JPS5850652B2 - Production method of polyoxymethylene polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a process for making thermally stable polyoxymethylene polymers having desirable molecular weights and improved processability.

More specifically, the present invention relates to a method of polymerizing formaldehyde using a polyhydric alcohol of triol or higher as a molecular weight regulator to obtain a polyoxymethylene polymer having excellent thermal stability and processability.

Japanese Patent Publication No. 35-9435 states that the molecular weight of a formaldehyde polymer is determined by the amounts of trace amounts of water, methanol, and formic acid present in the polymerization system.

Further, US Pat. No. 3,017,389 describes that formaldehyde is polymerized in the presence of an initiator and a chain transfer agent such as a monoester, monoalcohol, acid anhydride, amide, or imide.

Among the chain transfer agents found in these publications, compounds with so-called active hydrogen have a sufficiently fast chain transfer rate, but
The thermal stability of the resulting polymers, on the other hand, is not necessarily good.

Furthermore, compounds such as monoesters, acid anhydrides, amides, imides, etc. have the disadvantage that chain transfer rates are slow and molecular weight control is insufficient.

Furthermore, the processability of polymers produced using these compounds as chain transfer agents is insufficient, and there is a large room for improvement.

On the other hand, Japanese Patent Publication No. 44-23341 describes that trioxane or formaldehyde is polymerized using a cationic polymerization catalyst in the presence of a polyhydroxy compound.

During polymerization using a cationic polymerization catalyst, a main chain scission reaction called a hydride shift reaction occurs, resulting in a decrease in the molecular weight of the polymer.

Furthermore, this main chain scission reaction is particularly noticeable in formaldehyde polymerization, and when a cationic polymerization catalyst is used, it is extremely difficult to obtain a polymer having a sufficiently high molecular weight.

Polyoxymethylene polymers are widely used as thermoplastic engineering plastics, and are usually shaped using molding methods such as injection molding, extrusion, and molding.

Improving the processability of polyoxymethylene during molding is expected to greatly open up new uses for polyoxymethylene polymers.

As a result of extensive studies on methods for controlling the molecular weight of polyoxymethylene polymers, the present inventors found that polyhydric alcohols of triol or higher function as good molecular weight control agents, and that the resulting polymers have good thermal stability and processability. The present inventors have found that the results are good and have completed the present invention.

That is, the present invention provides a method for controlling the molecular weight in formaldehyde polymerization, as well as a method for producing a polyoxymethylene polymer having good thermal stability and processability.

The object of the present invention can be achieved by polymerizing formaldehyde in the coexistence of a polyhydric alcohol of triol or higher as an anionic polymerization catalyst.

When formaldehyde is polymerized in the coexistence of a polyhydric alcohol, chain transfer and chain branching occur, and the molecular weight of the polymer is controlled.

The branched polymers produced also have improved melt flowability and, as a result, exhibit good processability in extrusion molding, injection molding, and the like.

Chain branching of polyoxymethylene polymers occurs only with polyhydric alcohols having at least three alcoholic hydroxyl groups.

When an alcohol having one or two alcoholic hydroxyl groups is used, chain transfer occurs but chain branching does not occur.

In the present invention, polyhydric alcohols of triol or higher,
That is, a compound containing at least three alcoholic hydroxyl groups in one molecule can be used as a molecular weight regulator.

Examples of polyhydric alcohols include triol, tetraol, pentaol, hexaol, and the like.

A first group of triols includes glycerin or glycerin derivatives represented by the general formula %.

For example, glycerin, glycerin ethylene oxide adduct (average molecular weight 800), glycerin propylene oxide adduct (average molecular weight 4.200), glycerin ethylene oxide/propylene oxide mixed adduct (average molecular weight 2,000, ethylene oxide:propylene oxide)
3:1 (weight ratio) etc. are included in this group.

A second group of triols includes trimethylolpropane or trimethylolpropane derivatives with the general formula %.

For example, trimethylolpropane, trimethylolpropane ethylene oxide adduct (average molecular weight 1,680)
, trimethylolpropane propylene oxide adduct (
(average molecular weight 4,500), trimethylolpropane ethylene oxide/propylene oxide mixed adduct (average molecular weight 2,500, ethylene oxide:propylene oxide -2:1 (weight ratio)), etc. are included in this group.

