CA1178388A - Polyphenylene ether resin composition having improved heat stability - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The invention relates to a polyphenylene ether com-position having improved heat stability. The composition com-prises a polyphenylene ether resin matrix and, dispersed therein a phosphonous acid or its ester of the formula

Description

1.7~38~3 This invention relates to a polyphenylene ether resin composition having improved heat stability, Polyphenylene ethers are known resins which are disclosed, for example~ in U. S. Patents Nos, 3306874, 3306875, ~257357, 3257358 and 4011200 and Japanese Laid-Open Patent Publication No. 126800/1975, Since poly-phenylene ethers having a molecular weight above a certain limit have a high softening point, they are useful in applications which require heat stability. In formulat-ing a polyphenylene ether into resin compositions, however,its high so~tenin~ point makes it necessary to use higher kneading and extruding temperatures than in ~he case of other versatile resins~ and high temperatures are also required in molding the resin compositions. Moreover, molded articles of the polypheny]ene ether resin composi-tions are frequently used at relatively high temperatures over long periods of time in contrast to those from versatile resins~
Because polyphenylene ethers are relatively unstable to heat as is well known, they undergo degrada-tion during extrusion and molding at high temperatures, and result in polyphenylene ether resin compositions and molded articles having degraded properties and/or dis-coloration. These deleterious effects limit widespread utili7ation of polyphenylene ether resin compositions, and it has been desired to remedy these defects, particu-larly to improve their heat stability at high temperatures.
Various methods have alr~ady been proposed for the stabilization of resin compositions containing - :.

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- 2 -polyphenylene ethersO These methods are classified lnto a group involvlng capping the hydroxyl grcups present at the terminals of the polyphenylene ether molecule by acylation, etcO 9 and a group comprising adding various stabilizers to polyphenylene ethers.
Known stab~lizers used in the latter group include, for example, benzoates (U. S. Patent No. 37~79~875), hexa-alkylphosphoric triamides or combinations thereo~
with other compounds ~U. S. Patents Nos. 3414536, 3420792, 3429850, 3465062, 3472814, 3483271, 3792121 and 3816562), octa-alkylpyrophosphoramides or combinations thereof with other compounds ~U. ~. Patent No. 3,450,670), amines (U. S. Patents Nos, 3,563,934 and 3,956,423), pho~phites or hydrazines (U. ~. Patent Mo. 3,639,334), alkanolamines (U. S. Patent No. 3,761,541), arylphosphonic amides (U. S. Patent No. 3,792,120), sterically hindered phenols having a triazine or isocyanuric ring (U. S, Patent No.
4,154,719), sub~tituted dicarboxylic acid dihydrazides (U. S. Patent No, 3,954,904), high-molecular-weight phosphites or combinations thereof with other compounds (U. S. Patent No. 3,952,072), amides (Japanese Patent Public~tion No. 29748/1969), metal dithiocarbamates (Japanese Patent Publications Nos. 19395/1970 ~nd 8352/1970)~ carboxylic acid anhydrides (Japanese Patent Publ~cation No. 29,750ll969), phosphites (Japanese Patent Publication NOr 29,751/1969), sterically hindered phenols or combinations thereof with other compounds (Japanese Patent Publications Mos. 43473/1971, 42029/1971, 42030~1971, 42031/1971, 42032/1971 and 4Z033/1971), - l 1783~

sterically hindered phenols having one amide linkage in the molecule (Japanese Patent Publication Mo, 24782/1971), sterically hindered phenols having one ester linkage in the molecule (Japanese Patent Publication No, 38623/1973), high-molecular-weight phosphites (Japanese Laid-Open Patent Publications Nos. 23846/1974, 31755/1974 and 40476/1975), and combinations o~ phosphorous acid amides and boron compounds (Japanese Laid-Open Patent Publication No. 129750/1974).
None of these numerous stabilizers previously proposed have been conductive to the provision of polypheny-lene ether resin compositions having fully satisfactory heat stability, particularly at high temperatures> in practical applications~
It is an object of this inven-tion therefore to improve the heat stability of a polyphenylene ether resin composition~
Another object of this invention is to provide a polyp~enylene ether resin composition having excellent heat stability at high temperatures.
Still another obJect of this invention is to provide a polyphenylene ether resin composition showing inhibited degradation against a long heat history at high temperatures, which can withstand high temperatures during kneading, extrusion and molding and give molded articles having excellent heat stability in long~term use at high temperatures.
Other objects and advantages of this invention will become apparent from the following description.

