CA2050684A1 - Styrenic copolymer blend compositions having improved color stability - Google Patents

Abstract

The present invention pertains to thermoplastic polymer blends which contain a monovinylidene aromatic copolymer and an acetal polymer and which may also optionally contain an elastomeric material such as an elastomeric thermoplastic polyurethane or an elastomeric copolyester and/or a non-elastomeric polycarbonate or polyester resin. The indicated polymer blends are characterized in that they also contain one or more oxirane-containing stabilizer ingredients and are thereby imparted with improved thermal stability and, surprisingly, with improved U.V. stability and improved impact strength as well. Said polymer blends have good processability and are suitable for use in the preparation of a variety of molded utilitarian articles having a beneficial combination of chemical and physical properties.

Description

WO9~/11487 PCT/US91/~0673 STYRENIC COPO~YMER BLEND COMPOSI~IONS
HAVING IMPROVED COLOR STABIL-TY
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The present invention pertains generally to thermoplaqtic polymer blends which contain a monovinylidene aromatic copolymer in combination with an acetal polymer and which contain a minor ?roportion of an oxirane-containing ingredient. In certain preferred embodiments hereof, the indicated polymer blends also oontain an elastomeric polymer such aq elastomeric thermoplastic polyurethanes or copolyester elastomers and/or one or more non-elastomeric thermoplastic polycarbonate or polyester homopolymer or copolymer reqin ingredients. In another preferred embodiment, the monovinylidene aromatic copolymer i~ a rubber~modified monovinylidene aromatic copolymer having from 1 to 40 weight percent of dispersed rubber particles contained therein.
Blends of various types of polymeric materials have been suggested over the years in a variety of ?rior art references. For example, U.S. Patent 4~665,1j26 to usumgar et al. discloses certaln ?olymeric ~olding eo~positlons containing a predomir.ant amount (for ~; example from 60 to 95 weight rereentj of an acetal 25 ~polymer lngredient in combination with rela~ively lesser :

WO9l/11487 PCT/US91/00673 ~3 ~

amounts (~or example from 4 to 30 and from 1 to lO
weight percent, respectively) of a thermoplastic polyurethane (TP~) and a multiphase composite interpolymer such as. for example~ a butadiene-based, rubber-modified styrene/methyl- methacrylate polymer.
Such Kusumgar et al. ~ormulations are said to have improved impact strength relative to that of the acetal polymer per se and relative to that of comparable two component acetal/TPU or acetal/multiphase composite interpolymer blends and t~ be useful in various molding applications.
U.S. Patent 4,694,042 to McKee et al. pertains to thermoplastic polymer blends containing a minor proportion (that is from 5 to ~0 parts) by volume of a partially or completely crystalline polymer such as nylon, polyacetal, etc~ wherein said crystalline polymer, even though employed in minor volumetric proportion, is nevertheles~ considered to form a coherent phase and wherein the second, major proportion component forms a dispersed phase therein. Within the -~
indicated McKee et al. blends, said major proportion (that is from 50 to 95 parts by volume) component consists of one or more crosslinked, emulsion-polymerized elastomeric polymers such as, for example, butadiene or acrylate rubber-based graft copolymers containing either from 10 to ~0 weight percent of a shell having a glass transition temperature of less than -10C or a 3ubstantially lesser amount of a hard polymer shell of styrene, methylmethacrylate or styrene acrylonitrile copolymer. Acetal resin-based compositions are not e~ident in ~ne working examples.
Bri'ish Paten~ l.311.^0~ discloses thermoplastic molding composltions composed of a mixture ' . .

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wos~ 487 PCT/US91/00673 -3~

of from 50 to 99 weight percent of an acetal polymer and from 1 to 50 weight percent of a butadiene or acrylate rubber-modified. two-phase polymer mixture. Such thermoplastic molding compositions are described as having considerably improved impact strength relative to that of the acetal polymer per se. Preferred embodiments of this reference utilize 80 to 95 weight percent of the acetal polymer component.
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U.S. Patent 4,639,488 to Schuette et al.
0 disclose~ impact resistant polyacetal-based molding materials containing from 30 to 95 weight ?ercent of an acetal polymer and from 5 to 70 weight percent of an emulsion polymerized elastomeric graft copolymer composed, on a graft copolymer weight basis. of from 60 to 90 weight percent of a butadiene-based core (or "grafting base") and from 10 to 40 weight percent o~ a grafted shell o~ a styrene and/or methylmethacrylate-based polymer or copolymer. Such molding materials are said to have high impact strength at iow temperatures, to exhibit good thermal stability and to resist discoloration ln the presence of light.
U.S. Patent 4,179,479 to Carter discloses thermoplastic polymer blend compositions containing from 40 to 100 weight percent of a thermoplastic polyurethane in combination with up to 60 weight percent of a thermoplastic polymer which can be an ABS resin, an acetal resin, a polycarbonate resin, a poiye~ter resin or mixtures thereof. Such compositions are also ~re~uired to contain 0.5 to 10 weight percent of an acrylic polymer ?rocessing aid to improve the processability and moldlng characteristics thereof.

~3~ 4-U.S. Patent 4,117,033 to Gale discloses polymer blends containing an acetal resin in combination with ~ ;
from 0.1 to 5 weight percent cf a low molecular weight copolyether-ester resin. Sai~ copolyether-ester resin is said to improve the melt processability of the indicated acetal resin.
U.S. Patent 4,683,267 to Lindner et al.
discloses molding compounds consisting of a mixt~re of from 60 to 99.00 parts by weight of an acetal resin, from 0 to 40 parts by weight of an elastomer softening below the melting point of said acetal resin and from 0.01 to 40 parts by weight of an aliphatic, rubber~like, high molecular weight adipate-carbonate mixed ester.
Elastomers iaid to be useful in the Lindner et al.
blends include homopolymers and copolymers of alpha-olefins, homopoly~ers and copolymers of 1,3-dienes, copolymers and homopolymers of vinyl esters and copolymers and homopolymers of acrylate and methacryl~te esters.
... .
Another publication concerned w-ith blends of polyacetal resins and poiystyrene resins is Japanese Kokai No. 64-38463, published February 8, 1989. Such publication is eissentially concerned with polyacetal/
polystyrene blends wherein the ?olyace~al constitute~
the major portion by weight thereof and requires in all event~ that the ratio o~ the polyacetal melt flow rate (MFR, ASTM D-11238 at 190C and 2160g) to the 3 polystyrene melt flow rate (ASTM D-16238 at 200C and ~5000g) be from 5:1 to 100:1. According to such publication, excellent surface a?pearance is obtained by oDeratLng within. and only by o?erating within. the indicated range of ?olyacetal: ?olystyrene melt ~low rate ratios. Al.so accor~ing to such ?ublication~ the .' : ',. . ` ' ' :

WO 91/11487 PCT'/VS91~00673 ~ -3 ~.~ $ ~

polymer blends thereof optionally may contain small amounts of additional polymer ingredients such as a polyurethane resin. an olefinic homopoiymer or copolymer resin, acrylate resins, polyamide resin, ABS resins or polyester resins.
Certain blends of rubber-modified styrenic copolymers such as ABS resins with polycarbonate resins are discussed and described in U.S. Patents 4,526,926 and 4~624,986 (Weber et al.) and in U.S. Patents 4,163,762 and 4,243,764 (Rudd). Not contemplated~
however, by said patents are acetal resin-containing (or acetal resin and thermoplastic polyurethane or elastomeric copolyester-corltaining) blends as are provided in accordance with the present invention~
Published German application DE 3,802,753 Al discloses polymeric molding materials containing homo-or copolyoxymethylene (POM), thermoplastic polyurethane elastomers (TPU), obtained by the reaction of aromatic di-isocyanates with linear polyols, and polyalkylene terephthalate resin. Such mixtures are described as being useful for applications in vehicles and electrical appliance~ and to provide improved impact resistance.
, 25 Preferred compo3ition~ are from 40-95 percent POM and from 5~60 percent of a mixture consisting of 60-9B
percent TPU and 2-40 percent polyalkylene terephthalate.

In spite of the foregoing prior art activities, there ha~ remained a continuing need to provide improved engineering thermoplastic materials having a balance o~
proce~sability, good aesthetics with no pearlescence and having alternative. advantageous property profiles such as mechanical strength. impact resistance, environmental .', :

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~ ~.0 ~ 6- -stress crack resistance, creep and chemical resistance and practical toughness.
Certain improved styrenic copolymer/acetal polymer-based blend compositions of the sort indicated are disclosed and claimed within U.S. patent applications 474,415; 474,~16 and 474,171 all of which were filed on February 2, 1990. The present application is directed to a further improvement in such blend compositions which are characterized in that one or more oxirane-containing ingredients are incorporated therein and in that the resulting compositions have notably improved thermal and ultraviolet (U.V.) light stability and improved impact strength.
In accordance with the ~oregoing, the present invention, in one of its aspects, is a polymer blend composition which contains:
(A) a monovinylidene aromatic copolymer ingredient which is either (1) a non-rubber-modified monovinylidene aromatic copolymer containing, in polymerized form and on an aromatic copolymer ingredient weight basis, from 55 to 99 weight percent of one or more monovinylidene aromatic monomers and from 1 to 45 weight percent of one or more relatively polar comonomer ingredients; or (2) a rubber-modified monovinylidene aromatic copolymer containing, on a rubber-modified copolymer weight basis, from 30 to 99 weight percent of one or more monovinylidene aromatic copolymers as described in item (A) (1) above and from 1 to 70 weight percent of dispersed particles of a rubbery polymer having a glass transition temperature of 0C or lower;
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WO91/t1487 PCT/US91/00673 7 2 ~

(B) an acetal homopolymer or copolymer ingredient which can be either linear or branched and which can be employed either singly or in combination;
said composition being characterized ln that it contains, on a total polymer blend composition weight basis, from 0.01 to 15 weight percent o~ an oxirane-containing stabilizer in~redient.

