JPH04108819A - Degradable polyoxymethylene copolymer - Google Patents

Abstract

PURPOSE:To provide the title polymer excellent in degradability along with outstanding mechanical properties and fatigue characteristics etc., useful as an engineering plastic, having a specific main chain composition with oxyalkylene group and limited terminal group composition. CONSTITUTION:The objective polymer having such compositions that a polymer made up of recurring oxymethylene unit (CH2O) has been incorporated with 0.1-5mols per 100mols of the oxymethylene unit of oxyalkylene unit of the formula [R0 and R'0 are each H, alkyl or phenyl, and may be bound to carbon atoms differing from each other; n is >=1, the proportion for n=1 being 60mol% of the whole oxyalkylene unit; (m)is 2-6] and the terminal groups are made up of alkoxy, hydroxyl and formate groups with the proportions for the hydroxyl and formate groups being <=45mol% and <=35mol%, based on the total terminal groups in the final polymer, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to polyoxymethylene copolymers. More specifically, the present invention relates to a polyoxymethylene copolymer that has a limited main chain composition and a limited terminal group composition, and has excellent degradability.

[Conventional technology]

In recent years, polyoxymethylene has been shown to have excellent mechanical properties, creep properties, fatigue properties, and electrical properties.
It is widely used as an engineering plastic in many fields, and the demand for it is increasing.

By the way, plastics lack degradability, such as biodegradability, and are difficult to decompose in nature, so recently, plastics have been
The issue of waste disposal after use has been attracting attention, and polyoxymethylene is no exception.

Conventionally, methods for imparting degradability to plastics include introducing natural polymeric substances such as cellulose and starch into molecules, but none of these techniques regarding polyoxymethylene have been disclosed. . Also,
The introduction of these cellulose, starch, etc. into plastics, for example, greatly impairs the inherent mechanical properties and moldability of plastics, so it is not preferable as a method of imparting degradability to plastics and is impractical. ing.

On the other hand, polyoxymethylene copolymers are usually obtained by copolymerizing formaldehyde or trioxane with a cyclic ether. U.S. Patent 3,027.352
In the publication, trioxane and ethylene oxide, 1,3
- There is a description of a copolymer obtained by cationic copolymerization with dioxolane.

US Pat. No. 3,337,503 discloses the use of methylal as a molecular weight regulator during the polymerization of trioxane.

When methylal is used as a molecular weight modifier, the terminal groups of the resulting polymer are methoxy or alkoxy groups.

Additionally, during polymerization using cationic catalysts such as formaldehyde and trioxane, hydride shift (hydrogen abstraction reaction) occurs, and at the same time, the main chain of the polymer is cleaved.
It is known that the cleaved end becomes a methoxy group and a formate group.

On the other hand, during copolymerization of trioxane and ethylene oxide, a compound having a hydroxyl group, such as water or methanol, functions as a chain transfer agent and forms a hydroxyl group at the end of the resulting polymer.

[Problem to be solved by the invention]

An object of the present invention is to provide a polyoxymethylene copolymer that has excellent degradability and also has the excellent mechanical properties, fatigue properties, etc. that polyoxymethylene originally has.

[Means to solve the problem]

As a result of extensive research, the present inventors have discovered that a polyoxymethylene copolymer with a limited main chain composition and a limited terminal group composition has excellent degradability and is inherently polyoxymethylene. The present inventors have discovered that methylene copolymers have excellent mechanical properties, fatigue properties, etc., and have completed the present invention.

That is, in the present invention, oxyalkylene units of the following formula are selected differently in a polymer consisting of repeating oxymethylene units (-CH2O-). n is an integer of 1 or more, the proportion of n = 1 is 6011ioρ% or more of the total oxyalkylene units, and m = 2 to 6) is an oxymethylene unit of 10
It has a structure in which 0.1 to 5 moρ is inserted per 0 moρ, and the terminal groups of the polymer are composed of alkoxy groups, hydroxyl groups, and formate groups, and the ratio of hydroxyl groups is 45% of the total terminal groups of the polymer. The following describes a degradable polyoxymethylene copolymer characterized in that the proportion of formate groups is 35 moΩ% or less based on the total terminal groups of the polymer.

