CA1045745A - Polymeric composition possessing built-in antioxidant characteristics - Google Patents

Abstract

Abstract of the Disclosure An oxidation resistant polymeric composition comprising the reaction product of some carbon-to-carbon double bond unsaturated polymers and a 1,3-dipolar compound corresponding to the general formula

Description

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This invention relates to age resistant polymeric com-positions. More particularly~ the invention relates to poly-meric compositions that possess a high degree of resistance to the deleterious effects o~ oxidative aging.
Essentially all types of ru~bers, both na-tural and syn-thetic~ and particularly rubbers formed from dienes are knDwn to be susceptible to deterioration resulting from prolonged exposure to oxidative aging. A great deal of effort has been expended by those engaged in the field of polymer tech-nology to develop various stabilizers or antioxidants that will effectively inhibit the adverse effects o~ aging of these -types of polymeric compositions. Many ef~ective sta-bilizing materials, such as various aromatic amines and phe-nolic compounds have been developed to combat oxidative a~ng.
However, the prior art types of antio~idants~ which are mixed into rubbers using conventional rubber compounding techniques, are subject to volatilization when the rubbers are exposed to elevated temperatures for prolonged periods of time. Also, many of the prior art antioxidan-ts may be extracted from the rubbers i~ exposed to repeated contact with water or aqueous detergent solutions, for instance, wh~
the rubber is exposed to weathering or is employed in wear-ing apparel. I~ the rubber containing the prior art antioxi-dant is subjected to organic solvents~ the antioxidant may also be ex-tracted.
I-t is therefore an object of this invention -to provide polymeric materials, particularly rubbers~ that are highly resistant to oxidative attack. It is an object to provide compositions in which the antioxidants are not subject ~ .'i3 ~ ~ ~S ~ ~5 to loss either by volatilization or extraction. Another object is to provide rubber compositions containing anti-oxidants which are chemically bound to the rubber. Further objects will become apparent as the description of the in-vention proceeds.
In accordance with the present invention there is pro-vided an oxidation resistant polymer composition comprising the reaction product of ~A) a rubbery polymer9 having car-bon-to-carbon double bond unsatura-tion in or pendant from the polymer chain, s.elected from the group consis-ting of (1) natural rubber, (2) homopolymers and copolymers of con-jugated diolefins 7 ( 3) copolymers of conjugated diolefins and monovinyl-substituted aromatic hydrocarbons, ~4) copoly-mers of conjugated diole~ins and acrylonitrile, (5) copoly-mers of conjugated diole~ins and alpha ole~ins~ and (6) in--terpolymers of one or more lower alkyl a~olefins and a diene monomer, and (B) a 1,3-dipolar compound corresponding to the general formula 0~ ~C(CH3)3 R - N _ G~H ~ O ~

. C(CH3)3 wherein R is selected from a group consisting o:~ (1) alkyl radical containing ~rom 1 to 12 carbon atoms, (2) condensed ring aromatic radicals, (3) cycloalkyl radicals, (4) a phe~yl radical and (5) substituted phenyl radical containing at least one substituent ~rom the group consisting of chlorine~
bromine, iodine and fluorine atoms and alkyl, alkoxy, nitro, tertiary amino, cyano~ carboxyl and carboalkoxy radicals.

