JP2948015B2 - Method for producing polyoxymethylene copolymer having high polymerization degree - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polyoxymethylene copolymer having a high degree of polymerization. More specifically, in the cationic copolymerization of trioxane with a cyclic ether or a cyclic acetal, a specific linear polymerization condition and a catalyst deactivation treatment are employed to produce a substantially linear polyoxymethylene copolymer having a high degree of polymerization. On how to do it.

[0002]

2. Description of the Related Art Polyoxymethylene (hereinafter abbreviated as POM) copolymers have been known for many years as engineering plastic materials, and the polymerization method is generally based on a cyclic acetal such as trioxane. As a monomer, a cyclic acetal or cyclic ether having adjacent carbon atoms as a comonomer,
The copolymerization is carried out using a cationically active catalyst, and then the polymerization product is deactivated by contacting with a catalyst neutralizer or deactivator, or a solution thereof, and then is subjected to a stabilization step to obtain a product. Conventionally, the molecular weight can be adjusted to a certain limit or less by using a chain transfer agent. However, there is almost no proposal as a method for obtaining a POM copolymer having a high molecular weight exceeding a certain limit. It is said that it is desirable to carry out the polymerization while minimizing active impurities in the system. In addition, it is naturally preferable to prevent the main chain from being cut as much as the treatment method after the polymerization.However, there is no specific proposal for the specific method, and conventionally, the polymerization product is generally finely pulverized, It has been recommended that a wetting agent or a quenching agent or a solution thereof be brought into contact with the polymer at a relatively high temperature (for example, 50 ° C. or higher) and neutralized (for example, US Pat. No. 2,989,509; JP-A-58-34819). However, the P obtained by such prior art is
There is a limit to the degree of polymerization of the OM copolymer, and in particular, unless a crosslinkable special monomer is used, a substantially linear PO
In the case of M copolymer, the melt index (MI) value (19
0 ° C, load 2160g) 2.0g / 10min or less, especially 0.1 ~
It was very difficult to obtain a copolymer having a high degree of polymerization such as 1.5 g / 10 min. This means that when this copolymer is used for extrusion molding, blow molding, etc., the molten resin tends to draw down due to lack of tension at the time of melting, causing not a little hindrance to moldability, and generally, The fact is that the performance and quality of the molded product, such as mechanical properties, especially toughness, are limited. Further, such a POM copolymer according to the prior art has a considerable amount of unstable terminal portions, and in order to put this into practical use, the unstable portion must be removed and stabilized. It requires a complicated post-processing step, requires a large amount of energy for the processing, and is economically disadvantageous. If the crude POM after polymerization has few unstable parts, the stability of the final product will be more excellent, and there are advantages such as simplification of post-treatment steps such as stabilization. A method for obtaining a polymer having a small number of unstable parts is desired.

[0003]