In one of its preferred embodiments, the aforementioned polymer blend composition employs as its monovinylidene aro~atic copolymer ingredient a rubber-modi~ied monovinylidene aromatic copoiymer containing, on a rubber-modified copolymer weight basis, from 2 to 35 weight percent of dispersed particles of a rubbery polymer such as a homopolymer oP a 1,3-conjugated alkadiene monomer or a copolymer o~ from 60 to 99 weight percent of a l,3-conjugated alkadiene monomer with from 1 to 40 weight percent of a monoethylenically unYaturated monomer.
In another preferred embodiment, the indicated polymer blend composition further contains one or more elastomeric thermoplastic polyurethane ingredients and/or o~e or more copolyester elastomer ingredients.
Particularly preferred elastomeric polymers for use within such embodiment are ester-containing or ester-ba~ed elastomeric materials (such as, ~or example, ester-based elastomeric thermoplastic polyurethanes and capolyester elastomers) used either alone or in combination with each other or n combination with up to 70 weight on a total elastomer weight basis o~ a non-ester-based elastomeric materiai such as, for example, an ether-Dased t~ermoplastic ?oiyurethane.

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' In another preferred embodiment hereof, the subject poivmer blend composition further contains, in addition to the indicated elastomeric copolyester or thermoplastic polyurethane ingredient~ one or more non-elastomeric thermoplaqtic polycarbonate or polyester resin lngredients.
The indicated polymer blends can have a highly advantageous and controllable combination of physical.
chemlcal and aesthetic proDertie~q and can be beneficially employed in the preparation of molded articles for use in a wide variety o~ applications including various interior and exterior automotive applications. houseAold appliance applications, housings for electronic and/or business equipment and the like.
While oxirane-containing materials have been known in the prior art as being thermal stabilizers for glass reinforced polyacetal compositions (see, ~or example, Published European Application Number 281,148) and as being thermolysis stabilizerq for polyurethanes (see, for example, U.S. Patent 4,775,558), the use of such materials as additives or stabilizers within monovinylidene aromatic copolymer/acetal polymer blend~
of the type of concern herein is not thought to have been known heretofore. Moreover, the beneficial U.V.
stabilization and impact strength improvements which are achieved by incorporating such ingredients within the subject polymer blends is believed to constitute a 3 totally unexpected and surprising technical result.
As has been noted above~ the Dolymer blend compositions hereof contain a monovlny~idene aromatic copoly~er ngredient which can either be rubber-modified or non-rubber-modified. In either case, suitable : '"
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monovinylidene aromatic monomer constituents include styrene, alkyl substituted styrenes such as alphà-alkyl-styrene (for example alpha-methylstyrene, alpha-ethylstyrene etc.). various ring-substituted styrene~
such as para~methylstyrene, ortho-ethyls~yrene, 2,4-dimethylstyrene, etc., ring-substituted halo--styrenes such as chloro-styrene, 2,4-dichloro-styrene, etc. and the like. Such monovinylidene aromatic monomer (especially styrene) typically consti~utes f om 5~ to 99 weight ~ercent of said monovinylidene aromatic co301ymer and preferably constitutes from 60 to 95 (more preiferably from 65 to 90) weight percent thereof. Such monovinylidene aromatic copolymers are typically normally solid, hard (that is non-elastomeric) materials having a glass transition temperature in excess of 25C.
Suitable relatively polar comonomer ingredients for use as the minor constituent in (that is constituting from 1 to 45 weight percent of) the 20 indicated monovinylidene aromatic copvlymers include `
ethylenically unsaturated nitriles such as acrylonitrile, methacrylonitrile, ethacrylonitrile, etc.; ethylenically unsaturated anhydrides such as maleic anhydride; ethylenically unsaturated amides such as acrylamide, methacrylamide, etc.; esters (especially lower, for example C1-C6, alkyl ester~) of ethylenically unsaturated carboxylic acids such as methyl methacrylate, ethylacrylate, hydroxyethylacrylate, n 3G butyl acrylate or me~hacrylate, 2-ethyl-hexylacrylate, etc.; ethylenically unsaturated dicarDoxylic acid imides ; such as N-alkyl or N-aryl maleimides such as N-phenyl maleimide, etc. ~specially ore~erred ~or use as the relative polar ~co~onomer ingredien. herein are rhe aforementioned ethylenically unsa.-ra~ed ~.itriles.

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WO91/11487 PCT/US9t/00673 -- 1 o-- , . .

Preferably said relatively polar comonomers or mixtures thereof constitute from 5 to 40 (more preferably from 10 to 35) weight percent of the indicated monovinylidene aromatic copolymer.
Especially preferred polyme blend compositions hereof are those wherein the monovinylidene aromatic copolymer is rubber modified and comprises on a total rubber modified-copolymer weight basis from 1 to 70 (preferably from 1 to 40, more preferably from 2 to 35, 0 and most preferably from 3 or 5 to 20, 25 or 30) weight percent of dispersed particles of a rubbery polymer having a glass transition temperature of 0~C or lower.
Especially preferred rubbery polymers for use herein are those having a glass transition tempera~ure of -20C or lower. Examples of suitable such rubbery polymers include homopolymers of 1,3-conjugated alkadiene monomers; copolymers of from 60 to 99 weight percent of said 1,3-conjugated alkadienes with from 1 to 40 weight percent of a monoethylenically unsaturated monomer such as, for example, monovinylidene aromatic monomers (for example styrene, etc.) and ethylenically unsaturated nitriles such as acrylo-nitrile, methacrylonitrile etc.;
ethy}ene/propylene copolymer rubbers and rubbery ~ .
'' ethylene/propylene/non-conjugated diene copolymers.
Especially-preferred rubbery polymers for use herein include polymers composed of ~rom 60 to 100 weight percent of 1,3-butadiene and from 0 to 40 weight percent of styrene or acrylonitrile.
One particular class of rubber-modified .
monovinylidene aromatic copolymer ngredients of interest ,or use nerein are graft copolymer compositions wherein ~ne above-discussed rubbery polymer particles serve as subs.rates having grafted thereto a portion of :

the above-described monovinylidene aromatic copolymer as a grafted superstrate and wherein the remainder of said monovinylidene aromatic copolymer constitutes a continuous matrix phase in which the indicated grafted rubbery particles are dispersed. In such instances, the matrix phase typically constitutes from 40 to 95 (preferably from 60 to 95) percent of the overall weight of the indicated rubber-modified compositions and the grafted copolymer constituents constitutes the remainder thereof. Typically the grafted copolymer constituent will have a grafted superstrate to graftable rubber substrate ratio (that is a graft to rubber or "G/R"
ratio) of from 0.1:1 to 1:1 (preferably from 0.35:1 to 0 45:1).
Typically, the above-described rubber-modified monovinylidene aromatic copolymer ingredient will have a melt flow rate (MFR) of from 0.5 to 12 ~preferably from 1 to 10) grams per 10 minutes as determined pursuant to ASTM D-1238 at 230C and 3.8 kg.
In certain especially preferred embodiments hereof, the dispersed rubbery polymer particles are of a sort which have a bimodal particle si~e distribution.
For example, it has been observed that substantially higher impact strength is obtained within the polymer blend compositions of interest when the indicated rubbery particles are predominantly composed (for examplefrom 50 to 90, preferably from 65 to 75, weight 3 percent on a total rubbery particle weight basis) of particles having a volume average ~article size of less than one micron (preferably from 0.05 to 0.8 micron) and wherein the remainder of said rubbery par.icles (for example from 10 to 50, preferablv rom 25 to 35, weigh~
percent thereof) have a volume average particle size of : ~ '' .

wo9~ 487 ~ J ~ 3 !~ 12 PCT/US91/00673 one micron or greater (preferably from l to 3 micron).
The use of such bimodai rubber polymer particle has been found to give notably higher im~ac~ strength relative to comparable polymer blend compositions wherein the dispersed rubbery polymer particles are composed completely of rubber particles having sizes (that is diameters) of one micron or greater.
The aforementioned rubber-modified monovinylidene aromatic graft copolymer hereof can suitably be prepared in any known manner by free radical polymerization of the selected comonomer materials in the presence o. the modifying rubber material. Sui.able techniques thus include conventional mass, solucion, suspension or emulsion polymerization processes. If emulsion polymerized graEt copolymers are to be employed, care should be taken to remove or neutralize residual acid moieties. Otherwise decomposicion of the acetal polymer component can result. Especially preferred for use herein are rubber-modified monovinylidene aromatic graft copolymers prepared via mass, solution, mass/sus~ension or mass/solution polymerization techniques.
In general, mass polymerization involves polymerizing a solution of the rubber and monomer(s) at conditions sufficient to form discrete rubber particles of the desired particle size dispersed throughout the polymerized monomer. ~he polymerization is 3 advantageously conducted in one or more substantially linear strati~ied flow or so-cailed plug-flow reactors such as described in U.S. Paten- No. 2,727,884 ~hich may or may not comprise recirculation of a portion of the partially polymerized product c- n a scirred .ank WO 91/11487 PCI/US91~00673 ~ t reactor wherein the contents of the reactor are essentially uniform throughout.
The polymerization is advantageously conducted in an organic liquid reaction diluent or solvent such as aromatic or inertly substituted aromatic hydrocarbons (for example benzene or toluene) and in the presence of a free-radical initiator such as the peroxide initiators, (for example dibenzoyl peroxide or l,l-bistertiary butylperoxycyclohexane). In general, the initiator will be employed in an amount from lO0 to 5000 weight parts per million weight parts o~ the monomers employed. The organic liquid reaction diluent is generally employed to control the viscosity of the polymerization mixture and is generally employed in an amount from 2 to 20 weight percent based on the total weight of the rubber, monomer and diluent. The polymerization mixture can further contain other adducts such as a plasticizer or lubricant (for example mineral oil); and antioxidant (for example an alkylated phenol such as di-tert-butyl-p-cresol); a polymerization~
aid (for example a chain transfer agent such as an alkyl mercaptan) or a mold release agent, (for example zinc stearate). Temperatures at which polymerization is normally conducted are dependent on the specific components employed but will generally vary rom 60 to In the preparation of the rubber-reinforced polymer resin, the mass polymerization can be continued to the desired completion and then t;eated to remove any unreacted monomer such as by flashing off the monomer and other volatiles at an elevated temperature under vacuum.

