GB2046273A - Stabiliser for polymers - Google Patents

Abstract

A polymer stabiliser composition comprising a bis-(2,4-dialkyl- phenyl) pentaerythritol diphosphite and a minor proportion of triisopro- panolamine is provided. The triiso- propanolamine is present to reduce or prevent the stabiliser composition from absorbing moisture prior to the addition of the composition to a polymer such as a vinyl chloride polymer, an olefin polymer or a polycarbonate.

Description

SPECIFICATION Stabilizer for polymers The purpose of stabilizers for polymers is to prevent deterioration of the polymers during processing at high temperatures, and also to permit manufacture of products with increased intrinsic quality because of the enhancement of their resistance to thermal and light degradation during use. In addition, because of the ability of these products to withstand more rigorous conditions, their versatility is increased and new areas of application are hereby opened.

An important class of polymer stabilizers are the organic phosphites.They include, as an especially useful group, the bis-(2,4-dialkylphenyl)pentaerythritol diphosphites. They are useful in the stabilization of vinyl chloride polymers, polyolefins and styrene polymers such as ABS.

They have the structural formula:

where R and R' are 2,4-dialkylphenyl groups. The alkyl groups preferably contain 3-9 carbon atoms.

Despite their considerable stabilizing properties, however, this type of stabilizer, like other phosphite esters, tends to absorb moisture from a moist environment and their effectiveness as stabilizers for polymers seems to decline in direct proportion to the amount of water absorbed.

This disadvantage can be avoided by taking care to store and transport the stabilizer only in a dry atmosphere. Once incorporated in a vinyl polymer composition, no problem is presented apparently because of the essentially anhydrous condition of such polymer compositions.

Obviously, though, elimination or at least amelioration of the problem is desirable. A moistureinsensitive phosphite stabilizer will preclude the many inconveniences and expense associated with having to maintain an anhydrous environment.

U.S. 3;553,298 (Hodan) shows the stabilization of phosphite esters broadly by using any of several classes of amines including triisopropanolamine. See column 2, line 24 and Examples l-lV.

M. G. Imaev, Zhurnal Obshcei Khim. 31, 1767-70 (1961) shows the stabilization of lower trialkyl phosphites with organic and inorganic bases. The organic bases shown include pyridine, triethyl amine and dimethyl aniline.

U.S. 2,114,866 (Vaughn) shows the stabilization of esters of inorganic esters with an amine.

While Vaughn is interested primarily in organic silicates he does mention also (see page 2, column 2, lines 17-22) borates, phosphates, "symmetrical" phosphites, arsenates and symmetrical arsenites.

U.S. 3,787,537 (Marcq) discloses a class of phosphite esters which are said to be stable to hydrolysis. Marcq refers also (see column 2, lines 9-10) to the stabilization of previously known phosphites by "a small quantity of a heavy amine, usuaily triisopropanolamine (French Patent No. 1,582,387)." The cited French patent is a counterpart of the above Hodan et al U.S.

patent.

The stabilization of certain narrowly defined classes of phosphite esters is shown in Specification No. 1511105. The stabilization is accomplished by means of triisopropanolamine.

None of the above disclosures, however, deal with the type of specific phosphites which are rendered resistant to hydrolysis by the invention here.

Accordingly, the present invention is directed to the stabilization of a bis-(2,4-dialkylphenyl)pentaerythritol diphosphite wherein the alkyl groups each contain 3-9 carbon atoms, with a minor proportion of triisopropanolamine, and to polymer compositions containing the thus stabilized phosphites.

The Bis-(2, 4-Dialkylphenyl)Pentaeryfhritol Diphosphites The bis-(2,4-dialkylphenyl)pentaerythritol diphosphites above may be prepared by reaction of the corresponding 2,4-dialkylphenol with diphenyl pentaerythritol diphosphite, according to the following equation:

The reaction is best carried out with an alkaline catalyst, preferably an alkali or alkaline earth metal compound. This method of preparation is described more specifically in Specification No.

1 506603. The preferred species here, viz., bi(2,4-ditertiarybutylphenyl)pentaerythritol diphosphite, can be purified by crystallization from any of a number of solvents including heptane, perchloroethylene and the like. Its melting point is 167-1 72 C. These diphosphites may be prepared also from dichloro pentaertythritol diphosphite.

The diphosphites of this invention normally are solids. The handling of solids, i.e., in storage and transportation, requires considerably more exposure to the atmosphere (and its humidity) than is the case of a liquid. Furthermore, a solid presents a greater surface area per unit weight to the humidity of an atmosphere. Thus, the problem of hydrolytic stability is made more difficult than for liquid phosphites.

It is of course well known that triisopropanolamine itself is hygroscopic. Thus, its property of stabilizing the phosphites herein against hydrolysis is surprising. The addition of one hygroscopic material, i.e., triisopropanolamine, to a second hygroscopic material, i.e., the phosphites herein, would not ordinarily be expected to result in a composition which is less hygroscopic than either of these, and which is stable in a humid environment.

