DK141102B - Process for stabilizing an oxymethylene copolymer solid under normal conditions by extrusion. - Google Patents

Description

<11) PUBLICATION MANUAL 141102 DENMARK s »intci. * C os e 2/30 § (21) Application No. 2253/75 (22) Filed on 25 Apr. I973 (23) Race day 25 · Apr. 1973 (44) The application presented and. ^ The publication document published on * J · J911 * 1

DIRECTORATE OF

PATENT AND TRADE MARKET (30) Priority granted from it

Apr 26 1972, 247624, US

(71) CELANESE CORPORATION, 522 Fifth Avenue, New York, N.Y., US.

(72) Inventor: Michael David Golder, 2441 Webb Avenue, Bronx, New York, US.

(74) Plenipotentiary in the proceedings:

The engineering firm Hofman-Bang & Bout ard._ (54) Procedure for stabilizing an oxymethylene copolymer under normal conditions by extrusion.

The invention relates to a method of stabilizing an oxymethylene copolymer which is solid under normal conditions against degradation, of the kind set forth in the preamble of claim 1. ·

Polyoxymethylenes are a group of thermoplastic resins which are very suitable for producing molded articles by injection molding or extrusion processes, possessing very advantageous mechanical properties resulting from shaped articles made therefrom and characterized by their hardness, strength and toughness.

However, the resins are subject to degradation, especially under the influence of heat. In particular, the degradation is the result of the following two processes: - 1) Thermal decomposition of the chain end with the release of gaseous formaldehyde. This degradation, which takes place largely under the influence of heat, is often avoided by the presence of either an ether or an ester group at the end of the polymer chain.

2) Oxidative attack leading to chain cutting and depolymerization. This is often delayed by the addition of antioxidants to the mixture, such as compounds containing phenolic or amino groups.

3) Acidolytic cleavage of the chain may occur, thereby also releasing formaldehyde. Acidolytic degradation occurs in the presence of acidic materials resulting from one of several (A) acidic catalyst residues that may have been used in the preparation of the polymeric (B) formic acid formed in situ when the trace amounts of formaldehyde which is formed during treatment, oxidized, and (C) acetic acid formed from acetate end groups when a given chain thus stabilized is depolymerized as a result of the occasional oxidative or acidolytic chain cut.

To alleviate this condition and to prevent degradation of the polyoxymethylene copolymer, especially during subsequent treatment in the hot state, "formaldehyde acceptors" or "acidic cleansers" are often added to the polymer blend. Among the compounds that can be used for this purpose are listed hydrazines and derivatives thereof, ureas, certain amides and diamides, polyamides and metal salts of acetic acid and long chain fatty acids.

Most polyoxymethylenes are heterogeneous polymers, i.e. the polymer contains both stable and unstable units. A common method of stabilizing such a polymer is to treat it in such a way as to selectively degrade the end portion of the molecules constituted by the relatively sensitive, monomeric units, usually via a hydrolysis reaction, leaving a residual polymer which contains the relatively stable monomeric units in 3,111,102 terminal portions of the molecules thereof.

However, usually at least 90 $ of the polymer's molecular chains of the treated polymer have relatively stable or relatively thermally resistant units in terminal positions during the subsequent heat treatment, however, further release of formaldehyde and accompanying acids, etc, which in turn leads to attack and degradation, occurs. of the polymer dies. Therefore, after the aforementioned hydrolysis treatment, the extruder is often mixed with a stabilizer mixture comprising an acidic cleanser or acidic cleanser and an antioxidant to neutralize the effect of any released compounds. This mixing step of the stabilizer is itself often accompanied by unwanted degradation of the polymer resulting from the necessary heat processing of the polymer to ensure uniform mixing of the stabilizer mixture.

The addition of an acidic acceptor prior to the hydrolyte treatment has so far been impossible due to the large volume of acids, etc. present during the hydrolysis reaction.

However, it has been found and described in this specification that the presence of an acidic cleanser or acidic cleanser and an antioxidant in the case of using a heterogeneous melt hydrolysis reaction (according to application no. 2252/73) to hydrolyzing the polyoxymethylene polymers results in (1) a completely unexpected increase in thermal stability, and (2) of course the elimination of a subsequent stabilizer addition process with its accompanying molecular weight reduction of the polymer.

