GB2039492A - Stabilized olefin polymers - Google Patents

Abstract

Tris-(o-alkylphenyl) phosphites are more stable to hydrolysis than the corresponding tris-(p-alkylphenyl) phosphites and this makes them more useful as heat-stabilizing additives in olefin polymer compositions, especially in polypropylene compositions. The alkyl groups are those having a higher number of carbon atoms, namely those having 8 to 12 carbon atoms.

Description

SPECIFICATION Stabilized olefin polymers This invention relates to phosphite esters which are unusually stable to hydrolysis. More particularly, it relates to the use of such stable phosphite esters as heat-stabilizing agents for olefin polymer compositions.

The normal processing operations to which olefin polymers are subjected invariably involves high temperatures and these promote deterioration of the polymers. The formulation of a thermoplastic polymer composition, i.e., one which contains the various stabilizing additives ordinarily required, usually is accomplished on a heated two-roll mill, or in a heated Banbury mixer, or both, and the temperatures at which such mixing steps are carried out are quite high, well above the temperature at which the polymer becomes fluid. At these temperatures the polymer will develop color, become brittle, etc., and such evidence of deterioration cannot be tolerated in the final product.

There are a number of heat-stabilizing additives available which are effective to protect olefin polymers from such deterioration. Among these are the organic phosphites. While these are very effective heat-stabilizing additives, their usefulness is limited by their susceptibility to hydrolytic decomposition in a humid environment. Such hydrolysis is accompanied by a corresponding loss of heat-stabilizing effectiveness with respect to the olefin polymer compositions in which they are used for that purpose. Moreover, where the phosphite is a solid, such hydrolysis also frequently is accompanied by a ten deny to blocking, i.e., a tendency for the ordinarily granular phosphite material to congeal into a single solid block.

Many attempts have been made to solve this problem. Additives such as triisopropanolamine have been found to impart a significant hydrolytic stability to organic phosphite esters. The solid phosphite can be stored in moisture-proof containers such as polyethylene bags until just before use. All of these have been very helpful, but they have not eliminated the problem, northe desirability of a solution to the problem.

U.K. 1,490,938 (Ciba-Geigy) shows symmetrical triarylphosphites having the formula:

wherein R1 represents tertiarybutyl, 1, 1 - dimethylpropyl, cyclohexyl or phenyl, and one of R2 and R3 is hydrogen and the other is hydrogen, methyl, tertiarybutyl, 1, 1 - dimethylpropyl, cyclohexyl or phenyl. The use of these compounds in combination with phenolic antioxidants in polyolefins is also shown.

U.S. 2,773,226 (Hunter) shows aryl phosphites substituted with alkyl groups containing eight or more carbon atoms and their use as stabilizers for synthetic rubber. The alkyl groups may be ortho, para or meta to the oxygen.

U.S. 3,578,620 (Prucnal) shows the stabilization of non-rubbery, unsaturated interpolymers of cyclic polyenes by means of a mixture of a tri-(alkylphenyl) phosphite in which the alkyl group has from 8 to 30 carbon atoms and an epoxide. Tri-(o-octylphenyl) phosphite is shown.

U.S. 3,080,338 (Nudenberg et al) shows the use of "any conventional phosphite" in combination with a phenolic antioxidant to stabilize synthetic rubbery polymers. Tri-(ortho-octyl-phenyl) phosphite is shown.

U.S. 2,752,319 (Lipke petal) shows the stabilization of polyvinyl chloride compositions by means of a combination of a glycol ester of an organic acid, a triaryl phosphite (to stabilize the ester), and a metal compound. The aryl phosphite can be tri (orthocyclohexyl - phenyl) phosphite.

