JPH0689089B2 - Method for producing polyacetal resin having blocked end groups - Google Patents

Description

TECHNICAL FIELD The present invention relates to improvement of a method for producing a polyacetal resin.

More specifically, the present invention relates to a method for producing a polyacetal resin having a terminal group blocked with a stable functional group immediately after polymerization in a high yield.

(Prior Art) It is a well known fact that formaldehyde is polymerized and the polymer is used as a polyacetal resin. Substantially anhydrous formaldehyde is usually used as formaldehyde. Such anhydrous formaldehyde is industrially polymerized by using a quaternary ammonium salt as a polymerization catalyst, as shown in JP-B-34-4287, to form a polymer.

During this polymerization, water, methanol, formic acid, etc., which are impurities in the formaldehyde gas, act as a chain transfer agent, that is, a molecular weight modifier, as disclosed in JP-B-35-9435.

As a result, the polymer end groups are terminated with thermally labile -OH groups.

Therefore, the polyformaldehyde (polyacetal resin) immediately after the polymerization is thermally unstable and requires a terminal stabilizing step.

In these methods, the terminal group is acetylated with acetic anhydride as shown in JP-B-33-6099. However, it is troublesome that the polymer is decomposed in the acetylation step and the yield of the polymer is lowered. Furthermore, what is more troublesome is that the formaldehyde generated by decomposition reacts with acetic anhydride to produce methylene diacetate as a by-product.

The yield of the polymer in the acetylation step is about 90%. Further, the formaldehyde produced by decomposition reacts with acetic anhydride almost quantitatively to produce methylene diacetate as a by-product, so that a large amount of acetic anhydride is lost.

The molecular weight of polyformaldehyde, which can be used as an industrial material, is 1.0 or more when expressed in terms of reduced viscosity. The reduced viscosity here is expressed as η _sp / c at 60 ° C. when 0.5 g of the polymer is dissolved in 100 ml of a mixed solvent of p-chlorophenol and tetrachloroethylene.

Preferred values are in the range 1.2-3.5.

On the other hand, it has been proposed to block the polymer end with a thermally stable group.

For example, British Patent No. 1,120,524 describes R ₁ O (CH ₂ O)
_It has been proposed to polymerize formaldehyde in the presence of a compound of _n R ₂ to attach a thermally stable —OCH ₃ group to the polymer terminal. However, this method is difficult to obtain a polymer having a high degree of polymerization due to the use of a cationic catalyst.

Also, British Patent No. 796,863, the acid anhydrides, for example acetic anhydride acts as a chain transfer agent, discloses that provides a thermally stable -OCOCH ₃ group at the terminal.

JP-A-61-242522 also proposes a polymerization method in which a specific quaternary ammonium salt is used and acetic anhydride is used as a chain transfer agent.

However, in British Patent No. 796,863 or Japanese Patent Laid-Open No. 61-42522, it is not clarified to what extent the terminal groups are blocked.

(Problems to be Solved by the Invention) The present invention provides a polyformaldehyde having a controlled molecular weight, in which 75% or more of the terminal groups are blocked, immediately after polymerization.

Surprisingly, the polyformaldehyde immediately after the polymerization has a very low polymer loss in the terminal acetylation step subsequent to the polymerization, and a small amount of a by-product of a side reaction product, methylene diacetate. It was found to be significantly improved. Such a discovery was a new fact never seen before.

(Means for Solving the Problems) That is, the present invention is: acetic anhydride as a molecular weight modifier or water in addition to acetic anhydride;
Reduced viscosity (η _sp / obtained by polymerizing one or more of methanol and formic acid under conditions satisfying the following relational expression:
a formaldehyde polymer in which c) is 1 or more and 75% or more of the unterminated groups are blocked with an acetyl group,
A method for producing a polyacetal resin which is terminally acetylated with acetic anhydride.

[In the formula, E _{CH 2} and E _{C = 0} are main chain —CH ₂ O—
(6.8 μ) and the infrared absorbance of the terminal CH ₃ COO group (5.7 μ) are shown. ].

Next, the present invention will be specifically described.

A measure of the molecular weight of polyformaldehyde immediately after polymerization is represented by the reduced viscosity (η _sp / c).

Reduced viscosity (η _sp / c) of the formaldehyde polymer of the present invention
Is 1.0 or more, preferably 1.2 to 3.5.

Anhydrous formaldehyde is preferably used to obtain polyformaldehyde.