It is known from US Patent Nos. 3,318,848 and 3,418,280 to a method of stabilizing oxymethylene copolymers in the presence of a reactant and these processes are carried out under such conditions that the copolymer is melted while the reactant is in solution, thus that the stabilization process is of a homogeneous nature. The stabilization obtained which can be quantitatively measured by the later mentioned Κ ^ 2 ^ 0 # is relatively good.

However, it would be desirable to improve these known processes so that the resulting stabilized product exhibited better stability as measured by

It is thus the object of the invention to provide a process of the kind set forth in the preamble of claim 1, thereby forming a stabilized oxymethylene copolymer, the stability of which is measured by the value of K₂₂ 2₂ is better than the stability of the known oxymethylene copolymers known .

The process according to the invention is characterized by the characterizing part of claim 1. In the practice of the method according to the invention a removal of unstable monomeric oxymethylene units is obtained from the terminal part of the copolymer molecules, so that at least 90% of the resulting polymeric chains of the molecules are terminated by the stable monomer units.

A particularly preferred embodiment of the method according to the invention is characterized by the characterizing part of claim 2. Using this temperature range in conjunction with a suitable pressure and residence time ensures that the stabilization reaction proceeds to its full extent.

A particularly preferred embodiment of the method according to the invention is characterized by the characterizing part of claim 3. At most pressures within this range, it is ensured that the polymer is kept in liquid state and the reactant in the vapor state, thereby allowing the stabilization reaction to proceed to its full extent.

A particularly preferred embodiment of the method according to the invention is characterized by the characterizing part of claim 4. This ensures a product with a particularly high stability against thermal degradation.

A particularly preferred embodiment of the method according to the invention is characterized by the characterizing part of claim 5. This ensures that unreacted reactant is volatilized and thereby removed from the polymer.

A particularly preferred embodiment of the method according to the invention is characterized by the characterizing part of claim 5 141102 6. These alcohols can be particularly easily vaporized so that the reaction can be particularly easily carried out with the polymer in liquid state and the reactant in vapor form so that the stabilization reaction can proceed to its full extent.

A particularly preferred embodiment of the method according to the invention is characterized by the characterizing part of claim 7. This results in a polymer which exhibits both excellent thermal stability and excellent stability against degradation in the hydrolytic environment.

Surprisingly, it has been found that the process of the invention carried out under such conditions that the copolymer is in molten state while the reactant is in vapor form gives rise to the formation of a stabilized copolymer whose stability properties are better than the stability properties of the previously known products of the same kind. Furthermore, according to the invention, there is provided a process of the kind set forth in the preamble of claim 1, whereby an even more stable and more stable process than has been possible with the prior art methods is produced. , copolymerized polyoxymethylene product, and a stabilized polyoxymethylene copolymer with natural, ie, non-pigmented Hunter color "b" values below +7. Hunter color is the color determined by - 1 a "Hunter Multipurpose Refleetometer spectral properties and color are given in ASTM D 304-44 and the coloration study method characterized by trichromatic coefficients is given in federal specification TT-P-1411 b, methods 425.1 and 425.2. Furthermore, since the acidic cleanser or acidic cleanser and the antioxidant are added already during the heterogeneous hydrolysis and not - as it has been done so far - after the hydrolysis, the previously mentioned undesired degradation of the polymer is eliminated.

The object of the invention is achieved as stated by subjecting the polyoxymethylene copolymers to a heterogeneous melt hydrolysis in the presence of an acidic acceptor or acid acceptor and an antioxidant.

The invention is based on the recognition that a more stable, 6 U1HT2 final product is obtained when an acidic cleanser or acidic cleanser and an antioxidant is present during the heterogeneous melt hydrolysis or extrusion of a polyoxymethylene-c polymer, as opposed to the known process. wherein these materials are mixed with the copolymer after hydrolysis or extrusion.

Given the amount of formaldehyde and associated acids produced during the hydrolysis or extrusion, this result is most surprising. It is important to note that the highly colored, cyanoguanidine-formaldehyde, polymeric: adduct which is usually formed when the preferred acidic cleanser cyanoguanidine is present in the formaldehyde-rich hydrolysis environment is not formed in a heterogeneous melt hydrolysis zone.

Although the applicant does not wish to be bound to any hypothesis, it can be stated that during the specific heterogeneous melt hydrolysis described in this specification, vapor stripping occurs in situ, whereby the formaldehyde and associated acids is brought out of the melt and into the vapor state immediately after its manufacture, thereby minimizing contact. i.e. the available reaction time, with the liquid acidic cleaner.