The invention here is a polymer composition comprising an olefin polymer and a minor amount, sufficient to impart improved heat stability to said polymer, or a tris - (alkylphenyl) phosphite mixture wherein (1 ) the alkyl group contains 8-12 carbon atoms, (2) at least about 85% of one of the ortho positions in each phenyl group are substituted by said alkyl groups, and (3) at least about 85% of the para positions in each phenyl group are unsubstituted, or substituted by methyl groups. The phosphite can be represented by the structure:

wherein at least about 85% of R2 is alkyl of 8-10 carbon atoms, the remainder being hydrogen, and at least about 85% of R' is methyl or hydrogen.

The preparation of tris-(alkylphenyl) phosphites requires, first, preparation of the alkylphenol and then, reaction of this alkyl-phenol with phosphorous trichloride. The first of these reactions can be accomplished by hydrogenating an acylphenol. This may be done conveniently by means of zinc plus hydrochloric acid. An alternative method affords somewhat better yields; it involves alkylation of phenol (or p-cresol) with an appropriate olefin in the presence of a catalyst. A preferred catalyst is aluminum powder, or, more particularly, the aluminum phenate which results from the reaction of aluminum and the phenolic reactant. Such alkylation yields a high proportion of ortho isomer and relatively little or no para isomer.

The reaction of the o-alkylphenol and phosphorous trichloride proceeds with good yields, at relatively high temperatures. The product may be distilled to yield a clear, colorless liquid product; alternatively, it may be stripped in vacuo and the residual liquid taken as the product.

This product, i.e., a tris-(o-alkylphenyl) phosphite is as indicated characterized by unusual hydrolytic stability and, correspondingly, long-lived effectiveness as a stabilizer in polymer compositions, espe cially in olefin polymer compositions. It is particularly effective in such compositions which also contain a phenolic antioxidant.

The olefin polymer most usually is polypropylene although other olefin polymers are contemplated.

These include polyethylene, copolymers of ethylene and propylene, polyisobutylene, and EPDM polymers, i.e., terpolymers of ethylene, propylene, propyiene and a small proportion of a non-conjugated diene.

The alkyl groups in the tris-(alkylphenyl) phosphite contain, as indicated earlier, 8-12 carbon atoms.

Thus, octyl, nonyl, decyl, undecyl and dodecyl groups are specifically contemplated. These groups may be attached to the phenolic ring through a primary, secondary or tertiary carbon atom.

Thetris-(alkylphenyl) phosphite herein is derived from an alkylphenol of the structure:

where R' is methyl or hydrogen and R2 is alkyl of 8-12 carbon atoms.

The amount of the tris-(o-alkylphenyl) phosphite which is to be used ranges from about 0.1 phr (parts per 100 parts of resin) to about 5.0 phr.

The phenolic antioxidants are well known. Specifically contemplated are the following: 2,6 - di - tert. butyl - 4 - methylphenol, 2,6 - di - tert. - butyl - 4 methoxy - methylphenol or 2,6 - di - tert. - butyl - 4 methoxyphenol; 2, 2' - methylene - bis - (6 - tert. butyl - 4 - methylphenol), 2, 2' - methylene - bis - (6 tert. - butyl - 4 - ethylphenol), 2, 2' - methylene - bis [4 - methyl - 6 (a - methylcyclohexyl) - phenol, 1, 1 bis (5 - tert. - butyl - 4 - hydroxy - 2 - methylphenyl) butane, 2,2 - bis - (5 - tert, - butyl - 4 - hydroxy - 2 methylphenyl) - butane, 2, 2 - bis - (3, 5 - di - tert.