As a method for purifying formaldehyde, a cooling trap method,
A hemiacetal cleaning method, a cleaning method using another organic solvent, or the like can be applied.

The substantially anhydrous formaldehyde thus obtained is polymerized in a hydrocarbon solvent containing a polymerization catalyst.

The polymerization solvent used, for example, hexane, heptane, cyclohexane, aliphatic such as toluene, alicyclic,
An aromatic hydrocarbon etc. can be mentioned. These solvents may be used alone or in combination of two or more.

As the polymerization catalyst used, a cation catalyst, an organometallic catalyst, an anion catalyst, etc. can be mentioned.
Examples of preferable catalysts are organic tin compounds such as dibutyltin dimethoxide and dioctyltin dimethoxide; quaternary ammonium salts such as dimethylstearyl ammonium acetate.

The addition amount of these polymerization catalysts is not particularly limited, but is generally 0.0005 to 5 parts by weight with respect to 100 parts by weight of the starting monomer.

The polymerization reaction is usually −30 to 100 ° C., preferably 30 to 80 ° C.,
More preferably, it is carried out at a reaction temperature of 4 to 70 ° C.

During the polymerization of formaldehyde, acetic anhydride is used as a molecular weight regulator (or chain transfer agent). The acetic anhydride used is introduced as acetyl groups in the polymer end groups.

Incidentally, the acetic anhydride as a molecular weight regulator methanol,
You may use what added a small amount of water, formic acid, etc.

The concentration of the molecular weight regulator, acetic anhydride, introduced during this polymerization depends on the desired reduced viscosity of the formaldehyde polymer produced,
It is easily determined by the acetyl group blocking rate.

In the method of the present invention, 75 of the polymer end groups immediately after polymerization are
It has been experimentally discovered that the polymer yield is significantly improved by polymerizing with a specific molecular weight regulator under the condition that at least% is acetylated and the following relational expression is satisfied.

In addition, here, E _{CH 2} and E _{C = 0} are main chain —CH ₂ O—
(6.8μ) and the unterminated CH ₃ COO group (5.7μ) are shown by the infrared absorbance, and Kern et al., Makromol Chemie 114 (196
8) It can be determined by the infrared spectroscopy described on pages 92 to 112.

Further, the blocking rate of the polymer terminal group with an acetyl group is calculated by the following formula.

Here, R _V means the weight residual ratio when 1 g of the polymer is heated under a vacuum of 222 ° C. for 50 minutes.

The blocking rate immediately after polymerization is 75% or more, preferably 80% or more,
It is more preferably 85% or more, and particularly preferably 90% or more.

The formaldehyde polymer of the present invention can be subjected to a stabilization treatment such as terminal acetylation after the polymerization, if necessary, and even with this treatment, polymer loss is small and a high-quality polyacetal resin can be obtained.

The formaldehyde polymer of the present invention, if necessary,
Various additives conventionally used for polyacetal resins, such as antioxidants, ultraviolet absorbers, lubricants, lubricants,
Fillers, reinforcing agents, flame retardants, pigments and the like can be added alone or in various combinations.

(Examples) Hereinafter, the present invention will be specifically described with reference to Examples, but these do not limit the scope of the present invention.

Example 1 Formaldehyde is polymerized using substantially anhydrous formaldehyde gas.

As a polymerization catalyst, dimethyl distearyl ammonium acetate is dissolved in 50 ppm hexane and the solution is supplied to the tank 2. The tank is equipped with a powerful stirrer.

Hexane as a solvent is continuously supplied at 300 ml / hour.

60 g of formaldehyde gas are fed into the polymerizer every hour. Acetic anhydride and water, which serve as molecular weight regulators, are supplied to the polymerization vessel in vapor form. In addition, the polymerization slurry produced from the polymerization vessel is continuously withdrawn. Furthermore, the internal temperature of the polymerization vessel is
The temperature of the polymerization vessel was adjusted with a jacket so that it was 55 ° C.

The polymer in the extracted slurry has a reduced viscosity (η _sp
/ c), the terminal acetyl group concentration (EC _{= 0} /
The terminal acetylation rate is calculated on the basis of E _{CH 2} ), 222 ° C., and heat loss for 50 minutes.

The reduced viscosity (η _sp / c) of the polymer is adjusted by adjusting the vapor amounts of acetic anhydride and water supplied to the polymerization vessel so that the desired molecular weight is obtained.

