STABILIZED NITRILE POLYMER

Abstract: Crossinked nitrile polymers are stabilized against exces­ sive crosslinking and degradation when subjected to high temperature processing by incorporation into the polymer of a stabilizer system comprising at least one phenolic com­ pound and at least one antimony containing compound.

Description: Stabilized Nitrile Polymer FIELD OF THE INVENTION This invention is directed to rubbery nitrile polymers containing improved stabilization systems making the nitrile polymers especially suitable for blending with polyvinyl chloride and/dr acrylonitrile-butadiene-styrene polymers. PRIOR ART Due to the presence of unsaturation in nit rile polymers, that is copolymers of butadiene and acrylonitrile and optionally also containing crosslinking monomers such as divinylbenzene, it is well known in the art that these polymers must be stabilized against oxidation and the action of heat by the incorporation therein of suitable antioxidants or stabilizers. Phenolic compounds, amine-containing compounds and organo-phosphite compounds have been used, alone or in various combinations, in the prior art to provide the necessary stabilization. Certain such combinations have proven to be suitable for general use in nitrile polymers. The crosslinked nitrile polymers, especially those containing divinylbenzene as the crosslinking monomer, are frequently used for blending with thermoplastics such as polyvinyl chloride (PVC) and/or acrylonitrile-butadiene-styrene polymers (ABS), and the high temperatures and mixing conditions encountered in such blending require special stabilization of the nitrile polymer to prevent the occurrence of crosslinking and/or excessive degradation of the nitrile polymer during the blending operation. U.S. Patent 3,661,825, incorporated herein by reference thereto, teaches the stabilization of divinylbenzene containing nitrile polymers by the incorporation of a stabilizer system comprising at least one phenolic compound, at least one epoxy stabilizer for PVC, at least one other stabilizer for PVC and preferably at least one organo-phosphite compound. This patent teaches that such divinylbenzene containing nit rile polymers which contain the defined stabilizer system are protected against oxidation degradation and crosslinking reactions. SUMMARY OF THE INVENTION According to the present invention, there is provided a crosslinked rubbery nitrile polymer containing a stabilizer system comprising at least one phenolic compound and at least one antimony containing compound. In a preferred embodiment of the invention, there is provided a crosslinked rubbery nitrile polymer containing a stabilizer system comprising at least one phenolic compound, at least one antimony containing compound and at least one organo-phosphite compound. In a further preferred embodiment of the invention, there is provided a cross linked rubbery nitrile polymer containing a stabilizer system comprising at least one phenolic compound, at least one antimony containing compound, at least one organo-phosphite compound and a di(C11-C17 alkyl group containing carboxyl group)-thio-dipropionate. DETAILED DESCRIPTION AUB PREFERRED EMBODIMENTS The crosslinked rubbery nitrile polymers of this invention are well known in the art. They are prepared by the aqueous emulsion free radical polymerization of butadiene, acrylonitrile and divinylbenzene and contain from about 45 to about 79.5 weight per cent of butadiene, from about 20 to about 50 weight per cent of acrylonitrile and from about 0.5 to about 5 weight per cent of divinylbenzene. A preferred crosslinked nitrile polymer contains from about 55 to about 79.5 weight per cent of butadiene, from about 20 to about 40 weight per cent of acrylonitrile and from about 0.5 to about 5 weight per cent of divinylbenzene and a most preferred crosslinked nitrile polymer contains from about 62.5 to about 72.5 weight per cent of butadiene, from about 27 to about 35 weight per cent