butyl - 4 - hydroxyphenyl) - propane, 1, 1,3 - tris - (5 - tert. - butyl - 4 - hydroxy - 2 - methylphenyl) - butane, 2,2 - bis - (5 - tert. - butyl - 4 - hydroxy- 2 - methylphenyl) - 4 - n - dodecylmercapto - butane, 1, 1, 5, 5 tetra - (5 - tert. - butyl - 4 - hydroxy - 2 - methylphenyl) - pentane, ethylene glycol - bis [3, 3 - bis - (3' - tern. butyl 4' hydroxyphenyl) - butyratej, 1,1 - bis - 5 - dimethyl - 2 - hydroxyphenyl) - 3 - (n - dodecylthio) - butane, or 4, 4' - thio - bis - (6 - tert. butyl - 3 - methyl phenol); 1,3, 5-tri-(3, 5-di-tert. -butyl-4- hydroxybenzyl) - 2, 6 - trimethylbenzene, 2, 2 - bis - (3, 5 - di - tert. - butyl - 4 - hydroxy - benzyl) - malonic acid - dioctadecyl ester, 1, 3, 5 - tris - (3, 5 - di - tert. butyl - 4 - hydroxybenzyl) - isocyanurate, or 3, 5 - di tert. - butyl - 4 - hydroxybenzyl - phosphonic acid diethyl ester; amides of 3 - (3, 5 - di - tert - butyl - 4 hydroxy - phenyl) - propionic acid, such as 1, 3, 5 tris - (3, 5 - di - tert. - butyl - 4 - hydroxyphenyl propionyl) - hexahydro - s - triazine, N, N' - di - (3, 5 di - tert. - butyl - 4 - hydroxyphenyl - propionyl) hexamethylenediamine; esters of 3 - (3, 5 - di - tert butyl - 4 - hydroxyphenyl) - propionic acid with methanol, octadecanol, 1,6 - hexanediol, ethylene glycol, thiodiethylene glycol, neopentyl glycol, pentaerythritol, tris - hydroxyethyl - isocyanurate; diphenolic spiro - diacetals or spiro - diketals, such as 2,4,8, 10 - tetraoxaspiro -15, 51 - undecane substi tuted in the 3- and 9-position with phenolic radicals, such as 3,9 - bis - (3, 5 - di - tert. butyl - 4 - hydrox yphenyl) - 2,4,8,10 - tetraoxaspiro - ! 5.5j - unde- cane, 3, 9-bis-Il, I-dimethyl-2-(3, 5-ditert. - butyl - 4 - hydroxyphenyl) - ethyl - 2,4,8,10 - tetra oxaspiro -) 5, 5) - undecane.

Particularly preferred are: 1,3,5 - tri - (3,5 - di - tert. - butyl - 4 - hydroxybenzyl) - 2,4,6 - tri - methyl benzene, pentaerythritol - tetra 13 - (3, 5 - di - tert. butyl - 4 - hydroxy - phenyl) - propionatej, '3 - (3, 5 - di - tert. - butyl - 4 - hydroxyphenyl) - propionic acid - n octadecyl ester, thiodiethylene glycol - p - 04 - hydroxy - 3, 5 - di - tert. - butyl - phenylj - propionate, 2, 6 - di - tert. - butyl - 4 - methyl - phenol, and 3, 9 - bis 1-1,1 1,1 - dimethyl -2 - (3,5- ditert. - butyl -4- hydrox- yphenyl) - ethyls - 2,4,8, 10 - tetraoxaspiro [5, 51 undecane, and 2,2' - methylene - bis - (6 - tertiarybutyl - 4 - ethylphenol).

The amount of phenolic antioxidant which is to be used ranges from about 0.05 phr to about 1.0 phr.

Preparation of the phosphite esters herein is illustrated by the following specific examples.

Example 1 To 200 g. of amalgamated zinc there is added a solution of 200 ml. of concentrated hydrochloric acid in 300 ml. of water, then a 25% ethanolic solution of 729. (0.29 mol) of 4 - methyl - 2 - nonanoyl-phenol.

The mixture is heated at reflux for nine hours with stirring, treated with 200 ml. of toluene and then permitted to cool. The organic layer is isolated, washed with water, filtered and freed of solvents by stripping. The residue is distilled to yield 57% (of the theory) of 4 - methyl - 2 - n - nonylphenol.

Example 2 The procedure of Example 1 is repeated using 80 g. (0.29 mol) of4 - methyl - 2 - dodecanoylphenol as a reactant instead of4 - methyl - 2 - nonanoylphenol.

The yield of4 - methyl - 2 - dodecylphenol is 56% of the theory.