Next, the present invention will be specifically explained.

The polyoxymethylene copolymer of the present invention can be prepared by combining formaldehyde or trioxane with the formula (wherein R8 and Ro' may be the same or different and are selected from hydrogen, an alkyl group, and a phenyl group. R attached to an atom 1 R attached to a different carbon atom
' can also be obtained by copolymerizing with a cyclic ether represented by the same formula or a cyclic formal represented by the formula -.

Moreover, the polymer of the present invention is a polyoxymethylene homopolymer and the above-mentioned cyclic ether or ring.

It can also be obtained by reacting with formal formal in the presence of a cationic catalyst.

Examples of the cyclic ether used to synthesize the polymer of the present invention include ethylene oxide, propylene oxide, butylene oxide, and styrene oxide.

Examples of the cyclic formal include ethylene glycol formal, diethylene glycol formal, 1.3
-propanediol formal, 1,4-butanediol formal, 1,5-bentanediol formal,
Examples include 1,6-hexanediol formal.

The important point here is the sea fence of oxyalkylene units in the polymer. That is, from the viewpoint of improving degradability, it is necessary for the oxyalkylene unit to be dispersed independently in the polymer as much as possible without forming blocks. That is, n, which represents the sea fence of oxyalkylene units, needs to be in a range where the proportion of n=1 is 6011IOρ% or more of the total oxyalkylene units. When the ratio of n=1 is less than 60 moΩ%, degradability decreases.

Such sea fencing of oxyalkylene units can be achieved by the following method.

Formaldehyde or trioxane and cyclic ether or cyclic formal are heated at 100°C in the presence of a cationic catalyst.
Thoroughly mix at the following temperature to generate a cyclic intermediate in advance. The higher the ratio of the cyclic ether or cyclic formal incorporated into the cyclic intermediate to the cyclic ether or cyclic formal present alone, the better the dispersion of the oxyalkylene units becomes. In that sense, the ratio of cyclic ether and cyclic formal existing alone is 40 mo11
%, the oxyalkylene units can be well dispersed.

In this way, a polyoxymethylene copolymer with good degradability can be obtained by copolymerizing the previously produced cyclic intermediate with formaldehyde or trioxane.

The sea fence of oxyalkylene units in the polymer is confirmed by the following method.

The polymer was dissolved in l/ION HCρ aqueous solution at 120°C for 2
When hydrolyzed over time, the oxymethylene units become formaldehyde and the oxyalkylene units become alkylene glycols represented by: n can be determined by analyzing and quantifying alkylene glycol using gas chromatography and liquid chromatography.

The next important point is the insertion rate of oxyalkylene units. That is, the insertion rate of oxydialkylene units in the polymer is 100 mo of oxymethylene units per Q,
A polyoxymethylene copolymer with excellent degradability can be obtained only when the mop is in the range of 0.1 to 5 mo.

When the insertion rate of oxyalkylene units is less than 0.1 mo, Q, or exceeds 5IIIOΩ, degradability decreases, and polyoxymethylene copolymers are superior only within a very limited range of oxyalkylene units. It can be degradable. This is a truly surprising discovery.

Furthermore, when the insertion rate of oxyalkylene units is less than 0.1 moρ, stability, especially stability against chemicals, decreases;
If it exceeds 5 moρ, the mechanical properties will deteriorate significantly, and both will greatly lack practicality as engineering plastics.

The insertion rate of oxyalkylene units in the polymer can be determined using the polymer hydrolysis method described above.

Next, the number m of carbon atoms in the oxyalkylene unit needs to be in the range of 2 to 6. When m is 1, the obtained polymer is a polyoxymethylene homopolymer and lacks thermal stability during molding.

When m is 7 or more, the mechanical properties of the obtained polymer are significantly reduced.

The terminal group structure and terminal group composition of the polymer of the present invention are also extremely important points.

The terminal group of the polymer of the present invention is an alkoxy group (-O
R, R are alkyl groups), hydroxyl groups (-OH),
It is composed of a formate group (-〇CHO).

