Stabilized Ethylene-Carbon Monoxide Copolymers

This invention relates to ethylene-carbon monoxide copolymers and more particularly to heat stable ethylene-carbon monoxide copolymer compositions.

Ethylene-carbon monoxide copolymers are of considerable interest because of their potential as engineering plastics. These materials have physical properties which are superior to many other materials commonly used in industry and, in addition, offer the advantage of low cost since carbon monoxide is readily available as a by-product in the manufacture of steel and can also be inexpensively prepared from other chemical processes.

In spite of the advantages offered by ethylene-carbon monoxide copolymers, they have not attained commercial acceptance partly due to the fact that they have poor resistance to thermal degradation during post polymerization processing operations. Since polymeric end products such as films, sheets and shaped articles are most commonly made by heating and melting polymeric compositions and extruding or injection molding the melt, it is very important that these compositions be able to withstand the temperatures encountered in such post forming operations.

Ethylene-carbon monoxide copolymer compositions have now been discovered which have greater resistance to thermal degradation. Accordingly, it is an object of the invention to present improved ethylene-carbon monoxide copolymer compositions. It is another object of the invention to present ethylene-carbon monoxide which have improved heat stability. It is another object of the invention to present ethylene-carbon monoxide copolymers which will not undergo serious color degradation during post polymerization processing operations at elevated temperatures. These and other objects of the invention will become more apparent from the description and examples which follow.

In accordance with the present invention, the thermal stability of ethylene-carbon monoxide copolymers is significantly improved by incorporating therein a small amount of a substituted 2-(2'-hydroxyphenyl)-benzotriazole compound which contains one or more substituents selected from the group consisting of H, halogen, cyclohexyl or straight or branched-chain alkyl groups having up to 8 carbon atoms.

The molecular weight and chemical constitution of the ethylene-carbon monoxide copolymers treated in accordance with the invention are not critical and, in general, any ethylene-carbon monoxide copolymer can be stabilized by the disclosed stabilizers. The following details are intended to be descriptive and not limitative. The ethylene-carbon monoxide copolymer compositions most improved by the stabilizers of the invention are those having molecular weights in the range of about 500 to 50,000 or more and containing up to 50 weight percent carbon monoxide. The most useful ethylene-carbon monoxide copolymers contain about 1 to 50 weight percent carbon monoxide. As can be readily appreciated, the copolymer compositions may contain additional polymeric components which may be either physically admixed with the ethylene-carbon monoxide copolymer or chemically combined with the ethylene and carbon monoxide as components of the copolymer. Monomers which may be copolymerized with the ethylene and carbon monoxide include ethylenically unsaturated aliphatic or aromatic compounds including olefins, such as propylene, isobutylene, etc.; dienes, such as butadiene, isoprene, etc.; acrylic monomers, such as acrylic acid, methyl methacrylate, acrylonitrile, etc.; aromatic compounds, such as styrene, vinyl toluene, etc. The additional polymeric component is usually present in amounts up to about 50% by weight.

The preparation of ethylene-carbon monoxide copolymers is well-known and is described in detail in U.S. Pat. Nos. 2,495,286; 2,641,590; 3,083,184; 3,530,109; 3,694,412; and 3,689,460.

Compounds suitable as stabilizers in accordance with this invention are those having the structural formula: ##STR1## wherein R, R' and R" are the same or different radicals or atoms selected from the group consisting of H, halogen, cyclohexyl, and straight or branched-chain alkyl radicals containing up to 8 carbon atoms and preferably up to 6 carbon atoms.

In most preferred embodiments of the invention R is in the 5 position and is H or halogen, preferably chlorine or bromine; and R' and R" are in the 3' and 5' positions and are H or straight or branched chain alkyl groups having up to 5 carbon atoms. Typical stabilizers useful in the compositions of the invention include 5-chloro-2(3',5'-di-t-butyl-2'-hydroxyphenyl)-benzotriazole, 2(3',5'-di-t-amyl-2'-hydroxyphenyl)-benzotriazole, 2(2'-hydroxy-5'-methylphenyl)-benzotriazole, 2-(5'-t-butyl-2'-hydroxyphenyl)-benzotriazole, 2-(5'-t-butyl-2'-hydroxy-3'-methylphenyl)-benzotriazole, 6-bromo-2(3'-cyclohexyl-2'-hydroxyphenyl)-benzotriazle, etc. The preferred stabilizers are 5-chloro-2-(3',5'-di-t-butyl-2'(-hydroxyphenyl)-benzotriazole, 2(3',5'-di-t-amyl-2'-hydroxyphenyl)-benzotriazole and 2(2'-hydroxy-5-methylphenyl)-benzotriazole. The above compounds and their preparation are described in detail in U.S. Pat. No. 3,189,615. Several of the above compounds are available on the market; for example, they are sold by Ciba-Geigy Corporation under the trademark Tinuvin.