In addition, when the copolymer melts initially, i.e., the presence of the acidic cleaner or cleaner plus antioxidant just before the hydrolysis stabilization zone or the extrusion zone, the decomposition which usually begins at this stage slows down.

Oxymethylene polymers with recurrent -QCHg units directly linked to each other have been known for many years. They can be prepared by polymerization of anhydrous formaldehyde or by polymerization of trioxane, which is a cyclic trimer of formaldehyde. High molecular weight oxymethylene polymers vary in thermal stability, and in accordance with a preferred embodiment of the invention, the polymer which is stabilized is an oxymethylene polymer containing single carbon-to-carbon bonds in the main polymer chain.

In a particularly preferred embodiment of the invention, the polymeric compounds to be treated are oxymethylene eopolymers, having at least one chain containing recurrent oxymethylene units distributed between -OR groups in the main polymer chain, where R is a divalent radical containing at least two carbon atoms directly bonded to each other and arranged in the polymer chain between the two valences, whereby any substituents · 'on the R radical are inert, i.e. they are free of interfering, functional groups and will not induce undesirable reactions. Copolymers containing between 60 and 99.6 mole percent of returning oxymethylene groups are used. In a preferred embodiment, for example, R may be an alkylene group or a substituted alkylene group containing at least two carbon atoms.

Among the copolymers which may be used in this embodiment of the invention may be mentioned those having a structure including the recurring units represented by the formula r? ((-O-CH 2 -O) -), V iV 1 where n is an integer from 0 to 5 and where n is 0 in from 60 to 12 99.6 percent of the recurring units. R and R are inert substituents, i.e. substituents which are free of interfering functional groups and will not induce undesired reactions.

Particularly preferred oxymethylene polymers are those incorporating oxyalkylene units having adjacent carbon atoms derived from cyclic ethers with adjacent carbon atoms.

These copolymers can be prepared by copolymerizing trioxane with a cyclic ether having the structure:

CHp - O

I in CH2 - (OCH2) n where n is an integer from 0 to 2.

8 141102

Examples of preferred polymers include copolymers of trioxane and cyclic ethers containing at least two adjacent carbon atoms such as the copolymers disclosed in U.S. Patent 3,027,352

Among the specific cyclic ethers that can be used are ethylene oxide, 1,3-dioxolane, 1,3,5-trioxepane, 1,3-dioxane, trimethylene oxide, pentamethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide , neoptentyl-glycol formal, pentaerythritaldiformal, paraldehyde, tetrahydrofuran and butadiene monoxide.

As used herein, the term "copolymer" means polymers having two or more monomeric groups, including terpolymers and higher polymers. Such polymers comprise moldable oxymethylene polymers having branched chains comprising a plurality of branches of successive recurrent oxymethyl units. Such polymers can be prepared by copolymerizing trioxane with a small amount of a chain branching agent, this small amount being sufficient to bind some primary oxymethylene chains to provide a branched structure but insufficient to make the polymer difficult to process.

Primary chains are linear chains comprising successive oxymethylene units, and it is these chains that will emerge if chain branching agents are excluded from the system. The amount of chain branching agent used is generally no more than the amount required to provide a bond to another chain for each primary chain in the system. Since the polymeric components are incorporated into the polymeric structure during the polymerization process and not by a post-treatment of the polymeric, the units bionized by the chain branching agent are randomly and uniformly distributed in the polymeric and not concentrated at the surface of the polymeric ones. particles. Suitable chain branching agents, depending on the particular circumstances, include those exhibiting at least two functional oxygen groups, including (l) cyclic ethers with at least two cyclic ether rings such as 2,2- (trimethylene) bis-1,3-dioxolane and especially those compounds having at least two epoxy rings such as polyepoxides, including deep oxides, triple oxides, etc., at least two formal rings such as pentaerythritol diformal, and at least one epoxy ring, and at least one formal ring such as monoerotylidene trimethylol-ethane monoepoxide; and (2) compounds having at least two oxo groups such as dialdehydes and diketones such as glutaraldehyde, terephthaldehyde and acrolein dimer.

