POLYOXYMETHYLENE COMPOSITIONS

Abstract

This document describes polyoxymethylene (POM) compositions comprising polyoxymethylene and styrene-maleic anhydride (SMA) copolymers or modified SMA copolymers, the POM compositions exhibiting improved physical properties, such as thermal deflection temperatures, compared to POM compositions that do not comprise SMA copolymers.

Description

POLYOXYMETHYLENE COMPOSITIONS FIELD OF INVENTION This document describes polyoxymethylene (POM) compositions comprising polyoxymethylene and styrene and maleic anhydride (SMA) copolymers or modified SMA copolymers, the POM compositions exhibiting improved physical properties, such as thermal deflection temperatures, compared to POM compositions that do not comprise SMA copolymers. BACKGROUND OF THE INVENTION POM compositions with a relatively high molecular weight, between 50,000 and 100,000, can be used to manufacture articles using any of the techniques commonly employed with thermoplastic materials, such as compression molding, injection molding, extrusion, blow molding, melt spinning, stamping, and thermoforming. Articles made from these relatively high molecular weight POM compositions possess desirable physical properties, such as stiffness, strength, toughness, dimensional stability, and solvent resistance. POM compositions are commonly used in the automotive, industrial, electronics, and consumer goods sectors. Unmodified or pure POMs typically have a Ref. 325504 iviA / a / zuzi / uiu / Heat deflection temperature (HDT) of approximately 96 °C and good melt viscosity retention. For many engineering applications, POM compositions with an HDT of 100 °C or higher are desirable. A conventional method for increasing the HDT of POM has been to add a reinforcing agent, such as glass fibers. Although it increases the HDT, the addition of glass fibers increases weight, promotes a poor surface appearance, creates molding difficulties, and decreases toughness. Efforts to improve the thermal stability of articles prepared from POM compositions by adding materials such as thermal stabilizers and other additives to the POM compositions may improve thermal stability at the expense of other physical properties. International patent publication No. WO2013 / 081785 describes polyoxymethylene compositions comprising imidized acrylic resins exhibiting improved thermal deflection temperatures. U.S. Patent Application Publication No. 2008 / 0097012 describes a polyoxymethylene composition comprising a combination of an amine-substituted triazine compound, a compound prepared by grafting 0.05–5 parts by weight of anhydrous maleic acid onto an ethylene-propylene copolymer and an ethylene-propylene terpolymer, and 1,12-dodecanedicarboxylic acid. The compositions exhibit improved thermal stability. U.S. Patent No. 6,191,222 describes a polyoxymethylene composition comprising a conventional additive and a copolymer obtained by polymerizing a mixture of one or more (meth)acrylates and one or more (meth)acrylamides. The compositions exhibit improved thermal stability and discoloration stability. International patent publication No. WO90 / 15840 describes a polyacetal composition consisting essentially of a stabilizer selected from microcrystalline cellulose and fibrous cellulose, and a co-stabilizer. These compositions provide an improvement in the thermal stability of polyacetal compositions. It is desirable to develop POM compositions with higher heat deflection temperatures and, if possible, simultaneously improve the HDT while maintaining or improving other desirable physical properties, such as melt viscosity stability and flow properties. BRIEF DESCRIPTION OF THE INVENTION This document describes POM compositions comprising: (A) 80 to 99 percent by weight of at least one polyoxymethylene polymer; (B) from 1 to 20 percent by weight of at least one styrene and maleic anhydride copolymer; and (C) optionally from 0.5 to 5 percent by weight of at least one additive selected from the group consisting of antioxidants and heat stabilizers; where the POM composition exhibits a heat deflection temperature of at least 100 °C when measured in accordance with ISO 75-2A:2013; and where the weight percent is based on the weight of components (A), (B) and (C) in the POM composition and sums to 100 percent by weight. Additionally, this document describes POM compositions that comprise: (A) 80 to 99 percent by weight of at least one polyoxymethylene polymer; (B) 1 to 20 percent by weight of at least one modified styrene-maleic anhydride copolymer having an acid number of 50 mg KOH / g less when measured in accordance with ASTM D974-14; and (C) optionally 0.5 to 5 percent by weight of at least one additive selected from the group consisting of antioxidants and heat stabilizers; where the weight percent is based on the weight of components (A), (B) and (C) in the POM composition and sums to 100 percent by weight; and where the POM composition exhibits a heat deflection temperature of at least 100 °C when measured in accordance with ISO 75-2A:2013. These POM compositions comprising modified SMA copolymers can also exhibit a melt viscosity retention of at least 90 percent when measured at 215 °C and a shear rate of 100 s-1 after 20 min of holding time. These POM compositions comprising modified SMA copolymers may also exhibit tensile creep up to a strain of at least 