The desired reduced viscosity was set to 2.03, and formaldehyde was polymerized. The [acetyl group concentration (E _{c = 0} / E _{CH 2} )] × (η _sp / c)) ^1.16 of the obtained polymer was 0.18, which was within the range calculated by the above formula (1). The acetylation ratio of the obtained polymer was 77%.

When the polymer was subjected to terminal acetylation in acetic anhydride by a known method, the yield of the obtained polymer was 97.6%.
Met.

Comparative Example 1 As in Example 1, the desired reduced viscosity of the polymer was set to 2.03, but ((aceter group concentration (E _{C = 0} / E _{CH 2} )) × (η
_sp / c) ^1.16 produced a polymer having a deviation of 0.07 from the formula (1), and the acetylation rate of the obtained polymer was 32%.

When this polymer was subjected to terminal acetylation in acetic anhydride by a known method, the yield of the obtained polymer was 91.2%. In addition, a large amount of methylene diacetate was by-produced in the solution subjected to terminal acetylation.

Example 2 The reduced viscosity of the desired polymer was set to 1.61, the same operation as in Example 1 was performed while adjusting the vapor amounts of acetic anhydride and water supplied to the polymerization vessel, and the range of the formula (1) was satisfied. [Acetyl group concentration (E _{c = 0} / E _{CH 2} )] × (η _sp / c))
^1.16 made a polymer of 0.19.

The terminal acetylation ratio of this polymer was 83%. Further, this polymer was subjected to terminal acetylation in acetic anhydride by a known method. The yield of the obtained polymer was 98.1%.

Example 3 The reduced viscosity of the desired polymer was set to 1.46, the same operation as in Example 1 was performed while adjusting the vapor amounts of acetic anhydride and water supplied to the polymerization vessel, and the formula (1) was satisfied. [Acetyl group concentration (E _{c = 0} / E _{CH 2} )] x (η _sp / c)
^1.16 made a 0.21 polymer.

The terminal acetylation ratio of this polymer was 87%. Further, this polymer was subjected to terminal acetylation in acetic anhydride by a known method. The yield of the obtained polymer was 98.3%.

Example 4 The reduced viscosity of the desired polymer is set to 1.23, the same operation as in Example 1 is performed while adjusting the vapor amounts of acetic anhydride and water supplied to the polymerization vessel, and the range of formula (1) is satisfied. [Acetyl group concentration (E _{c = 0} / E _{CH 2} )] x (η _sp / c)
^1.16 made a 0.22 polymer.

The terminal acetylation ratio of this polymer was 91%. Further, this polymer was subjected to terminal acetylation in acetic anhydride by a known method. The yield of the obtained polymer was 98.6%.

Comparative Example 2 The reduced viscosity of the desired polymer was set to 1.23 as in Example 4, but (E _{c = 0} / E _{CH 2} )] × (η _sp / c) ^1.16 is calculated from the equation (1). The vapor amounts of acetic anhydride and water were adjusted to be 0.11 which was out of the range. The rate of terminal acetylation of the obtained polymer was 52%. When the polymer was subjected to terminal acetylation in acetic anhydride by a known method, the yield of the polymer was 92.3%.

Example 5 The reduced viscosity of the desired polymer was set to 3.2, and the same operation as in Example 1 was performed, while (E _{c = 0} / E _{CH 2} )] × (η _sp /
c) A polymer of 0.17 in which ^1.16 is within the range calculated from the formula (1) was used.

The terminal acetylation ratio of the obtained polymer was 77%.
Further, this polymer was subjected to terminal acetylation in acetic anhydride. The yield of the obtained polymer was 97.7%.

(Effect of the Invention) The present invention makes it possible for the first time to obtain polyformaldehyde in which most of the end groups are blocked during polymerization.

These polymers provide a high-quality polyacetal resin with little loss of the polymer in the terminal acetylation step after the polymerization.

Claims (1)

[Claims] 1. A reduced viscosity (η) obtained by polymerizing acetic anhydride or acetic anhydride and one or more of water, methanol and formic acid as a molecular weight modifier under conditions satisfying the following relational expression: _sp / c) is 1 or more and
A method for producing a polyacetal resin, which comprises terminally acetylating a formaldehyde polymer, 75% or more of which is blocked with acetyl groups, using acetic anhydride. (In this formula, E _{CH 2} and E _{c = 0} are main chain —CH ₂ O—
(6.8 μ) and the infrared absorbance of the terminal CH ₃ COO group (5.7 μ) are shown. )