A third group of triols includes sorbitan monoesters or sorbitan monoester derivatives represented by the general formula % R'=alkyl group.

For example, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monolaurate ethylene oxide adduct (average molecular weight 3,
100), sorbitan monooleate propylene oxide adduct (average molecular weight 5.300), etc. are included in this group.

In addition to the above three groups, compounds having three alcoholic hydroxyl groups in the molecule are naturally included in triols.

For example, 1,2.6-4 hydroxyhexane, ■, 3,
5-trihydroxy-3-methylpentane, diglycerin monoacetate, trimethylolethane, 1,1.3
-tris(hydroxyphenyl)furopane, trimethylolethanepropylene oxide adduct (average molecular weight 1,
200) etc.

Among these triols, glycerin, glycerin derivatives, trimethylolpropane, trimethylolpropane derivatives, sorbitan monoester, and sorbitan monoester derivatives are particularly preferred from the viewpoint of ease of acquisition and purification.

The first group of tetraols includes pentaerythritol and pentaerythritol derivatives represented by the general formula %CH3.

For example, pentaerythritol, pentaerythritol ethylene oxide adduct (average molecular weight 1,500), pentaerythritol propylene oxide adduct (average molecular weight 3.3 o □), pentaerythritol ethylene oxide/propylene oxide mixed adduct (average molecular weight 1. g 201 ethylene oxide) :propylene oxide - weight ratio of 1:4) and the like are included in this group.

As a second group of tetraols, the general formula (nl
tn2yn3tn4=o ~50 +R=H+CH3)
There are diglycerin and diglycerin derivatives represented by

For example, diglycerin, diglycerin ethylene oxide adduct (average molecular weight 3,150), etc. are included in this group.

A third group of tetraols includes sorbitan and sorbitan derivatives.

For example, 1,5-sorbitan, ■, 4-sorbitan, 3,
Included in this group are 6-sorbitan, 1,5-sorbitan ethylene oxide adduct (average molecular weight 2,500), and 4-sorbitan propylene oxide adduct (average molecular weight 5.800).

In addition to the above three groups, it is natural that tetraols include compounds having four alcoholic hydroxyl groups in one molecule.

For example, 1,1,2.2 tetrakis(hydroxyphenyl)ethane, polyhydroxypolyolefin (average molecular weight: 3,100°) A compound in which the double bonds of polybutadiene are epoxidized and the epoxy ring is opened after hydrogenation. Polymers containing an average of four alcoholic hydroxyl groups in the molecule), etc.

Among these tetraols, pentaerythritol, pentaerythritol derivatives, digcerin, digcerin derivatives, sorbitan, and sorbitan derivatives are particularly preferred.

Examples of pentaols include compounds collectively called hexoses, such as fructose and glucose, which include compounds having five alcoholic hydroxyl groups in one molecule.

Examples of hexaol include sorbitol, sorbitol ethylene oxide adduct, sorbitol ethylene oxide adduct, and the like.

In addition to these compounds, hexaol naturally includes compounds having six alcoholic hydroxyl groups in one molecule.

These polyhydric alcohols are used alone or in combination for the polymerization reaction.

Further, prior to the polymerization reaction, it is desirable to purify the polyhydric alcohol by removing impurities such as water contained in the polyhydric alcohol as much as possible.

In the present invention, catalysts generally known as anionic polymerization catalysts and coordination anionic polymerization catalysts can be used for formaldehyde polymerization.