In addition, the ratio of hydroxyl groups to all end groups consisting of alkoxy groups, hydroxyl groups, and formate groups, that is, the ratio of hydroxyl groups to all end groups of the polymer is 45 mo, Q% or less, and the ratio of formate groups to 35 m0Ω% or less. There is a need.

When the ratio of hydroxyl groups exceeds 45mo, Q%,
Alternatively, when the ratio of formate groups exceeds 35 mo, Q%, surprisingly, the degradability of the resulting polyoxymethylene copolymer is significantly reduced.

Among the alkoxy groups, methoxy groups are particularly preferred from the viewpoint of stability during molding.

Here, the analysis of the terminal group is performed by the following method.

■Alkoxy group: quantified using the modified Zeisel method, the ratio of methoxy group per 100 moΩ of oxymethylene group is γ
It is expressed as (mo, Q).

■Hydroxyl group: Acetylate the polymer with acetic anhydride,
Convert a hydroxyl group to an acetyl group (-0-C-CH3). Next, using an infrared absorption spectrum, the absorbance of the carbonyl group of the acetyl group at 1755 cm' and the absorbance of the oxymethylene group at 1470 cm' are measured. oxymethylene group 100mo,
The ratio of hydroxyl groups per Q (α) is calculated using the following formula.

■Formate group: 1 using infrared absorption spectroscopy
The carbonyl group of the formate group at 710 cm-' is analyzed and quantified. The ratio (β) of formate groups per 100 moρ of oxymethylene groups is calculated using the following formula.

The polyoxymethylene copolymer of the present invention is a polymer with excellent degradability.

Degradability in the present invention refers to biodegradation by enzymes, biodegradation, etc., and is a rough guide to the decomposition in the natural world after use as engineering plastics, in other words, the ease of waste disposal after use. becomes.

Degradability can be evaluated by, for example, leaving a polyoxymethylene copolymer film in water (preferably seawater), soil, or water containing enzymes, observing the appearance of the film over time, and observing changes in weight loss. It can be easily done by asking.

The number average molecular weight (Mn) of the polyoxymethylene copolymer of the present invention is from 10,000 to 100,000 (7)
Preferably in between. Number average molecular weight is 10.000
If it is less than that, the mechanical properties will be poor. On the other hand, when the number average molecular weight exceeds 100.000, moldability becomes poor. The number average molecular weight of the polymers of the present invention is usually determined using an end group assay. That is, the number average molecular weight can be determined by quantifying the terminal alkoxy group, hydroxyl group, and formate group. That is, α
, β, and γ are quantified, and Mn is calculated according to the following formula.

〔Example〕

The polymers of the present invention will be explained in detail with reference to Examples below. The measurement items in the examples are as follows.

■Tensile strength Add the antioxidant 2,2-methylene-bis(4-methyl-6-tert-
Butylphenol) OJO part, heat stabilizer nylon 6.6
0.10 part was added and pelletized using a 30 mmφ twin screw extruder. This pellet was molded into a test piece and AST
Tensile strength was measured according to MD-638.

Tensile strength is a measure of mechanical properties.

■Degradability A test film of polyoxymethylene copolymer (approximately 0.1 mm thick) was placed in 100 ml of seawater at a constant temperature of 30°C.

The number of days (half-life) for the weight of the film to decrease by half was determined. The smaller the half-life, the better the degradability.

■Terminal group ratio Using the ratio of hydroxyl groups (α), formate group ratio (β), and alkoxy group ratio (γ) per 100 moΩ of oxymethylene group, the ratio of hydroxyl groups to all terminal groups (α′), The ratio of formate groups (β') is determined by the following calculation.

α a' = xloo (moΩ
%)α10β+γβ Example 1 (1) Production of polyoxymethylene copolymer 1.150 gr of anhydrous trioxane, 0 gr of ethylene ethylene oxide, and 2.53 gr of methylal were placed in a kneader with two Σ blades and heated to 80°C. did. Next, 0.05g of boron trifluoride dibutyl etherate was added to start the reaction. After 240 seconds had elapsed, the contents of the kneader were sampled and analyzed using gas chromatography and liquid chromatography, and it was found that all ethylene oxide had changed to the following cyclic compounds (calculated from the concentration analysis values).