Means for Solving the Problems The present inventors are a POM copolymer having a substantially linear structure with a high degree of polymerization, which is difficult to obtain by the conventional method, which is suitable for blow molding and the like, and has very few unstable terminal portions. As a result of intensive research on the purpose of obtaining a POM copolymer that significantly reduces the load in the stabilization process and has excellent mechanical properties such as high quality, that is, toughness, and is extremely stable thermally, Sometimes, the amount of active impurities that can be a polymerization terminator or a chain transfer agent contained in the reaction system is kept below a certain level, and the amount of the catalyst used during the polymerization reaction is limited to a specific range. It has been found that the above object can be achieved by adopting specific conditions. In particular, the conventional method for deactivating a polymerization catalyst has a problem. Surprisingly, deactivation treatment at a relatively high temperature (for example, 50 ° C. or higher), which has been conventionally proposed as a preferable method, has an adverse effect, Competition between neutralization deactivation of the catalyst and decomposition reaction by the remaining catalyst.At high temperatures, the latter takes precedence, and side reactions such as decomposition occur while the deactivation does not proceed sufficiently, and the polymerization catalyst is deactivated. It was found that in the process, the main chain was decomposed by the remaining catalyst in a short time, causing a decrease in the degree of polymerization and a new generation of an unstable portion based on the reduction until the catalyst was sufficiently deactivated. From such a viewpoint, the present inventors have conducted intensive studies on the deactivation of the polymerization catalyst, and rather found that it is preferable that rapid cooling is performed to suppress side reactions such as decomposition, and various factors related to the polymerization reaction are considered. By combining this with the requirements, a linear POM copolymer having a very high degree of polymerization and having few unstable parts, which has not been obtained conventionally, was successfully obtained. That is, the present invention uses trioxane as a main monomer and a cyclic ether or cyclic formal having a carbon atom adjacent thereto and having no substituent or having a part of hydrogen atoms substituted with an alkyl group as a comonomer. In a method of copolymerizing using a catalyst consisting of boron fluoride or a coordination compound thereof to obtain a polyoxymethylene copolymer,
The total amount of impurities having a polymerization termination and chain transfer action in the reaction system should be 1 × 10 ⁻² mol% or less based on all monomers, and the amount of catalyst used in the polymerization reaction should be 1% based on all monomers.
The copolymerization is carried out at × 10 ^{−3 to} 7 × 10 ⁻³ mol%, and after the copolymerization, the product is cooled to a temperature of 45 ° C. to 15 ° C. within 30 seconds,
A substantially linear melt index value (190 ° C., wherein the catalyst is deactivated at a temperature of at least 10 ° C. or higher).
The present invention relates to a method for producing a polyoxymethylene copolymer having a high degree of polymerization with a load of 2160 g) of 2.0 g / 10 min or less .

[0004] The basic requirement of the present invention is to keep the amounts of impurities and catalyst present in the reaction system during the polymerization reaction at a certain level or less, thereby suppressing side reactions during the polymerization reaction and giving priority to the growth reaction. First, the polymerization degree reached during the polymerization is kept high, and the reaction product after the polymerization reaction is immediately quenched under specific conditions. The purpose of the present invention is to extremely slow and suppress the reaction. At the time of the polymerization reaction, active impurities that can be a polymerization terminator and a chain transfer agent in the monomer include water, alcohol (eg, methanol), acid or its ester (eg, formic acid or formate), and low molecular weight linear acetal (eg, Methylal) and the like. It is first necessary that the total amount of these is 1 × 10 ⁻² mol% or less, and preferably 5 × 10 ⁻³ mol% or less, based on all monomers in the reaction system. If this content is excessively high, a POM copolymer having a high degree of polymerization (low MI) exceeding a certain level cannot be obtained even if other conditions are suitably maintained. The inclusion of a low molecular weight acetal compound having an alkoxy group at both ends such as methylal does not increase the unstable terminal of the copolymer, but acts as a chain transfer agent and lowers the degree of polymerization. It is not preferable from the viewpoint of the above, and it is desirable to keep within the above definition.

[0005] Next, the amount of catalyst used in the polymerization reaction is an important requirement. Catalyst is typically boron trifluoride or a coordinate compound thereof is used is used, the amount is ^{1 × 10 -3 ~7 × 10 -3} mol% to the total monomers. By setting the amount of the catalyst in such a limited range, it is effective to prevent a substantial decrease in the degree of polymerization and the generation of an unstable terminal during polymerization. If the amount of the catalyst exceeds 7 × 10 ⁻³ mol%, it becomes difficult to maintain the polymerization temperature at an appropriate value, and the decomposition reaction becomes dominant, which hinders the production of a polymer having a high degree of polymerization. On the other hand, if the amount of the catalyst is less than 1 × 10 ⁻³ mol%, the polymerization rate is reduced, the polymerization yield within a certain time is reduced, and the degree of polymerization tends to be unfavorable. In order to sufficiently obtain the effects of the present invention, the polymerization temperature is also an important factor.
It is always desirable to keep the temperature substantially between 60 and 105 ° C., preferably between 65 and 100 ° C., however, the polymerization temperature is closely related to the amount of the catalyst used, and it is usually required to use an aqueous solution under ordinary conditions, for example, on a general industrial scale. If the range of the jacket temperature is normally possible using the medium, it is a range that can be almost controlled by the amount of the catalyst, so that it can be obtained without specially specifying.However, strictly, conditions other than the amount of the catalyst, such as its scale, polymerization, etc. It is preferable to keep the above range in consideration of secondary requirements such as the structure of the reactor and the temperature of the jacket.