of acrylonitrile and from about 0.5 to about 2.5 weight per cent of divinylbenzene. The preparation of such polymers may be as described in the article Nitrile Rubber by W. Hofmann in Rubber Chemistry and Technology, 1964, Vol. 37, pages 1-262, especially at pages 88-99. The stabilizer system of the present invention is incorporated into the nitrile polymer during the manufacture thereof, being added to the polymer latex prior to coagulation or being added partially to the polymer latex prior to coagulation and partially to the coagulated polymer during the recovery thereof. The stabilizer system of the present invention comprises at least one phenolic compound and at least one antimony containing compound. Suitable phenolic compounds include the well known hindered phenols, that is phenols having alkyl substituents at the two carbon atoms ortho to the carbon atom having the hydroxy group attached. They also include the alkylated bis-phenols, that is 4,4'-isopropylidene bis phenol, 2,2'-methylene bis (4-methyl phenol) 2,2'-methylene bis(2,4-dimethyl phenol), 2,21-methylene-bis(5-tert.butyl-4-methyl phenol), 4,4'-isopropylidene-bis(2,6-di-tert. butyl phenol), 2,6-ditert.butyl-4-0-hydroxyethyl phenol, tert. butyl catechol, tert. butyl resorcinol and other like compounds known in the art. Suitable phenolic compounds also include the polymeric substituted phenols, such as the butylated reaction product of p-cresol and dicyclopentadiene. Preferred among the phenolic compounds are those having a low volatility and therefore generally having a relatively high molecular weight such as the alkylated bis phenols and the polymeric substituted phenols. Suitable antimony containing compounds for use in the stabilizer system of the present invention include those products consisting primarily of antimony thioglycolates or mixtures of antimony and tin thioglycolates and mixtures of antimony compounds and oroano-tin compounds generally described as antimony tin mercaptides and other commercially available products described as being sulphur-containing antimony compounds and believed to be antimony thioglycolate or mercaptide compounds. In a preferred embodiment of the invention, the stabilizer system also contains an organo-phosphite compound. Suitable such organo-phosphite compounds include tris (nonylphenyl) phosphite, tris (octylphenyl) phosphite and the polymeric phosphite compounds which contain two phosphite groups linked by a short chain polymer, each phosphite group also being attached to two phenyl groups. Also suitable for use are tris(p-hexylphenyl) phosphite, tris(cyclohexylphenyl) phosphite and tris(p-benzylphenyl) phosphite. In a further preferred embodiment of the invention, the stabilizer system also contains a di(C11-C17 alkyl group substituted carboxyl group)-thio-dipropionate. Suitable such compounds include the dilauryl, dimyristyl, dipalmityl and distearyl-thio-dipropionates. The amounts of each component in the stabilizer system are important. Based on 100 parts by weight of the cross linked nitrile polymer, the amount of phenolic cdmpound will be from about 1 to about 2, preferably from about 1 to about 1.5, parts by weight and the amount of antimony compound will be from about 0.3 to about 0.8, preferably from about 0.3 to about 0,6, parts by weight. When an organo-phosphite compound is present, the amount will be from about 0.3 to about 0.8, preferably from about 0.4 to about 0.6, parts by weight per 100 parts by weight of crosslinked nitrile polymer. When a di(Cll-C17 alkyl group containing carboxyl group)-thio-dipropionate is present, the amount will be from about 0.1 to about 0.4, preferably from about 0.15 to about 0.3, parts by weight per 100 parts by weight of crosslinked nitrile polymer. The stability of the crosslinked nitrile polymer containing the present stabilizer system is readily observed when the polymer is subjected to high temperature processing as on a rubber mill or in an internal