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2 ~ 4_ Mass/suspension polymerization involves initially mass polymerizing the monomer/rubber mixture and, following phase inversion (that is the conversion or the polymer from a discontinuous phase dispersed in a continuous phase of the rubber solution through the point where there is no distinct continuous or discontinuous phase ln the polymerization mixture and to the point where there is a continuous polymer phase having the rubber dispersed therethrough) and subsequent size stabilization of the rubber particles, suspending the ~artially polymerized product, with or without additional monomer(s), in an aqueous medium which generally contains a polymerization initiator.
Subsequently, polymerization is completed using -suspension polymerization techniques.
In one preferred embodiment hereof, the above-described mass or mass/suspension-polymerized rubber-modified monovinylldene aromatic graft copolymer ingredient is employed in combination with a finely divided, emulsion polymerized particulate elastomeric material. Such particulate elastomeric materials typically have a volume average particle size in the range of ~rom 0.05 to O.S (especially from 0.15 to 0.2 micron and, when employed, constitut@ from l to 15 percent by weight of the overall blend composition.
Such emulsion polymerized particulate elastomeric materials may be suitably prepared by 3 emulsion polymerizing suitable monomers such as butadienej isoprene or higher alkyl esters of acrylic acid or methacrylic acid, optionallv in the presence of not more than 30 ~ercent by weight of moncmers, such as styrene, ac~ylonitrile, methyl ac y_ate, methyl WO9t/11487 PCT/US91/00673 ~15~ Q~

methacrylate or any other monomer and polar comonomer described above.
Preferably such elastomeric materials contain adhesion promoting groups such as car~oxyl, carboxamido, carboxylic anhydride or epoxide groups. This can be suitably achieved if acrylic or methacrylic acid, an amide of one of these, glycidyl acrylate or, instead of the free acid, tert.-butyl acrylate is used as a comonomer~ in an amount of from O.l to lO percent by weight. It is particularly advantageous if a shell which has a glass transition temperature of less than -10C and which contains such an adhesion promoting monomeric building block is grafted onto the indicated emulsion-polymerized elastomeric polymer. Graft monomers which have proven particularly useful are esters of acrylic acid, such as n-butyl acrylate, preferably in combination with multifunctional crosslinking agents and/or with comonomers contailling the stated adhesion promoting groups. Advantageously, the shell amounts to~10-50 percent by weight of the total elastomeric polymer.
While not being particularly critical for the purposes of the present invention, the above-described monovinylidene aromatic copolymer ingredient will generally constitute from 5 to 90 weight percent of the polymer blend compositions hereof. Preferably, said monovinylidene aromatic copolymer is employed in amounts 3 corresponding to from lO to 90 (more preferably from 15 to 85, especially from 20 to 65) parts by weight per lO0 parts of the comhined or total weight of the overall polymer blend composition.
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WO91/11487 PCT/US9l/00673 -l6-In those embodiments wherein ~he blends hereof are binary in character and are composed of the monovinylidene aromatic copolymer and ne acetal polymer only, said blends will preferably contain from S0 to 80 (more preferably from 55 to 75) parts by weight of the monovinylidene aromatic copolymer per 100 parts by weight of the polymer blend composition. On the other hand, when three component monovinylidene aramatic copolymer/acetal polymer/-elastomeric polymer 0 compositions are involved, then the aromatlc copolymer ~ill preferably be employed in amounts ranging from 10 to 65tmore preferably ~rom 15 to 60) parts by weight ~er 100 parts by weight of the polymer blend composition.
Furt~ermore, when 4 component polycarbonate or polyester resin containin~ systems are prepared, the monovinylidene aromatic copolymer will preferably be employed in a~.ounts ranging ~rom S to 6~ (more preferably from 10 to 40 and most preferably from 15 to 30 or 35) parts by weight per 100 parts by weight of the overall polymer blend composition.
~ he acetal (sometimes termed polyoxymethylene) resin can be any of those commonly known in the art or commerically available. Thus the acetal resin either can be linear or branched and can be a copolymer or a homopolymer or mixtures of these. Copolymers can contain one or more comonomers such as those generally used in preparing acetal resins. Comonomers more commonly used include alkylene oxides of 2 to 12 carbon atoms, in a less than 20 wt. percent amount.
Polyoxymethylenes which contain fro~ 0.5 to 10 percent, in particular from 1 to 5 percent of erhylene oxide are particularly important commercially and are especially preferred for use ne~ein. As a general rule, ~he .

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available acetal resins have thermally stable terminal groups, such as ester or ether groups, for example acetate or methoxy groups. The polyoxymethylenes have, in general, a molecular weight of from iO,000 to 100,000. As an alternative to molecular weight, melt flow rate (MFR) is commonly used to characterize resins, and those with higher molecular weights have lower melt flow rates. Preferred acetal resins for use in the compositions of the present invention have M~Rs of from tO 0.1 to 60 (preferably from 0.5 to 30 and most preferably from 0.5 to 5 or 10) grams/10 minutes, as measured pursuant to ASTM D-1238 at 190C and 2.16Kg. If the MFR
is too high, the melt viscosity of the acetal will be too low and it will bé difficult to achieve sufflcient intimate mixing of components at appropriate shear rates. If the M~R is too low, the temperature for the compounding operation may become too high and degradation can result. As will be evident in the examples, and assuming all other parameters are equal, the lower the MFR, the higher the toughness of the compositions of the present invention.
While not critical, the acetal polymer ingredient of the sub~ect polymer blend compositions can generally constitute from 5 to 90 weight percent) of said polymer blend compositions. Preferably, said acetal polymer is utilized in an amount corresponding to from 10 to 90 (more preferably from 15 to 85, and especially from 15 to 55) parts by weight per 100 parts by weight of the total or combined weight of the indicated polymer blend composition.
In certain preferred embodiments hereof, i.t is desirable to employ the indicated acetal polymer ingredient in relatively larger prooortions sucn as for : ' "
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2 ~ 18-example at levels ran~ing (on a per lO0 parts by weight total polymer blend composition basis) from 40 to 90 (more preferably ~rom 45 to 80 and most preferably from 50 to 75) parts by weight. These latter types of blend compositions are particularly beneficial in those instances wherein high heat dlstortion characteristics are desired.
In other preferred embodiments, it may be desirable to employ said acetal polymer in smaller 0 proportions such as, for example, at levels ranging f om 20 to 50 (especially from 25 to 35 or 40) parts by weight per lO0 parts by weight of the polymer blend composition in question.
t5 As has been noted above, the polymer blend compositions hereof also contain a mlnor proportion (for example, from O.Ol to 15 parts by weight per lO0 parts by weight of the subject polymer blend compositions) of one or more oxirane~containing stabilizer ingredients.
The inclusion of the indicated oxirane-containing ingredients within the polymer blend compositions hereof has been observed to substantially improve the thermal color stability of the subject polymer blends during the melt processing (for example, melt ~lending and/or injection molding) thereof and to thereby widen the processability window of such blends by allowing the use of increased processing temperatures without encountering severe thermally induced discoloration problems. Additionally, lt has been surprisingly found that 'he indicated oxirane-containing additives or ingredients can also imparc notably improved impact strength to che subject polymer blends ' '. ' ' ' '' .. ' ~ '' ~ ' ' ' ' . . ' _ 1 9~

a5 wel 1 as providing une~pectedly enhanced ultraviolet ~u.v. ) li~ht stabili~y cha~ t~i~is~ics .
oxirane-containing ingredients suitable for use herein include the various known epoxidized organic materials which have sufficiently high boiling points and decomposition temperatures (for example, preferably at least 180C, more prererably at least about 200C and most preferably at least about 220C) so as to be melt processable within the subject polymer blend compositians without undergoing substantial decomposition or evaporative 105s thereof. ~xamples of suitable oxirane-containing materials for use herein include epoxide derivativesi, of unsaturated triglyceride such as epoxidized soybean oil, epoxidized linseed oil, epoxidized palm oil, epoxidized tung oil, epoxidiæed coconut oil, epoxidized peanut oil, epoxidized olive oil~ epoxidized rape~eed oil, etc.; epoxy phenol novolac resins; epoxy cresol novolac resins, diglycidyl ethers of bisphenol A; diglycidyl ethers of poly (oxypropylene) glycol; glycidyl ethers of polyethylene glycols;
glycidyl ethers of polyhydroxy aliphatic alcohols such as 1~4-butanediol, 1,4-butenediol, glycerin, trimethylol propane, pentaerythritol, etc.; and glycidyl esters of polyvalent aromatic, aliphatic or cycloaliphatic carboxylic acids such as phthalic acid, terephthalic acid, tetrahydrophthalic acid, adipic acid, etc.
Particularly suitable and pre~erred for use 3 herein are the aforementioned epoxidized unsaturated triglycerides (especially epoxidized soyDean oil and epoxidized linseed oil) and epoxy resins derived from the reaction of epichlorohydrin with aromatic or ;' .
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W O 91/11487 PC~r/US91/00673 `f~

aliphatic polyols such as bisphenol A, polyethylene glycol, polypropylene glycol, etc.
As a general proposition,the aforementioned oxirane-containing stabilizer ingredients can be employed within the polymer blend compositions hereof in an amount ranging rrom 0.01 to 15 weight percent based upon the total weight of said compositions. Preferably, however, said stabilizer ingredient will more typically be employed in an amount ranging from 0.1 to 10 (more preferably from 0.2 to 5 and most preferably from O.S to 2 or 3) parts by weight per 100 parts by weight of the subject polymer blend composition.
Polycarbonate resins suitable for use herein include aromatic polycarbonates which contain the repetitive carbonate group, ~ .

