Disclosed herein as novel antioxidant compounds are hindered phenolic norbornene dicarboximides, oligomers, polymers and copolymers of such antioxidant compounds and polymeric compositions stabilized by such antioxidant compounds, oligomers, polymers and copolymers.

BACKGROUND OF THE INVENTION Except in the cases where environmental degradation is desired, polymeric compositions are generally combined with stabilizing agents to prolong their useful life in hostile environments, e.g. the presence of oxidizing agents or ultraviolet light. The art of stabilizing polymeric materials is both complex and unpredictable. Ordinarily stabilizing agents are physically combined with the polymer thereby prolonging its useful life. Stabilizing agents are commonly monomeric or oligomeric compounds which are free to migrate, albeit slowly, within the polymeric composition and to the surface thereof. This often presents a problem manifested by a bloom of powder on the surface or extraction of the stabilizer into a fluid which not only reduced environmental stability but also detracts from the aesthetic appearance of a polymeric article. Furthermore, some stabilizers have a sufficiently low molecular weight that they may be vaporized, or otherwise become ineffective, at elevated service temperatures especially in high performance thermoplastics.

Antioxidants derived from cyclic olefins have been proposed. For instance. Layer discloses in U.S. Patent 4,484,010 hindered hydroxybenzylcyclo- pentadiene antioxidants prepared by reacting cyclo- pentadiene, an alkali metal, and a hindered para methylphenol having attached to the methyl group a displaceable group, e.g. dimethylamino group, for up

to a couple of days at 60"C in a non-protic solvent. Because conjugated dienes like cyclopentadiene are easily oxidized. Layer's antioxidants are preferably hydrogenated and thus not amenable to incorporated into polymeric compounds or grafted to polymers.

In U.S. Patents 4,045,404 and 3,896,147 Stephen discloses hindered phenolic stabilizers derived from alkylthionorbornane dicarboximides. Due to their preparation by free radical addition of a mercaptan to 5-norbornene-endo-2,3-dicarboximide, these stabilizers are not amenable to be incorporated into polymeric compounds or grafted to polymers.

It is an object of this invention to provide antioxidants which can stabilize polymer compositions without adverse consequences of leaching, vaporization or other deficiency which commonly occur at elevated temperatures.

Another object is to provide cyclic olefinic antioxidants which can be incorporated into polymeric compounds or grafted to polymers, especially unsaturated polymers or metathesis ring-opening polymerized polymers and copolymers, so as to provide a polymeric compounds with inherent and enhanced antioxidant character. Thus, another object of this invention is to provide polymeric compounds which are inherently antioxidant and which can be blended with other polymers to provide oxidation resistant polymer compositions. SUMMARY OF THE INVENTION

This invention provides hindered phenolic norbornene dicarboximides which are useful for inhibiting oxidation of polymer compositions. This invention also provides polymeric compounds, e.g. homopolymers, of such hindered phenolic norbornene dicarboximides which are useful both in low molecular weight oligomeric species and in higher molecular

weight polymeric species as polymeric oxidation inhibitors. Another aspect of this invention provides polymeric compounds, e.g. copolymers having such hindered phenolic norbornene dicarboximide incorporated therein or grafted thereto. Useful oxidation inhibitors can also comprise a mixture of monomeric and polymeric species. For instance, where monomeric hindered phenolic norbornene dicarboximide is grafted to a polymer, e.g. a polymer having terminal alpha olefin groups such as polybutadiene, both the grafted monomer and residual free monomer can be effective in inhibiting oxidation.

The hindered phenolic group of the norbornene dicarboximide antioxidant of this invention is preferably a 3,5-dialkyl-4-hydroxy-phenyl group, where preferred alkyl is t-butyl. Thus, preferred embodiments of this invention include, as a monomeric antioxidant, N-(3,5-di-t-butyl-4-hydroxy)phenyl norbornene dicarboximide; as a polymeric antioxidant, poly(N-(3,5-di-t-butyl-4--hydroxy)phenyl norbornene dicarboximide) and copolymers having N-(3,5-di-t- butyl-4-hydroxy)phenyl norbornene dicarboximide incorporated therein or grafted thereto.

