JPH0380809B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for continuously producing polyoxymethylene copolymers, more specifically,
The present invention relates to a method for efficiently producing a polyoxymethylene copolymer having high thermal stability during polymerization using a special polymerization apparatus. It is heretofore known to polymerize purified substantially anhydrous trioxane with other oxyalkylene feedstocks in the presence of a catalyst to obtain polyoxymethylene copolymers. However, when a polymerization catalyst is added to liquid trioxane and brought under polymerization conditions, the reaction generally proceeds rapidly and the reaction product solidifies, making removal and pulverization difficult, as well as causing undesirable side reactions and coloring. etc. In order to solve these problems, a so-called slurry polymerization method in which polymerization is carried out in the presence of a large amount of inert solvent has been proposed, but it is time-consuming to recover the solvent and the molecular weight of the resulting polymer is reduced. However, it cannot be said to be a satisfactory industrial method. Therefore, improvements in the bulk polymerization process are currently a goal in this field of technology for the production of polyoxymethylene polymers or copolymers. Many methods and devices for bulk polymerization of trioxane have been proposed so far. So-called co-kneaders (KO-
(Japanese Patent Publication No. 44-5234), a method using a twin-screw extruder type reactor (Japanese Patent Publication No. 47-629, Japanese Patent Publication No. 47-42145), It consists of a long twin-hulled case extending substantially along the outer boundary of the shaft, and on said shaft a number of interlocking elliptical plates are pivotally supported, the longitudinal ends of the plates stroking the surfaces of their mating members. A method using a self-cleaning polymerization reactor with interlocking flat ends (Japanese Patent Application Laid-Open No. 1983-
84890) have been proposed. However, the method using a co-kneader has the disadvantage that, due to insufficient mixing, the reaction mixture does not come into smooth contact with the cooling surface of the outer wall, resulting in a high reaction temperature. In addition, when using a conventional twin-screw extruder type reactor in which a pair of parallel screws that mesh with each other are arranged in a long double-barreled case, the reaction mixture solidifies rapidly, to the extent that it becomes impossible to rotate the screws. The load is applied to
It is often seen that the extrusion becomes substantially unsuitable, and it cannot be said that it is necessarily satisfactory in practical terms. Furthermore, although the method using a self-cleaning polymerization reactor produces a product with relatively fine particle size, it is not possible to obtain a high conversion rate when used alone.
In order to increase the conversion rate, it is necessary to connect two or more reactors of the same or different types, or to take measures to increase the hold-up of the reactors, as disclosed in JP-A-53-86794. , equipment costs, and operating costs will inevitably increase. Generally, copolymers obtained by polymerization must be stabilized by decomposing and removing unstable portions. The copolymer with a high conversion rate obtained by the method described above has many thermally unstable parts, and if a polyoxymethylene copolymer with a high degree of stabilization can be obtained, the subsequent stabilization process can be greatly simplified. There is. The present inventors have conducted intensive research to overcome the various drawbacks of such conventional methods and to develop a method for efficiently producing polyoxymethylene copolymers with higher thermal stability. The inventors have discovered that the object can be achieved by performing the bulk polymerization of trioxane under specific conditions using a specific reactor, and based on this knowledge, the present invention has been accomplished. That is, according to the present invention, when continuously copolymerizing a raw material mixture containing toluoxane and ethylene oxide or 1,3-dioxolane, the polymerization reaction apparatus includes a jacket substantially aligned with the outer boundary of a pair of shafts. It consists of a long case, each of the shafts has a pseudo-triangular plate consisting of a large number of mutually interlocking arcuate sides, and the structure is such that they interlock with each other so as to stroke the surface of the other plate, and the catalyst amount and residence time selected in advance are used. Correspondingly, the initial temperature of the jacket was set at 75 to 83°C, and the shaft was rotated in the same direction to finely pulverize the produced polymer, while adjusting the temperature of the polymerization reaction zone to achieve a conversion rate of 81 to 94%. By carrying out polymerization to a range of 2% and removing the polymer from the polymerization reaction zone in this state, a highly thermally stable polyacetal copolymer with a weight range of 2% or less when heated under vacuum at 222°C for 50 minutes can be produced. can be obtained. Next, the reaction apparatus used in the method of the present invention will be explained in detail with reference to the accompanying drawings. FIG. 1 is a partially sectional side view of an example of a reaction apparatus used in the method of the present invention, and FIG. 2 is a cross-sectional view thereof. This reactor consists of two shafts 2, 1' in two cylindrical cases 1, 1' that communicate in the central longitudinal direction.
2' is housed, and a jacket 4 for heating or cooling the reaction mixture is provided on the outside of the case. The shafts 2, 2' have pseudo-triangular paddles 3, 3... and 3', each having an arcuate cross section.
3'... is fixed. These paddles may be of the same type and may be attached out of phase, or two or more types of paddles may be attached in any combination. The apex of the paddle 1 on one shaft always rotates while being in contact with the inner surface of the case or the corresponding paddle on the other shaft with a slight gap. Trioxane and ethylene oxide or 1,
A raw material mixture containing 3-dioxolane is supplied, the shaft is rotated in the same direction, polymerization is performed while moving the raw material mixture, and the polymerization product containing 6 to 19% of unreacted materials is turned into fine powder from the discharge port 6. Take it out. In the method of the present invention, it is preferable to use as a raw material a mixture of trioxane and ethylene oxide or 1,3-dioxolane in a ratio that yields a copolymer containing 0.4 to 15 mol% of oxyethylene units in the main chain. . As the polymerization catalyst, commonly used cationic polymerization catalysts can be used, but in particular boron trifluoride or a complex compound of boron trifluoride and an organic oxygen or sulfur compound in combination with an inert organic solvent. is suitable. These may be used alone or in combination of two or more. Examples of this include boron trifluoride dibutyl etherate and boron trifluoride diethyl etherate. Further, as the inert organic solvent, aliphatic and aromatic hydrocarbons and halogenated hydrocarbons such as anhydrous hexane, heptane, cyclohexane, and benzene are used. These may dissolve raw material monomers and catalysts, or
It may also be one that does not dissolve. In the method of the present invention, the conversion rate of the polymerization product is
It is important that it is removed from the polymerization reaction zone in a range of 81-94%. In this way, by always maintaining the conversion rate of the polymerization product within the range of 81 to 94%, a thermally stable polymer can be obtained, which facilitates the stabilization process and improves the yield. can be increased. In this way, by limiting the range of conversion of the polymerization product within a specific range,
It was completely unexpected that a copolymer with excellent thermal stability was obtained. This polymerization conversion rate depends on the amount of catalyst added, the polymerization temperature, the polymerization time, that is, the residence time in the polymerization reaction zone, etc., but in the present invention, the amount of catalyst selected in advance through preliminary experiments etc. The polymerization reaction is started by setting the initial temperature of the jacket at 75 to 83°C according to the temperature and residence time, and the temperature in the reaction zone, which increases as the polymerization progresses, is controlled by the jacket temperature, and the conversion is carried out. Adjust the rate so that it is in the range of 81-94%. To suitably carry out the method of the present invention, an anhydrous inert organic solvent is used in a volume 5 to 1000 times the volume of the polymerization catalyst, and is poured as a dilute solution into the raw material mixture to react. In this way, the copolymerization reaction can proceed smoothly and at a high conversion rate. Then, from the reaction mixture thus obtained,
Unreacted raw materials and other volatile components therein are removed by distillation under reduced pressure, heat drying under inert gas scavenging, and the like to obtain a copolymer. The copolymer obtained by the method of the present invention has very good thermal stability, with a weight loss of 2% or less when heated in vacuum at 222° C. for 50 minutes. On the other hand, all the products obtained by the conventional method had a weight loss of 3% or more. Next, the present invention will be explained in more detail with reference to Examples. Example 1 2 parts of ethylene oxide in 100 parts by weight of trioxane
Parts by weight and 200 ppm of boron trifluoride dibutyl etherate (diluted to 200 times the volume with cyclohexane) were mixed and introduced into a polymerization apparatus having a pseudo-triangular paddle as shown in the drawing. By maintaining the jacket temperature at 80°C, the polymerization conversion rate was maintained at 90%. The fine powdery copolymer thus obtained was vacuum dried at 80° C. for 3 hours to remove unreacted raw materials and low-boiling point products. The obtained copolymer was dissolved in an equal mixture of p-chlorophenol and tetrachloroethane at a concentration of 0.2%, and
The reduced viscosity (ηsp/c) measured at °C is 3.8
It was hot. Furthermore, the weight loss after being placed in vacuum at 222°C for 50 minutes was 1.7%. Example 2 The same reaction as in Example 1 was carried out except that the jacket temperature was changed. The results obtained are shown in Table 1.