The invention relates to a method of stabilizing an oxymethylene copolymer solid under normal conditions with a melting point above 150 ° C, whereby the molecules of this copolymer contain between 60 and 99.6 mole percent of relatively unstable monomeric oxymethylene units distributed between relatively stable, monomeric -OR units wherein R is a di valent group containing at least two carbon atoms directly bonded to each other and arranged in the polymer chain between the two valences, whereby any substituents on the R group are inert and at least a portion of the terminal portions of the molecules comprises the indicated, unstable monomeric units, and the invention is characterized by introducing this copolymer into an extruder and between about 10%. 2 and approx. 25% by weight of the copolymer of a reactant selected from the group comprising water, alcohol and mixtures thereof, and. from between approx. 0.05 and 10.0% by weight (based on the weight of the copolymer) of a stabilizer mixture comprising an acidic cleanser or acidic cleanser and an antioxidant in a heterogeneous reaction zone consisting essentially of molten copolymer and vaporous reactant, by maintaining the reaction zone at a temperature above the melting point of the copolymer and under a pressure sufficient to keep the copolymer in the molten state and the reactants in the vapor state, thereby reacting the mixture under the above-mentioned temperature and pressure conditions. a period of time that is within the range of approx. 0.1 and approx. 15 minutes.

The polymers treated in this invention are thermoplastic materials having a melting point of at least 150 ° C and are usually machinable at a temperature of 200 ° C. These polymers have a high thermal stability prior to treatment in accordance with the invention. but this stability is greatly improved by such treatment.

The preferred polymers treated according to the invention have a melt index (M.I.) of less than 50, preferably below 30, according to ASTM D 1238-62T. After treatment, the preferred copolymers 141102 exhibit considerable alkaline stability. For example, if the treated copolymers are refluxed at a temperature of ea. 142 ° C to 145 ° C in a 50 $ solution of sodium hydroxide in water for a period of 45 minutes, the weight of the copolymer will be reduced by well below 1

The preferred catalysts used in the preparation of the desired copolymers are boron fluoride and coordinate complexes of boron fluoride with organic compounds, especially those in which oxygen or sulfur is the donor atom.

For example, the coordinate complex of boron fluoride may be a complex with a phenol, an ether, an ester or a dialkyl sulfide. Boron fluoride dibutyl etherate, the coordinate complex of boron fluoride with dibutyl ether, is a preferred coordinate complex. The boron fluoride complex with diethyl ether is also very effective. Other useful boron fluoride complexes are the methyl acetate, ethyl acetate, phenyl acetate, dimethyl ether, methyl phenyl ether and dimethyl sulfide complexes. Suitable catalysts are disclosed in U.S. Patents 2,989,505, 2,989,506, 2,989-507, 2,989,509, 2,989,510 and 2,989,511.

The coordinate complex of boron fluoride should be present in the polymerization zone in such quantities that its boron fluoride content is between 0.001 and ea. 1.0% by weight, calculated relative to the weight of the monomers in the polymerization zone. Preferably, amounts between about 1 and about 10 should be used. 0.003 and approx. 0.1% by weight.

The monomers in the reaction zone are preferably anhydrous or substantially anhydrous. Small amounts of moisture, such as the amounts of moisture that may be present in commercial grade reactants or which can be introduced by contact with atmospheric air, will not prevent polymerization, but should be obtained for best results.

In the preparation of the preferred copolymers, the trioxane, the cyclic ether and the catalyst are dissolved in a common anhydrous solvent such as cyclohexane and the components are reacted in a sealed reaction zone. The temperature in the reaction zone can vary from approx. 0 ° C to approx. The reaction period can range from approx. 5 minutes to approx. 72 hours. Pressures from subatmospheric pressures to approx. 100 atmospheres or more, although atmospheric pressure is preferred.

The chemical composition of the cyclic ether must be taken into account. Thus, 1,3-dioxolane contains both an oxymethylene and an oxyethylene group. The incorporation thereof into the copolymer molecule increases both the content of oxymethylene and oxyethylene of the polymeric molecule.

Generally, the cyclic ether is present in the reaction mixture in amounts between about 0.2 and approx. 30 mole percent, calculated relative to the total number of moles of monomer. The optimum proportion will depend on the particular copolymer desired, the expected degree of conversion and the chemical constitution of the cyclic ether used.

The copolymers prepared from the preferred cyclic ethers have a structure which substantially comprises oxymethylene and oxyethylene groups in a ratio of approx. 250: 1 and approx. 1.5: 1.

At the end of the polymerization reaction, it is desirable to neutralize the activity of the polymerization catalyst because prolonged contact with the catalyst degrades the polymer. The polymerization product may be treated with an aliphatic amine, such as tri-n-butylamine or triethylamine, in stoichiometric excess relative to the amount of free catalyst in the reaction product, and preferably in an organic liquid which is solvent for unreacted trioxane. Or, if desired, the reaction product can be washed with water that neutralizes the catalyst activity. A detailed description of suitable methods for neutralizing catalyst activity can be found in U.S. Patent No. 2,989,509.