~O~C 0--and which have a divalent aromatic radical attached to said carbonate group. Preferably, the polycarbonate can be characterized as possessing recurring structural units of the following formula and structural isomers thereof:
wherein A is a single bond or is a divalent aliphatic radical such as an alkylene or an alkylidene radical usually with 1-7 carbon atoms, or a cycloalkylene or cycloalkylidene radical usually with 5-15 carbon atoms, with all including their aromatically and aliphatically substituted derivatives. In other varia~ions of the .

WO91/11487 PCT/US91/0~673 21~ $~

-O - ~ A ~ -O -C _ ~R)n (R )n , - .
polycarbonate resin, A can also represent -O-, -S-, C0-, -SO- or - SO2-. In the indicated structural formula, R' and R'' are substituents other than hy~rogen such as, for example, halogen or a saturated or ::
unsaturated monova~ent aliphatic radical having usually 1-7 carbon atoms, and n equals 0 to 4.
;
Typical of the above-mentioned structural unit are those which result from the reaction of phosgene (or other carbonyl-providing species) with::bis- ::
(hydroxyphenyl) alkanes, bis (hydroxyphenyl) : .
: ~:20 ~cycloaIkanes, bis (hydroxyphenyl) sulphides, bis .
(hydroxyphenyl) ~thers, bis ~hydroxyphenyl) ketones, bis :: (hydroxyphenylj sulphoxides, bis-(hydroxyphenyl) sulphones, a, a ' -bis (hydroxyphenyl)-isopropylbenzene, ~bls (3,:5-b~omo-4-hydroxyphenyl) sulfone, bis te:trabromo-4-hydroxyphenyl) propane, bis-(3,5,6-tri- :-chloro-2-hydroxyphenyl) methane, 2,2'-chloro-4,4'- ::
cyclohexylidene phenol, tetrachlorohydroquinone and chloroethylene phenol. Further possible structural : ~30: units are those which result from bis-(3,5-methyl~
hydroxyphenyl)~ propane, 4,4'-bis (4-hydroxy-phenylthio~ :
phenylsulf~one:and:phenophthalein.
It~is~understood, of course, that the carbanate :.
polymer~:;may be~derived from two or more differer.t hydric .~.
phrncls or a copolymer of a~n-àr~c p~1enol ~1-1 a glyc~l .

~ 22-if a copolymer carbonate rather than a carbonate homopolymer is desired. Also suitable for the practice of this invention are blends of any of the above carbonate Dolymers.
Also included in the term "polycarbonate polymer" are the ester carbonate copolymers of types described in U.S. Patent Numbers 3,169,121; 4,330,662 and 4,105,633. Typical comonomers are dicarDoxylic acid, for example, terephthalic acid.
Additionally included in the scoDe of this invention are so-called "branched polycarbonates" which are made Dy using the above-described polyhydric monomers in combination with a suitable branching agent, normally tri- or higher polyfunctional molecules.
Suitable polyhydric reactants for use in preparing various polycarbonate resins are also described, in U.S. Patent Numbers 3,062,781; 2,9701131 2a and in German Offenlegungsschrift Nos. 1,5701703;
2,2111956 and 2,211,957.
The polycarbonate resins employed herein preferably have a melt flow rate, measured according ASTM D-1238 ~condition O : 300C, 1.2 kg load)l of from 0.5 to 200 g/10 minl preferably from ~.5 to 100 g/10 min, more preferably from 5 to 90 g/10 min, and especially preferred from 8 to 75 g/10 min.
3 Thermoplastic polyester resin components suitab~e for use herein are those which are obtained by reaction of glycol and dicarboxylic acid such as, or example, as are described in U.S. Patent Number 21465l319.

~ . . . .... . . . . .. . . . .. . . . .

W O 91/11487 PC~r/VS91/00673 -23~

The glycol preferably has the general formula:

HO ~(CH2)n ~OH

in which n is an integer from 2 to 12, such as for example ethylene glycol, 1,2- or 1,3-propane diol, 1,2-, 1,3- or 1,4- butane diol, 1,5- or 1,4-pentane diol, 1,6-hexane diol, 1,7- heptane diol or 1,8-octane diol. In other preferred cases cycloaliphatic diols, typically containing up to 21 carbon atoms, are employed, such as, for example, cyclohexane-1,4-dimethanol, 2,2-bis-(4-hydroxycyclohexyl) propane, 2,4-dihydroxy-1,1,3,3- :
tetramethyl cyclobutane and 2,2 bis-(3-~-hydroxy-ethoxyphenyl)-propane.
Dicarboxylic acid components suitably employed to prepare said polyester resins include those having : ~: 20 the general formula -, O o ,: :
;: : 25 H O~ C - R"' B - R" " - C - O H :~

with R"' and R"" each representing the -(CH2)m-group, with m being zero or an integer rrom 1 to 4. B is a ` "` ` `divalent aromatic radical represented by the following formulas or~ structurai isomers thereof: .

' ~ :: ,' : : : ' .
: : : . , : ~,.. - ., . - .. ,, . . , , ...... . . . .. , :... . ..

WV9~ 487 PCT/US91/00673 ' (J ~ 2~--_ ~ _ ~ ~ D ~

or a cyclo aliphatic group.

D may be: o Il .
--(CH2)p~ cH2)p C~(cH2)p-- ; --(CH2)p- O~(CH2)p--;

-'O--(CH2)q~0 ~ clt2)p--S--(CHi)p--;--S--(CH2)q--5 ~;

SO2-; and where p may be zero or an integer from 1 to 5 and q ii3 an integer of ~rom 1 to 5.
~D may al~o be:

O ~ ~ ~O ~ or ~ 5~ ~ 5 ~:25 ~and~structural lsomer thereo~.
, .
~ ypical dicarboxylic acids include phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic : 30 aci~d, 4,4'-diphenyl dicarboxylic acid, succinic acid, adipi:c acid,:~sebacic acid, azelaic acid and cyclohexane diace~ic acid:.
The polyester resin~obtained from reaction of the;~indicated dicarboxylic acid:and 2 glycol may be ranc~hed by lncorpora~ion of relatively small quantities Wo91/11487 PCT/US91/00673 ~ ~ Y` ~

of tri-or tetrahydric alcohols or tri- or tetrabasic polycarboxylic acids of the type described, for example~
in German Offenlegungsschrift No. l,900,Z70 and in U.S.
Patent Number 3~692,744.
In addition to the homopolymer derived from one type of dicarboxylic acid and one type glycol, copolymer :.
resins are often preferred, polymerized from a combination of one or more dicarboxylic acids and a combination of one or more glycols. Such a product, :-0 made from terephthalic acid, and a combination of cyclohexane dimethanol and ethylene giycol is commerically available from Eastman Laboratories under the tradename KODAR PETG (TM) Copolyes~er.
The homo- and copolyesters derived from dicarboxylic acid and glycol have preferably a molecular weight ranging from 5,000:to 200,000, more preferably from l0,000 to 60,000.
Mixtures of various thermoplastic polyester and/or polycarbonate resins can suitably be employed if and as desired such as, for example, polycarbonate and polyethylene glycol terephthalate or polybutylene glycol terephthalate or any other combination of the various polyester and polycarbonate resins mentioned above.
: The indicated thermoplastic polyester or polycarbonate resin lngredient, when e~ployed within the compositions hereof, can typically be employed in amounts ranging from 5 to 90 par~s by weight thereof Der l00 parts by weight of the su~ject polymer blend . -compositions. Preferably, said ingredient is employed in an amount corresponding to from l0 to 75 (more preferably from 15 to 55, especially 'rom 20 to 45 or : . .