mixer at temperatures of about 1500C and higher. One method whereby the stability may be readily determined is by mixing the polymer containing stabilizers in a laboratory scale internal mixer at a temperature of 1650C, the mixing being for a time of up to 30 minutes. The torque developed on the shaft connecting the drive motor to the mixing head is measured. When the polymer is initially put into the mixer and the ram closed, there is an initial very high torque which, within about 30 seconds, drops to a stable value which then depends on the mixing time. If the polymer is not adequately stabilized against crosslinking, the torque will increase after one or two minutes of mixing time. For a very poorly stabilized polymer, this increase may continue to be seen for the full 30 minute mixing time. For a polymer having generally adequate stabilization, but inadequate for this type of use, the torque will increase, to a greater or lesser extent from the onset at 1 or 2 minutes for up to 10 minutes and then may decrease as degradation becomes predominant. For a polymer containing the stabilizer system of the present invention, the torque will show, from the 1 or 2 minute mixing time, no or very little increase but rather will tend to decrease at a slow fairly steady rate with mixing time. Such thermal stability as decribed above permits the nitrile polymers containing the stabilizer system of the present invention to be used in blends with PVC and/or ABS, wherein the mixing and processing temperatures are frequently at 150 0C or higher, without further extensive crosslinking of the nitrile polymer occurring. When such further crosslinking of the nitrile polymer does occur, it leads to inhomogeneous blends containing discrete particles of crosslinked nitrile polymer and the blend has inadequate strength properties and an undesirable appearance. The color of crosslinked nitrile polymers incorpo rating the stabilizer system as herein defined is good and the change in color which occurs on exposure to high temperature processing is minimal. The following examples illustrate the invention. All parts are parts by weight per 100 parts by weight of crosslinked nitrile polymer. EXAMPLE 1 The base polymer used was a crosslinked nitrile polymer containing a bound acrylonitrile level of about 34 weight per cent, a bound butadiene level of about 65 to 65.5 weight per cent and a bound divinylbenzene level of about 0.5 to 1 weight per cent. Various stabilizers were incorporated into the polymer which was then masticated in a BRABENDERmixer (BRABENDER is a registered Trademark) at a temperature of 1650C. The mixer was equipped with a roller head No. 5 or o. 6 type mixing blade and the torque was continuously measured and recorded for a total of 30 minutes. After mastication, a sample of the polymer was used to determine the Mooney (ML 1 + 4 &commat; 1000C) value. The stabilizers were incorporated into the polymer by addition of the required quantity to a latex of the polymer, following which the latex was coagulated with calcium chloride and the polymer recovered and dried. The stabilizers used were: Stabilizer 1 - alkylated bis-phenol (NAUGAWHITE # Stabilizer 2 - alkyl tin mercaptide (MARK 900) Stabilizer 3 - antimony thioglycolate AMAKK #2115) Stabilizer 4 - organo-phosphite (MARK W C) Stabilizer 5 - antimony tin mercaptide (MARK# 9000) Stabilizer 6 - barium/cadmium carboxylate (MARKRWS) The amounts of the stabilizers used and the results of the evaluation are shown in Table I, in which Experiments #1, 3, 5 and 6 are outside the scope of the present invention. The color of the polymer before and after mastication was recorded by visual observation and these observations are given in Table I. TABLE I Experiment No. 1 2 3 4 5 6 Stabilizer 1 1.25 1.25 1.25 1.25 1.25 1.25 Stabilizer 2 0.5 - 0.5 - 0.5 Stabilizer 3 - 0.5 - - - Stabilizer 4 - - 0.5 0.5 0.5 0.5 Stabilizer 5 - - - 0.5 0.5 0.5 Stabilizer 6 - - - - - 0.5 Mooney Before Mastication 