In accordance with the invention, the relatively unstable monomeric moieties of units of the polymer can be removed using a process by which the polymer is treated with an reactant at elevated temperature in the presence of an acidic cleaner or acidic cleaner and an antioxidant. under elevated pressures so that the system is heterogeneous, i.e. * a two-phase system, the polymer being in the molten state and the reactant being in the vapor state, and continuing the reaction for a period of time sufficient to remove relatively unstable parts or units. from the ends of the polymeric molecules so that the molecules are terminated by relatively stable units.

The blend constituted by polymer, stabilizer and reactant can achieve this biphasic state, using a number of methods such as (1) melting the copolymer and adding the reactant and stabilizer or stabilizers thereto under conditions such that the reactant remains in the vaporous state. or (2) mixing the polymer, stabilizer or stabilizers and reactant followed by heating under pressure until the mixture comprising polymer, stabilizer and reactant is in the molten liquid-vapor state.

In the case that the copolymer is a heterogeneous copolymer (a heterogeneous copolymer is understood in this context a non-stabilized copolymer which therefore still contains unstable oxymethylene units), where the relatively unstable units are oxymethylene units, it is the preferred treatment is a "stabilization hydrolysis" treatment under alkaline conditions. The polymer is reacted with from ca. 2% by weight to approx. 25% by weight of the preferred hydrolysis reactant in the presence of about 0.05 to 10.0% by weight (calculated by weight of the polymer) of an acidic cleanser or acidic cleanser and an antioxidant. The reaction takes place at an elevated temperature and under an elevated pressure so that the polymer will be in the molten, liquid state and the reactant will be in a vaporous state, i.e. gaseous state. Thus, the treatment can be termed a "heterogeneous melt stabilization hydrolysis", in contrast to the homogeneous melt hydrolysis disclosed in U.S.

3,318,848 and 3,418,280.

The hydrolytic reactant is water, a primary, secondary or tertiary, aliphatic or aromatic alcohol or mixtures thereof. It is of primary importance in selecting this alcohol that its thermodynamic properties are such that the alcohol and / or mixtures of alcohol and water under the treatment criteria of the present invention are in the vapor state. Suitable alcohols include aliphatic alcohols and preferably, for example, methyl alcohol, ethyl alcohol, n-propyl alcohol and isopropyl alcohol.

The term "hydrolysis" in the present context encompasses the reaction between the polymer and water or the previously mentioned hydroxyl group-containing materials or mixtures thereof.

The terminal units of the oxymethylene polymer are often hydroxy-substituted oxymethylene units, (-o-ch 2 -oh), and release of an oxymethylene group from the polymeric molecule by the hydrolysis reaction has the effect of transferring the hydrogen atoms from the hydroxyl group to the oxygen atoms of the adjacent oxymethylene group.

Preferably, the stabilization hydrolysis reaction takes place under alkaline, vaporous conditions such that the pH of the hydrolysis reactant is above 9.0 when added to the polymer; hereby the pH of the alkaline reactant is determined in liquid form before being evaporated. To achieve such a pH, alkaline material must be present. The alkaline material is preferably water-soluble or soluble in the hydroxyl group-containing material, and it may be a strong basic hydroxide such as the hydroxide of an alkali metal or an alkaline earth metal, or it may be the salt of a strong base and a weak acid, or it may be ammonia. or an organic base such as an amine or an amidine.

Examples of the specific alkaline materials which may be used may be sodium hydroxide, potassium hydroxide, sodium carbonate, sodium acetate, ammonium hydroxide, triethylenamine, tri-propylamine, tetramethylguanadine, trimethylamine, triethylamine, tri-butylamine, melamine and calcium hydroxide. The amount of the alkaline material present in the chemical reaction is between approx. 0.001 and approx. 10.0% by weight, preferably between ca. 0.001% by weight and approx. 1.0% by weight.

14 141102

An advantage of the alkaline hydrolysis compared to neutral hydrolysis is that the alkaline hydrolysis is faster and that the alkaline material will neutralize any excess polymerization catalyst or any acidic material formed during the reaction, which might otherwise tend to degrade the polymer during the hydrolysis step or binding the specific acid acceptors of the invention * In some cases, it is desirable to achieve the desired pH by adding an alkaline material such as triethylamine in an amount sufficient for triethylamine to maintain basic conditions. during the course of the hydrolysis reaction and will react with any acidic materials formed.

