Stabilization of Polymeric Compositions

The present invention relates to halogenated polymeric compositions stabilized against the degradative effects of heat. When used herein the term "halogenated polymeric composition" means polymers or co-polymers containing at least 25% by weight of vinyl and/or vinylidene halide and products obtained by post halogenation of such polymers.

Monoalkyltin compounds have been employed as stabilizers for poly(vinyl chloride) (P.V.C.) and similar resins; however, it has been preferable to employ diorganotin compounds, which in general exhibit a superior stabilizing effect.

It has now been found that an unexpected synergistic stabilizing effect, as demonstrated by improved color and prolonged resistance to color change, can be obtained for halogenated polymeric compositions by incorporating into them a mixture of particular monoalkyltin compounds and alkyl, aryl, or mixed alkyl-aryl esters of phosphorous acid, which are themselves quite widely used as secondary stabilizers in combination with various heat stabilizers for P.V.C. We have found that this synergistic effect is most pronounced for monoalkyltin compounds containing no tin-oxygen bonds, is very much less evident for the analagous di- or tri-alkyltin compounds, and appear to be absent for monoalkyltin compounds which do not contain a tin-sulfur bond.

The present invention provides halogenated polymer compositions wherein the stabilizer comprises (1) one or more organotin compounds exhibiting a general formula selected from the group consisting of ##EQU1## (R.sup.1 SnS.sub.1.5).sub.n, and ##EQU2## wherein R.sup.1 and R.sup.3 each represent an alkyl radical of from 3 to 18 carbon atoms, an aryl or an alkaryl radical, R.sup.2 represents an alkylene hydrocarbon radical and R.sup.4 represents the radical ##EQU3## and (2) an alkyl, aryl, or mixed alkyl-aryl ester of phosphorous acid and n is an integer between 2 and 5.

This invention also provides compositions suitable for stabilizing halogenated polymeric compositions, said compositions comprising (1) a monoorganotin compound as described hereinabove and (2) an alkyl, aryl, or a mixed alkyl-aryl ester of phosphorus acid.

Halogenated polymers for which the stabilizers of the present invention are particularly suited include poly(vinyl chloride), poly(vinylidene chloride), post chlorinated products thereof, copolymers of vinyl chloride with vinylidene chloride or copolymers of either or both with acrylic and methacrylic acids, vinyl acetate, diesters of fumaric or maleic acids, ethylene and propylene. Such copolymers contain at least 25% by weight of vinyl chloride or vinylidene chloride.

Organotin compounds useful in the present invention are those having at least one monoorganotin group (i.e. compounds wherein at least one tin atom has only one tin-carbon bond), the tin atom of which is directly bonded to a sulfur atom. Suitable compounds are those having an ##EQU4## grouping. These include monalkyl thiostannoic anhydrides and their esters and condensation polymers. Preferred, however, are monoalkyltin tris mercaptocarboxylic acid esters, in particular, monoalkyltin tris alkyl thioglycollates, compounds of the formula ##EQU5## produced by the reaction of diorganotin sulfides with monoorganotin tris mercaptocarboxylic acid esters and mixtures of these sulfides with monoorganotin tris-mercaptocarboxylic acid esters. R.sup.1 and R.sup.4 represent a hydrocarbon radical and a residue of a mercaptocarboxylic acid ester, respectively as previously defined. Other organotin compounds may be present in the present compositions. For example, di- or trialkyltin mercaptocarboxylic acid esters may be present in admixture with the monoalkyltin compounds.

Among the monoalkyltin compounds which are particularly useful are butyl thiostannoic anhydride, octylthiostannoic anhydride, n-butyltin tris-iso-octylthioglycollate, n-octyltin tris-iso-octyl thioglycollate, monobutyltin iso-octylthioglycollate sulfide, i.e. ##EQU6## and the 2-ethylhexyl ester analogue, n-butyltin tris iso-octyl-.beta.-mercaptopropionate, n-octyltin tris iso-octyl-.beta.-mercaptopropionate, methyltin tris octylthioglycollate, phenyltin trisisooctyl thioglycollate. Preferred compounds of the formula ##EQU7## referred to above are the condensation product of dibutyltin sulfide with monobutyltin tris iso-octyl thioglycollate and of dioctyltin sulfide with octyltin tris iso-octyl thioglycollate. Other compounds which may be employed include cyclohexyltin tris-iso-octyl thioglycollate, n-butyltin tris-decyl thioglycollate, octyltin tris nonyl thioglycollate, cyclohexyl tin tris-iso-octyl thioglycollate and n-butyltin tris hexylthioglycollate, benzyltin tris iso-octyl thioglycollate.

