ] · yH 2 O Where M represents one or two central elements selected from P and Si; M 'represents one or more coordination elements selected from W, Mo, and V; l is 10 to 100; m is 1 to 10; n is 6 to 40; x is an integer of 1 or more; y is 0-50. The method of claim 2, Heteropolyacids or acid salts thereof include phosphomolybdic acid, phosphotungstic acid, phosphomolybido tungstic acid, phosphomolybido dovanadinic acid, phosphomolybido tungstovanadic acid, phosphotungsutovanadine acid, silico tungsten At least one compound selected from the group consisting of acid, silicomolybdic acid, silicomolybdo tungstic acid, silicomolybdo tungstovavanadic acid and acid salts thereof. The method of claim 2, The isopoly acid or acid salt thereof is represented by the following formula (2) or (3): Formula 2 ^{_{xM I 2 O · pM V 2}} O 5 · yH 2 O Formula 3 ^{_{xM I 2 O · pM VI O}} 3 · yH 2 O Where M ^I may be hydrogen or partially substituted by a metal; M ^V is V, Nb, or Ta (each belonging to group V of the periodic table of elements); M ^VI is Cr, Mo, W, or U (each belonging to group VI of the periodic table of elements); p is an integer of 1 or more; x is an integer of 1 or more; y is a number from 0 to 50. The method of claim 2, The isopoly acid or acid salt thereof is selected from the group consisting of paratungstic acid, metatungstic acid, paramolybdic acid, metamolybdic acid, paravanadic acid, metavanadinic acid and any acid salts thereof. The method of claim 1, The comonomer is at least one monomer selected from 1,3-dioxolane, diethylene glycol formal, 1,4-butanediol formal and ethylene oxide. The method of claim 1, Separation for recovery of unreacted monomers is achieved by evaporating and removing unreacted monomers by vacuum suction, passing inert gas, or using a combination of both. The method of claim 1, Using a continuous polymerization reactor equipped with a vacuum suction device or a device for passing an inert gas around the outlet, the polymer mixture discharged by evaporating and removing unreacted monomer from the discharged polymer mixture and separating and collecting the unreacted monomers. To reduce the monomer content of to 5% by weight or less. The method of claim 1, Using a polymerization reactor arranged in two or more stages, the polymerization is carried out in the first stage polymerization reactor until the conversion rate reaches 60% (based on the total monomers) and then the polymerization is continued in the second stage polymerization reactor. And simultaneously evaporating and removing to recover unreacted monomers, thereby discharging the crude polymer having a residual monomer content of 5% by weight or less from the second stage polymerization reactor. The method of claim 1, A method of evaporating and removing unreacted monomer after pulverizing the polymerization mixture to a content of 90% or more of particles having a particle diameter of 3 mm or less. The method of claim 1, A method of reusing unreacted monomers removed and recovered from a polymerization system by evaporation. The method of claim 1, Adding a basic component as a catalyst deactivator to a crude polymer having a residual monomer content of 5 wt% or less and contacting the basic component with the crude polymer to inactivate the catalyst. The method of claim 13, Contacting the basic gas as a catalyst deactivator with the crude polymer to inactivate the catalyst and then heating and melting the crude polymer without washing. The method of claim 14, The basic gas as a catalyst deactivator is ammonia and / or an amine compound having a boiling point of up to 150 ° C. The method of claim 13, Adding a basic compound solution as an inactivating agent to the crude polymer in an amount of 0.3 to 7% by weight (based on the crude polymer) and heating the resulting mixture without washing without melting. The method of claim 16, The solution of the basic compound as a catalyst deactivator is an aqueous solution or an organic solvent solution of ammonia, an amine compound and at least one basic compound selected from oxides, hydroxides, inorganic acid salts and organic acid salts of alkali and alkaline earth metals. The method of claim 13, A method of inactivating the catalyst after pulverizing the crude polymer obtained by the polymerization reaction to the extent that the content of particles having a particle diameter of 3 mm or less is 90% by weight or more. The method of claim 14, Heat melting in the presence of a stabilizer. The method of claim 14, Heat melting in the presence of 0.1 to 7% by weight (based on polymer) of water.