[Table] Comparative Examples 1 to 5 The same reaction as in Example 1 was carried out except that the jacket temperature was changed. The results obtained are shown in Table 2. This result indicates that the thermal stability of the polymer is poorer than in Examples 1 and 2, or that the state of the polymer is undesirable.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a partially sectional side view of an example of the apparatus used in the method of the present invention, and FIG. 2 is a cross-sectional view thereof, in which reference numerals 1 and 1' indicate a case, 2 and 2' indicate a shaft,
3 and 3' are paddles.

Claims (1)

[Claims] 1 trioxane and ethylene oxide or 1,3
- for the continuous copolymerization of a raw material mixture containing dioxolane, the polymerization reaction apparatus consists of a long case having a jacket substantially aligned at the outer boundary of a pair of shafts, each of said shafts having a plurality of interlocking arcuate shapes. Using a pseudo-triangular plate consisting of sides that interlock with each other so as to stroke the surface of the other plate, the initial temperature of the jacket is set to 75 to 83°C according to the pre-selected catalyst amount and residence time. setting and rotating the shaft in the same direction to finely pulverize the produced polymer and adjusting the temperature of the polymerization reaction zone to achieve a conversion rate of 81 to 94%.
Polymerization is carried out in the range of 222℃, and the polymer is taken out from the polymerization reaction zone in this state.
A method for producing a highly thermally stable polyacetal copolymer that exhibits a weight loss of 2% or less when heated under vacuum for 50 minutes.