10% for 2 hours when measured at 90 °C and a load of 25 MPa, determined in accordance with ISO 899-1:2017. This document also describes articles comprising the POM compositions described herein. Depending on the POM composition used to prepare the articles, these articles have at least a specified heat deflection temperature, determined according to ISO 75-2, that exceeds that of an identical article not comprising SMA copolymers or modified SMA copolymers. It was surprisingly found that certain POM compositions described herein exhibit a combination of improved physical properties compared to POM compositions not comprising a modified SMA copolymer. Specifically, the articles WIÁ / clMUZI / UlUÍ / 4 prepared from these POM compositions may exhibit a combination of properties including a heat deflection temperature of at least 100 °C when measured in accordance with ISO 75-2A:2013, a tensile yield to a strain of 10% at 90 °C and a pressure of 25 MPa for at least 2 hours, determined in accordance with ISO 899-1:2017, and a melt viscosity retention of at least 90 percent when measured at 215 °C and a shear rate of 100 s-1 after 20 min of holding time. This document also describes methods for preparing articles comprising the composition of POM, including the following method: (1) combine by fusion at least one polyoxymethylene resin with at least one copolymer and / or a modified copolymer and any optional additives to provide a molten POM composition; (2) shaping the molten POM composition into a desired shape; and (3) cooling the molten POM composition to provide a shaped article; where the formed article has a thermal deflection temperature determined according to ISO 752A:2013 of at least 100 °C. It is preferred that, when the copolymer or copolymers of SMAs are combined by fusion with polyoxymethylene resin, the particle size of the SMA copolymer being within a specific range so that the formed article exhibits the desired properties. DETAILED DESCRIPTION OF THE INVENTION Definitions The following definitions are to be used to interpret the meaning of the terms discussed in the description and cited in the claims. As used in this document, the article un / a indicates one as well as more than one and does not necessarily limit its referring noun to the singular. As used herein, the term "article" refers to an unfinished or finished article, thing, or object, or to an element or feature of an unfinished or finished article, thing, or object. As used herein, when an article is unfinished, the term "article" may refer to any article, thing, object, element, device, etc., that will be included in a finished article and / or undergo further processing in order to become a finished article. As used herein, when an article is finished, the term "article" refers to an article, thing, object, element, device, etc., that has undergone processing to completion so that it is suitable for a IVIA / a / ZUZ l / UI UZ / 4 private use / purpose. As used herein, the term melt viscosity refers to a measure of the flowability of a thermoplastic polymer melt. Melt viscosity is measured in accordance with ASTM D-3835-08 at 215 °C and a shear rate of 100 s⁻¹. The units for melt viscosity are Pa·s. The lower the melt viscosity, the better the thermoplastic composition flows in the molten state. As used herein, the terms polyoxymethylene and polyoxymethylene resin refer to one or more homopolymers, copolymers, and mixtures thereof, having a repeating unit of *CH2O·. The terminal groups of these polymers are derived by initiating, terminating, or chain-transferring groups, such as water or alcohols, or by chemical reaction, such as that which results in ester or ether groups, including acetate, acetyl, alkyl, or methoxy groups. As used herein, the terms tensile yield and tensile yield to 10% strain generally refer to the time it takes for a test specimen to reach a specific percentage of strain under a given load and at a given temperature. The term tensile yield to 10% strain at 90 °C and a load of 25 MPa refers to the time it takes for the test specimen, heated to 90 °C, to reach a strain of 10% under a load of 25 MPa. Tensile yield is determined in accordance with ISO 899-1:2017 and provides information on the long-term yield strength of a test specimen molded under specified conditions. As used herein, the terms heat distortion temperature, heat deflection temperature, and HDT refer to the temperature at which a polymer sample deforms under a specified load. The determination is performed in accordance with ISO 752A:2013, using a load of 1.8 MPa. Abbreviations The claims and description in this document shall be interpreted using the abbreviations and definitions set forth below. % refers to the term percentage. % by weight refers to percentage by weight. s refers to seconds. min refers to minutes. g refers to grams. mi refers to milliliter. mg refers to milligram. Tg refers to glass transition temperature. kg refers to kilogram. Pa*s refers to Pascal·seconds MPa refers to Megapascal Pm refers to average molecular weight Preferred intervals and variations Any range presented herein includes its endpoints, unless expressly stated otherwise. The presentation of a quantity, concentration, or other value or parameter in range form specifically describes all ranges formed from any pair of any upper range limit and any lower