The stability of the compositions herein is shown by the results of tests carried out under conditions of controlled humidity and temperature. Five-gram samples of a bis(2,4-ditertiarybutylphenyl)pentaerythritol diphosphite, with and without 0.5% of triisopropanolamine, are weighed carefully, then placed in a humidity cabinet wherein the relative humidity and temperature are maintained at 68% and 28"C, respectively. The sample is weighed periodically and the percentage increase (owing to water absorption) recorded.The results are shown in TABLET, TABLE I Weight Gain (%) Time With Without (hours) Triisopropanolamine Triisopropanolamine 0 0 0 1 0 0 3 0 0.2 7 0 1.0 15 0 5.2 24 0 10.2 36 0 11.2 48 0 12.6 60 0 13.2 72 0 13.6 84 0 13.6 96 0 13.4 The above samples of b;a(2,4-ditertiarybutylphenyl)pentaerythritol diphosphite were prepared as indicated earlier-herein, i.e., from diphenyl pentaerythritol diphosphite by transesterification with 2,4-ditertiarybutylphenol. Samples prepared from dichloro pentaerythritol diphosphite invariably are characterized by a relatively high acid number and are not as susceptible to stabilization, with respect to hydrolysis, by triisopropanolamine. This is so even if the sample is washed with alkali in an attempt to eliminate the acid number. Test results obtained under the same conditions as above, i.e., 68% relative humidity and 28"C, are set out in TABLE II. The samples are bis(2,4-ditertiarybutylphenyl)pentaerythntol diphosphite, with and without 0.5% triisopropanolamine, prepared from dichloro pentaerythritol diphosphite, and then washed with 2% aqueous sodium carbonate solution. The washed samples had an acid number of 1.4; the addition of 0.5% triisopropanolamine reduced this value further to 0.3.

TABLE II Weight Gain (%) Time With Without (hours) Triisopropanolamine Triisopropanolamine 0 0 0 2 0 0 4 0 0 7 0 0.8 10 0.6 4.2 14 3.8 7.0 23 7.2 8.0 31 7.0 8.6 47 8.6 9.0 It will be noted that absorption of moisture in each case is significantly diminished by the presence of the triisopropanolamine. Such absorption of moisture is a direct reflection of hydrolysis of the phosphite stabilizer which in turn diminishes the effectiveness of the phosphite as a stabilizer.

The triisopropanolamine should be present in a cbncentration within the range of from about 0.01% to about 5% based on the weight of the stabilizer composition. Preferably, the concentration should be within the range of from about 0.1 % to about 3.0%.

The stabilized phosphites herein are used in polymers in concentrations ranging from about 0.5% to about 3.0% based on the entire composition. They are especially useful in vinyl chloride and olefin polymers, and in polycarbonates.

All parts and percentages herein are by weight unless otherwise expressly stated.

Claims (11)

1. A polymer stabiliser composition comprising a bis-(2,4-dialkylphenyl)pentaerythritol diphosphite, wherein the alkyl groups each contain from 3 to 9 carbon atoms, and a minor proportion of triisopropanolamine.

2. A composition according to claim 1 wherein the alkyl groups are tertiary alkyl groups.

3. A composition according to claim 2 wherein the alkyl groups are tertiary butyl groups.

4. A composition according to any one of the preceding claims wherein the triisopropanolamine is present in an amount of from 0.01% to 5% based on the weight of bis-(2,4dialkylphenyl)pentaerythritol diphosphite.

5. A composition according to claim 4 wherein the triisopropanolamine is present in an amount of from 1.0% to 3.0% bsed on the weight of bis-(2,4-dialkylphenyl)pentaerythritol diphosphite.

6. A composition according to any one of the preceding claims wherein the bis-(2,4dialkylphenyl)pentaerythritol diphosphite has been prepared from diphenyl pentaerythritol diphosphite.

7. A composition according to any one of claims 1 to 5 wherein the bis-(2,4-dialkylphenyl)pentaerythritol diphosphite has been prepared from dichloro pentaerythritol diphosphite.

8. A composition according to claim 1, wherein the bis-(2,4-dialkylphenyl)pentaerythritol diphosphite has been prepared from diphenyl pentaerythritol diphosphite, substantially as hereinbefore described.

9. A composition according to claim 1, wherein the bis-(2,4-dialkylphenyl)pentaerythritol diphosphite has been prepared from dichloro pentaerythritol diphosphite, substantially as hereinbefore described.

10. A polymer composition comprising sufficient of the composition claimed in any one of the preceding claims to stabilise the polymer.

11. A composition according to claim 10 wherein the polymer is a vinyl polymer, an olefin polymer or a polycarbonate.

1 2. Shaped articles of the polymer composition as claimed in claim 10 or 11.