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~5~5 The oxidation resistant polymeric compositions o~ the present inven~ion are prepared by contacting a sulfur-cur-able rubbery polymer having carbon-to-carbon double bond un-sa-turatiorl in the polymer chain with a 1,3-dipolar compound corresponding to -the general formula above. The ],3-dipolar compound adds to -the polymeric material by means of a 1,3-dipolar cycloaddition reaction. This addi-tion takes place ~ across the carbon-to-carbon double bond of the polymeric ma-; terial employed. The result of this addition is a polymericcomposition contaîning five-membered heterocyclic rings iIl the polymer chain and having chemically bound thereto anti-oxidant func-tional groups. In other words, a polymeric com-position possessing built-in antioxidant characteristics.
The 1,3-dipolar cycloaddi-tion reaction is generally and conveniently carried out by mixing the polymeric material and the 1,3-dipolar compound together in an inert solvent, heating this reaction mixture to the reflux temperature and maintaining the reaction mixture at said temperature, with continuous agitationa u~til the addition reaction is complete.
Solvents suitable for preparing the oxidation resistant poly-meric compositions of the present invention are those inert hydrocarbon solvents selected from a group consisting of aliphatic, cycloaliphatic and aromatic hydrocarbons. By the ~erm "inert" ~s meant that the solvent employed neither in-terferes with the c~cloaddition reaction nor enters into the structure ofi~the resultant product of the cycloaddition re-action. Representative examples of suitable inert hydrocar-bon solvents include hexane~ heptane~ cyclohexane~ benzene, toluene and the like.

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As noted previously, the temperatures at which the 153-dipolar cycloaddition reactions are usually carried out are the reflux temperatures or more specifically the boiling point temperatures o~ the various solutions employed. It can be seen that the reaction temperatures may vary over a wide range. Therefore, the reaction temperature is not a critical parameter in preparing the polymeric compositions of ~his invention. However9 it is generally preferred to em-ploy solven-ts having high boiling points since higher tem-peratures generally give ~aster reaction rates. By the term "high" is meant temperatures of 670C. or higher.
The reaction time required to obtain the polymeric com-positions o~ this invention are of course dependent upon the temperatures at which the reactions are carried out and also upon the relative reactivity of the particular 1,3-dipolar compound employed toward the particular polymeric material employed. Generally it has been found that good results are obtained over a period of time ranging from a few hours to several days.
The amount of the 1~3-dipolar compounds~ corresponding to the general formula above~ employed to ~orm the oxidati~e resistant polymeric compositions of this invention can also vary over a wide range, but must be at least a stabili~ing amount. Satis~actory results may be obtained with weight ratios ranging from about 0.01 part per hundred parts of rub-ber (phr) to about 5 phr. A more preferred range is one ~rom about 0.1 phr to about 2.0 phr.
The 1,3-dipolar compounds useful in preparing the oxi-dation resi~tant polymeric compositions of the present in-.

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57~5 vention are those 1,3-dipolar compounds corresponding to the general ~ormula above and which may be prepared by the reac-tion of a nitroso compound corresponding to the formula R-N=0 where ~ is selected from the group consisting o~ (1) alkyl r~dical containing ~rom 1 to 12 carbon atoms~ (2) con-densed ring aromatic hydrocarbon radicals, (3) cycloalkyl radicals9 (4) phenyl radical and (5) substituted phenyl radi-cal containing at least one substituent selected ~rom the group consisting o~ chlorine, bromine, iodine and fluorine atoms and alkyl, alkoxy~ nitro, tertiary amine, cyano~ car-boxy and carboalkoxy radicals, with 3~5-di-t-butyl-4 hydroxy-benzyl pyridinium chloride~ In general, these reactions may A be carried out in any suitable inert organic solvent. Bythe term "iner-t" is meant that the solvent nei-ther enters in-to the structure nor interferes ~ith the preparation of the desired antioxidant. Suitable inert solvents include alco-hols such as methanol, ethanol, isopropanol and the like, ethers such as dioxane a tetrahydrofuran and the like, and ke-; tones and ni-triles such as acetone~ ace-tonitrile and the like.
Mixtures o~ the above solvents may also be employed with sa-tisfactory results. The amount o~ solvent employed may ran~
from about 2 to about 20 times the weight o~ the reactants present. Representative examples of the 1,3-dlpolar compounds which can be prepared by the above described reaction include:
1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-naphthyl nitrone;
1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-phenyl nitrone;
1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-butyl nitrone-1-(3,5-di--t-butyl-4-hydroxyphenyl)-N-(2-bromobutyl3nitrone;
1-(3~5-di-t-butyl-4~hydroxyphenyl)-N-cyclohexyl nitrone;
1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-(4~itrophenyl~itrone;
1-(3,5 di-t-butyl-4-hydroxyphenyl)-N-(3~thylphenyl)nitrone;
! 1-(3~5-di-t-butyl-4-hydroxyphenyl)-N-tolyl nitronei and 1-(3~5-di-t-butyl-4-hydroxyphenyl)-N-(2-ethoxypheny~nitrone.