1.3-dioxolane 0.042m
oΩ1.3.5-trioxepane 0.0
33moρ1.3.5.7-titraoxacyclononane 0.025mol11 At this stage, the content of the kneader was clear, and no polymer formation was observed.

When 270 seconds had passed after the start of the reaction, 15 gr of boron trifluoride dibutyl etherate O was further added to continue the reaction. Simultaneously with the additional addition of boron trifluoride dibutyl etherate, the contents of the kneader became cloudy, showing signs of polymer formation.

At 1,800 seconds after the start of the reaction, 150 gr of tributylamine was added to stop the reaction. The contents of the liquid were taken out, and unreacted substances were extracted with acetone and analyzed, and the following results were obtained.

Trioxane 130 gr 1.3-dioxolane 0.080 gr Formaldehyde 31 gr The weight of the polymer after extraction is 9
It was 93 gr.

Next, 2.500g of water and 50g of triethylamine were added to this polymer, and the mixture was heated at 130°C for 1 hour. The polymer was separated by filtration, washed and dried to obtain 988 gr of polyoxymethylene copolymer.

(2) Confirmation of the structure of polyoxymethylene copolymer ■ 100g of the polymer obtained in (1) was added to 300ml of INH
The mixture was heated at 130° C. for 2 hours in a Cρ aqueous solution. By this heating operation, all oxymethylene units were converted to formaldehyde. As a result of analysis, the amount of formaldehyde was 99.56.
It was gr. In addition, the oxyethylene unit in the polymer is
When n=1, it is ethylene glycol, when n=2, it is diethylene glycol, and when n=3, it is triethylene glycol.

As a result of the analysis, 0.623 gr of ethylene glycol was detected, but diethylene glycol and triethylene glycol were not detected.

Therefore, the composition of the main chain of this polymer is as follows.

Oxymethylene unit: 100 moΩ Oxyethylene unit: 0.30 moΩ Also, the sea fence of oxyethylene unit is as follows.

n=1 +CH2CH2O)-T 100moρ%
n≧2 −+ CH2CH2O←10moρ%■(1)
When the terminal methoxy groups of the obtained polymer were measured using the modified Zeisel method, the ratio (γ) of methoxy groups per 100 moΩ of oxymethylene group was 7-11.70 Xl.
It was 0-2n+oρ.

In addition, the polymer was heat-pressed into a 15μ film, and the terminal formethod group was measured using infrared absorption spectroscopy.
A result of β-2,40×10−2 moρ was obtained.

After the polymer was acetylated using acetic anhydride, a film was created using a hot press. The terminal hydroxyl groups of this film were measured using infrared absorption spectroscopy,
A result of α-1,31×10 −2 moΩ was obtained.

From these results, α′ and β′ are α −8,5
moΩ% β' −15.6 moΩ%.

(2) The number average molecular weight (Mn) of this polymer is calculated according to the following formula.

(3) Physical properties of polyoxymethylene copolymer The tensile strength of the polymer obtained in (1) was 72 Okg/cJ, which was very excellent. This excellent mechanical property is due to the insertion rate of oxyethylene units being 0.30 mo, Q.

(4) Degradability of polyoxymethylene copolymer When the degradability of the polymer obtained in (1) was evaluated, the weight of the film was reduced by half in 30 days, indicating excellent degradability.

Examples 2 to 5 Polyoxymethylene copolymers were produced and evaluated in the same manner as in Example 1, except that the amount of ethylene oxide added during production of the polyoxymethylene copolymers was changed.

The evaluation results are summarized in Table-1.

All of the polyoxymethylene copolymers of this example had excellent degradability.

Comparative Examples 1 and 2 A polyoxymethylene copolymer was produced and evaluated in the same manner as in Example 1, except that the amount of ethylene oxide added during production of the polyoxymethylene copolymer was changed.

The evaluation results are summarized in Table-1.

