STABILIZED CARBOXYL-CONTAINING ETHYLENE INTERPOLYMERS

Abstract: The oxidative, process, and/or color stability of carboxyl-­ containing ethylene interpolymers is improved by incorpor­ ating therein at least one biphenylene phosphorous com­ pounds with or without a dicarboxylic acid or a hindered phenol antioxidant.

Description: STABILIZED CARBOXYL-CONTAINING ETHYLENE INTERPOLYMERS Interpolymers of ethylene containing pendent carboxyl groups are highly susceptible to thermal oxidation. This inherent instability results in significantly reduced production rates due to oxidative gels (crosslinked polymer), polymer discoloration, and degradation by-products which can corrode process equipment. This instability also seriously limits the useful life of such polymer products as films, coatings, and adhesives. The thermal stability of carboxyl-containing ethylene interpolymers is improved by incorporating minor amounts of a biphenylene phosphorous compound, alone or in combination with a dicarboxylic acid, optionally, or also combined with a hindered phenolic antioxidant. Ethylene interpolymers containing carboxyl groups are well known, especially interpolymers containing ethylene and olefinically unsaturated carboxylic acids, e.g., acrylic acid or methacrylic acid, such as shown in U.S. 3,239,370 and U. S. 3,520,861. The ethylene/acid interpolymers often containing relatively minor amounts of other polymerizable olefins, such as propylene, butene, hexene, and octane Other ethylene polymers containing carboxyl groups are known, such as those prepared by grafting unsaturated carboxylic acids onto ethylene polymer chains. Suitable monomers for use in incorporating carboxyl groups into ethylene polymers are, e.g., acrylic acid, methacrylic acid, crotonic acid, methyl methacrylic acid, alkyl acrylates, and vinyl acetate. The carboxylic groups may be provided by monomers of the formula EMI2.1 where R and R' are, independently, hydrogen or methyl groups and R" is hydrogen or alkyl groups of 1-10 carbon atoms. Other carboxylates are provided by monomers of the formula: EMI2.2 where R is preferably an alkyl group of 1-4 carbon atoms. One or more of such carboxyl containing monomers may be used to provide about 0.01 to 60% by weight of the ethylene polymer. The carboxyl-containing polymers may exhibit melt flows of from 0.01 gm/10 min. as measured by ASTM-D-1238, Condition E, to 500 gm/10 min. as measured by ASTM-D-1238, condition B; i.e., they range from very high mol. wt to very low mol. wt. The dicarboxylic acid additives of the present invention have the formula: EMI3.1 where R represents an aliphatic (C0 to C24) or aromatic radical; R' and R" each independently, represent amino, mercapto, phosphato, carboxyl, or hydroxyl groups or other nucleophilic groups or hydrogen groups. Where R is CO, then the compound is HOOC-COOH and there are nQ R' and R" groups. Where R is from C1 to C24 there may be only one R' and/or only one R" or there may be a plurality of R' and/or R" groups other than hydrogen. Where R is C2 to C24 there may be one or more double -bonds in the carbon chain. The following list of dicarboxylic acids is representative of the compounds contemplated within this invention: Name Formula oxalic HOOC-COOH malonic HOOC-CH2-COOH succinic HOOC-CH2-CHz-COOH tartaric HOOC-CH(OH)-CH(OH)-COOH glutaric HOOC- ( CH2 ) 3-COOH adipic HOOC-(CH2)4-COOH pimelic HOOC-(CH2)5-COOH suberic HOOC-(CH2)6-COOH azelaic HOOC- (CH2 )7-COOH sebacic HOOC-(CH2)8-COOH maleic HOOC-CH=CH-COOH acetone dicarboxylic HOOC-CH2 -CO-CH2-COOH malic HOOC-CHOH-CH2-COOH phthalic HOOC- -COOH Other substituted or unsubstituted bis-dicarboxylic polymethylenes will become apparent to practitioners of the relevent arts. The biphenylene phosphorous compounds for use in the present invention conform, generally, to the following structure, EMI4.1 where R represents C0 or C1 to C4 and C1 to C4 can be substituted or unsubstituted, including C < CH3)2, R' represents C0, C1 to C14, phenylene, or -O-R"-O- where R" is an aliphatic or aromatic radical; and where IV can be terminated by EMI5.1 to form a bicyclic compound, or by EMI5.2 to form a bis acyclic compound, where, in II and III P represents phosphorous, P=O, or P=S; the phenyl rings of III may be substituted or unsubstituted. Some representative compounds are: (a) 2,2'-[(1-methylidene) bis (4,1-phenylene oxy-2, 1-ethane diyloxy)] bis 5,5-dimethyl-1,3,2 -dioxaphosphorinane; (b) 2,2'-[(1-methyl ethylidene) bis (4,1-phenylene -oxy-2, 1-ethane diyloxy)] bis 5,5'-dimethyl -1,3,2-oxo phosphate; (c) 2,2'-[(1-methyl ethylidene) bis (4,1-phenylene -oxy-2, 1-ethane diyloxy)] bis 5,5'-dimethyl -1,3,2,-thio phosphate; (d) 2,2'-[(1-methyl ethylidene) bis (4,1-phenylene -oxy-l-methyl-2,1-ethane diyloxy)j bis 5,5' -dimethyl-1,3,2-dioxaphosphorinane; and (e) tetrakis (2,4-di-tert-butyl phenyl )4, 41 -biphenylene diphosphonite. U.S. Patent 4,254,104 discloses preparation of various biphenylene phosphrous compounds, e.g., aromatic bis(dioxaphosphorinanes) and discloses the use of such compounds as additives to polycarbonates. The hindered phenols for use in the present invention generally have structures illustrated by, for example, EMI6.1 where X represents one or more pendant groups, such as (a) l,3,5-trimethyl-2,4,6-tris(3' ,51-di-tert-butyl- -4'-hydroxyl benzyl) benzene; (b) 2,2'-oxamidobisethyl, 3(31,5 '-di-tert-butyl-4- -hydroxy phenyl) propionate; (c) tetrakis [methylene-3-(3',5'-di-tert-butyl-4' -hydroxyl-phenyl) propionate] methane; (d) 1,1,3-tris-(2'-methyl-4'-hydroxy-5'-tert-butyl phenyl) butane; (e) 2,6-di-tert-butyl-4-ethyl phenol; (f) 2,2'-oxamidobis ethyl-3(3',5'-di-tert-butyl-4 -hydroxyl phenyl) propionate; (g) tris (4-tert-butyl-3 hydroxy-2,6-dimethyl benzyl) 2-triazine 2,4,6-(lH,3H,5H) trione; (h) 2,6-di-tert-butyl-4-methyl phenol; or (i) octadecyl-3 , 4-di-tert-butyl-4-hydroxy-hydrocin- namate. Suggested operative ranges and preferred ranges (percent by wt.) for the components of the present blends or alloys are as follows: Component Operative Preferred carboxyl-containing polymer 79-99.9 99.7-99.8 hindered phenol 0.01-3.0 0.02-01 biphenylene P compound 0.01-3.0 0.02-0.1 dicarboxylic acid 0.01-15 0.02-0.1 The mixing of the interpolymers with the other components of the present invention may be done by any convenient means, such as by employing a compounding extruder, Banbury mixer, intensive mixers, or multi-screw mixing extruder, or any combination thereof, preferably by masterbatch concentrates letdown to the desired additive concentrations in an extruder equipped with one or more mixing screws. Usually, one seeks to distribute additives substantially uniformly through the base resin. The Oxidative Induction Period is measured by an oxygen-uptake apparatus similar to that described by Grieveson in Society of Chemical Industries, Monograph No. 13, 1961, pp. 413-431, published in London, England, and the Gardner Yellowness Index is measured by a Gardner XL-23 colorimeter according to ASTM-D-1925. The following examples are for illustration of various embodiments. Example 1 An ethylene/acrylic