range limit, regardless of whether the pairs are described separately herein. The processes and items described herein are not limited to the specific values ​​described in the range definition in the description. The description herein of any variants in terms of materials, methods, steps, values, and / or intervals, etc., whether identified as preferred variants or not, of the processes, compositions, and articles described herein is intended specifically to describe any process and article that includes ANY combination of the materials, methods, steps, values, intervals, etc. For the purpose of providing photographic and sufficient support for the claims, any such combination described is intended specifically to be a preferred variant of the processes, compositions, and articles described herein. The compositions described herein include all possible variations when the polyoxymethylene polymer is selected from the group consisting of polyoxymethylene homopolymers, polyoxymethylene copolymers, and mixtures thereof. POM Compositions The POM compositions described herein comprising at least one SMA copolymer or a modified SMA copolymer exhibit an improved heat deflection temperature (HDT) compared to an identical POM composition lacking an SMA copolymer. Specifically, the HDT of the POM compositions described herein is at least 100 °C, preferably at least 102 °C, and more preferably at least 104 °C. POM compositions comprising at least one modified SMA copolymer surprisingly exhibit a combination of improved HDT, creep resistance, and melt viscosity stability compared to an identical POM composition lacking a modified SMA copolymer. iviA / a / zuzi / uiu / / 4 Polyoxymethylene (A) The polyoxymethylenes used in the POM compositions described herein include homopolymers, copolymers, and mixtures thereof. Polyoxymethylene homopolymers include formaldehyde homopolymers or cyclic formaldehyde oligomers, for example, trioxane and tetraoxane. POM homopolymers are preferred due to their greater stiffness and strength. Preferred polyoxymethylene homopolymers include those whose terminal hydroxyl groups have been terminally protected by a chemical reaction to form ester or ether groups, preferably acetate or methoxy groups, respectively. Polyoxymethylene copolymers include formaldehyde copolymers or cyclic oligomers of formaldehyde and monomers that yield oxyalkylene groups having at least two adjacent carbon atoms in the polymer chain. Comonomers commonly used in the preparation of polyoxymethylene copolymers include those without alkylene oxides and those with alkylene oxides of 2–12 carbon atoms and their cyclic addition products with formaldehyde. The comonomer is generally no more than approximately 20 percent by weight, preferably no more than approximately 15 percent by weight, and much more preferably approximately 2 percent by weight, of the total weight of the polyoxymethylene polymer. IVIA / a / ZUZ l / UI UZ / 4 The polyoxymethylene polymers in the PON compositions described herein may be characterized by the polymer melt flow index, which ranges from any decimal value from 0.1 g / 10 min up to and including 50 g / 10 min. Preferably, the POMs in the POM compositions described herein have a melt flow index of 0.5 to 35 g / 10 min, more preferably approximately 1 to 20 g / 10 min, and much more preferably approximately 1 to 5 g / 10 min. The concentration of polyoxymethylene polymers in POM compositions can range from approximately 80 to approximately 99 percent by weight, preferably from approximately 85 to 98 percent by weight, more preferably from approximately 90 to 95 percent by weight, based on the total weight percent of components (A), (B), and (C) in the POM composition, the sum of which amounts to 100 percent by weight. Styrenic Maleic Anhydride Copolymers (B) The styrenic maleic anhydride copolymers that are useful as a copolymer (B) in the POM compositions described herein include SMA copolymers and modified SMA copolymers and may comprise a range of maleic anhydride (MA) monomer content with a practical limit of approximately 50 mol% maximum MA content in the SMA or SMA copolymers Modified IVIA / a / ZUZ l / UI UZ / 4 (a 1:1 molar ratio of styrene:MA). The molecular weights of the SMA or modified SMA copolymers are preferably less than or equal to approximately 20,000 g / mol, more preferably less than or equal to approximately 10,000 g / mol with a minimum molecular weight of approximately 2,500 g / mol. The glass transition temperature of the SMA or modified SMA copolymers can range from approximately 125 °C to approximately 160 °C, preferably from approximately 130 to approximately 155 °C, more preferably from approximately 135 to approximately 150 °C. Modified SMA copolymers are copolymers in which the anhydride functional group has been converted or modified into other functional groups, resulting in a modified SMA copolymer with an acid value of 50 mg KOH / g or less. SMA copolymers can be modified by any method known in the art to convert anhydride functional groups into other functional groups. For example, the SMA copolymer can be modified by converting the anhydride functional group into an imide, ester, amide, or other functional group, resulting in a modified SMA copolymer with an acid value of 50 mg KOH / g or less.To achieve an acidity index of 50 mg KOH / g less, most or essentially