As in this comparative example, the insertion rate of oxyalkylene units is less than 0.1 moρ per 100 moΩ of oxymethylene units,
Alternatively, if it exceeds 5 moΩ, a polyoxymethylene copolymer with excellent degradability cannot be obtained.

Comparative Examples 3 and 4 In Example 1, the amount of ethylene oxide added during the production of polyoxymethylene copolymer was changed, the amount of boron trifluoride dibutyl etherate (0.05 gr) added at the beginning was changed to 0.35 g, A polyoxymethylene copolymer was produced by carrying out the same procedure as in Example 1, except that borohydride dibutyl etherate was not additionally added and tributylamine was added to stop the reaction 600 seconds after the start of the reaction. did.

The evaluation results are shown in Table-2.

As in this comparative example, in the sequence of oxyalkylene units, when the ratio of n=1 is less than 60mo, Q%,
It is not possible to obtain a polyoxymethylene copolymer with excellent degradability.

Examples 6 to 8 Regarding the production of the polyoxymethylene copolymer of Example 1, water and/or methanol was used instead of methylal, and the addition amount, reaction time, and reaction time of dibutyl trifluoride dibutylnitele-1. Polyoxymethylene copolymers having different terminal group compositions were produced by the same procedure as in Example 1 except that the temperature was changed.

The evaluation results are summarized in Table-1.

The polyoxymethylene copolymer of this example had excellent degradability.

Comparative Examples 5 to 7 In the same manner as Examples 6 to 8, polyoxymethylene copolymers having different end group compositions were produced and evaluated.

The evaluation results are summarized in Table-1.

As in this comparative example, when α' exceeds 45 moρ% or when β' exceeds 35 moΩ%, a polyoxymethylene copolymer with excellent degradability cannot be obtained.

(Left below) Examples 9-2O Cyclic ether shown in Table 2 in place of ethylene oxide,
Examples 6 to 8 except that a predetermined amount of cyclic formal was used.
A polyoxymethylene copolymer was produced in the same manner as above.

The evaluation results are summarized in Table-2.

The polyoxymethylene copolymer obtained in this example was
As shown in Table 2, all were excellent in degradability.

Comparative Example 8.9 A polyoxymethylene copolymer was produced in the same manner as in Examples 6 to 8 except that a predetermined amount of ethylene glycol formal was used.

The evaluation results are summarized in Table-2.

As shown in Table 2, even when a cyclic formal is used, if the insertion rate of oxyalkylene units exceeds 5 mOΩ%, if the ratio of sea fence n = 1 is less than 60 moρ%, or if β' If it exceeds 35 moρ%, it is impossible to obtain a polyoxymethylene copolymer with excellent degradability as referred to in the present invention.

(The following is a blank space) [Effects of the invention] The polyoxymethylene copolymer of the present invention has excellent mechanical properties originally possessed by polyoxymethylene copolymers,
It has good fatigue properties and excellent degradability. That is, the polyoxymethylene copolymer of the present invention is easily decomposed in nature after use, and greatly contributes to the problem of waste disposal.

Patent applicant: Asahi Kasei Industries, Ltd. teenager Reason Man

Claims (1)

[Claims] 1. In a polymer consisting of repeating oxymethylene units (-CH_2O-), there are oxyalkylene units of the following formula ▲ mathematical formulas, chemical formulas, tables, etc. ▼ (in the formula, R_o and R_o' are the same) or may be different, and is selected from hydrogen, an alkyl group, and a phenyl group.In addition, R_o bonded to different carbon atoms and R_o' bonded to different carbon atoms are also selected to be the same or different, respectively.
is an integer of 1 or more, the proportion of n = 1 is 60 mol% or more of the total oxyalkylene units, and m = 2 to 6) is 0.1 to 5 m per 100 mol of oxymethylene units.
ol inserted structure, and the terminal groups of the polymer are composed of alkoxy groups, hydroxyl groups, and formate groups, and the ratio of hydroxyl groups to all terminal groups of the polymer is 45.
A degradable polyoxymethylene copolymer, characterized in that the proportion of formate groups is 35 mol% or less based on the total end groups of the polymer.