acid copolymer prepared by free-radical initiation in a stirred autoclave under high ethylene pressure and high temperature was used. The copolymer contained 6.5% by weight of acrylic acid units and had a melt flow of 2 gm./10 minutes as measured by ASTM-D-1238 condition E. Small particles of the copolymer were dry-blended with 0.25% tartaric acid and then compounded at 3500F (-1770C) on a 6.35 cm (2.5 inch), 20/1 L/D compounding extruder equipped with a metering, compression and mixing section. The pelletized product had an oxidative induction period of > 60 minutes according to oxygen-uptake analysis at -1490C. The oxidative induction period at l490C for the base resin without the addition of tartaric acid was 9.0 minutes, Examples 2 An ethylene/acrylic acid copolymer containing 6 5% acrylic acid by weight, a melt flow of 2 gm./10 min., and a density of 0.9325 gm/cc was used as the base resin in the following evaluations: Oxy dative Concentration, Induction Period Run Stabilizer* ppm &commat; 1770C, minutes 1 None ---- 3.5 2 A 2500 15.0 3 B 2500 11.0 * A is tartaric acid B is a 2:1 physical blend of 1,1,3-tris(2'-methyl 4'-hydroxy-5'-tert-butyl phenyl )butane and distearylthiodipropionate (a thioester stabilizer). The above evaluation indicated that at an equivalent concentration, tartaric acid out-performed a conventional hindered phenol-thioester composition. Example 3 An ethylene/acrylic acid copolymer containing 6.5% acrylic acid, having a melt flow of 5.5 gm/10 min. and a density of 0.9325 gm/cc was used in the following evaluation. Additive A* Additive B** Oxidative Induction Run ppm ppm Period &commat; 1770C, mins. 1 None None 7.0 2 1000 None 21.0 3 None 1000 39.0 4 500 500 48.0 *A is 1,1,3-tris-(2'-methyl-4-hydroxyl-5'-tert-butyl phenyl) butane **B is tartaric acid The above evaluation indicated that a hindered phenol-dicarboxylic acid composition is highly synergistic. Example 4 Using the same copolymer as in Example 3, the following evaluation was performed: Additive A* Additive B** Oxidative Induction Run ppm ppm Period &commat; 1770C, mins. 1 None None 7.0 2 1000 None 21.0 3 None 1000 35.0 4 500 500 78.0 * Additive A is 1,1,3-tris-(2'-methyl-4-hydroxyl-5'- tert-butyl phenyl) butane. ** Additive B is 2,2'-[1-methylidene) bis (4,1-phenylene oxy-2,1-ethane diyloxy)] bis 5ff5-dimethyl-1,3,2- dioxaphosphorinane. This evaluation showed that a hindered phenolbiphenylene phosphorous composition is also highly synergistic. Example 5 Using the same copolymer as in Example 3 the following evaluation was conducted. Concentration Oxidative Induction Run Stabilizer* ppm Period &commat; 1770C, mins. 1 A 1000 23.0 2 B 1000 39.0 3 C 1000 21.0 4 D 1000 35.0 5 E 1000 > 143.0 6 - -- 7.0 *A is tetrakis methylene 3-(3',5'-di-tert-butyl 4'-hydroxyl phenyl) propionate] methane B is tartaric acid C is 1,1,3-tris-(2'-methyl-4-hydroxyl-5'-tert butylphenyl) butane D is 2,2'-[(l-methylidene) bis (4,1-phenylene oxy 2,1-ethane diyloxy)] bis 5,5'-dimethyl-1,3,2 dioxaphosphorinane E is tetrakis (2,4-di-tert butyl phenyl)4,4'-biphenylene diphosphonite. The above evaluation showed that at equivalent concentrations the dicarboxylic acid and the biphenylene phosphorous compound were more effective thermal stabilizers than either of the conventional hindered phenol stabilizers. Example 6 Using the same copolymer as in Example 3 the following multiple-extrusion evaluation was performed. Stabilizer** Other Stabilizer Run A, ppm Identity ppm 0 ambi* :mi* 1 None None None 0.147 2 500 B 500 0.087 41.06 3 500 C 500 