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I ~ 783 In accordance with this invention, the objects and advantages of this invention are achieved by a poly-phenylene ether resin composition having improved heat stability9 said composition comprising a polyphenylene ether resin matrix and dispersed therein, a phosphonous acid or its ester represented by the following ~ormula (I) ~ OR2 Rl - P \ (I) ~herein Rl represents an alkyl group, an aryl group which may be substituted by an alkyl group, or an aralkyl group which may be substituted by an alkyl group, R2 and R3 are identical or different and each represents a hydrogen atom, an alkyl group, an aryl group which may be substituted by an alkyl group, or an aralkyl group which may be substi-tuted by an alkyl group.
According to this invention, there is preferably provided a polyphenylene ether resin composition having improved heat stability~ comprising a polyphenylene ether resin matrix and dispersed therein, both the aforesaid phosphonous acid or its ester and a sterically hindered phenol.
According to an espeoially preferred aspect of this invention, there is provided a polyphenylene ether resin composition having improved heat stability, compris-ing a polyphenylene ether resin matrix and dispersed therein, an organic monophosphite or an organic polyphosphite as well as the aforesaid phosphonous acid or its ester and -` I 17~8~

~he aforesaid sterically hindered phenol.
The polyphenylene ether resin forming the resin matrix in the composition of this invention can be a polyphenylene ether homopolymer or copolymer obtained by polycondensing at least one mononuclear phenol o~ the formula OM
6 ~ ~ -4 (II) ~ R5 wherein R4, R5 and R69 independently from each other, represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms~ provided that at least one of R4 and R6 is an alkyl group having 1 to 3 carbon atoms, or a grafted polyphenylene ether ob-tained by graft-polymerizing such a polyphenylene ether with a vinyl aromatic compound~
Methods for producing these polyphenylene ethers are w`ell known E~ se.
~xamples of the mononuclear phenols of general formula (II) include 2,6-dimethylphenol, 2,6-diethylphenol, 2,6-dipropylpheno~, 2-methyl-6-ethylphenol, 2-methyl_6-propylphenol, 2-ethyl-6-propylphenol, m-cresol, 2,3-dimethylphenol, 2 9 3-diethylphenol, 2~3-dipropylphenol~
2-methyl-3-ethylphenol, 2-methyl-3-propylphenol~ 2-ethyl-

3-methylphenol, 2-ethyl-3-propylphenol, 2-propyl-3-methylphenol, 2-propyl-3-ethylphenol, 2,3,6-trimethylphenol, 2,3,6-triethylphenol, 2,3,6-tripropylphenol 9 2 9 6-dimethyl-3-ethylphenol, and 2,6-dimethyl-3~propylphenol.