Example 3 An 83-9. sample of phenol is dried by azeotropic distillation until no more water distills, then heated at 155 C and treated portionwise, under argon, with 0.83 g. of aluminum granules. After the evolution of hydrogen has ceased, the temperature is allowed to drop to 145 C and 50 g. of 1-nonene is added slowly.

The temperature is maintained with stirring, at 145-150 C for six hours. The excess phenol and unreacted nonene are removed by distillation at reduced pressure and the residue washed with 5% aqueous hydrochloric acid solution, then with water until the washings are neutral to litmus. Distillation of the residue yields 30 g. (34% of the theory, 93% conversion) of a clear, colorless liquid boiling at 94"C110 mm. Over 98% of it is the o - (1 - methyloctyl) phenol.

Example 4 The procedure of Example 3 is repeated using 1 octene instead of 1-none. The product, a clear, water-white liquid boiling at 100-107 C/0.10-0.18 mm., contains 93% of the desired o-(1-methylheptyl) phenol; it was obtained in a 76% (of the theory) yield.

Example 5 The procedure of Example 3 is repeated using propylene trimer instead of 1-nonene. The product is a clear, water-white liquid boiling at 105-1100C/0.25 mm. It is obtained in a 39% yield and contains 88% of the desired o-nonylphenol.

Example 6 The procedure of Example 3 is repeated using diisobutylene instead of 1-nonene. A 45% yield of clear, water-white liquid is obtained containing 89% of the desired o-octylphenol.

The hydrolyticallystable phosphites of the invention may be prepared as follows: To 1.0 mol ofthe o-alkylphenol, at 55or, there is added, slowly, 0.30 mol of phosphorous trichloride.

The reaction initially is exothermic, but late., external heating is required to maintain the temperature at 55"C. When all of the phosphorous trichloride has been added, the temperature is raised, in an argon atmosphere, to 180-2500C and kepttherefor23-33 hours. The residue is distilled yielding a clear, colorless liquid.

The following tris - (o - alkylphenyl) phosphites, having the structural formula

are prepared by this method: R' R Yield Example7 methyl n-nonyl 99% Example8 methyl n-dodecyl 99% Example 9 H 1-methylheptyl 99% Example 10 H 1-methyloctyl 41% The purity of the products obtained as above is high, ranging from 93% to 99%.

The hydrolytic stability of these tris-) oalkyl-phenyl) phosphites may be shown by the results of a test carried out in aqueous tetrahydrofuran. A 2% solution of the phosphite sample in a mixture of 80 parts of tetrahydrofu ran and 20 parts of water is maintained at 44"C and a pH of 4.5 for 48 hours. The disappearance of phosphite is monitored by means of liquid chromatographic analyses.

A commercial sample of tris - (nonylphenyl) phosphite containing 92% of the para isomer, 6% of the ortho isomer and 2% of the dinonyl compound, is found to be completely hydrolyzed after 140 hours. A corresponding sample of tris - (nonylphenyl) phosphite containing 88% of the ortho isomer and 12% of the para isomer is 10% hydrolyzed after 140 hours and only 50% hydrolyzed after 760 hours.

Similarly, a sample of tris - (1 - methylheptylphenyl) phosphite (wherein 92% of the alkylphenyl groups are 2-alkylphenyl and 7% are 2,4 - dialkylphenyl) was only 50% hydrolyzed after 700 hours.

The hydrolytic stability of these tris - (o - alkylphenyl) phosphites in acidic aqueous emulsions is shown by the results of a test where 10 parts of a phosphite sample is mixed with a solution of 2.1 parts of an anionic organic phosphate in 34 parts of water. The resulting emulsion is added to 400 parts of water, warmed to 550C and the pH adjusted to 2.5 by the addition of concentrated hydrochloric acid.