In suitable embodiments, an amount of 0.25% by weight of triethylamine, calculated relative to the weight of the polymer, would be sufficient. Therefore, if 5 1 ° hydrolysis reactant was added. the polymer, the hydrolyzed solution could contain 5.0% by weight of triethylamine, and the pH of the hydrolysis solution would be adjusted prior to addition to the polymer. In some cases, there may be some water in the polymer besides that added to the hydrolysis solution.

After the polymerization reaction, it may be desirable to subject the polymer to washing and drying to neutralize the active catalyst and remove unreacted monomers, solvent and catalyst residues. Specifically, water or a mixture of an alcohol such as methanol and water may be used, whereby small amounts of ammonia or an amine such as triethylamine may be present.

In some cases, it may be desirable to neutralize the catalyst and then filter, wash and dry the polymer. Ken polymers may then conveniently be stored until subjected to the treatment comprising stabilization hydrolysis at a later date.

Among the acidic cleansers which can be used in accordance with the invention may be mentioned the hydrazines and derivatives thereof ureas, amides, amidines and polyamides as well as metal salts of long chain fatty acids. Particularly preferred acidic cleansers are dicyanodiamide (cyanoguanidine), magnesium acetate, calcium hydroxysteorate and calcium recinoleate.

15 141102

In addition to the detergents used in the process of the invention, it is also contemplated to incorporate one or more other chemical stabilizers into the copolymer to bring its thermal decomposition rate to an even lower level. The proportion of the stabilizer incorporated depends on the specifically used stabilizer. It has been found that a proportion between approx. 0.05 and 10% by weight (calculated relative to the weight of the polymer) is suitable for most stabilizers.

A suitable stabilizer is an antioxidant, such as a phenolic antioxidant, and most conveniently a substituted bis-phenol.

A suitable category of substituted bis-phenols are the alkylene-bis-phenols, including compounds containing between 1 and 4 carbon atoms in the alkylene group and containing between 0 and 2 alkyl substituents on each benzene ring, each alkyl substituent containing between 1 and 4 carbon atoms. The preferred alkylene bisphenols are 2,2'-methylene bis- (4-methyl-6-tert.-butylphenol) and 4,4'-butylidene-bis- (6-tert.-butyl-3-methylphenol). Suitable phenolic stabilizers in addition to alkylene bisphenols include: 2,6-ditert.-butyl-4-methylphenol, octylphenol and p-phenylphenol.

Particularly suitable as antioxidants are the inhibited phenols which are ester derivatives of 3,5-di-t-butyl-4-hydroxyphenylpropionic acid, for example tetrakis- [methylene-3- (3 ', 5,5-di-t.-butyl) -4 *, hydroxy-phenyl) propionate] -methane, ethyl 1,1,1-tris- [methylene-3- (3 ', 5'-di-butyl-4'-hydroxyphenyl) propionate ] and hexane-1,6-bis- [3- (31-di-t.-butyl-4'-hydroxyphenyl) propionate].

After the heterogeneous melt stabilization hydrolysis reaction is complete and a satisfactory number of unstable monomeric units have been removed from the copolymeric molecules, the residual chemical reactant is removed from the treated copolymer. In addition, the degradation or reaction products and the occasional unreacted materials such as trioxane should also be removed. Formaldehyde is the essential hydrolysis degradation product of oxymethylene polymers and is believed to be formed by the successive release of the terminal oxymethylene units from the end of the copolymer chain. In some cases, especially when the polymerization reaction product is hydrolyzed immediately, the hydrolyzed material may comprise a certain amount of unreacted trioxane. According to a preferred embodiment of the invention, the chemical reactant, formaldehyde, trioxane and other evaporable materials can be removed by abruptly reducing the pressure under which the materials have been kept, resulting in the evaporation of the volatile materials. The lower pressure should be between approx. 0.007 o kg / cm absolute and 3.5 kg / cm absolute, and it is preferably produced by exposing the materials to atmospheric pressure or a low

ISLAND

vacuum (about 0.0035 kg / cm absolute).

In the practice of the invention, the time during which the molten copolymer and the stabilizer mixture are exposed to elevated temperatures and pressures in the presence of a vaporous reactant (this period is known as the residence time) is between 0.1 and approx. 15 minutes. The temperature range is preferably between ca. 160 ° C and approx. 240 ° C.

The pressure interval is what is needed to maintain the two-phase reaction, ie. the polymer in the molten state and the reactants in the vapor state, preferably below ca. 10.5

ISLAND

kg / cm absolute.