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,'' ' '' l l7s3~a Polyphenylene ethers derived from these mono-nuclear phenols, therefore, include homopol~Jmers such as poly(296-dimethyl-1,4-phenylene)ether, poly(2,6-diethyl-1,4-phenylene)ether, poly(2,6-dipropyl-1,4-phenylene) ether, poly(2-methyl-6-e-thyl-1,4-phenylene)ether, poly(2-methyl-6-propyl-1,4-phenylene)ether, and poly(2-ethyl-6-propyl-1,4-phenylene)ether; and copolymers such as a 2,6-dimethylphenol/2,~,6-trimethylphenol copolymer (which denotes a polyphenylene ether copolymer derived ~rom 2~6-dimethyl phenol and 2,3,6-trimethyl phenol, and in the following description polyphenylene ether copolymers are represented in the same manner), a 2,6-dimethylphenol/
2,3,6-triethylphenol oopolymer, a 2,6-diethylphenol/2,3,6-trimethylphenol copolymer and a 2,6-dipropylphenol/2,3,6-trimethylphenol copolymer.
The grafted polyphenylene ethers used equally to these homopolymers and copolymers in this invention are obtained by grafting vinyl aromatic compounds such as styre~e, alpha-methylstyrene, vinyltoluene and vinylxylene to these homopolymers or copolymers t and include, for example, styrene-grafted poly(2,6-dimethyl-1,4-phenylene) ether, and a styrene-grafted 2,6-dimethylphenol/2~3,6-trimethylphenol copolymer.
Preferably, such grafted polymers have a grafting ratio of about 10 to about 50%, especially about 20~ to about 40%.
Among these polyphenylene e-thers, p~ly(296-dimethyl-1,4-phenylene)ether, a 2,6-dimethylphenol/2,3,6-trimethylphenol copolymer, and grafted polyphenylene ethers l 1 783 obtained by grafttng styrene to such polymers are especially preferred for use in this invention.
The resin matrix in the composition of -this invention may be composed of such a polyphenylene ether 5 alone, or a mixture o~ it with another polymer. m e other polymer may be a thermoplastic resin or an elastomer.
The thermoplastic resin as referred to herein is a resin containing at least 25~ by weight of a recurring structural unit of the following general formula (III) -C-CH2~
I (III) ~ ~Z)P

wherein R7 represents a hydrogen atom or a lower alkyl group, Z represents a halogen a-tom or a lower alkyl group, and p is 0 or a positive integer of 1 to 3,5 in the polymer chain~
The lower alkyl group for R8 and Z is, for example, methyl or ethyl, and examples of the halogen atom for Z are chlorine and bromine.
Examples of such a thermoplastic resin are polystyrene, a rubber-modi~ied polystyrene (a high-impact polystyrene), a styrene/butadiene copolymer, a styrene/butadiene/acrylonitrile copolymer, a styrene/
acrylic rubber/acrylonitrile copolymer, a styrene/alpha-~ethylstyrene copolymer, and a styrene/butadiene block copolymer.
At leas-t one such -thermoplastic resin can be .

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l l783~8 used in combination with the polyphenylene ether.
The thermoplastic resin may be included in the resin matrix in an amount of preferably not more than 95%, especially preferably not more than 80/
The elastomer which may be used in this invention is an elastomer in the ordinary sense Accordingly, the elastomer in this invention, for example, includes polymers having a Young's modulus at ordinary temperature of 105 to 109 dynes/cm2 (0.1 to.1020 kg/cm2), the Young's modulus being defined at pages 71 to 78 of A. V. Tobolsky, "Properties and Structurss of Polymers" (John Wiley ~ Sons, Inc., 1960).
Examples of such an elastomer include poly-butadiene, polyisoprene, a nitrile rubber, an ethylene/
propylene copolymer, an ethylene/propylene/diene copolymer (~.P~M), polypentenamer, Thiokol rubbers, polysulfide rubbers, an acrylic rubber, a polyurethane rubber, a grafted product formed between a butyl rubber and poly-ethylène, polyester elastomers, and block copolymers, such as A-B-A' type block copolymers and A-B'-A' type block copolymers o~ diene compounds and vinyl aromatic compounds, In the above A-B-A' type block copolymers and A-B'-A' type block copolymers, the terminal blocks A and A' are polymer chain blocks o~ the vinyl aromatic compounds.
The central block B in the A-B-A' type block copolymers is a polymer chain block of a conjugated diene, and the central block B' in the A-B'-A' type block copolymers is a block resulting ~rom the hydrogenation of a polymer ~ 178388 _ g _ chain block of a conjugated diene.
In the above description, the diene, diene com-pound and conjugated diene are used in the same sense, and may, for example, specifically represent 1,3-butadiene, 2,3-dimethylbutadiene~ isoprene, 1,3-pentadiene or a mixture of these. The vinyl aromatic compound may, for example, denote styrene, alpha-methylstyrene, vinyltoluene 9 vinylxylene~ ethylvinylxylene, vinylnaphthalene, or mixtures thereof.
Preferably, the aforesaid A-B-At type block copolymers or A~B'-A' type block copolymers are used as ~le elastomer in this invention. The terminal blocks A
and A' of these block copolymers preferably have a number average molecular weight of about 2~000 to about 100,000, and the central blocks B and B' pre~erably have a number average molecular weight oP about 25,000 to about 1,000 9 000.
The elastomer may be included in the resin composition of this invention in an amount oP preferably not more than 2~o by weight, especially preferably not more than lOyo by weight, based on -the resin matrix.
In the polyphenylene ether resin composition of this invention, the polyphenylene ether may be incl~de~
in an amount of at least 5% by weight, preferably at least 15% by weight, based on the resin matrix.
` In the polyphenylene ether type resin composition oP this invention, the polyphenylene ether resin matrix composed of the polyphenylene ether alone or a mixture oP
it with the other polymer contains, dispersed therein, a phosphonous acid or its ester represen-ted by the following , , .