0.097 34.33 4 500 D 500 0.137 7.08 5 500 E 500 0.176 -19.67 *ami is the standard deviation in melt indices of each sample extruded five times at 2040C on the aforementioned extruder. Emi is the percent melt stability relative to the base resin in this evaluation and was calculated from: EMI12.1 Where 0 was the a mi of the unstabilized base resin and at was the ami of each stabilized sample independently. ** A is tetrakis [methylene 3-(3',5'-di-tert-butyl-4' hydroxylphenyl) propionate] methane B is 2,2'-[(l-methylidene) bis (4,1-phenylene oxy-2, l-ethane diyloxy)] bis 5,5'-dimethyl-1,3,2-dioxa phosphorinane C is tartaric acid D is tris-(mixed mono-and dinonyl phenyl) phosphite E is thiobis (6-tert-butyl-3-methyl phenol). The above multiple-extrusion evaluation indicated that phenolic/biphenylene phosphorous and phenolic/dicarboxylic acid compositions offer exceptional process stability in contrast to conventional phosphite and thio-bisphenol compositions which offer little or no stability, or may even adversely affect polymer stability. Example 7 In this evaluation an ethylene/acrylic acid copolymer containing 6.5% by wt. acrylic acid, having a melt flow of 9.0 gm/l0 min. and a density of 0.9325 gm/cc was used. Run Stabilizer* Conc. ppm m 1 None None - 2 A 1000 16.2 3 B 1000 72.5 4 C 1000 43.8 * A is tetrakis [methylene 3-(3',5'-di-tert-butyl 4-hydroxylphenyl) propionate] methane B is,2,2'-(l-methylidene) bis (4,1-phenylene oxy-2, l-ethane diyloxy)] bis 5,5'-dimethyl-1,3,2-dioxa phosphorinane C is tartaric acid The above evaluation showed that at equivalent concentrations the dicarboxylic acid and the biphenylene phosphorous compound were significantly more effective process stabilizers than the conventional hindered phenol. Example 8 Following the multiple-extrusion evaluations of Example 6 above, Gardner Yellowness Index determinations of the samples were made according to ASTM-D-1925. Gardner Yellowness Stabilizer* Index, Pass: Run A,ppm B,ppm C,ppm D,ppm 0 1 2 3 4 1 1000 ---- ---- ---- -3.4 6.2 6.4 8.97 11.7 2 500 ---- 500 ---- -3.4 -2.8 -1.2 0.54 4.03 3 500 500 ---- ---- -2.06 -0.85 0.75 1.88 3.34 4 500 ---- ---- 500 -0.90 -0.25 0.50 1.56 3.07 * Stabilizers A, B, and C are same as in Example 6. Stabilizer D is same as E in Example 5. This evaluation showed that the dicarboxylic acid and the biphenylene phosphorous compositions imparted good color stability to an ethylene/acrylic acid copolymer while a conventional hindered phenol stabilizer imparted less than acceptable color stability as denoted by the relatively high measurement, 11.7; the higher the value the more objectionable the color. Example 9 Using the same base resin as in Example 7 above the following evaluation was made. Stabilizer* Run A, ppm B, ppm C, ppm zmi 1 500 500 ---- 30.8 2 500 250 250 72.2 * A is 1,1,3-tris-(2'-methyl-4-hydroxyl-5'-tert-butyl phenyl) butane. B is tetrakis (2,4-di-tert-butyl phenyl)4,4' biphenylene diphosphonite. C is 2,2'-f(l-methylidene)bis(4,1-phenylene oxy 2,1-ethane diyloxy)Jbis 5,5-dimethyl-1,3,2 dioxaphosphorinane. This evaluation showed that the combination of two biphenylene phosphorous compounds and a hindered phenolic antioxidant was very effective. Example 10 Using the same base resin as in Example 7 above the following evaluation was made: Stabilizer* Run A, ppm B, ppm C, ppm mi 1 500 500 ---- 30.8 2 500 250 250 58.1 3 ---- 1000 ---- 19.1 4 1000 ---- ---- 16.1 *A is 1,1,3-tris-(2'-methyl-4-hydroxyl-5'-tert butyl phenyl) butane. B is tetrakis (2,4-di-tert-butyl phenyl)4,4' biphenylene