all of the anhydride functional groups present in the SMA copolymer must be converted into other functional groups that do not contribute to the acidity index, such as imide, ester, or amide groups. Molecules that can be used to convert the anhydride functional groups of SMA copolymers into imide functional groups include molecules comprising primary and / or secondary amino groups, with primary amino groups being preferable. Examples of such molecules include linear, branched, or cyclic aliphatic primary amines and aromatic primary amines. Examples of aliphatic primary amines include amines comprising 1 to 20 carbon atoms, such as propylamine, butylamine, octylamine, and cyclohexylamine. Examples of aromatic primary amines include aniline, 4-aminophenol, 2-aminophenol, 4-aminotoluene, and 2-aminotoluene. Molecules that can be used to convert anhydride functional groups of SMA copolymers into ester functional groups include molecules comprising hydroxyl groups such as phenol, linear, branched, cyclic or aromatic C2 to CIO alcohols such as methanol, ethanol, hexanol, cyclohexanol and phenol. Formula 1 shows an example of a modified SMA copolymer in which the anhydride functional group has reacted to form an imide functional group. R1 is selected from an aliphatic or aromatic substituent group, including linear, branched, or cyclic aliphatic groups comprising from one to 20 carbon atoms. Examples of aliphatic substituent groups for R1 include substituents such as methyl, ethyl, n-propyl, s-propyl, butyl, hexyl, octyl, decyl, dodecyl, and cyclohexyl. Examples of aromatic substituent groups for R1 include phenyl, tolyl, and substituted phenyl, such as 4-aminophenyl, 2-aminophenyl, 4-aminotolyl, 2-aminotolyl, 4-methylphenyl, 2-methylphenyl, and other substituted phenyl groups. R may be hydrogen or a linear, branched, or cyclic aliphatic substituent comprising one to 20 carbon atoms or an aromatic substituent on the phenyl ring. The phenyl ring of Formula 1 may be substituted with more than one R group. For example, the phenyl ring may have methyl groups at positions 2 and 4 of the ring. Formula 1 Formula 2 shows an example of a modified SMA copolymer in which the anhydride functional group has reacted to form functional groups such as amide or ester groups. R2 and R3 are preferably the same and can be the substituents -NR4R5 or -OCR6R7R8. R4, R5, R6, R7, and R8 can be the same or different and can be selected from aliphatic or aromatic substituent groups, including linear, branched, or cyclic aliphatic groups comprising from one to 20 carbon atoms. Examples of aliphatic substituent groups for R4 and R5 or R6, R7, and R8 include methyl, ethyl, n-propyl, s-propyl, butyl, hexyl, octyl, decyl, dodecyl, and cyclohexyl substituents. Examples of aromatic substituent groups for R4, R5, R6, R7, and R8 include phenyl, tolyl, and substituted phenyl, such as 4-methylphenyl, 2-methylphenyl, and other substituted phenyl groups. R in Formula 2 is the same as in Formula 1. Formula 2 For Formulas 1 and 2, the molar ratio of styrenic monomer to maleic anhydride monomer (x:y) can vary from approximately 1:1 to approximately 6:1, preferably from approximately 2:1 to approximately 4:1. In other words, x can vary from 1 to 6 when y is 1. Preferably, the modified SMA copolymers do not comprise essentially anhydride functional groups. In other words, the concentration of residual anhydride functional groups in the modified SMA copolymers must be sufficiently low so that the acid number of the modified SMA copolymers is 50 mg KOH / g less of the modified SMA copolymer, preferably 25 mg KOH / g, and more preferably 10 mg KOH / g less. The SMA copolymers used in the POM compositions described herein have a molecular weight (MW) ranging from approximately 2,500 g / mol to approximately 20,000 g / mol, preferably from approximately 5,000 to 20,000 g / mol, and more preferably from approximately 5,000 to 15,000 g / mol. It is understood that the modified SMA copolymers are normally prepared from SMA copolymers and that the molecular weight range of the modified SMA copolymers will normally be higher than the molecular weight of the SMA copolymer. Therefore, for the purpose of determining the molecular weight of the modified SMA copolymers, it is assumed that the modified SMA copolymers are prepared from SMA copolymers having the molecular weight range described above. A person skilled in the art can calculate IVIA / a / ZUZ l / UI UZ / 4 easily determine the molecular weight of the modified SMA copolymer based on the molecular weight of the starting SMA copolymer. The glass transition temperature of SMA copolymers and modified SMA copolymers ranges from approximately 125 °C to approximately 160 °C. Therefore, when preparing modified SMA copolymers from SMA copolymers, it is important that the resulting modified SMA copolymer has a glass transition temperature within the range of approximately 125 °C to approximately 160 °C. Additionally, SMA copolymers and modified SMA copolymers, when dispersed within the POM matrix of the POM composition, must be uniformly dispersed within the POM composition and must be dispersed as discrete domains / particles that vary in size (average) from approximately 5 to approximately 0.1 micrometers or less, preferably from approximately 4 to 0.5 micrometers, and more preferably from approximately 3 to 0.5 