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1~4~7~5 The sul~ur-curable rubbery polymers use~ul in prepar-ing the oxidation resistant polymeric compositions of this invention are those rubbery polymers having carbon-to-carbo~
double bond unsaturation in or pendant from the polymer chain. Said polymers include natural rubber, homo- and co-polymers of conjugated diolefins~ copolymers of conjugated diolefins and monovinyl-substituted aromatic hydrocarbons, copolym~rs oL conjugated diolefins and acrylonitrile, copoly-mers of conjugated diolefins and alpha olefins and polymers of lower alkyl alpha olefins and diene monomers. They also include polymers or copolymers prepared by ring opening of one or more cyclic monomers such as polypentenamer, polyoc-tenamer, etc.
Representative examples of the above rubbery polymers include natural rubber~ polybutadiene~ polyisoprene, buta-diene/isoprene copolymers~ butadiene/styrene and isoprene/
styrene copolymers, butyl rubber which is prepared from a mixture of a major proportion of isobutylene and a minor pro-portion of a conjugated diole~in, butadiene/acrylonitrile copolymer, butadiene/ethylene copolymer, ethylene/propylene/
hexadiene terpolymer and the like.
The following examples are representative of the inven-tion and are not intended to be restrictive in their nature as to the scope.
LE I
To a clean dry 250 ml. round bottom 3-neck flask equip-ped with a magnetic stirrer, thermometer and addition ~unnel was added 6.69 g. (0.02 mole) of 3,5-di-t-butyl-4-hydroxy-benzylpyridinium chloride in 100 ml. of e-thanol and 2.36 g.

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(0.022 mole) of nitrosobenzene. The clear solutio.n was cool.ed to 0 to 50C. and sodium hydroxide (2.~5 g.; o.o6 mole) in 60 ml. of water was added dropwise in 40 minutes. The reaction mixture was stirred an additional 3 hours at am-bient temperature and -then diluted with 50 ml. water, fil-tered, and the collected product dried to yield 5.07 g.
(79.2~ yield) of 1-(3,5-di-t-butyl-l~-hydroxyphenyl)-N-phenyl-nitrone, MP-137-140C.
The theoretical amount of carbon, hydrogen and nitro-gen in the nitrone compound was calculated to be 77.49%9 8.37% and ~.30% respectively. An analysis of the compound for carbon, hydrogen and nitrogen found it to actually be 77.54%, 8.46% and 4.22% respectively.
EXAMPLE II
This example shows how various antioxidant compounds, including the compound of this inven-tion, were added to poly-butadiene rubber and the resulting antioxidant effect.
The polybutadiene rubber was dissolved in benzene and mixed at room temperature with the various antioxidants enu-merated in Table 1. The resulting polymer cements were evaporated to dryness and the polymers were submitted for oxygen absorption at 100C.
The higher the number of hours required to reach one percent oxygen absorption~ the more e~fective the compound is against oxidative attack.