-- l 1783~8 formula (I) p--OR2 (I) wherein Rl represents an alkyl group, an aryl group which may be substituted by an alkyl group, or an aralkyl group which may be substituted by an alkyl group, R2 and R3 are identical or different and each represents a hydrogen atom, an alkyl group~ an aryl group which may be substituted by an alkyl group, or an aralkyl group which may be substituted by an alkyl group, w~ich serves to improve the heat stability of the poly-phenylene ether.
In the definitions of ~ormula (I), the alkyl group is preferably an alkyl group having 1 to lO carbon atoms such as methyl, ethyl, propyl, butyl, pentyl,hexyl, amyl, octyl9 and decyl. ~xamples of the aryl or aralkyl group which may be substituted by an alkyl group are phenyl, naphthyl, diphenyl, benzylphenyl, ben~yl, tri-phenylmethyl, methylphenyl, dimethylphenyl9 trimethyl-phenyl and ethylphenyl.
The phosphonous acids(monophosphonous acid) corresponding to ~eneral formula (I) in which R2 and R3 are hydrogen atoms include ~or example, the compounds described at page 5 of Gennady M. Kosolapoff, "Organo-phosphorus Compounds" (John Wiley & Sons, Inc., 1950).
Specific examples of the phosphonous acids are ethyl~
phosphonous acid9 propylphosphonous acid, isopropyl-phosphonous acid, isobutylphosphonous acid~ isoamylphosphonous 3 ~ 8 -- 11 ~
acid, n-octylpllosphonous acid, benzylphosphonous acid, triphenylmethylphosphonous acid~ phenylphosphonous acid, 3-methylphenylphosphonous acid 9 2-methylphenylphosphonous acid, 4-methylphenylphosphonous acid, 4-ethylphenyl-phosphonous acid, 2,4-dimethylphenylphosphonous acid7 2,5-dimethylphenylphosphonous acid, 2,4,5-trimethylphenyl-phosphonous acid, 2,4,6-trimethylphenylphosphonous acid, l-naphthylphosphonous acid, 2-naphthylphosphonous acid,