.,. . :

~ : ' 4~7 PCT/US91/00673 ~ S\~ 26 50) parts of the combined weight of the polymers contained within the subject polymer blend composition.
Elastomeric materials suitable for use herein include, as noted above, thermoplastic polyurethanes and elastomeric copolyester materials. Thermoplastic polyurethanes suitable for use herein include any of those generally known in the art and thus include those prepared from a diisocyanate, a polyester, poly-caprolactone or polyether and a chain extender. Such thermoplastic ~olyurethanes are substantially linear and maintain thermoplastic Drocessing characteristics.
A preferred group or polyether-based polyurethanes used in the polymer blend composition of the present invention are the reaction products of~
~,4'-methylene bis(phenyl isocyanate), (ii) a polyether polyol (such as for example, a poly (oxy-1,2 propylene) glycol or a polyoxytetramethylene glycol) having a number average molecular weight within the range of 60~
to 3000 (preferably from lO00 to 2500) and (iii) chain extending agent such as diol extenders selected from the ~roup consisting of aliphatic st~aight chain diols having from 2 to 6 carbon atoms, bis(2-hydroxy-ethyl) ether of hydroquinone, bis(2-hydroxy-ethyl) ether of resorcinol, and mixtures of any .wo or more of such dlol -extenders and/or other difunctional chain extending agents containing 2 active hydrogen-containing groups which are reactive with isocyanate groups.
3~
Suitable chain extendina agents for use herein may~include any difunctional compounds containing two active hydrogen-containing groups which are reactive with lsocyanate groups. Examples of such sui~able chain extending agents thus include diols including ethylene . ~. .

~ : :
,. , .

. .: ~ , .. . . .. .. . . . .. . . . .. . ... ... . . .

WO91/1l487 PCT/US91/00673 -27- ~c~ $~

glycol, propylene glycol, butylene glycol, 1,4-butanediol, butenediol, butynediol, xylylene glycols, amylene glycols, 1,4-phenylene-bis-~-hydroxyethyl ether, 1,3-phenvlene-bis-~-hydroxy ethyl ether, bis-(hydroxy-methyl-cyclohexane), hexanediol, thiodiglycol and the like; diamines including ethylene diamine, propylene diamine, butylene diamine, hexamethylene diamine, cyclohexalene diamine, phenylene diamine, toluylene diamine, xylylene diamine, 3,3'-dichlorobenzidine, 3,3'-0 dinitrobenzidine and the like; alkanol amines such as,for example, e~hanol amine, aminopropyl alcohol, 2,2-dimethyl propanol amine, 3-aminocyclohexyl alcohol, p-aminobenzyl alcohol and the like. If desirable, a small amount of polyfunctional material may be utilized. This polyfunctional chain extender, however, should not be present in an amount greater than about 1 percent by weight. Any suitable polyfunctional compound may be used for such purpose such as, for example, glycerine, trimethylolpropane, hexanetriol, pentaerythritol and the like.
.~s used herein, the term "aliphatic straight chain diols having from 2 to 6 carbon atoms" means diols of the formula HO(CH2)n O~ wherein n is 2 to 6 and there is no branching in the aliphatic chain separating the OH
groups. The term is inclusive or ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol. Preferred diol extenders for use herein include 1,4-butanediol, 1,6-hexanediol and the bis(2-hydroxy-ethyl) ether of hydroquinone; an especially preferred diol extender being 1,4-butanediol.
Other diisocyanates which may be used in place of or in combination with the preferred species mentioned above ~that is 4,4'-methylene bis (phenyl .
.:

W O 91/11487 PC~r/US91/00673 ~ Z8-isocyanate)] include ethylene diisocyanate, ethylidene diisocyanate, propylene diisocyanate, butylene diisocyanate, cyclopentylene-l,3-diisocyanate, cyclohexylene-l,4-diisocyanate, 2,6-~olylene diisocyanate, 2,2-diphenylpropane-4,4'-diisocyanate, P-phenylene diisocyanate, m-phenylene diisocyanate, xylylene diisocyanate, l,4-naphtylene diisocyanate, l,5-naphthylene diisocyanate, diphenyl-4,4r-diisocyanate, azobenzene-4,4'diisocyanate, diphenyl sulfone 4,4'diisocyanate, dichlorohexamethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, l-chlorobenzene-l,4-diisocyanate, furfurylidene diisocyanate and the like.

The polyether polyol and chain extending agent are typically used in the polyurethane reaction medium in a ratio of 0.5 to 2.5 equivalents (~or example mole equivalents) of the chain extender per equivalent of the polyol. Preferably, the equivalents ratio is from l to 2. Moat preferably the ratio is from 1.2 to 1.6 equivalents of extender per equivalent of the polyol when said polyol has a moleculax weight of 2030, and especially when the extender is an aliphatic straiyht chain diol. When the aforementioned hydroqulnone or resorcinol extender are used, the equivalents ratio may -be lower than the above-mentioned preferred ranges, for example, as low as 0.5 equivaients of the extender per equivalent of ~he polyol~
In preparing .he foregoing polyether-based polyurethanes, the polyether poiyol and the chain extender and the diisocyanate are typically used in relative proportions to each otner such that the overall ratlo of isocyanate equivalents or groups to cotal .

WO91/11487 PCl`/US91/00673 ~ 3 hydroxyl equivalents or groups or other active hydrogen-containinq groups (that is polyol plus extender) Ls within the range of 1:1 to 1.08:1.0 and preferably is within the range of 1.02:1.0 to 1.07:1Ø The mos~
preferred ratio of isocyanate (~CO) groups to total hydroxyl (OH) groups (or combined hycroxyl plus other active hydrogen groups) is within the range o from 1.03:1.0 to 1.06:1Ø
The term equivalent(s) as used with res~ect to the polyurethane preparation herein is based on the hydroxyl (or other active hydrogen) groups and the isocyanate groups within the reactan~s.
Suitable techniques for the preparation of the aforementioned polyether-based thermoplastic polyurethanes are known in the art and are discussed, for example, within the teachings in Columns 4-6 of U.S.
Patent 4,665,126 to Kusumgar et al.
The polyether-based thermoplastic polyurethanes employed in the practice of the present . .
invention are typically characterized by a ClashBerg modulus (Tf) which is less than -10C The To (glass ~ .
transition temperature) of the polyurethanes is essentially the same value. The polyether-based polyurethanes may suitably have, for example a Shore A
~ardness o~ 95A or less, and a weight average molecuLar weight in excess of 100,000.
:
A preferred group of ~hermoplastic ~olyester- :~
based polyurethanes for use in the ~resent invent.on axe the reaction producls of: (i) 4,4'methylenebis(phenyl isocyanate; (ii) a polyester of adipic acid and a glycol .
having at least one erimary hydroxyl group; and ( ii) a , ', ' ' ';" ' ', ',, ' . ' ' .'' ',: ', .'. ~ ' ', .~' ' . .

3 ~ :

difunctional chain extender of the sort described above having 2 active hydrogen-containing groups which are reactive with isocyanate groups.
In preparing the polyester precursor of this group of polyurethanes the adipic acid is c:ondensed with a suitable glycol or mix~ure of glycols which have at least one primary hydroxyl group. The conclensation is stopped when an acid number of ~rom 0.5 to 2.0 is reached. The water formed during the reaction is removed simultaneously therewith or subsequently thereto such tha~ the final water content is from O.Ol to 0.02 percent preferably from O.Ol to 0.05 percent.
Any suitable glycol may be used in reaction -with the adipic acid such as, for example, ethylene glycol, propylene glycol, butylene glycol, hexanedio:l, bis-(hydroxymethylcyclohexane), l,4-butanediol, diethylene glycol, 2,2-dimethyl propylene glycol, l,3-propylene glycol and the like. In addition to theglycols, a small amount of trihydric alcohol up to l percent may be used along with ~he glycols such as, for example, trimethylolpropane, glycer-ne, hexanetrio and the ~ike. The resulting hydroxyl polyester has a molecular weight of at least 600, a hydroxyl number of 25 to l90 and preferably between 40 and 60~ and an acid number of between 0.5 and 2 and a water content of O.Ol to 0.2 percent.
Any suitable chain extending agent incLuding those described above for the polye~her-based thermoplastic polyurethanes) having active hydrogen containing groups reactive with isocyanate groups may be used in preparing the subject polyester-based materials.
Examples of such extenders thus nclude diols such as . : .
'.

WO9~/tl487 PCT/US91/00673 -31- 2 ~

ethylene glycol, propylene glycol, butylene glycol, 1,4-butanediol, butenediol, butynediol, xylylene glycols, amylene glycols, 1,4-phenylene-bis-~-hydroxyethyl ether, 1,3-phenylene-bis-~-hydroxy ethyl ether, bis-(hydroxy-methyl-cyclohexane), hexanediol, thiodiglycol and the like. Moreover, polyether polyols may also be employed as the chain extending agent (or as a Dortlon thereof) with the result being a copolyester/polyether based thermoplastic ~olyure~hane which is also suitable for use in the practice of the present invention.
Although thermoplastic polyurethanes based upon ~:
adipate polyesters are generally preferred for use herein, other polyester-based thermoplastic polyurethanes can also be suitably employed within the present invention such as, for example, those in which there is employed tin place of the adipic acid) succinic acid, suberic acid, sebacic acid, oxalic acid, methyl adipic acid, glutaric acid, pimelic acid, azelaic acid, ! 20 phthalic acid, terephthalic acid, isophthalic acid and the like as well as those prepared using hydroxycarboxylic acids, lactones, and cyclic carbonates such as ~-caprolactone and 3-hydroxy-butyric acid in place of the adipic acid component. Similarly polyester-based thermoplastic polyurethanes prepared using the above-described alternative diisocyanates in place of 4,4'-methylene bis (phenyl isocyanate) can also be suitably employed in the practice of the present invention.
The aforementioned types`of polyester-based thermoplastic polyurethanes are generally known materials. Suitable methodology for the preparation ', .