The residence time, temperature and pressure are interdependent, and. they are maintained at such values that the mixture constituted by copolymer, stabilizer and reactant remains in the previously stated state and the reaction proceeds sufficiently, so that the desired amount of unstable units is removed from the ends of the copolymer molecules, so that they are terminated by relatively stable units.

In the following examples, a trioxane-ethylene oxide copolymer containing approx. 2% by weight oxyethylene groups that are. distributed in the oxymethylene chains. The reaction product of the polymerization reactor was also washed with water and dried to neutralize and remove the catalyst and to remove unreacted trioxane.

Κβ refers to the percentage weight loss of the copolymer per minute. determined by heating the copolymer in an open container in a circulating air oven at a temperature of 230 ° 0.

17 141102

Examples 1-6

Examples 1-6 illustrate the results obtainable when performing a homogeneous hydrolysis reaction via a single screw extruder, both in the presence of the stabilizer mixture comprising. the acidic cleanser or acidic cleanser and the antioxidant according to the invention and in the absence thereof. In the examples where the stabilizer or stabilizers are not present during the hydrolysis, the copolymer is mixed and re-extruded prior to examination.

The copolymer or copolymer and stabilizer is applied under force to a 2.54 cm extruder having a single screw having a length to diameter ratio of 20 / l. The feed section of the extruder had five threads and a channel depth of 4700 µ. Thus, the copolymer is supplied under pressure to the measuring or melt hydrolysis section having six threads with a channel depth of 1524 μ. The reactant is pumped into the extruder at the beginning of the melt hydrolysis section. Next, there is a limited section of 1.5 threads with a channel depth of 559 μ.

This restricted section maintains pressure in the melt hydrolysis section.

The mixture comprising copolymer and reactant or copolymer, stabilizer and reactant is then fed to a vented section (which may be termed low pressure section) of four threads with a channel depth of 5590 µ. As the heated pressurized mixture is fed to the vented section, the pressure is abruptly reduced and the formaldehyde, reactant and other evaporable components are removed through the vent. The treated copolymer is then passed through a 3.5 thread pump section (or pre-extrusion section) with a channel depth of 1524 µ where the polymer is compressed. The copolymer is then extruded through a nozzle. If no chemical stabilizers are present, they are then mixed with the copolymer and re-extruded. This will be referred to as a "double passageway" as opposed to the "single passageway" where the stabilizer or stabilizers are present during the hydrolysis.

The operating parameters and the resulting data are summarized in Table I.

18 141102

Table I

Hydrolysis temperature range: 160 - 240 ° 0 Hydrolysis pressure:? over 52.7 kg / cur

Example Number of Passages Composition% 230 1 Single OAR1 (0.10) 2, 0.016

Anti Ox (0.50) 5 AcrawaxC (0.03) 2 Double OAR (0.10) 0.012 'Anti Ox (0.50) ACRAWAXC (0.03) 3 Single CFG5 (0.10) 0.030

Anti Ox (0.50)

Melamine (0.03)

Acrawax G (0.03) 4 Single CFG (0.10) 0.040

Melamine (0.03)

Acrawax, -C (0.03)

Anti Ox (0.50) 5 Double CFG (0.10) 0.025

Anti Ox (0.50) • Melamine (θ, 03)

Acrawax O (0.03) 6 Double CFG (0.10) 0.028

Anti Ox (0.50)

Melamine (0.03)

Acrawax C (0.03) 1. CAR: Calcium ricinoleate 2. The numbers in brackets in this table and Table XI indicate the percentages by weight based on total copolymer weight 3. Anti Ox: 2,2 * -methylene bis- (4 -methyl-6-t.-butyl-phenol) 4. Acrawax C; ethylene bis-stearamide 5. CFG: Cyanoguanidine 6. Mixed in another extrusion

As can be seen from the above table, there is a significant decrease in stability, namely, an increase of K . It should also be noted that in the case where the homogeneous melt hydrolysis proceeds with the stabilizers present, severe and totally unacceptable discoloration occurs, ie. staining to dark yellow to brown, of the copolymer product, which is believed to be due to quinoidal ring formation in the CAR case and CFG formaldehyde reactions in the second case. The degree of yellowness of the discolored products usually exceeds Hunter color wbn values of +15 «When there is a stabilizer or stabilizers present during the homogeneous hydrolysis melting reaction, a significant reduction of short-term stability is evident, which is exemplarily manifested. in the percentage weight loss data after 5.5 hours at 110 ° 0. For the experiments carried out with a double passage, such as Examples 5 and 6, the weight loss is of the order of 9.5, whereas in the experiments performed carried out with a single passage such as that illustrated in Example 1 is of the order of $ 82.