micrometers. There is no absolute minimum particle size that may be used and it is limited only by the ability to disperse particles having an average particle size less than approximately 0.5 micrometers. A person skilled in the art may determine that the average particle size is less than 0.5 micrometers. iviA / a / zuzi / uiu / The concentration of SMA or modified SMA copolymers in POM compositions may vary from approximately 0.1 to approximately 20 percent by weight, preferably from approximately 0.5 to 8 percent by weight, more preferably from approximately 1 to 8 percent by weight, based on the total weight percent of components (A), (B), and (C) in the POM compositions. Additives (C) Optional additives that may be used in the POM compositions described herein include, but are not limited to, heat stabilizers such as polyacrylamides, processing aids, light / UV stabilizers, antioxidants, colorants, nucleating agents, lubricants, release agents, plasticizers, reinforcing agents, antistatic agents, and surfactants. However, some additives can destabilize the melt viscosity of POM compositions through the reaction of one or more of their chemical groups with the POM. This can lead to a breakdown of the POM's molecular weight, resulting in a decrease in the viscosity of the POM melt. Therefore, additives that maintain melt stability are preferred in these POM compositions.The total concentration of all additional additives should not exceed approximately 5 percent by weight, preferably approximately 3 percent by weight, and more preferably approximately 2 percent by weight or less of the total weight of all ingredients in the POM composition. Optional additives should not include materials that can hydrolyze to acids or that contain free acid groups. These materials can cause POM depolymerization. Examples of suitable antioxidants include phosphites, aromatic secondary amines, and spherically hindered phenolic compounds. Examples of spherically hindered phenol include, N,N'-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide) ), pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), octadecyl3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 2',3-bis[3,5-di-tert-butyl,4-hydroxyphenyl)propionyl]propionohydrazide, N,N'-hexane-1,6-diylbis[3,5-di-tert-butyl-4-hydroxyphenyl propionamide or the like. N,N'-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)) is preferred. Examples of aromatic secondary amines include 4,4'-bis(alpha,alpha-dimethylbenzyl)diphenylamine, 2,4-bis(n-octylthio)-6-(4'-hydroxy-3,5-di-tert-butylaniline)-1,3,5-triazine.Examples of phosphites include tris(2,4-di-t-butylphenyl) phosphite, tris(nonylphenyl) phosphite, diphenyl mono(tridecyl) phosphite, and similar compounds. Non-limiting commercial examples of antioxidants include hindered phenolic antioxidants such as Irganox® 245, 1098, 1090, and 1010, available from BASF. Suitable heat stabilizers include calcium carbonate, magnesium carbonate, and calcium stearate. Suitable UV stabilizers include benzotriazoles, benzophenones, aromatic benzoates, cyanoacrylates, and oxalic acid anilides. Examples of reinforcing agents that may be used in the POM compositions described herein include, but are not limited to, glass fibers, glass beads, ceramics, calcium carbonate, metal oxides such as alumina oxide, silicates, titanium dioxide, sulfates such as barium sulfate, titanates, kaolin clay, magnesium hydroxide, talc, wollastonite; minerals, graphite, carbon fiber, carbon black, and combinations thereof. Suitable lubricating additives include silicone lubricants such as dimethylpolysiloxanes and their derivatives; oleic acid amides; and alkyl acid amides. Other suitable additives include nonionic surfactants; hydrocarbon waxes; chlorohydrocarbons; fluorocarbons; oxy-fatty acids; esters such as lower alcohol esters of fatty acids; polyvalent alcohols such as polyglycols and polyglycerols; and metallic salts of fatty acids, such as lauric acid and stearic acid. Suitable nucleating agents include titanium oxides and talc. Manufacture of POM compositions described herein and of articles made from them The POM compositions described herein are mixed melt combinations in which the SMA copolymers and / or modified SMA copolymers are well dispersed within the POM resin, and any optional additives, when present, are well dispersed in and bonded to the polymer matrix, so that the combination forms a unified whole. It is understood that some of the additional additives may be present as solid particles during melt processing. The POM compositions may be prepared by combining the components in any order or combination, at any convenient temperature, preferably at or above the melting point of POM. Any melt-mixing method can be used to combine the polymer components (POM and SMA copolymers) and any additional additives. For example, the polymer components and additives can be added to a melt mixer, such as a single- or twin-screw extruder; a mixer; or a single- or twin-screw kneader. WIÁ / clMUZI / UlUÍ / 4 or a Banbury mixer, either all at once in a single-stage addition, or sequentially in stages, and then they can be melt-mixed. When polymer components and additives are added in stages, a portion of the polymer components and / or additives are normally added first and melt-mixed, and then the remaining polymer components and additives are