: , " , ' ' ~.: : .,, .,.' ', ,-' ` ` ,, ' ,, : ' :~ : ': ` " .. ' ' ; , ' ' ,: :, , : ' ' , , ' ' WO91/t1487 PCT/US91/00673 thereof is disclosed within Column 7 of U.S. Patent 4,665,126.
Especially preferred thermoplastic polyurethanes for use herein include those having a Shore hardness (ASTM D2240) between 70 on the "A" scale and 60 on the "D" scale.
If desired, the thermoplastic polyurethane employed in the ~ractice of the ~resent invention can have incorporated in it additives such as pigments, ~illers, lubricants, stabilizers, antioxidants, coloring agents, fire retardants, and the like, wnich are commonly used in conjunction with polyurethane elastomers.
Elastomeric polymer ingredients suitable for use herein also include polyester-based elastomers other than the ester-based polyurethane materials which have bee~ discussed above. Examples of such other elastomers include elastomeric copolyether-ester resin material and elastomeric adipate-carbonate mixed ester resin materials.
, Suitable copolyether-ester elastomer ingredients can be generally described as comprising a multiplicity of recurring intralinear long-chain and short-chain ester units connected head-to-tail through ester linkages, said long chain ester units generally constituting from 25 to 85 weight percent o~ said copolyether-es~er elastomer and corresponding to the ~ ~ormula:
':
, '~ ' .

.
: : :

WO91/114g7 PCT/US91/00673 O O
Il 11 : ' .' OGO CRC-wherein :
G is a divalent radical remaining after removal 10 of terminal hydroxyl groups from a poly-(allcylene oxide) : .:
glycol having a carbon-to-oxygen mole ratio of 2-4.3 and a molecular weight of 400 60001 and ~.
R is a divalent radical remaining after removal of carboxyl groups from a dicarboxylic acid having a molecular weight less than 300; and said short chain . :
ester units generally constituting from l5 to 75 weight percent of said elastosner and corresponding to the : 20 formula~
: : : : ' , :.
- - ~ . . .
8 1l ~
25~ ODO-CRC- .
: ;' :
wherein D is a divalent radical remaining a~ter removal : of hydroxyl:~groups from a low molecular weight dioi havlng a molecular welght less than 250; and s~as defined above.

3r~ 34_ Preferably, the indicated polyether-ester elastomers have a relatively low molecular weight as evidenced by their exhibiting an inherent viscosi~y of 0.05-0.95 (preferably from 0.1 to o.8 and most preferably from 0.1 to 0.5) when measured in m-cresol at a O.lg/dl concentration at 30C.
A more detailed description of the aforementioned polyether-ester elastomers (including preferred embodiments thereof, preparation methodology, 0 the use of small amounts of the low molecular weight materlals as a processing aid for polyacetal resins and the use, as per German Patent 2,443,343, of hi.gher molecular weight version.s as impact modifiers ~or polyacetal resins) i5 presented within U.S- Patent 4,117,033 to Gale.
Suitable elastomeric adipate-carbonate mixed ester materials for use herein include those described within U.S. Patent 4,683,267 to Lindner et al. for use as property modifiers for polyoxymethylene resin-based ..
molding compositions. Such materials are rubber-like ..
high molecular weight compounds corresponding to the ~ormula : 25 X~O~l I ~ ( O X ~O~If ) k--m wnerein , '.. :' '"

'.:, "
' ' .~
:: .
: ::

.

-35- ~3c ~

X and X' represent residues of the reaction product of a polyhydric alcohol and adipic acid having a molecular weight of from 800 to 3,500;
k represents an integer of from 0 to l0; and m represents an integer greater than 20, preferably from 22 to l00; which compounds have a limiting viscosity number [~] (Staudinger Index) in tetrahydrofuran of from 0.8 to 2.5 dl/g.
The followlng are examples of polyhydric alcohols which may be used, optionally as mixtures, for the poiyesters rrom which the residues X and X' are ~
derived: ethylene glycol, propylene glycol-(l,2) and - ~.
(l,3), butylene glycol-(l,4) and -(2,3), hexane diol-~l,6), octane diol-(l,8), neopentyl glycol, cyclohexane dimethanol, l,4-bis-(hydroxymethyl cyclohexane), 2-methyl-l,3-propane diol, diethylene glycol, triethylene ylycol, tetraethylene:glycol, dipropylene glycol and dibutylene glycol.
The reaction products obtained from adipic acid and the alcohols are polyesters having hydroxyl end groups. The molecular weights thereof range from 800 to 3,50~, The adipate-carbonate mixed esters are prepared f.rom these polyesters by a reaction with difunctional carbonic acid ary:~ esters. These correspond in partlcular to the following general formula: .
: 30 . . -.
: ArO-C _ ~ (O-X'-O-ICl) - ;OAr ~: _ O k ~ ~:
' :
.: :

:

~s~ 36-wherein Ar represents a substituted or unsubstituted aryl group having from 6 to 18 carbon atoms, preferably 6 carbon atoms; and k and X' are as deflned above.
Further details concerning preferred embodiments of the indicated adipate-carbonate mixed esters and concerning suitable techniques .or the preparation thereof are contained in the indicated Lindner et al. patent. .;:
When the above-described elastomeric polymer ingredients are employed within the subject polymer blends hereof, they are typically utilized in an amount ranging from l to 80 (preferably from 3 to 70 and most preferably from lO to 65) parts by weight per lQ0 parts of the combined weight of the stated polymer ingredients. In certain preferred embodiments, said elastomeric ingredient is employed in amounts ranging : .
from 3 to 40 (especially from 5 to 30 and most preferably from lO to 25) parts by weight per lO0 parts by weight of the total polymer ingredients.
In some instances, it is preferr~d that the elastomerlc ingredient be employed at relatively lower : .
levels such as, for example, in amounts of from 3 to 25 (especially from 5 or lO to 20 or 25) parts by weight on :
30 a lOO parts total Dolymer weight basis. .. -, In other cases, as for example when a more elastomeric character is desired in the subject blend :-:
composition, it is Dreferred that the indicated ~ . -elastomeric ingredient be employed in amoun~s ranging .: .

.

from 20 or 25 to 60, 70 or 80 (more preferably from 20 or 25 to 35 or 40) parts by weight per l00 parts total weight of the specified polymer ingredients.
In those instances wherein relatively low levels (for example from 3 to 20 or 25 parts by weight/l00 parts total polymer) of the elastomeric ingredient is to be employed, it has been found to be especially advantageous and preferred to either (a) employ one or more of the above-described ester-containing or ester-based elastomeric materials (especially the ester-based thermoplastic polyuretAane) either alone or in combination with each other as the elastomeric ingredient or (b) to employ, on a total elastomeric ingredient weight basis, at least 30 weight percent (preferably 50 weight percent or more) of such an ester-based or ester-containing elastomer in combination with up to 70 weight percent (preferably 50 : .
weight percent or less) of an ether-based thermoplastic polyuxethane material.
On the other hand, in those cases where a relatively larger amount(such as t for example, and on a l00 parts by weight total polymer basis, from 20 or 25 to 40 or 70 parts by weight) of the elastomeric rnaterial is to be employed, it has been round that elastomeric ~:
materials which are somewhat less effective and/or desirable for use as the sole elastomeric ingredient at low usage levels can in fact be more satisfactorily 3 employed~as the sole elastomeric ingredient at said higher usaye levels.
.
: The polymer blend comDositions hereof are : : conveniently prepared by dry biending ~he individual , polymer ingredients to be emDloyed ln particulate (for ~ ~ .
.

, . ,. , .. , , . . , . .. ... ,, , , . . . . . ... , , . , ., . ; . .

WO91/lt487 PCT/US91/00673 ~ 2L~ -38-example pelletized) form along with the oxirane-containing stabilizer ingredient in ~he quantitative proportions desired in a given instance and therea~ter melt compounding the ?articulate polymer mixture in accordance with known extrusion compounding techniaues.
In connection with the indicated melt compounding operation, it is generally preferred to conduct such operation at a temperature of not exceeding 240C, especially at a melt temperature in the range of from 180 to 230C (more preferably from 180 to 210C).
Various optional additives may also be included in the polymer blend comDositions hereof for different purposes as well known in the art, ncluding bisphenol- - -type, ester-type or hindered phenol-rype additives and anti-oxidants as disclosed, far examule, in U.S. Patent Nos. 3,103,499 and 3,240,753, amine and amidine as disclo~ed, for example, in U.S. Patent Nos. 3,313,767 and 3,314,918, nucleants, W screens and absorbers, metal soaps, glass fibers, glass beads, talc, polymerlc substances other than those critical to this invention such as additives commonly known as mold release agerlts, plasticizers, antistatic agents, etc. which are compatible with the blends and color pigments which are compatible with acetal poIymers. However, the use of the mentioned additives is not considered to be necessary for the operability of present invention.
As has been noted above, the inclusion of the 3 aforementioned oxirane-containing ingredien~s has been found to substantially improve ~he :hermal stability, U.V. light resistance and impac~ st:ength of .he subjec-polymer blends and can thereby serve to enhance the recycling capability of such blends which may of . ':
. . .