4-diphenylphosphonous acid, and 4-benzylphenylphosphonous acid.
Monophosphonous acid esters corresponding to general formula (I) in which R2 and/or R3 are o-ther than hydrogen in the above definition can be produced by reacting the aforesaid phosphonous acids with corresponding alcohols or aromatic hydroxy compounds. Examples of these esters include methyl triphenylmethylphosphonite;
dimethyl, diethyl, diisopropyl, dipropyl and diisobutyl phenylphosphonites; diethyl 4-methylphenylphosphonite;
and diethyl and diphenyl 2,4,5-trimethylphenylphosphonites.
The phosphonous acid or its ester represented by general formula ~I) may be included in an amount of about 0.01 to about 10 parts by weight, preferably about 0.05 to about 5 parts by weight, especially preferably about 0.1 to about 3 parts by weight, per 100 parts by weight of the resin matrix.
Even when these compounds are used in amounts exceeding the above upper limits, the heat stability of the resulting resin composition is not corresponding improved. Rather, it is frequently deleterious on the I ~ 78388 properties of the resin composition, resulting in lowered heat distortion temperatures, for example~ If the amount of the stabilizer compound is below the specified limit, the heat stability of the resin composition is not improved to the expected exten-t.
The resin composition of this invention shows better heat stability by dlspersing both the above phospho-nous acid or its ester and at least one sterically hindered phenol in the matrix resin. It is believed that the lQ better heat stability is due to the synergistic action of the two kinds of stabilizer compounds.
Examples of sterically hindered phenols which can be effectively used in this invention include monohydric phenols such as 2,6-di-tert -butyl-p-cresol, 2-tert.-butyl-4-methoxyphenyl, 2,4-dinonylphenyl, octadecyl-3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate, diethyl 3,5-di-tert -butyl-4-hydroxybenzylphosphonate, and 2-(3',5'-di-tert -butyl-4'-hydroxyanilino)-4,6-dioctylthio-1,3,5-triazine; dihydric phenols such as 2,2'~methylenebis(4-methyl-6-tert.-butylphenol),2~2'-methylenebis(4-ethyl-6-tert.-butylphenol), butylidenebis(methyl-butylphenol), 4,4'-thiobis(6-tert.-butyl-3-methylphenol), lpl-bis(4-hydroxyphenyl)cyc~ohexane, 1,6-hexanediol-bis-3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate, 2,2'-thiodiethyl-bis~3-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionate) and N,N'-hexamethylenebis(3,5 di~tert -butyl-4-hydroxy-hydrocim1amide)~ -trihydric phenols such as 1,3,5-tris(4~tert.~butyl-3-hydroxy-2,6-dimethylbenzyl)-isocyanuric acid, 2,4,6-tris~3',5'-di-tert.-butyl-4'-` ;

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~ 1 78~8 hydroxybenzyl)-1,3 9 5-triazine, a triester of 3,5-di-tert.-butyl-4-hydroxyhydrocinnamic acid with 1,~,5-tris(2-hydroxyethyl-S-triazine-2~4,6-(lH, 3H, 5H)-trione) and 1~1,3-tris(2'-methyl-4'-hydroxy-5'-tert.-butyl)-phenyl) butane; and tetrahydric phenols such as pentaerythrityl-tetrakis(3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate).
The sterically hindered phenol may be included in the resin composition of this invention in an amount of about 0.05 to about 10 parts by weight, preferably about 0.1 to about 5 parts by weight, especially pre~erably about 0~5 to about 3 parts by weight, per 100 parts by weight of the matrix resin.
The resin composition of this invention shows much better heat stability by dispersing an organic mono-phosphite or organic polyphosphite as well as the phospho-nous acid or its ester and the sterically hindered phenol in the resin matri~.
~ xamples of effective organic phosphites for use in this invention include organic monophosphites such as triphenyl phosphite, tricresyl phosphite, triisooctyl phosphite, tridecyl phosphite, tri-2-ethylhexyl phosphite~
trioctadecyl phosphite, tri(octylphenyl)phosphite~ tri(nonyl-phenyl) phosphite, tridodecylthio phosphite, phenyldiethyl phosphite, phenyl-di(2-ethylhexyl) phosphite, isooctyl-diphenyl phosphite, diisooctylmonophenyl phosphite anddi(2-ethylhexyl)mono(isooc-tylphenyl) phosphi-te; and organic polyphosphites such as a phosphite resin o~
hydrogenated bisphenol A. Among these organic phosphites, the organic polyphosphites are preferred. An organic ~ 17838 _ 14 ~
monophosphite may be used in combination with an organic polyphosphite.
The organic phosphite may be included into the resin composition of this invention in an amount of about 0.05 to about 10 parts by weight, preferably about 0.1 to about 5 parts by weight9 especially preferably about 0.5 to abou-t 3 parts by weight, per 100 parts by weight of the resin forming the matrix.
The resin composition of this invention may further contain various additives depending upon the intended uses. ~xamples of the additives include lubricants?
such as olefin waxes -typified by polyethylene wax and polypropylene wax9 phosphate-type fire retardants typified by triphenyl phosphate or tricresyl phosphate; bromine-type fire retardants typified by decabromobiphenyl,pentabromotoluene or decabromobiphenyl ether; pigments typified by titanium dioxide or ~inc oxide; inorganic fillers typified by glass fibers, asbestos, wollastonite, mica or`talc; and organic fillers -typified by carbon fibers. The amounts of these additives vary depending upon their types 9 but should be within the ranges which do not degrade the heat stability of -the resin compositian O~f this invention.
The resin composi-tion of this invention can be easily produced by melt-mixing methods known with regard to thermoplastic resins. For example, it can be prepared conveniently by a method which comprises mixing the polyphenylene ether or a mixture of it with another polymer such as a thermoplastic resin or elastomer, .
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I ~ 783~f~