added and further melt-mixed to obtain a well-blended composition. The POM compositions described herein can be molded or shaped into articles using methods known to those skilled in the art, such as injection molding, blow molding, injection blow molding, extrusion, thermoforming, melt molding, vacuum forming, rotational molding, calendering, and casting. Examples of molded articles include gears, sliding and guiding elements, housing parts, springs, chains, screws, nuts, propeller wheels, turbine blades, pump parts, valve bodies, insulators, connectors, parts for electronic devices such as televisions, telephones, automotive lights, etc., fuel emission units, aerosol cans, vehicle tanks, coffee maker parts, and grips and handles for guns and knives. The articles prepared from the compositions of The POMs described herein exhibit, at a minimum, an improvement in melt viscosity retention (DVR) compared to POM compositions that do not include SMA copolymers. Furthermore, the POM compositions comprising modified SMA copolymers exhibit a combination of properties, including DVR, time to 10% creep strain, and melt viscosity stability, compared to identical POM compositions that do not include modified SMA copolymers. This combination of improved DVR, improved time to 10% creep strain, and improved melt viscosity retention compared to an identical POM composition lacking at least one modified SMA copolymer is unexpected. Examples The Examples (E) and Comparative Examples (C) below are intended only to further explain and not to limit the scope of the compositions and articles described herein. Methods In the compositions listed in the tables below, the following methods were used: Melting point and glass transition temperatures Melting points and glass transition temperatures were determined using a TA Instruments Q1000 unit. Melting points were determined at a scan rate of 10 °C / min during the first heating scan, with the melting point recorded at the peak of the endothermic temperature. Tensile creep The tensile yield test, i.e., the time to 10% strain, was performed at 90 °C with a load of 25 MPa. Strain was determined according to ISO 899-1:2017, and the test was stopped once the measured strain reached 10%. Thermal deflection temperature (HDT) A Nissei 4000 molding machine was used to mold 4 mm ISO 527 test bars with a cycle time of 60 s and a melting temperature of 215 °C. The test bars were used for thermal deflection temperature measurements according to ISO 75-2A:2013 at a load of 1.8 MPa. Retention of melt viscosity The viscosity retention of the melt was determined by measuring the melt viscosity of the POM compositions after a holding time of 6 minutes at 215 °C (this allows sufficient time for the POM compositions to reach equilibrium in the molten state), which is the initial melt viscosity. The POM compositions were then held in the molten state at 215 °C for an additional 20 minutes (14 minutes from the 6-minute mark), and the melt viscosity was measured again. The melt viscosity after the 20-minute holding time was compared to the initial melt viscosity and recorded as the percentage of melt viscosity retained after 20 minutes.For example, if the initial melt viscosity is 90 Pa*s and the melt viscosity after a retention time of 20 minutes is 85 Pa*s, the melt viscosity retention is 85 / 90 or approximately 94.4 percent. Melt viscosity measurements were performed at 215 °C at a shear rate of 100 s⁻¹ according to ASTM D3835-08. Stable compositions have a melt viscosity retention close to 100%. Acid number. The acid value was determined according to ASTM D974-14, except that a xylene / butanol / propylene glycol mixture (75 / 15 / 10 volume ratio) was used as the solvent. Four grams of the test material were added to the solvent mixture and dissolved under reflux. The solution was titrated with 0.1 N KOH to the endpoint. Phenolphthalein was used as the indicator to mark the endpoint. The resulting acid value is expressed in mg of KOH / g of copolymer. flow index The melt flow index was determined according to ASTM D1238:2013 (190 °C, 2.16 kg). Molecular weight Molecular weight was determined using size exclusion chromatography. A Waters Corporation (Milford, MA) Alliance 2690™ was used in combination with a Waters 410™ differential refractive index (DRI) detector and the Viscotek Corporation (Houston, TX) Model T-60A™ dual detector module (Trisec® SEC Triple Detector version 3.0) incorporating static right-angle light scattering detectors and a differential capillary viscometer. The samples were prepared by dissolving the polymer under test in an HFIP at 23 °C (room temperature) with moderate stirring for 2 hours. Sample concentrations were selected to be approximately 2 mg / ml. All sample solutions were filtered through a 0.45-micrometer PTFE membrane filter before injection. For the separation, two Shodex GPC HFIP-806M™ styrene-divinylbenzene columns with an exclusion limit of 2 x 10⁷ and theoretical plates of 8,000 / 30 cm² and one Shodex GPC HFIP-804M™ styrene-divinylbenzene column with an exclusion limit of 2 x 10⁵ and theoretical plates of 10,000 / 30 cm² were used. The column temperature was 35 °C with a flow rate of 1.00 mL / min and an injection volume of 100 microliters. The run time was approximately 50 min. The solvent used was 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) with 