Typical groups of these catalysts include alkali metals such as sodium and potassium, alkali metal complex compounds such as sodium-naphthalene and potassium-anthracene,
Hydrogenation Alkali metal hydrides such as IJium, alkaline earth metal hydrides such as calcium hydride, alkali metal alkoxides such as sodium methoxide and potassium t-butoxide, alkali carboxylic acids such as sodium caproate and potassium stearate. Metal salts, alkaline earth metal carboxylic acid salts such as magnesium caproate and calcium stearate, amines such as n-butylamine, diethylamine, trioctylamine, pyridine, ammonium stearate, tetrabutylammonium methoxide, dimethyl distearyl ammonium acetate Quaternary ammonium salts such as 1., phosphonium salts such as tetramethylphosphonium propionate, trimethylbenzylphosphonium ethoxide, tributyltin chloride, diethyltin dilaurate, dibutyltin dimethoxide, etc.
Examples include organic tin compounds, alkyl metals such as n-butyllithium and ethylmagnesium chloride, and organic chelate compounds such as trisacetylacetone cobalt.

Further, in the present invention, polymerization is usually carried out in an organic medium.

Organic media that can be used in the present invention include aliphatic hydrocarbons such as n-hexane, n-heptane, and cyclohexane, aromatic hydrocarbons such as benzene, toluene, and xylene, and halogens such as methylene chloride, chloroform, and trichloroethylene. Examples include halogenated aliphatic hydrocarbons, halogenated aromatic hydrocarbons such as chlorobenzene, and ether compounds such as ethyl ether and tetrahydrofuran.

These organic media may be used alone or in combination of two or more.

The formaldehyde used in the present invention needs to be substantially anhydrous and needs to be purified using a known method such as a cold trap method or a solvent washing method.

For producing the polyoxymethylene polymer of the present invention, methods conventionally known as formaldehyde polymerization methods such as blow polymerization method and solution polymerization method can be used.

The blow polymerization method is a method in which formaldehyde gas is directly blown into an organic medium containing a polymerization catalyst and a polyhydric alcohol, and the solution polymerization method is a method in which the organic medium containing a polyhydric alcohol is cooled and the solution is This is a method in which a polymerization catalyst is added to start polymerization after the formaldehyde is absorbed.

The polyhydric alcohol is used after being uniformly dissolved or dispersed in an organic medium.

The concentration of the polyhydric alcohol in the organic medium can be easily determined experimentally depending on the molecular weight requirements of the desired polyoxymethylene polymer.

The polymerization catalyst is used in a concentration of 1×10 −2 to 1×10 −6 mol/l of organic medium.

The polymerization temperature is -50 to 118°C in the case of the blow polymerization method.
In the case of solution polymerization, the temperature is often set between -70 and 50°C.

There is no particular restriction on the polymerization time, but it is between 5 seconds and 30 seconds.
Set between 0 minutes.

After completion of the polymerization, the polyoxymethylene polymer is separated from the organic medium and the terminal labile moieties are then capped by known methods such as acetylation using acetic anhydride.

Then, stabilizers, antioxidants, etc. are added, and the mixture is put into practical use.

By using the manufacturing method of the present invention described in detail above,
It has become possible to obtain a polyoxymethylene polymer that has both the desired molecular weight and excellent thermal stability and processability.

Here, the features of the present invention are listed as follows.

(1) It is possible to arbitrarily control the molecular weight of the polyoxymethylene polymer.

(2) It is possible to control the molecular weight and at the same time impart excellent thermal stability and processability to polyoxymethylene polymers.

Measurement items in the following examples are as follows.

Reduced viscosity: Polymer concentration 0.5 gr in p-chlorophenol-tetrachlorethylene (1:1 weight ratio) solution
/dl, measured at 60°C.

A measure of the molecular weight of polyoxymethylene polymers.

RA222: Amount remaining after heating a terminal acetylated polymer at 222° C. for 90 minutes in air, a measure of thermal stability of polyoxymethylene polymers.

M, F, R,: Melt index (MI) measured under standard load of 2.16 Ky at 190°C, (ASTM-D123
8-57T) Measured the high load melting index (IOXMI) at 190°C under a high load of 21.60Kp, M, F, R.

10XMI/MI, a measure of the processability of polyoxymethylene polymers.

The present invention will be explained below with reference to Examples, but these are not intended to limit the scope of the present invention.

Example 1 Thoroughly dehydrated and dried paraformaldehyde was heated at 150°C.
By thermally decomposing the mixture and passing it through a cooling trap several times, formaldehyde gas with a purity of 99.9% was obtained.