with predetermined amounts of the phosphonous acid or its ester J and op-tionally the s-terically hindered phenol and optionally the organic phosphite in a mixer, then kneading th~ mixture fully in a mel-t-extruder~ and pelletizing the rèsulting homogeneous molten mixture.
The following ~xamples and Comparative ~xamples illustrate the resin composition of this invention more specifically. Unless otherwise specified, all parts and percentages in these examples are by weight.
xam~le 1 and Comparative ~xample 1 Sixty (60) parts of a 2,6-dimethylphenol/2,3,6-trimethylphenol copolymer (2,3,6-trimethylphenol 5 mole%) having an intrinsic viscosity, measured at 25C using chloroform as a solvent, of 0.52 dl/g, 37 parts of a high-impact polystyrene (the polystyrene matrix having an intrinsic viscosi-ty, measured at 25C using chloro~orm as a solvent, of 0.89 dl/g; gel content analyzed by using a mixture of methyl ethylketone and acetone as a solvent of 1~.9% b`y weight), 2 parts of a polystyrene/polybutadiene-polystyrene block copolymer (the weight ratio of thepolystyrene blocks to the polybutadiene block7 30:70;
the viscosity of a 20/Q toluene solution of the copolymer, measured at 25C using a Brookfield Model RVT viscometer, 1500 cps), 1 part of an ethylene/propylene copolymer (having a reduced specific viscosity, measured at 135C in a concentration of 0.1 g/100 ml using decalin as a solvent, of 2.0 and a glass transition point of -49C), 5.8 parts of triphenyl phosphate, 7 parts of titanium dioxide, 0.4 part of phenylphosphonous acid ~C6H5P(OH~2) and 0.6 part ~ 17~8 of 2,2~-methylenebis(4--me-thyl-6-tert.-butylphenol3 were fully mixed in a .~lenschel mixer. The resulting mixture ~as pelletized by a t~in-screw extruder (AS-30* a product of l~.~akatani l~ikai Seisakusho) in which the maximum temperature of the cylinder was set at 290C. A test specimen, 1/8 inch thick, for measurement of Izod impact strength was molded from the resulting pellets under an injection pressure of 1050 kg/cm2 using an injection molding mac~ine (SJ-35R*~ a product of Meiki Seisakusho).
~.`'ne test specimen was aged in hot air a-t 115C for 10 days. Its Izod impact strength was measured before and after the aging. The results are tabulated below.
For comparison, the above procedure was repeated except that the phenylphosphonous acid was not used. The Izod impact strength of the test specimen not containing -t~e phosphonous acid was measured and the results are also tabulated below (~omparative ~xample 1)..

Izod impact strength (notched, k~-cm/cm) ~g ~
~xample 1 24.0 17.9 (75,~') Comparative ~xample 1 18,0 11.3 (63/~) In the above and subsequent tables, the paren-thesized figures show the percent retention calculated as follows:

Izod impact strength Retention (~u) = aftdr a~in ~ t h x 100 be~ore aging *Trade Mark B

t8~88 The above table clearly shows that the use of phenylphosphonous acid improved the Izod impact strength of the molded product after the aging.

Th2 pellets produced in Example 1 and Comparative Example 1 were left to stand for 60 minutes in the molten state in the cylinder of an injection molding machine in which the maximum temperature of the cylinder was set at 280C 9 and thereafter in~ection-molded -to prepare test specimens for measurement of Izod impact streng-th~ The results are tabulated below together with the data obtained in Example 1.
Izod impact strength (notched, kg-cm/cm) Method of A~ter 60 minute ~xample 1 standing ~xample 2 24.0 14.2 (59%) Compara-tive Example 2 18.0 6,1 (34%) It is seen from the above -table that the resin composition of this invention shows a high retention of Izod impact strength even after it has been subjected to a heat history a-t high temperature.