0.01 M sodium trifluoroacetate. This triple detection method incorporates data from three detectors: a refractometer, a viscometer, and a right-angle light scattering photometer. The Flory-Fox equation is used to correct for angular asymmetry in light scattering. Data processing does not require column calibration. Particle size The particle size of the dispersed SMA copolymers or modified SMA copolymers was determined by taking molded test bars from the POM compositions (as for the HDT tests) and cutting the test bars into 20-micrometer sections using a cryo-ultra-microtome. These sections were stained with OSO4 and prepared for imaging under a transmission electron microscope. SMA copolymers were preferentially stained. The images were subsequently processed using ImageJ® processing software to measure the particle size of the dispersion. Compounding and Molding All compounding was carried out in a 26 mm Werner & Pfleiderer twin-screw extruder at a melting temperature of 203 °C. All materials were fed into the rear of the extruder. The resulting extrudates were quenched in a water bath and granulated. The granules were then dried in an oven at 80 °C for 4 hours. The dried granules were used for melt viscosity measurements and for molding test bars. Materials: POM-100: a polyoxymethylene homopolymer having a melting point of 178 °C and a melt flow index of 2.5 g / 10 minutes, measured at 190 °C using a weight of 2.16 kg, available from EI DuPont de Nemours and Company, Wilmington, Delaware, USA [DuPont] as DELRIN® 100. SMA-1: a styrene and maleic anhydride copolymer having a 1:1 molar ratio of styrene:maleic anhydride, a declared Tg of 155 °C, an acid value of 465-495 mg KOH / g, a MW of 5000, and available from Total Cray Valley, Exton PA, USA as SMA 1000. SMA-2: a styrene and maleic anhydride copolymer having a 2:1 molar ratio of styrene:maleic anhydride, a declared Tg of 137 °C, an acid value of 335-375 mg KOH / g, a MW of 7500 and available from Total Cray Valley, Exton PA, USA as SMA 2000. SMA-3: a styrene and maleic anhydride copolymer having a 3:1 molar ratio of styrene:maleic anhydride, a declared Tg of 125 °C, an acid value of 255-305 mg KOH / g, a MW of 9500, and available from Total Cray Valley, Exton PA, USA as SMA 3000. SMA-4: a styrene and maleic anhydride copolymer having a 4:1 molar ratio of styrene:maleic anhydride, a declared Tg of 116.5 °C, an acid value of 195-235 mg KOH / g, a MW of 11000 and available from Total Cray Valley, Exton PA, USA as SMA 4000. SMA-5: SMA 4000 that has been imidized with 4-aminophenol and has a declared Tg of 148 °C and is available from Total Cray Valley, Exton PA, USA as SMA EP 400. SMA-6: SMA 4000 that has been approximately 50% imidized with 4-aminophenol and has a declared Tg of 136 °C and is available from Total Cray Valley, Exton PA, USA as SMA EP 450. AO-1: Irganox® 1098, a spherically hindered phenolic antioxidant, with a molecular weight of 637 g / mol, available from BASF. HS-1: MAP 1070, a polyacrylamide heat stabilizer and is a polyacrylamide coated with 20 percent by weight polyethylene glycol with an average molecular weight (MW) of 24,000 g / mol and a polydispersity index of 3.1 by aqueous gel permeation chromatography, available from DuPont. Table 1 shows the physical properties of POM compositions comprising various SMA copolymers (E1-E4). Compared to a POM composition not comprising an SMA copolymer (control), all E1-E4 examples exhibit a melt viscosity (HDT) that is at least 4 percent or 4 °C higher than that of the control. The 10% creep strain is also improved in all examples by at least 200% compared to the control. It appears that as the maleic anhydride content of the SMA copolymer increases, the melt viscosity (MV) retention of the POM compositions improves compared to examples with an SMA copolymer comprising a lower maleic anhydride content. Table 1 Control E1 E2 E3 E4 POM-1 99.35 96.85 96.85 94.35 94.35 SMA-2 2.5 SMA-3 2.5 5 SMA-4 5 AO-1 0.15 0.15 0.15 0.15 0.15 HS-1 0.5 0.5 0.5 0.5 0.5 Physical Properties HDT (°C) 96 109 104 106 100 MV Retention (%) 100 33 59 47 77 10% Yield Strain (h) 0.75 4.12 3.77 n / mn / m The results in Table 2 show the physical properties of POM compositions comprising modified SMA copolymers that have: i) an acid value of less than 50 mg KOH / g, ii) a molecular weight (MW) ranging from approximately 2,500 g / mol to approximately 20,000 g / mol, and iii) a glass transition temperature ranging from approximately 125 °C to approximately 160 °C. These compositions surprisingly exhibit a combination of improved heat transfer coefficient (HDT), creep resistance, and melt viscosity stability compared to an identical POM composition lacking a copolymer. All examples E5–E8 show improved HDT, melt retention, and creep at 10% strain compared to the control, which is identical to the examples except that the control does not comprise any modified SMA copolymer. Table 2 Control E5 E6 E7 E8 POM-1 99.35 96.85 94.35 96.85 94.35 SMA-5 2.5 5 SMA-6 2.5 5 AO-1 0.15 0.15 0.15 0.15 0.15 HS-1 0.5 0.5 0.5 0.5 0.5 HDT (°C) 96 103 106 101 105 MV Retention (%) 100 99 98 100 100 10% Yield Strain (h) 0.75 3 3.3 n / m 2.45 It is noted that with regard to this date, the method known to the applicant to carry out the aforementioned invention is the one that is clear from the description of the invention. the best practice present