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Table 1 Evaluation of Various Nitro~en-Oxygen Compounds as Antioxidants _ _ Hours to 1~ Ox~en Absorption CH3 .~_E~hr 1.0 phr CH3 ~ C - N - O 1.~ 1.4

2,4,6-trimethylbenzonitrile-N-oxide 0 - CH = N - O 5.3 8.0 CEI2 - (,Z~
(~-phenyl-N-benzyl nitrone ( ~ CH2 ~ NOH 22.0 25.0 N,N-dibenzyl hydroxylamine HO - ~ ~ CH = NOH 60.0 198.0

3~5-di-t-butyl-4-hydroxy benzaldehyde oxime EO - ~ -CH = ~ - O 99.0 217.0 1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-phenyl nitrone ~ ~ -CH ~ NOH 118.0 268.0 N,N-bis(3~5-di-t-butyl-4-hydrox~benzyl) hydroxylamine HO ~ ~ - CE3 392.0 471.0 :
~l 2~6-di-t-butyl-4-methyl phenol ,. .
1 All compounds were added to the polymer cement.

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The inventive compound was added ~o polybutadiene in benzene at various concen-trations and reac-ted ~or varying times at 800C. as illus-trated in Table 2. The inventive com-pound can undergo a chemical reaction to build itself into the rubber compound.
This example illustrates the built-in antioxidan-t ef-fect of the claimed compounds as compared to other antioxi-dant compounds that are not of the built-in type and how the nonbuilt-in~compounds may be extracted and lose their effec-tiveness as compared to the inventive compounds.
The compound 3,5 di-t-butyl-p-cresol is considered to be a good ~ntioxidant but like many others, has the disad-vantage o~ being volatileO Table 2 illustra-tes how the an-tio~idant qualities of the 3,5-di-t-bu-tyl-p-cresol is lost when compared with the claimed buil-t-in an-tioxidant. The time to 1~ oxygen absorption is an illus-tration of the anti-oxidant effectiveness of a compound, as can be seen in Table 2. When rubber containing 3~5-di-t-butyl-p-cresol is ex-tracted with acetone the antioxidant's effectiveness is greatly reduced~ whereas the inventive compounds are s-till very effective.

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~04S745 While certain representative embodiments and details have been shown for the purpose of illustrating the inven-tion, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

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Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An oxidation resistant polymeric composition comprising the reaction product of (A) a sulfur-curable rubbery polymer having carbon-to-carbon double bond unsa-turation in or pendant from the polymer chain selected from the group consisting of (1) natural rubber, (2) homopoly-mers and copolymers of conjugated diolefins, (3) copoly-mers of conjugated diolefins and monovinyl-substituted aromatic hydrocarbons, (4) copolymers of conjugated diole-fins and acrylonitrile, (5) copolymers of alpha olefins and conjugated diolefins, (6) interpolymers of one or more lower alkyl alpha olefins and a diene monomer, and (7) polymers or copolymers prepared by ring opening of one or more acyclic monomers, and (B) a 1,3-dipolar compound cor-responding to the general formula wherein R is selected from a group consisting of (1) alkyl radicals containing from 1 to 12 carbon atoms, (2) conden-sed ring aromatic radicals, (3) cycloalkyl radicals, (4) phenyl radicals, and (5) substituted phenyl radicals con-taining at least one substituent selected from the group consisting of chlorine, bromine, iodine and fluorine atoms and alkyl, alkoxy, nitro, tertiary amino, cyano, carboxy and carboalkoxy radicals.

2. An oxidation resistant polymeric composition according to Claim 1 wherein the 1,3-dipolar compound is selected from the group consisting of 1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-naphthyl nitrone, 1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-phenyl nitrone, 1-(3,5-di-t-butyl-4-hy-droxyphenyl)-N-butyl nitrone, 1-(3,5-di-t-butyl-4-hydroxy-phenyl)-N-(2-bromohexyl) nitrone, 1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-cyclohexyl nitrone, 1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-(4-nitrophenyl) nitrone, 1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-(3-ethyl phenyl) nitrone, 1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-tolyl nitrone, and 1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-(2-ethoxy phenyl) nitrone.

3. An oxidation resistant polymeric composition according to Claim 1 comprising the reaction product of polybutadiene and 1-(3,5-di-t-butyl-4-hydroxyphenyl)-N-phenyl nitrone.