81 81 78 79 78 79 (ML 1+4 @ 100 C) Color White White Pale White White White Yellow Mastication Torque, mg/at - minutes running time At 1 minute 3200 3350 3100 3000 2350 3200 2 minutes 2800 3000 2700 2650 2200 2900 3 minutes 2550 2750 2500 2450 2100 2800 4 minutes 2500 2600 2450 2350 2000 2700 5 minutes 2500 2500 2300 2300 1950 2600 6 minutes 2400 2450 2250 2200 1900 2400 8 minutes 2200 2250 2150 2150 1850 2050 10 minutes 2050 2050 2050 2050 1800 1900 20 minutes 1800 1800 1850 1850 1600 1750 30 minutes 1750 1800 1800 1800 1450 1750 Mooney After Mastication 53 53 52 52 53 52 (ML 1+4 @ 100 C) Color Yellow Pale Yellow Yellow Yellow Yellow Brown EXAMPLE 2 The base polymer used was essentially similar to that used in Example 1. The stabilizers used were as given in Example 1, except for: Stabilizer 7 - methyl tin mercaptide (ADVA STAB # TM 181) Experiments &num;2 and 4 are controls and Experiments &num;6 and ; are commercially available crosslinked nitrile polymers. The results are given in Table II. TABLE II Experiment No. 1 2 3 4 5 6 7 Stabitizer 1 1.25 1.25 1.25 1.25 1.25 - Stabilizer 3 0.5 - - - 0.5 - Stabilizer 4 - - 0.5 0.5 0.5 - Stabilizer 5 - - 0.5 - - - Stabilizer 7 - 0.5 - 0.5 - - Mooney Before Mastication 79 80 79 81 77 109 115 (ML 1+4 @ 100 C) Color Pale White Pale Pale Light White White Yellow Yellow Yellow Brown Mastication Torque, mg/at - minutes running time At 1 minute 3250 3100 3050 3100 2900 3900 3800 2 minutes 2800 2650 2600 2650 2550 3250 3300 3 minutes 2700 2450 2500 2500 2400 3150 3100 4 minutes 2550 2400 2350 2350 2250 3150 3000 5 minutes 2350 2350 2250 2250 2150 3150 2950 6 minutes 2250 2250 2150 2150 2000 3100 2900 8 minutes 2000 2000 1950 1950 1800 3050 2850 10 minutes 1900 1900 1850 1850 1750 3000 2750 20 minutes 1800 1750 1750 1700 1600 2900 2650 30 minutes 1750 1700 1700 1650 1550 2800 2600 Mooney After Mastication 55 56 52 53 53 96 82 (ML 1+4 @ 100 C) Color Light Light Light Yellow Grey Light Yellow Brown Brown Brown Brown Brown Brown EXAMPLE 3 The base polymer used was the same as that used for Example 1. The stabilizers used were as given in Example 1, except for: Stabilizer 8 - antimony thioglycolate (THEtMOLITE 170) Stabilizer 9 - polymeric substituted phenol (WINGSTAY #L) No controls wers included in this Example. The stabilization systems used and the results obtained are given in Table III. TABLE III Experiment II 1 2 3 Stabilizer 1 1.25 1.25 Stabilizer 8 0.5 0.5 0.5 Stabilizer 4 - 0.5 0.5 Stabilizer 9 - - 1.25 Mooney Before Mastication 80 79 83 (ML 1+4 @ 100 C) Color White White White Mastication Torque, mg/at - minutes running time At 1 minute 3500 3000 3000 2 minutes 2900 2550 2650 3 minutes 2700 2500 2600 4 minutes 2600 2400 2550 5 minutes 2500 2350 2450 6 minutes 2300 2200 2300 8 minutes 2100 2050 2050 10 minutes 2000 1950 1950 20 minutes 1850 1850 1800 30 minutes 1800 1800 1800 Mooney After Mastication 58 55 57 (ML 1+4 &commat; 100 C) Color Very Pale Very Pale Very Light Yellow Yellow Brown EXAMPLE 4 The base polymer used was essentially similar to that of Example 1. The stabilizers that were added to the polymer were: Stabilizer 10 - antimony thioglycolate (MARK 2115D Stabilizer 9 - polymeric substituted phenol (WINGSTAY #L) Stabilizer 11 - dilauryldithiopropionate Stabilizer 12 - polymeric organo phosphite (WYTOX 345) Experiment &num;l is within the scope of the present invention and Experiments 22 and 3 are outside the scope of the invention by virtue of not containing one of or too low a level of the specified stabilizers. The quantities and types of stabilizers used and the results obtained are given in Table IV. TABLE IV Experiment &num; 1 2 3 Stabilizer 9 1.25 1.0 0.75 Stabilizer 10 0.375 - 0.375 Stabilizer 11 0.2 0.4 0.5 Stabilizer 12 0.5 0.5 Mooney Before Mastication 94 111 102 (ML 1+4 @ 100 C) Color White White White Mastication Torque, mg/at - minutes running time At 1 minute 4000 3750 3650 2 minutes 3000 3350 2950 3 minutes 2800 3550 2850 4 minutes 2750 3700 3050 5 minutes 2850 3650 3100 6 minutes 3000 3450 3100 8 minutes 2900 3100 2950 10 minutes 2750 3000 2850 20 minutes 2600 3050 2300 30 minutes 2750 3050 2900 Mooney After Mastication 94 133.5 107.5 (ML 1+4 @ 100 C) Color Very Pale Yellow Pale Yellow Yellow Brown