.. . ' WO91/114~7 PCT/US91~00673 -39- ~9~

necessity entail additional melt processing (that is more thermal exposure) and/or prolonged U.V. exposure.
In addition to .he foregoing, it has also been found that the i.nclusion of the indicated oxirane-containing ingredients can also serve to offset orminimize the adverse thermal and/or chemical destabilizing effect and/or reduced impact strength that can otherwise be imparted to the subject acetal-containLng polymer blends by virtue of the inclusion therein of various additives such as mold release agents, plasitcizers, antistatic agents, colorants, and the like.
The polymer blend compositions of the present invention have good processability characteristics and are suitable fcr use in a wide variety of injection molding and extrusion applications. Such compositions can be formulated so as to be particularly useful in such applications wherein good thermal/dimensional stability, creep resistance and chemical resistance properties and/or paintability is required. Suitable exemplary end-use applications thus include automotive interior and exterior parts, tool casings, appliance housings and the like.
The present invention is further understood and illustrated by reference to the following examples thereof. The various thermoplastic resin5 and oxirane-containing additives employed within such examples areidentiried and described in Tables A and B respec~iyely.
-.
: ~ "' .: :
~ ~ ~ , '.' . ' W09t/11487 PCT/US91/00673 -40~
~$~ ~c ~-~
Table A
__ ~_ Abbrev. Resin Identification ~_ POM ~E~TAL (TM) M25 Acetal Co~olymer (Hoechst/Celanese) MFR= 2.5g/lO min.
(190C, 2.16 kg) ~_ ABS A butadiene rubber modified styrene acrylonitrile copolymer having a MFR
of 3.3g/lO min. ~230C, 2.8 kg) and containing 16 weight percent acrylo~itrile and 12 weight percent polybutadiene (1.2 micron volurne average particle size) (THE DOW
CHEMICAL COMPANY) _--TPU PELLETHANE (TM) 2355~~OA Polyester-Based Thermoplastic Polyurethan2 Elastomer (THE DOW CHEMICAL COMPANY) PC CA~I3RE (TM) 200-20, Polycarbonate with a MFR of 20 g~lO min. (300C and 1.2 kg~ (THE DOW CHEMICAL COMPANY) _~ :
. ~ .

:., , ' . : .

.

. .
.

W09l/lt487 PCT/US9l/00673 2 ~ =r ~

Table B
_~
Additive Oxirane-Containing Additive Abbrev. Description ESO-l PLASTIPON (TM) 655 Epoxidized Soybean Oil (L'Air Liquide) _ ~ _ ESO-2 EDENOL ~TM) D81 E~oxidized Soybean Oil (Henkel) _ _ ~ .
ESO-3 PLASTIPON (TM) 656 Epoxidized Soybean Oil (~'Air Liquide) _~
ESO-4 P~S~IPON ~TM) 651 Epoxidized Soybean Oil (L'Air Liquide) _~
ELO Epoxidized Linseed Oil from Chempri B.V.
_ Epoxy D.E.R. (TM) 330 BisphenoL A /
Resin-l Epichlorohydrin Epoxy Resin (THE DOW ;
CHEMICAL COMPANY) _ Epoxy D.E.R. (~M) 331 Bisphenol A /
Resin-2 Epichlorohydrin Epoxy Resin (T~E DOW
C~EMICAL COMPANY) _ Epoxy D.E.R. (~M) 732 Polyglycol/
Resin-3 Epichlorohydrin Epoxy Resin (THE DOW
~ .
Example l :
In this example, a 4 component POM/ABS/PC/TPU .
blend was prepared containing the indicated polymer components, respectively, in a 30/23/30/17 weight ratio ~:
and also containing 5 weight percent oE ESO-l.
In preparing the indicated 4 polymer component blends the individual thermoplastic polymer components, in pelletized form, were weighed out and combined in the desired proportions, tumble blended for 15 minutes, melt compounded with the epoxidized soybean oil ingredient using a BUSS Ko-Kneader operated at approximately 220-240~C, 20 kg throughput and pelletized for subsequent ~ :

, . ~
.

. . ,, .:, ;, .. ; ., .; ; ... . . . . .. .. . . . . .. .

, ;: ,;, .. , :: , . . :

W091/1148~ PCT/US91/00673 drying and injection molding (at 180-240C) into appropriate testing specimens.
~ or comparative purposes, the corresponding polymer blend was prepared without the epoxidized soybean oil component (that is, ESO-l) being included.
Both of the resulting polymer blend compositions were injected molded under a variety of time and temperature conditions as set forth in Table I
below.
The degree of discoloration exhibited by the resulting molded samples was determined using a :~
DATACOLOUR DC 3850 photospectrometer using a sample of 15 the same resin composition molded at a temperature of .
180C and a 300 second resldence time as the color standard.
The delta E'g reported in Table I below represents the difference in color (that is, degree of discoloration) as between the 18aC/300 second molded "standard" and the sample molded under the more severe :
molding conditions described in Table I. : :

, - ~

;' '.,, :..
.. . .
:
~ ':
: ' ,, ' ~ , , .' ~ ~ '':,,, WO91~11487 PCT/US91/00673 -43- ~ "

Table I
: _ __ _ . Discoloration ~Ej Residenc~ ---Molding T~mpera~ure---Time ~ ~___~ _ _ T=225C ~=Z40C T=255C
. ___ __ ~__ Comparison ~No ESO) 450 Sec 6 12 _ ~:
Example 1 (With 54 ESO-l) 3.5 5.5 _ _ __ __ __ Comparison (No ESO) 820 Sec 9 28.5 >>30 1O Example 1 ~Wi~h 5~ ESO-l~ 7.5 13 16 _~ _ __ __ __ Co~parison (No ESO) 1210 Sec 15 _ _ Example 1 (With 5~ ESO-l) . 11 _ _ . ~ ........................ ... _. . ,_ :

As can be seen from the Table I results, the presence of the epoxidized soybean Qi} provided a substantial reduction in the degree of discoloration which was otherwise exhibited under a given set of molding condltlons.

EX~m~les 2-6 In these examples, a series of 4 component 30/23/30/17 weight ratio POM/ABS/PC/TPU blends were prepared containing from l to 5 weight percent of the different oxirane-containing additives identified in Table II below. For comparative purposes, the same polymer blend was also prepared without including any oxirane-containing additive.

Each of the resultiny blends were then ~injection molded under two different sets of molding conditions, namely at 210C for a medium residence time (that is, 210 seconds) and at 240C for a long residence time (that is, 475 seconds).

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2`~ ?~ 44-The color difference or discoloration encountered under the more severe molding conditions ~that is, relative to that of the samples molded at 210C and a medium residence time) is set forth in Table II below.
~. .
Table II
............ ,, ... __ Example Number Additive Additive Disc~loration (Weight Pe~cent~ (~E) ___ _ lO Control None _ 1~.6 __ .__ _ ,.
2 ESO-2 5.0 4.1 _ ~
3 ELO S.O l0.4 .
____ , ~.
4 Epoxy }.0 2.5 .
_ Resin 1 _________________ Epoxy 2.0 2.~ .
Resin 2 .
_ _ _ ___ 6 Epoxy 2.0 3.6 _ Resin ~
__ . , _ . . ' A~ can be seen from the Table II results 9 the .
various oxirane-containing additive~ tested provided :
sub~tantial thermal stability benefits within the ~ubject polymer blend compositions. . .
Exam~les 7-~0 In thi series of example~, the procedure o~ .. .
Examples 2-6 was repeated except that a 3 component 33/52/15 weight ratio POM/A8SiTPU polymer blend wa~
employed in place of the 4 component blend of Exam~les 2-6. .
The thermal stability evaluation results for : the~e ~lend3 are ~et ~orth in Table III below along with that of a control composition containlng no oxirane- : .
containing stabilizer ingredient.
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Wo91/11487 PCT/US91/00673 -~5-2~
Table III
_ .
Additiv~
Example Number Additive Concentrati2n Discoloration (Weight Percent) (~E) _ _. ____ Control None _ 15.7 _ __ __ __ ____ _ _________________ _ _____________ 7 ESO-2 5.0 7.6 8 ELO 5.0 15.5 ___ ~ ~
9 Epoxy-l 1.0 6.9 ..
__ .___.
10 Epoxy-2 2.0 5.0 1 0 . _ ' ~ . ' Exam~le~ 14 In the~e examples, several different 2 component ABS/POM and 3 component ABS/POM/TPU polymer blend compositions were prepared containing 3 weight percent of ESO-2 and were subjected to accelerated U.V.
stability testing in a Heraeu~ S-150 xenon-arc apparatus with intermittent expo~ure for 24 hours at 30-40 percent relative humidity and 95C.
Comparative oompo~itions were prepared and tested in each instance which did not contain the requisite ox1rane containing additive.
Delta E discoloration valueq for the various samples (that i~, on the basis of be~ore and after accelerated U.V. exposure photospectrometer readings) are set forth in Table IV below.
Also set ~orth in Table IV are the U.V.
stability reqults for a comparative 2 component POM/TPU
blend composi~ion both with (C-16) and without (C-15) 3 weight percent of ESO-3 having been added thereto.
As can be seen from the Table I'~i results. the 2 and 3 component ABS/POM and ABS/POM~TPU composition~
contalning the ESO-2 additive exhibit less discoloration ' .