The substituted 2-(2'-hydroxyphenyl)-benzotriazole stabilizers are effective in total amounts of about 0.1% to about 20%, based on the total weight of ethylene-carbon monoxide copolymer in the composition. The preferred concentration of these stabilizers in the composition is about 1 to 15% based on the total weight of ethylene-carbon monoxide present in the composition. If desired, mixtures of two or more substituted 2-(2'-hydroxyphenyl)-benzotriazole compounds may be used in combination to stabilize the ethylene-carbon monoxide copolymers. In this case the total amount of the substituted benzotriazole compounds used is about 0.1 to 20% and preferably about 1 to 15% based on the weight of ethylene-carbon monoxide copolymer in the composition.

The substituted 2-(2'-hydroxyphenyl)-benzotriazole compounds or mixture of these may be used in combination with other stabilizers or antioxidants if desired. The amount of other stabilizer or antioxidant used in the composition may vary over the same range as the substituted 2-(2'-hydroxyphenyl)-benzotriazole, i.e., about 0.1 to 20% and preferably about 1 to 15% based on the weight of ethylene-carbon monoxide in the polymeric composition.

The substituted 2-(2'-hydroxyphenyl)-benzotriazole stabilizer or mixture of stabilizers can be incorporated into the compositions by any of the known methods. For instance, they may be incorporated into the polymerization mixture prior to or during the polymerization. This method has the advantage of stabilizing the polymer from the time it is formed. The stabilizers can also be incorporated into the polymer after the polymerization is completed. This is most conveniently accomplished by blending the stabilizer into the copolymer which is usually in the form of a melt or fine particles. The stabilizer may be incorporated into the copolymer composition in the form of a powder or dissolved in a solvent. The method of incorporating the stabilizers into the copolymer composition is not considered to be critical.

Other additives such as fillers, extenders, plasticizers, coloring agents, other polymeric materials, etc., can be added to the copolymer compositions being stabilized. These are usually most conveniently added to the polymer after the polymerization.

The following examples illustrate specific examples of the invention. Unless otherwise indicated, parts and percentages are on a weight basis.

A sample of ethylene-carbon monoxide copolymer containing 48.6% by weight carbon monoxide is placed on a Fisher-Johns melting point block set at 250.degree. C and the melting is observed. After 11/2 minutes the melted polymer is examined and observed to have a dark brown color and exhibit gelling and surface skin formation.

A sample of the same ethylene-carbon monoxide copolymer used in Example I is ground with 10%, based on the weight of copolymer, of a mixture containing 50% by weight 2-(3',5',-di-t-amyl-2'-hydroxyphenyl)-benzotriazole and 50% by weight 5-chloro-2(3',5'-di-t-butyl-2'-hydroxyphenyl)-benzotriazole and placed on a Fisher-Johns melting point block set at 250.degree. C and the melting observed. After 5 minutes the melted polymer is examined and observed to have a light yellow color and no gelling or surface skin formation.

The procedure of Example II is repeated except that the stabilizer is replaced, on an equal weight basis, with a mixture containing 25% by weight 2-(3',5',-di-t-amyl-2'-hydroxyphenyl)-benzotriazole, 25% by weight 5-chloro-2(3',5',-di-t-butyl-2'-hydroxyphenyl)-benzotriazole and 50% by weight KH.sub.2 PO.sub.4. After 5 minutes on the Fisher-Johns melting point block the sample has a light yellow color and exhibits no gel or skin formation.

Examples II and III illustrate the improved color stability, gel, and skin formation resistance obtained when epoxy compounds are blended into an ethylene-carbon monoxide copolymer as stabilizers. Example I is a stabilizer-free control.

The procedure of Example II is repeated except that 2-(3',5'-di-t-amyl-2'-hydroxyphenyl)-benzotriazole is substituted for the stabilizer mixture on an equal weight basis. The resulting composition will exhibit improved thermal stability and improved gel and skin formation resistance.

The procedure of Example II is repeated except that 5-chloro-2-(3',5'-di-t-butyl-2'-hydroxyphenyl)-benzotriazole is substituted for the stabilizer mixture on an equal weight basis. The resulting composition will exhibit improved thermal stability and improved gel and skin formation resistance.

Although the invention is described with particular reference to specific embodiments, the scope of the invention is not limited thereto but is defined by the breadth of the appended claims.