Examples 7-12

The following examples are carried out using a twin screw co-rotating extruder which interacts with one another.

The machine has a total I / D ratio of 43 and is composed of feed and melt sections having a L / D ratio of 12.5, a hydrolysis section and a solution injection opening with a I / O ratio of 20.5, and condensation sections. and nozzle pump sections having a ratio of I / D of 10. A melt seal is formed at the beginning and end of the heterogeneous melt hydrolysis zone using left-turn screw bushings. Otherwise, the entire screw consists of right-hand screw bushes, ie no kneading blocks are used. If the chemical stabilizers are not present in the reaction zone, as in Examples 1-6, they are mixed with the hydrolyzed copolymer and the mixture is re-extruded. The operating parameters and the resulting data are summarized in Table II.

20 «11«

Table II

Hydrolysis temperature range: Hydrolysis pressure: below 10.5 kg / cm 2

160 - 240 ° C

Example Number of Passages Composition M.I.

--— - ------ i-1 --- -OZdO. 7 Single OAR (0.1) 0.010 9.0

Anti Ox (0.50) Acrawax C (0.03) 8 Double CAE (0.1) 0.013 9.9

Anti ox (0.50)

Acrawax C (0.03) 9 Single CEO (0.1) 0.011 9.5

Anti Ox (0.50)

Melamine (0.03)

Acrawax C (0.03) 10 Double CFG (0.1) 0.014 10.5

Anti ox (0.50)

Melamine (o, 03)

Acrawax 0 (0.03) 11 Single CFG (0.1) 0.013 9.3

Antiox (0.50)

Melamine (0.03)

Acrawax C (0.03) 12 Double CFG (0.1) 0.015 10.0

Antiox (0.50)

Melamine (0.03)

Acrawax C (0.03)

At the beginning, Examples 7-12 generally illustrate the definitely improved stability of the copolymer, as compared to the lower values of K two-phase melt hydrolysis as opposed to the homogeneous melt hydrolysis illustrated in Table I. '

Particular attention is paid to the significant improvements that occur in any case where the stabilizer is present during the hydrolysis reaction as opposed to just a later addition. In addition, melt indices of the finished copolymers are significantly higher with a stabilization-hydrolysis reaction.

It is of particular importance that the usually severe discoloration which occurs when the detergents used in the process of the invention are present during the polyoxymethylene hydrolysis reactions do not occur when they are present during the heterogeneous melt hydrolysis of the invention , as it is eczema-

Claims (3)

21 141102, as exemplified by Examples 7, 9 and 10, in which a final copolymer color of from light ivory to white is realized and whose Hunter color "b" values never exceeds +7. P_a_t e_n_t_k_r_a_v__; A method of stabilizing, by extrusion, an oxymethylene solid polymer under normal conditions having a melting point above ca. 150 ° C, whereby the molecules of the copolymer specified contain between 60 and 99.6 mole percent of relatively unstable monomeric oxymethylene units distributed between relatively stable monomeric -OR units wherein R is a divalent group containing at least two carbon atoms, directly linked to each other and arranged in the polymeric chain between the two valences, whereby any substituents on the R group are inert, with at least a portion of the terminal portions of the molecules comprising the unstable monomeric units, characterized in that in an extruder it is copolymerized and from 2 to approx. 25% by weight, calculated relative to the copolymer, of a reactant selected from the category consisting of water, an alcohol and bian. :. things thereof, and from ca. 0.05 to approx. 10.0% ~ (calculated by weight of the polymer) of a stabilizer mixture comprising an acidic cleaner or acidic cleaner and an antioxidant in a heterogeneous reaction zone consisting essentially of molten copolymer and vaporous reactant by maintaining the reaction zone at a temperature above the melting point of the copolymer and under a pressure sufficient to keep the copolymer in the molten state and the reactants in the vapor state, thereby reacting the mixture under the above-mentioned temperature and pressure conditions for a period of time. is within the range of approx. 0.1 and approx. 15 minutes. Process according to Claim 1, characterized in that the temperature is in the range between approx. 160 and 240 ° C. A method according to claim 1, characterized in that the pressure is below approx. 10.5 kg / cm 2 absolute.