The procedure of Example 2 was repea-ted except that 1 part of phenylphosphonous acid was used instead of 0.4 part of phenylphosphonous acid and 0.6 part of 2,2'-methylenebis(4-methyl-6-tert.-butylphenol). The test specimen was examined for Izod impact strength ln the same way as in Example 2.

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For comparison, the result of Comparative ~xample 2 wherein the phenylphosphonous acid Wfl8 not used is tabulated bel~w together with the result of .F,xample 3~
Izod impact strength (notched; k~-cm~cm) Method of A~ter 60 minute ~xample 3 21.8 10.5 (48%) Comparative ~xample 2 18 r 0 6 ~1 ( 34%~
It is seen from the above table that even when phenylphosphonous acid alone is used as a stabilizer, the resin composition o~ this invention shows a high retention of Izod impact strength after it has been subjected to a heat history~

39 Parts of poly(2,6-dimethyl-1,4-phenylene) ether having an intrinsic viscosity, measured at 25C in chloroform, o~ 0.54 dl/g, 59 parts of the same high-impact polystyrene as used in ~xample 1, 2 parts of thesame polystyrene/polybutadiene/polystyrene block copolymer as used in Example 1, 10.5 parts of triphenyl phosphate, 7 parts of titanium dioxide, 0.4 part of diethyl phenyl-phosphonite and 0.6 part of 2,6-di-tert,-butyl-p-cresol were fully mixed in a Henschel mixer. The mixture was pelletized by a twin-screw extruder (AS-30, used in ~xample 1) in which the maximum temperature of the cylinders was set at 290C. The pellets were injection-molded under an injection pressure of 1050 kg/cm2 using an in~ection ~ , '' ' ~

I ~ 783~8 molding machine (SJ-35B, used in Example l) to prepare a test specimens~ l/8 inch thick, for measuremen-t of Izod impact strength~ The resulting test specimen was aged in hot air at 85C for 20 hours, and its Izod impact strength was measured be~ore and after the aging. The results are tabulated below.
For comparison~ the above procedure was repeated except that the diethyl p~enylphosphononite and 2,6-di-tert.-butyl-p-cresol were not used. The results are also tabulated below (Comparative ~xample ~).
Izod impact strength ~ ~E~
Example 4 12.1 10.5 (87%) Comparative ~xample 3 ' 10.2 7.6 (75~/D) xample 5 and Comparative ~xam~l,e 4 85 Parts of the same 2,6-dimethylphenol/2,3,6-trimethylphenol copolymer as used in ~xample l, 15 parts of the same high-impact polystyrene as used in ~xample l,

5 parts of titanium dioxide, 0.4 part of phenylphosphonous acid and 1.6 parts of pentaerythrityl-tetrakis(3-(3,5-di-tert,-butyl-4-hydroxyphenyl)propionate) were fully mixed in a Henschel mixer. The resulting mixture was pelletized by a twin-screw extruder (AS-30, used in ~xample l) in which the maximum temperature of the cylinders was set at 300C. The pellets were injection-molded under an injection pressure of 1320 kg/cm2 by an injection molding machine (SJ-~5B, used in ~xample 1) in which -the maximum - l ~7838 temperature of the cylinder was set at 320C, to prepare a test specimen, 1j8 inch thick, .~or measuremen-t of Izod impact strength. The tes-t specimen was.aged in hot air at 120C for 100 hours. m e Izod impact strength o~ the specimen was meas.ured before and after the aging, and the results are tabulated below.
For comparison, the abo~e procedure was repeated except that the stabilizer compounds were not added. The results are also shown in the following table (Comparative ~xample 4).
Izod impact strength (notched, kg-cm/cm ~
Before agi~ e~E
~xample 5 9, 0 7 . 5 (83%) Comparative Example 4 8.8 5. 3 (6~/o) ~ .'