Claims: Claims: 1. A crosslinked rubbery nitrile polymer containing a stabilizer system, said nitrile polymer containing from about 45 to about 79.5 weight per cent of butadiene, from about 20 to about 50 weight per cent of acrylonitrile and from about 0.5 to about 5 weight per cent of divinylbenzene, characterized in that said stabilizer system comprising from about 1 to about 2 parts by weight per 100 parts by weight of polymer of at least one phenolic compound and from about 0.3 to about 0.8 parts by weight per 100 parts by weight of polymer of at least one antimony-containing compound. 2. The nitrile polymer of Claim 1 characterized in that said phenolic compound of the stabilizer system is selected from hindered phenols, alkylated bis-phenols and polymeric substituted phenols. 3. The nitrile polymer of Claim 1 characterized in that said antimony-containing compound of the stabilizer system is selected from antimony thioglycolates, mixtures of antimony and tin thioglycolates, antimony tin mercaptides and antimony mercaptide compounds. 4. The nitrile polymer of Claim 1 characterized in that said stabilizer system also contains an organophosphite compound. 5. The nitrile polymer of Claim 4 characterized in that said organo-phosphite compound is selected from tris(nonylphenyl) phosphite, tris(octylphenyl) phosphite, tris(p-hexylphenyl) phosphite, tris (cyclobexylphenyl) phosphite, tris(p-benzylphenyl) phosphite and polymeric phosphite compounds which contain two phosphite groups linked by a short chain polymer and each phosphite group also being attached to two phenyl groups. 6. The nitrile polymer of Claim 4 characterized in that said stabilizer system also contains a di(C11-C17 alkyl group substituted carboxyl group)-thio-dipropionate. 7. The nitrile polymer of Claim 6 characterized in that said di(C11-C17 alkyl group substituted carboxyl group)-thio-dipropionate is selected from dilauryl-thiodipropionate, dimyristyl-thio-dipropionate, dipalmitylthio-dipropionate and distearyl-thio-dipropionate. 8. The nitrile polymer of Claim 1 wherein said nitrile polymer contains from about 55 to about 79.5 weight per cent of butadiene, from about 20 to about 40 weight per cent of acrylonitrile and from about 0.5 to about 5 weight per cent of divinylbenzene, characterized in that said stabilizer system comprises, per 100 parts by weight of polymer, from about 1 to about 1.5 parts by weight of a phenolic compound selected from hindered phenols, alkylated bis-phenols and polymeric substituted phenols, from about 0.3 to about 0.6 parts by weight of an antimony-containing compound selected from antimony thioglycolates, mixtures of antimony and tin thioglycolates, antimony tin mercaptides and antimony mercaptide compounds, and from about 0.4 to about 0.6 parts by weight of an organo-phosphite compound selected from tris(nonylphenyl) phosphite, tris(octylphenyl) phosphite, tris(p-hexylphenyl) phosphite, tris(cyclohexylphenyl) phosphite, tris(p-benzylphenyl) phosphite and polymeric phosphite compounds which contain two phosphite groups linked by a short chain polymer and each phosphite group also being attached to two phenyl groups. 9. The nitrile polymer of Claim 8 characterized in that said stabilizer system also contains, per 100 parts by weight of polymer, from about 0.1 to about 0.4 parts by weight of a di(C11-C17 alkyl group substituted carboxyl group)-thio-dipropionate selected from dilaurylthio-dipropionate, dimyristyl-thio-dipropionate, dipalmityl-thio-dipropionate and distearyl-thiodipropionate.

Inventors: BLEY, JOHN WILLIAM FRANCISCUS
Applicants: POLYSAR LIMITED
Application year: 1982
Main classification: C08L9
IPC codes: C08L21, C08L51, C08L33, C08K5, C08L7