Conditions other than the above in the present invention are not particularly limited, and may be performed according to a conventionally known method. The cyclic ether or cyclic formal used as a comonomer is a compound represented by the following general formula.

[0007]

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(Wherein R ₁ , R ₂ , R ₃ or R ₄ represents a hydrogen atom or an alkyl group, which may be the same or different, but is generally a hydrogen atom. R ₅ is a methylene group. , An oxymethylene group, a methylene group or an oxymethylene group substituted with an alkyl group (where p represents an integer of 0 to 3) or a formula

[0009]

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(Where p represents 1 and q represents an integer of 1 to 4). Examples of the comonomer include ethylene oxide, 1,3-dioxolan, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane, propylene oxide and the like. Among these, preferred comonomers are ethylene oxide, 1,3-dioxolan, 1,4-butanediol formal, and diethylene glycol formal. The amount used is 0.2 to 10% by weight, preferably 0.2 to 5% by weight, based on trioxane.

The polymerization method of the present invention can be carried out with the same equipment and method as the conventionally known polymerization method of trioxane. That is, any of a batch type and a continuous type can be used, and any of a solution polymerization, a melt bulk polymerization, and the like may be used. However, a continuous bulk polymerization using a liquid monomer and obtaining a solid powder bulk polymer with the progress of polymerization is performed. The method is industrially common and preferred. In this case, an inert liquid medium can coexist as necessary. As a polymerization apparatus used in the present invention, a reaction vessel with a stirrer generally used in a batch type can be used, and as a continuous type, a co-kneader, a twin screw type continuous extrusion mixer, a twin-screw paddle type continuous mixing can be used. A continuous polymerization apparatus for trioxane, which has been proposed so far, can be used. If it is a closed system, it may be divided into two or more stages. In particular, those having a crushing function such that a solid polymer produced by a polymerization reaction can be obtained in a fine form are preferable.

The post-treatment conditions after the polymerization reaction are also extremely important requirements for obtaining the effects of the present invention. That is, after the polymerization reaction, the reaction mixture discharged from the polymerization machine needs to be cooled to substantially 45 ° C to 15 ° C within 30 seconds,
Preferably, the temperature is set to 45 ° C. or lower within 20 seconds after the polymerization reaction, and the temperature is preferably cooled to substantially 35 to 15 ° C. within 30 seconds. Here, "after the polymerization reaction" means "the point at which the resin is discharged from the substantially sealed polymerization machine", that is, the point at which it comes into contact with an atmosphere containing oxygen, moisture, or the like, or a medium such as water. The higher the cooling rate, the better, and it is particularly important to shorten the holding time at a high temperature. If the cooling rate is slow,
In addition, especially at a high temperature of 50 ° C. or higher as conventionally proposed, even if a neutralizing agent or a deactivator for a catalyst is immediately added, a side reaction takes precedence, and decomposition or a decrease in the degree of polymerization due to the decomposition is caused. It was found that new generation of unstable terminals could not be sufficiently suppressed and the degree of polymerization at the end of polymerization could not be maintained. Such side reactions such as decomposition occur preferentially as the temperature is higher. At a high temperature immediately after the polymerization, particularly, the moisture contained in the atmosphere in which the reactants come into contact adversely affects the reaction. Exposure to an atmosphere containing moisture is not preferred, even at normal atmospheric levels. Therefore,
In the case of an inert atmosphere containing substantially no water or the like, the degree of polymerization is less reduced, and such a state should be understood as continuation of polymerization, and the degree of side reactions decreases even if the cooling rate is relatively slow. I do. Therefore, after sufficiently cooling under an inert atmosphere containing substantially no water or the like, the catalyst may be deactivated over a sufficient time by contacting with a neutralizing agent or a deactivator. Even if it is present, it is not necessary to rapidly cool it and keep it at a high temperature, and it is generally effective to immerse it in a relatively large amount of low-temperature liquid to perform cooling most quickly. If it is used, it is effective for quick cooling. Although the presence of water is not preferred as described above for side reactions at high temperatures, relatively large amounts of water
From the viewpoint of the cooling rate, it is preferable to use an aqueous medium as a suitable medium, and to shorten the high-temperature elapsed time in which the side reaction takes precedence. It is naturally preferable that a neutralizing agent and a deactivating agent for a catalyst composed of a basic compound are contained in such an aqueous solution, and the catalyst is neutralized and deactivated simultaneously with cooling. In addition, it is naturally preferable that the substantial cooling of the reactant, particularly in the case of a bulk polymer, is preferably performed when the reactant is finely pulverized. In the case of relatively large particles, after discharging the polymerization machine,
It is preferred to pulverize quickly, particularly in a cooling medium, for example, water, in the initial stage of cooling.