~, :' ' .
,:' 6i~ 46-upon accelerated U.V. exposure than do the corresponding ESO-2-free comparative compo~itions.
As can also be seen, the U.V. stab:ility of the 2 component POM/TPU comparative composition is actually worsened when the epoxidized soybean oil ingredient ESC-5 3 i~ incorporated therein. ::

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~ , In this experiment the 2 component ABS/POM
compositions of Example 11 and comparative experiment C
11 above were molded into test specimens and were subjected to room temperature (that is, 23C) Notched :
Izod Impact Strength Testing pursuant to ISO 180.
The C-11 compo~ition had a room temperature Notched Izod i~pact strength of 15 kJ/m2 wherea~ the ESO-2-containing Example 11 compositlon had a corresponding value of 20 kJ/m2.
Examples 16-26 In these examples a series of 3 component 33/52/15 weight ratio POM/ABS/TPU co~positions were prepared containing dif~erent amounts of the variouq oxirane-containing ingredients identified in Table V
below. The resulting compositions were subjected to .
room temperature Notched Izod and Notched Charpy Impact Strength Testing (pursuant to testing method~ ISO 180 and ISO 179, respectively) along with a comparative control composition in which no oxirane-containing ingredient was included~
As can be seen from the results in Table V, the :~
compositions o~ the present invention (that is, containing the oxirane ingredient) have notably enhanced Charpy and/or Izod impact strength values relative to -30 those of the comparative control composition. :

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WO91/11487 PCT/US9t/00673 -49- 2~

Table V
_Addltive _ Notched Example Type Conten t kJ/ 2 Charpy Percent)( m ) (kJ/m2) _ __ ~
Control None 19 21 _ __ __ __ ~_ 16 Epoxy Resin 1 1 38 25 _ ~ __ ._ _ 17 Epoxy Resin 1 Z 29 24 _ ____ _. _ 18 Epoxy Resin 2 1 45 34 10 _ ~ _. _ 19 Ep~xy Resin 2 2 38 30 _ __ __ __ 20 Epoxy Resin 3 1 51 37 ~ __ __ _ 21 Ep~xy Resin 3 _ 49 37 c _ __ __ __ I J 23 ESO-l 5 ~ B 1 .
_ __ __ ___ __ ~ ._ _.

_ __ __ __ _ ~ :
1. N.8.-Sample did not break under the test c~nditions employed. :
Examples 27-40 :

In the~e examples, a ~erieq of 4 component ~ .:
30/23/30/15 weight ratio POM/ABS/PC/TPU polymer blend :~
compositions containing different amountq of various oxirane-containing additives were prepared and sub~ected to room temperature Izod and Charpy impact qSrength testing pursuanS to Examples 16-26 above. Also te~ted was a control compo ition having the typeq and .~.
:~ proportions of the 4 polymer ingredient~ but not having any oxirane-containing additive lncorporated therein.
The result~ for this series Qf examples are set forth in Table VI below and illustrate that ... .
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substantially improved Charpy impact strength can be obtained within the 4 component composition in question with several of the type~ and levels o~ the oxirane-containing additives that were tested.
Table VI
5 ~ . _ . Addi ei ve. _ _ ~No tched I zod Notched Example A~ount at 23C Charoy Type (Wt.(kJ~m2) (kJ/m2) percent) .
~_ ~ __ __ :
10 Control ~one ~ B.1 19 ._ _ ___ __ __ 27 EpoxyResinl 0.5 ~.B. 41 _ _ __ __ __ 28 Epoxy Resin 1 1 ?~.B. 34 ~_ ___ __ 29 Epoxy Resin 1 2 ~.B. 34 ~ __ __ __ l5 30 Epoxy Re~in 2 2 ~.B. 33 , .. ~ ~ . __ _. __ 31 EpDxyResin3 2 ~.B. 35 . ,. ___ __ _. . . .
32 ESO 2 2 ~J.B. 19 _ _ ~__ __ _. . . .
33 ESO-2 5 N.B. 21 __. _ __ , . ..
34 ESO-l 5 ~.B. 22 . . :
____________ _ ____________ _____________ ____________ 35 ESO-3 5 . ~.B. 23 :
_ _ __ __ ~ ._ . . .
36 ESO-4 5 ~T.B. 20 _ _ _ _~ ~
37 ELO 0. 5 ~.B. 31 _ ~ __ 38 ELC) 2 ~.B. 29 _ _ __ _.
39 . ELO 3 ~.B. 29 ____ _ _-_ , :.
40 ELO 5 .~.B. 27 .
~ ___ ....~_ _~ .
l. N.S. - Sample did not b~eak under the test ~onditions employ~d.
While the present invention has been de~cribed ~.
: and illustrated with re~erence to particular embodiments :
~ and example~ thereo~, such iq not be lnterpreted as in :~ any way limiting the scope of the instantly claimed invent i on O ~ ~

Claims (15)

1. A polymer blend composition which contains:
(A) a monovinylidene aromatic copolymer which is either (1) a non-rubber-modified monovinylidene aromatic copolymer containing, in polymerized form and on an aromatic copolymer weight basis, from 55 to 99 weight percent of one or more monovinylidene aromatic monomers and from 1 to 45 weight percent of one or more relatively polar comonomers; or (2) a rubber-modified monovinylidene aromatic copolymer containing, on a rubber-modified copolymer weight basis, from 30 to 99 weight percent of a monovinylidene aromatic copolymer as described in item (A) (1) above and from 1 to 70 weight percent of dispersed particles of a rubbery polymer having a glass transition temperature of 0°C
or lower; and (B) one or more acetal homopolymer or copolymers; said composition being characterized in that it contains on a total polymer blend composition weight basis, from 0.01 to 15 weight percent of an oxirane-containing stabilizer ingredient.

2. The polymer blend composition of Claim 1 further characterized in that the monovinylidene aromatic copolymer is a rubber-modified monovinylidene aromatic copolymer containing, on a rubber-modified copolymer weight basis, from 2 to 35 weight percent of dispersed particles of a rubbery polymer which is a homopolymer of a 1,3-conjugated alkadiene monomer or is a copolymer of from 60 to 99 weight percent of a 1,3-conjugated alkadiene monomer with from 1 to 40 weight percent of a monoethylenically unsaturated monomer.

3. The polymer blend composition of Claim 2 which is further characterized in that the rubber modified monovinylidene aromatic copolymer ingredient is one which is prepared by mass or mass/suspension graft polymerization techniques.

4. The polymer blend composition of Claim 3 which is further characterized in that said composition also contains one or more elastomeric thermoplastic polyurethane or copolyester elastomer ingredients.

5. The polymer blend composition of Claim 4 which is further characterized in that said composition also contains one or more non-elastomeric thermoplastic polycarbonate or polyester resin ingredients.

6. The polymer blend composition of Claim 1 which is further characterized in that the relatively polar comonomer of the monovinylidene aromatic copolymer is an ethylenically unsaturated nitrile, an ethylenically unsaturated anhydride, an ethylenically unsaturated amide, an ester of an ethylenically unsaturated carboxylic acid or an ethylenically unsaturated dicarboxylic acid imide.

7. The polymer blend composition of Claim 6 further characterized in that the monovinylidene aromatic copolymer is rubber-modified and in that the rubbery polymer of said rubber-modified monovinylidene aromatic copolymer is a homopolymer of a 1,3-conjugated alkadiene monomer; a copolymer of from 60 to 99 weight percent of a 1,3-conjugated alkadiene monomer with from 1 to 40 weight percent of a mono-ethylenically unsaturated monomer; an ethylene/propylene copolymer rubber; or a rubbery ethylene/propylene/non-conjugated diene copolymer.

8. The polymer blend composition of Claim 4 characterized in that the elastomeric thermoplastic polyurethane or copolyester elastomer ingredient contains one or more ester-containing elastomeric materials employed either alone or in combination with each other or in combination with up to 70 weight percent, on a total elastomeric material weight basis, of an ether-based thermoplastic polyurethane ingredient.

9. The polymer composition of Claim 2 characterized in that said composition contains, on a total composition weight basis, from 5 to 90 weight percent of the monovinylidene aromatic copolymer and 5 to 90 weight percent of the acetal homopolymer or copolymer ingredient.

10. The polymer blend composition of Claim 4 characterized in that said composition contains from 1 to 80 weight percent of the elastomeric copolyester or thermoplastic polyurethane ingredient on a total composition weight basis.

11. The polymer blend composition of Claim 5 characterized in that said composition contains from 5 to 90 weight percent of the non-elastomeric thermoplastic polycarbonate or polyester resin ingredient on a total composition weight basis.

12. The polymer blend composition of Claim 1 characterized in that said composition contains from 0.1 to 10 weight percent of the oxirane-containing stabilizer ingredient on a total composition weight basis.

13. The polymer blend composition of Claim 1 characterized in that said composition contains from 0.2 to 5 weight percent of the oxirane-containing stabilizer ingredient on a total composition weight basis.

14. The polymer blend composition of Claim 1 characterized in that the oxirane-containing stabilizer ingredient is an epoxidized unsaturated triglyceride or an epoxy resin derived from the reaction of epichlorohydrin with an aromatic or aliphatic polyol.

15. A method for preparing a polymer blend composition, said method being characterized in that it involves the steps of dry blending the following polymer ingredients together in particulate form and melt compounding the resulting mixture with from 0.01 to 15 weight percent on a total composition weight basis of an oxirane-containing stabilizer ingredient at a temperature of 240°C or less, said polymer ingredients being composed of:

(A) a monovinylidene aromatic copolymer which is either (1) a non-rubber-modified monovinylidene aromatic copolymer containing, in polymerized form and on an aromatic copolymer weight basis, from 55 to 99 weight percent of one or more monovinylidene aromatic monomers and from 1 to 45 weight percent of one or more relatively polar comonomers; or (2) a rubber-modified monovinylidene aromatic copolymer comprising, on a rubber-modified copolymer weight basis from 30 to 99 weight percent of a monovinylidene aromatic copolymer as described in item (A) (1) above and from 1 to 70 weight percent of dispersed particles of a rubbery polymer having a glass transition temperature of 0°C
or lower; and (B) one or more acetal homopolymer or copolymers.