Claims

1. A polyoxymethylene (POM) composition characterized in that it comprises: (A) 80 to 99 percent by weight of at least one polyoxymethylene polymer; (B) 1 to 20 percent by weight of at least one styrene and maleic anhydride copolymer; and (C) optionally 0.5 to 5 percent by weight of at least one additive; wherein the POM composition exhibits a heat deflection temperature of at least 100 °C when measured in accordance with ISO 75-2A:2013; and wherein the weight percent is based on the weight of components (A), (B) and (C) in the POM composition and sums to 100 percent by weight.

2. The polyoxymethylene composition according to claim 1, characterized in that the polyoxymethylene polymer is a homopolymer.

3. The polyoxymethylene composition according to claim 1, characterized in that the styrene and maleic anhydride copolymer has a molecular weight of approximately 2,500 g / mol to approximately 20,000 g / mol.

4. The polyoxymethylene composition according to claim 1, characterized in that the styrene and maleic anhydride copolymer has a styrene:maleic anhydride molar ratio ranging from approximately 1:1 to 6:

1.

5. The polyoxymethylene composition according to claim 1, characterized in that the styrene and maleic anhydride copolymer has a glass transition temperature ranging from 125 to 160 °C.

6. The polyoxymethylene composition according to claim 1, characterized in that an optional additive (C) is present.

7. The polyoxymethylene composition according to claim 6, characterized in that the additive (C) comprises one or more of an antioxidant and a heat stabilizer.

8. The polyoxymethylene composition according to claim 7, characterized in that the antioxidant is a spherically hindered phenolic compound or wherein the heat stabilizer is a polyacrylamide.

9. The polyoxymethylene composition according to claim 1, characterized in that it has: a heat deflection temperature of at least 100 °C when measured according to ISO 75-2A:2013; and optionally one or both of a tensile yield to 10% strain of at least 2 hours when measured at 90 °C and a load of 25 MPa, determined according to ISO 899-1:2017; and a melt viscosity retention of at least 90 percent when measured at 215 °C and a shear rate of 100 s-1 after a 20 min retention time.

10. The polyoxymethylene composition according to claim 9, characterized in that the modified styrene and maleic anhydride copolymer comprises an imidized styrene and maleic anhydride copolymer, an esterified styrene and maleic anhydride copolymer, or an amidized styrene and maleic anhydride copolymer.

11. An article characterized in that it comprises the polyoxymethylene composition according to claim 1.

12. The article according to claim 11, characterized in that it is in the form of a gear, a sliding and guiding element, a housing piece, a spring, a chain, a screw, a nut, a propeller wheel, a turbine blade, a pump part, a valve body, an insulator, a connector, a part for an electronic device, a fuel emission unit, an aerosol can, a vehicle tank, a coffee maker part, and a handle for a gun or knife.

13. The polyoxymethylene composition according to claim 1, characterized in that the styrene and maleic anhydride copolymer is dispersed within the polyoxymethylene matrix resin as discrete particles having a particle size ranging from approximately 5 to 0.1 micrometers.