[0013] Incidentally, 45 ° C. ~ within 30 seconds by the method of the present invention
If the temperature is rapidly cooled to 15 ° C. , preferably 35 to 15 ° C. , the neutralization and deactivation of the catalyst can be completely carried out without causing side reactions over a sufficient period of time, and the catalyst can be sufficiently cooled. The reaction product neutralized and deactivated is treated in a subsequent process even if the temperature is increased, unless the medium is acidic.
There is almost no decrease in the degree of polymerization and no generation of unstable terminals due to side reactions. Thereafter, washing and drying can be performed at a relatively high temperature. At an extremely low temperature of 10 ° C. or less, the deactivation reaction is extremely slow and takes a long time, which is not preferable.

In the present invention, examples of the basic compound for neutralizing and deactivating the polymerization catalyst include ammonia, amines such as triethylamine and tributylamine, hydroxide salts of alkali metals and alkaline earth metals, and others. A known catalyst deactivator is used. These quenchers are
It is preferable to dissolve the reaction product in a medium for cooling the reaction product such as water or an organic solvent such as cyclohexane, benzene, and toluene, and contact the catalyst with the catalyst simultaneously with cooling of the polymer to neutralize the polymer. It is particularly preferable to use an aqueous solution.

In the present invention, the copolymer in which the polymerization catalyst has been deactivated is further subjected to washing, separation and recovery of unreacted monomers, drying, etc., if necessary, and further to a stabilization step, if necessary.
Additives such as various stabilizers are added, melt-kneaded and pelletized to obtain a product. As described above, the POM copolymer of the present invention has a very small number of unstable terminals and the load of the stabilization treatment is reduced, so that a sufficiently stable polymer can be obtained by a simple finishing treatment. Can be used to volatilize and remove the remaining unstable portion.

Further, according to the method of the present invention, it is possible to obtain a POM copolymer having an extremely high degree of polymerization, having a MI value of not more than 2.0, and more preferably about 0.1 to 1.5. Processing by special molding such as molding becomes possible,
In addition, a remarkable improvement in physical properties such as toughness can be expected.

[0017]

The copolymer obtained by the method of the present invention is substantially linear and has an extremely high degree of polymerization of MI value of 2.0 or less, further 1.5 or less, and excellent thermal stability. It is possible to obtain a high-performance, high-quality molded product that could not be obtained by the above method. Further, not only injection molded products, but also extrusion molding and blow molding, which has been conventionally difficult, can be performed, and the applications are expanded. In addition, since there are few unstable parts, the post-processing step can be simplified, and the thermal stability of the final product is high.

[0018]