diphosphonite. C is tartaric acid. This evaluation showed that the combination of a dicarboylic acid, a biphenylene phosphorous compound, and a hindered phenol antioxidant significantly improved the process stability of a carboxyl-containing ethylene interpolymer. The evaluation also illustrated another synergistic biphenylene phosphorous/hindered phenol composition. Within the purview of the present invention, dicarboxylic acids and biphenylene phosphorous compositions, such as described herein, significantly improve the thermal-oxidative and color stability of carboxyl-containing ethylene interpolymers during their manufacturing processes, storage, fabrication, and end-usage. The applications of such heat stable ethylene interpolymers include such things as extrusion films (e.g., for paper, paperboard, metallic substrates, etc.), blister packages, flexible packages, adhesives (hot melts), primers, binders, laminates, adhesive composite structures, barrier films, metallized films, injection molded articles, rotomolded articles, wire and cable insulation, shielding tapes, and powder molding, including those embodiments wherein the polymers contain colorants, pigments, or fillers. Fillers include such things as silica, calcium carbonate, metal oxides, talc, clay, sawdust, rice hulls, wood flour, starch, and ground bark.

Claims: 1. A method for improving the thermal stability of carboxyl-containing ethylene interpolymers characterized by incorporating into said interpolymers a minor amount of at least one biphenylene phosphorus compound. 2. The method of Claim 1 wherein the amount of biphenylene phosphorous compound is 0.01% to 3% by weight. 3. The method of Claim 1 wherein the biphenylene phosphorous compound conforms generally to the formula EMI16.1 terminated by EMI16.2 groups, or by EMI16.3 groups, where R represents C or C1 to C4, where C1 to 0 C4 can be substituted or unsubstituted including =C(CH3)2; R' represents CO C1 to C14, phenylene, or -O-R"-O- where R" is an aliphatic or aromatic group; P represents phosphorus, P=O, or P=S, and the phenyl rings of VI may be substituted or unsubstituted. 4. The method of Claim 1 wherein there is also incorporated into said interpolymer 0.01% to 15% by weight of a dicarboxylic acid having the formula: EMI17.1 where R represents an aliphatic or aromatic grouping containing C0 to C24, R' and R" each, independently, represent amino, mercapto, phosphato, carboxyl, hydroxyl, hydro, or other nucleophilic group. 5. The method of Claim 4 wherein the dicarboxylic acid is tartaric acid. 6. The method of Claim 1 wherein there is also incorporated into said interpolymers a minor amount of at least one hindered phenolic antioxidant. 7. The method of Claim 6 wherein the hindered phenolic antioxidant comprises 0.01% to 3% by weight of at least one compound having the formula EMI17.2 or the formula EMI18.1 where X represents one or more pendant groups. 8. A composition of matter comprising a carboxyl-containing ethylene interpolymer having incorporated therein a minor amount of at least one biphenylene phosphorous compound and a minor amount of at least one hindered phenolic antioxidant. 9. A composition of Claim 8 having incorporated therein a minor amount of at least one dicarboxylic acid compound. 10. The composition of Claim 1, wherein the interpolymer is an ethylene-acrylic acid copolymer.

Inventors: MCKINNEY, OSBORNE KELLY, PEREZ FLORES, DAVID
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1983
Main classification: C08K5
IPC codes: C08L23, C08K5, C08L101, C08L33