100 tons of formaldehyde gas per hour, 2.5 X 10-4 mol/IJ of dioctyltin dilaurate as a polymerization catalyst, and 3. OX1
It was introduced into 500 parts of cyclohexane containing 0-3 mol/d of glycerin.

At the same time as formaldehyde gas supply, 2.5 x 1
0-'mol/4 dioctyltin dilaurate, 3. O
Cyclohexane containing Xlo-3 mol/d of glycerin was supplied at a rate of 500 parts per hour, and was continuously supplied for 3 hours.

Formaldehyde gas is also used at a rate of 100 parts per hour.
The polymerization temperature was maintained at 40°C during the continuous feeding for 3 hours.

Cyclohexane containing the polymer was continuously extracted in proportion to the amount supplied, and the polymer was separated by filtration.

After thoroughly washing the polymer with acetone, it was vacuum dried at 60°C to obtain 278 parts of a white polymer.

This polymer had a reduced viscosity of 2.35 and a desired molecular weight.

This polymer was then stabilized by terminal acetylation using acetic anhydride with sodium acetate as a catalyst.

RA 2 of stabilized polyoxymethylene polymer
No. 22 had a good thermal stability of 96.5%.

2,2-methylene-bis(4-
methyl-6-tert-butylphenol) 0.25 notes 8, polycaprolactam/polyhexamethylene adipamide/polyhexamethylene sebamide terpolymer 0.
After adding 7.5 parts and mixing using a 5 parts mmφ extruder,
MI, 10xMI? 1111, MI 1
0.5 g/l 0 min, 10XMI297.2g710
Min, M, F, R.

28.3, indicating improved workability.

Examples 2 to 12 99.9% pure formaldehyde gas per hour
00 parts of hexane containing the polymerization catalyst and polyhydric alcohol shown in Table 1 for 3 hours.

Similar to formaldehyde gas, the polymerization catalyst shown in Table 1, hexane containing polyhydric alcohol, was
The polymerization temperature was maintained at the temperature shown in Table 1 during this period.

After separating the polymer from hexane, terminal acetylation was performed with acetic anhydride, and the same antioxidant/stabilizer as in Example 1 was added.

The obtained results are also shown in Table 1.

In all Examples, it was possible to obtain a polymer having a desired molecular weight and excellent thermal stability and processability.

Comparative Example 1 All of the reagents used in Example 1 were operated in the same manner as in Example 1, except that octatool was used as a molecular weight regulator instead of glycerin, and the results are shown in Table 1.

Although it is possible to control the molecular weight by using Octatool, the thermal stability and processability are inferior to that of glycerin.

Comparative Example 2 All of the reagents used in Example 2 were the same as in Example 2, except that octylpropionate was used as a molecular weight regulator instead of trimethylolpropaneethylene oxide adduct (average molecular weight 3.620). The results are shown in Table 1.

In the case of n-octylpropionate, the molecular weight control of the polymer was incomplete, and at the same time, the thermal stability and processability were also poor.

The results of the above Examples and Comparative Examples are summarized in Table 1.

Claims (1)

[Scope of Claims] 1. A thermally stable polyoxymethylene polymer having a desired molecular weight and improved processability, characterized by anionic polymerization of formaldehyde in the coexistence of a polyhydric alcohol of triol or more. Manufacturing method. 2. The production method according to claim 1, wherein the polyhydric alcohol is a triol. 3. The method according to claim 2, wherein the triol is glycerin or a glycerin derivative represented by the general formula %. The method according to claim 2, which is trimethylolpropane or a trimethylolpropane derivative represented by (nl, n2.n3=O~50.R-H1CH3). 5. The method according to claim 2, wherein the triol is a sorbitan monoester or a sorbitan monoester derivative represented by the general formula % (alkyl group). 6. The production method according to claim 1, wherein the polyhydric alcohol is a tetraol. 7. The method according to claim 6, wherein the tetraol is pentaerythritol or a pentaerythritol derivative represented by the general formula (% R'-alkyl group). 8. The method according to claim 6, wherein the tetraol is diglycerin or a diglycerin derivative represented by the general formula %.