EXAMPLES Examples of the present invention will be shown below, but it is needless to say that the present invention is not limited to these examples. The terms and measuring methods in Examples and Comparative Examples are as follows. % Or ppm; by weight unless otherwise stated. Polymerization yield;% of polymer obtained relative to all monomers supplied (by weight). Melt index (MI): Indicates a melt index value (g / 10 min) measured at 190 ° C. under a load of 2160 g. This was evaluated as a characteristic value corresponding to the molecular weight. That is, the lower the MI, the higher the molecular weight (however, in order to prevent decomposition during measurement, a small amount of a certain stabilizer is added and mixed). Alkali decomposition rate (amount of unstable portion); 1 g of copolymer 50% containing 0.5% ammonium hydroxide
Put into 100 ml of aqueous methanol solution, and in a closed container at 170 ° C,
After heating for 45 minutes, the amount of formaldehyde eluted in the solution was quantitatively analyzed and shown as% of the polymer. Heating weight loss rate: 5 g of the copolymer was pulverized, and a stabilizer powder composed of 2,2'-methylenebis (4-methyl-6-t-butylphenol) (0.5%) and dicyandiamide (0.1%) was thoroughly mixed.
The weight loss rate when heated at 220 ° C. for 45 minutes in air was measured. Examples 1 to 3 and Comparative Examples 1 to 3 A cross section in which two circles partially overlapped each other was provided with a jacketed barrel through which a heat (cooling) medium passed, and a paddle for stirring and propulsion inside thereof. Using a continuous mixing reactor provided with two rotating shafts in the longitudinal direction, warm water of 80 ° C. is passed through the jacket, and the two rotating shafts are rotated at a speed of 100 rpm. Trioxane containing 3-dioxolane was continuously supplied, and at the same time, a solution in which boron trifluoride butyl etherate was dissolved in cyclohexane at a concentration of 1% was added to all monomers (trioxane + 1,3-
(Dioxolane) at a concentration shown in Table 1 to carry out copolymerization. The type and amount of impurities contained in the above-mentioned feedstock were as shown in Table 1 as a result of analysis. Next, the reaction product (approximately 90 ° C) discharged from the outlet of the polymerization machine is added immediately after discharge with an aqueous solution (finally, about 4 times) containing 1000 ppm of triethylamine at 20 ° C, and mixed and pulverized. Cool down to 45 ° C in 20 seconds, then 30 ° C after 10 seconds
After cooling, the mixture was stirred at this temperature for 60 minutes. Thereafter, centrifugation and drying were performed to obtain a final polymer. Table 1 shows the polymerization yield and the properties of the obtained polymer.

Examples 4 to 9 and Comparative Examples 4 to 7 Polymerization was carried out under exactly the same polymerization conditions as shown in Example 2 (Table 1), and the reaction products discharged from the discharge port of the polymerization machine were as shown in Table 2.
The mixture was pulverized while being mixed with an aqueous alkali solution shown in Table 2 and subjected to a catalyst deactivation treatment under the temperature conditions shown in Table 2. The temperature (cooling) conditions were adjusted by the temperature and amount of the aqueous alkaline solution used, and further by multistage addition at different temperatures. After cooling, the mixture was stirred at the indicated temperature for 60 minutes, centrifuged and dried to obtain a final polymer. In all cases, the polymerization yield was approximately 73%. Table 2 shows the properties of the obtained polymer.

[0020]

[Table 1]

[0021]

[Table 2]

Claims (4)

(57) [Claims] 1. Trifluoroxane as a main monomer and a cyclic ether or cyclic formal having a carbon atom adjacent thereto and having no substituent or a hydrogen atom partially substituted with an alkyl group as a comonomer. In a method of obtaining a polyoxymethylene copolymer by copolymerization using a catalyst comprising boron halide or its coordination compound, the total amount of impurities having a polymerization termination and chain transfer action in the reaction system is 1 to all monomers. X 10 ^-2 mol% or less, and the amount of catalyst used in the polymerization reaction is 1 x 10 ^{-3 to} 7 with respect to all monomers.
× 10 ^-3 mol% and copolymerized.
Cool to a temperature of 45 ° C to 15 ° C within 30 seconds, at least 10
A substantially linear melt index value (190 ° C., load 2160 g) characterized in that the catalyst is deactivated at a temperature of not less than ℃ 2.
A method for producing a polyoxymethylene copolymer having a high degree of polymerization of 0 g / 10 min or less . 2. The process according to claim 1, wherein the polymerization temperature is in the range of 60 to 105 ° C.
The method according to claim 1. 3. The cooling of the polymerization product after the copolymerization becomes basic.
3. The method according to claim 1, which is performed by a low-temperature solution in which the compound is dissolved.
The manufacturing method as described. 4. A water-soluble solvent for dissolving a basic compound.
4. The method according to claim 3, wherein an aqueous solution is used.