This diluted emulsion is allowed to cool and stand for 10 hours. The pH is adjusted to 7 with dilute aqueous potassium hydroxide solution and the emulsion poured into 600 parts of 5% aqueous calcium chloride solution at 85"C. The mixture is cooled, extracted with benzene and the benzene extract dried and evaporated to an oily residue. The extent of hydrolysis is determined by liquid chromatographic analysis.

Samples of the above commercially available tris (nonylphenyl) phosphite and tris - (ortho - 1 - methyl - heptylphenyl) phosphite are subjected to the above test: the former is completely hydrolyzed; the latter is hydrolyzed to the extent of 30%.

The effectiveness ofthetris-(o-alkylphenyl) phosphites herein as polymer stabilizers in a hydrolyzing environment is shown as follows: A stabilizing emulsion is prepared by adding a solution of 6.25 parts of the phosphite and 1.15 parts of oleic acid to a hot solution of 0.55 part oftriethanol amine in 17 parts of demineralized water and mixing with a high speed stirrer for one minute. The resulting emulsion is added to 325 parts of polybutadiene latex and the mixture stirred for 12 hours. The mixture then is coagulated at 85"C by addition of 1.5% aqueous sulfuric acid and the polybutadiene crumb collected, washed and dried.The dried crumb is aged in an oven atl000Candthetime requiredforthe development of an overall brown color taken as a measure of the stability of the polybutadiene.

Samples of the above commercially available tris - (nonylphenyl) phosphite (A) and the tris - (ortho 1 - methyl - heptylphenyl) phosphite (B) of Example 9 are subjected to this test, with the following results: Table I Phosphite Hours to Coloration A 100 B 130 none 30 The superiority of the o-alkylphenyl-substituted phosphite is apparent.

The efficacy of the tris - (o - alkylphenyl) phos phites of the present invention as stabilizers in polypropylene is shown by the results of heat stabil ity tests carried out as follows: The various ingre dients (including a phosphite stabilizer) of the polymer composition are dry blended in a mechanical blender, then extruded into a 1-mil sheet which is cut into 12-inch discs. These are aged in an oven, at 150 C, until they begin to develop color and surface crazing. The time required for such failure is taken as a measure of the effectiveness of the phosphite stabilizer. In each case the test sample contained the following ingredients: 100 parts of polypropylene, 0.10 phr (parts per 100 parts of resin) of calcium stearate, and 0.10 phr of the pentaerythritol ester of 3 - (3, 5 - di - tert - butyl - 4 - hydroxy - phenyl) propionic acid.

Tablell Hours Test Sample Phosphite to Failure 1. none 448 2. 0.25 phrtris-(2-tert- butyl-phenyl) phosphite 688 3. 0.25 phrtris-(nonylphenyl) phosphite where 88% of the nonyl groups are ortho and 11% are para 701 Other additives can also be added to the olefin polymer compositions of this invention, including ultraviolet stabilizers, anti-static agents, fillers, pigments, lubricants and the like.

Claims (6)

1. A polymer composition comprising an olefin polymer and a minor amount, sufficient to impart improved heat stability to said polymer, of a tris (alkylphenyl) phosphite material wherein (1) at least 85% of one of the ortho positions in each phenyl group are substituted by alkyl groups of 8 to 12 carbon atoms and (2) at least 85% of the para positions in each phenyl group are unsubstituted, or substituted by methyl groups.

2. A polymer composition according to claim 1 wherein the tris - (alkylphenyl) phosphite material has the structure:

wherein at least 85% of R2 is alkyl of 8 to 12 carbon atoms, the remainder being hydrogen, and at least 85% of R1 is methyl or hydrogen.

3. A polymer composition according to claim 2 wherein the tris (alkylphenyl) phosphite material has the structure:

wherein R is alkyl of 8 to 12 carbon atoms.

4. A polymer composition according to claim 1, 2 or 3 wherein the olefin polymer is polypropylene.

5. A polymer composition according to claim 1 wherein the tris (alkylphenyl) phosphite material is substantially as described in any one of Examples 1 to 10.

6. Shaped articles of a composition as claimed in any one of the preceding claims.