Esters of phosphorous acid which may be employed in compositions according to the invention include polymeric phosphites such as hydrogenated 4,4'-isopropylidene diphenol diphosphite. Preferred phosphites are monomeric compounds having no substitutents on the hydrocarbon radicals. These include triaryl, trialkyl, and mixed alkyl-aryl phosphites. Such compounds include, for example, triphenyl phosphite and trixylylphosphite. Suitable mixed alkyl-aryl phosphites include octyl diphenyl phosphite, isodecyl diphenyl phosphite and diisodecyl phenyl phosphite. Similar stabilization can also be obtained by employing a mixture of a triaryl phosphite and an aliphatic alcohol, preferably having from 8-20 carbon atoms, in conjunction with the organotin compound. A particularly suitable mixture is that of triphenyl phosphite and isodecanol.

We have further found that it is particularly beneficial if the compositions also contain a hindered phenol as secondary antioxidant. Such hindered phenols contain an alkyl group in both positions ortho to the hydroxyl group and are frequently present in amounts of from 0.05-0.15 of the total composition. Suitable compounds include 2,6-dimethylphenol 2,6-di-t-butylphenol, bisphenols such as 2,2'-bismethylene 6,6'-dimethyl phenol. Particularly preferred, however, is 2,6-di-ti-butyl-p-cresol, available under the tradename "Topanol O"

The stabilizer compositions of this invention are particularly useful when employed in polymer compositions containing an epoxy compound, which serves to delay the initial discoloration of the resin composition. Epoxy compounds which may be employed in such compositions include esters of epoxidized oleic acid and compounds of the formula ##EQU8##

The organotin compounds will normally be present in compositions of the invention in amounts of from 1-5%, preferably from 2-3% by weight based on the weight of halogenated polymer and the esters of phosphorous acid in amounts of from 2-10% by weight, preferably from 4-6% by weight on the same basis. We have found that it is particularly desirable to employ from 1.0-2.5 moles of phosphite for each mole of monoalkyltin compound.

In the practice of the invention the stabilizer system can be mixed with the halogenated polymeric compositions in conventional manner, for example, by milling with the resin on heated rolls at about 150.degree.C., although higher temperatures may be used when convenient, or by being mixed with particles of the polymer and then melting and extruding the mixture or by adding the stabilizer to a liquid resin.

The stabilizer systems of the present invention can be employed in plasticized resin compositions, for example, those plasticized with carboxylate ester plasticizers such as dioctyl phthalate and butyl benzyl phthalate or triaryl phosphate plasticizers (such as those derived from phenols obtained synthetically or from coal tar) or may be employed in unplasticized, that is rigid, compositions.

Compositions according to the invention are illustrated by the following Examples in which all parts are by weight unless otherwise stated.

The stabilizer (compound mixture and quantity as in the table that follows) was milled at 150.degree.C. for 10 minutes with 100 parts of Corvic D55/9 poly(vinyl chloride). Portions of the resulting sheet were oven aged in air at 200.degree.C. The heating time and color of the test samples are indicated in the table.

The stabilizer compositions shown in the following table were milled with 100 parts Corvis D55/9 polyvinyl chloride as described in Example 1 and tested in a similar manner.

Test compositions were prepared as in Example 1 and tested in a similar manner. The results of the tests are shown below.

Test compositions were prepared as in Example 1 and tested as shown below.

Test compositions were prepared as in Example 1 and tested as shown below.

Test compositions were prepared as in Example 1 and tested as shown below.

The compositions were prepared as described in Example 1 and tested with the following results.