Claims (19)

WHAT WE CLAIM IS:

1. A polyphenylene ether resin composition having improved heat stability, said composition comprising a polyphenylene ether resin matrix, and dispersed therein, a phosphonous acid or its ester of the formula wherein R1 represents an alkyl group, an aryl group which may be substituted by an alkyl group, or an aralkyl group which may be substituted by an alkyl group, R2 and R3 are identical or different and each represents a hydrogen atom, an alkyl group, an aryl group which may be substituted by an alkyl group, or an aralkyl group which may be sub-stituted by an alkyl group.

2. The composition of claim 1 which further comprises at least one sterically hindered phenol dispersed in the polyphenylene ether resin matrix.

3. The composition of claim 2 which further comp-rises at least one organic phosphite compound selected from organic monophosphites and organic polyphosphites dispersed in the polyphenylene ether resin matrix.

4. The composition of claim 1 wherein the polyphenylene ether constituting the matrix is a polyphenylene ether homopolymer or copolymer obtained by polycondensing at least one mononuclear phenol of the formula wherein R4, R5 and R6, independently from each other, represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, provided that at least one of R4 and R6 is an alkyl group having 1 to 3 carbon atoms, or a grafted polyphenylene ether obtained by graft-copolymerizing said polyphenylene ether with a vinyl aromatic compound.

5. The composition of claim 4 wherein the vinyl aromatic compound is selected from the group consisting of styrene, alpha-methylstyrene, vinyltoluene and vinyl-xylene.

6. The composition of claim 1 wherein the poly-phenylene ether resin constituting the matrix is poly(2,6-dimethyl-1,4-phenylene)ether, a polyphenylene ether copolymer derived from 2,6-dimethylphenol and 2 3 3,6-trimethylphenol copolymer, or a grafted polyphenylene ether obtained by grafting styrene to any of said poly-phenylene ethers.

7, The composition of claim 1 wherein the polypheny-lene ether resin matrix is a mixture of a polyphenylene ether with another polymer.

8. The composition of claim 7 wherein the other polymer is a thermoplastic resin containing at least 25%
by weight of a recurring structural unit of the formula wherein R7 represents a hydrogen atom or a lower alkyl group, Z represents a halogen atom or a lower alkyl group, and p is 0 or a positive integer of 1 to 3, in the polymer chain.

9. The composition of claim 7 wherein the other polymer is an elastomer having a Young's modulus at ordinary temperature of 105 to 109 dynes/cm2.

10. The composition of claim 9 wherein the elastomer is an elastomeric block copolymer of the type A-B-A' wherein A and A' represent a polymer chain block of a vinyl aromatic compound and B represents a polymer chain block of a conjugated diene, or the type A-B'-A' wherein A and At are as defined above, and B' represents a hydrogenated polymer chain block of a conjugated diene,

11. The composition of claim 10 wherein the vinyl aromatic compound is selected from the group consisting of styrene, alpha-methylstyrene, vinyltoluene, vinylxylene, ethylvinylxylene, vinylnaphthalene and mixtures thereof.

12. The composition of claim 10 wherein the conjugated diene is selected from the group consisting of 1,3-butadiene, 2,3-dimethylbutadiene, isoprene, 1,3-pentadiene and mixtures thereof.

13. The composition for claim 7 wherein the amount of the polyphenylene ether is at least 5% by weight of the resin matrix.

14. The composition of claim 1 wherein the alkyl groups for R1, R2, and R3 in the formula contain 1 to 10 carbon atoms.

15. The composition of claim 1 wherein the aryl group for R1, R2 and R3 in the formula is a phenyl, diphenyl or naphthyl group.

16. The composition of claim 1 wherein the aralkyl group for R1, R2 and R3 in the formula is a benzyl or triphenylmethyl group.

17. The composition of claim 1 wherein the amount of the phosphonous acid or its ester is 0.01 to 10 parts by weight per 100 parts by weight of the polyphenylene ether resin matrix.

18. The composition of claim 2 wherein the amount of the sterically hindered phenol is 0.05 to 10 parts by weight per 100 parts by weight of the polyphenylene ether resin matrix.

19. The composition of claim 3 wherein the amount of the organic monophosphite and/or organic polyphosphite is 0.05 to 10 parts by weight per 100 parts by weight of the polyphenylene ether resin matrix.