A useful embodiment of this invention comprises copolymers of N-(3,5-di-t-butyl-4- hydroxy)phenyl norbornene dicarboximide and other cyclic olefins, e.g. a norbornene or norbornene derivative. To avoid lowering the temperature resistance of polymeric compositions, it is advantageous to provide the oxidation inhibitor as a high temperature resistant copolymer, e.g. of a norbornene dicarboximide. Oxidation inhibitor copolymer according to this invention can be prepared having a glass transition temperature greater than 200 ^β C. Homopolymer oxidation inhibitors can be prepared having a glass transition temperature of about 235 ^β C.

EXAMPLE 1 This example illustrates methods of preparating the oxidation inhibitor N-(3,5-di-t-butyl- 4-hydroxy) phenyl norbornene dicarboximide. A mixture of 253 g of 2,6-di-t-butyl-4- nitrophenol, 1 liter of tetrahydrofuran (THF) and 2.57 g 5% palladium on carbon catalyst was maintained in a pressurized reactor for 2 hours at 70 ^β C under hydrogen pressurized to 5.3 atm. The reactor contents were cooled and transferred to a flask containing about 165 g of exo-5-norbornene-2,3-dicarboxylic anhydride which was stirred overnight. After the THF was removed by rotary evaporation, about 560 g anhydrous sodium acetate and about 1090 g of acetic anhydride were added to the mixture which was refluxed for 24 hours. Excess acetic anhydride was evaporated. The residual brown solid was dissolved in acetone and treated with concentrated hydrochloric acid. The resulting solid was recrystallized in methanol, yielding substantially pure N-(3,5-di-t-butyl-4-hydroxy)phenyl norbornene dicarboximide.

In an alternative method of preparing N-(3,5-di-t-butyl-4- hydroxy) phenyl norbornene dicarboximide, a mixture of 700 grams of 2,6-di-t-butyl-4-nitrophenol, 1 liter of THF and 7.1 grams of 5% palladium on carbon catalyst was pressurized with hydrogen to about 5.3 atm at 70 ^β C. When the hydrogen takeup stopped, the product was cooled, separated from the catalyst by filtration and added to a flask containing 457 grams of exo-5- norbornene-2,3- dicarboxylic anhydride. After four hours the THF was replaced with 1300 ml of xylene and the contents heated to reflux with water of cyclization removed with xylene by azeotropic

distillation. Crystalline N-(3,5-di-t-butyl- 4-hydroxy)phenyl norbornene dicarboximide recovered at below room temperature was purified by recystalization from xylene. EXAMPLE 2

This example illustrates the preparation of a polymeric oxidation inhibitor by the polymerization of N-(3,5-di-t-butyl-4-hydroxy)phenyl norbornene dicarboximide. Polymerization catalyst comprising about 0.9 ml of 0.5 M tungsten hexachloride solution in toluene and 0.14 ml of 2.05 M diethyl aluminum chloride in heptane were sequentially added to about 2 g of N- (3,5-di-t-butyl-4-hydroxy)phenyl norbornene dicarboximide dissolved in 6 ml of dichloroethane. The mixture was maintained at about 65"C overnight. Poly(N-(3,5-di-t-butyl-4-hydroxy)phenyl norbornene dicarboximide) was recovered in methanol and vacuum dried. EXAMPLE 3

This example illustrates the preparation of copolymer oxidation inhibitors.

Using the catalysts and procedures of Example 2, but using the monomers in the weight ratio identified in Table 1, copolymers of N-methyl norbornene dicarboximide (I) and N-(3,5-di-t-butyl-4- hydroxy)phenyl norbornene dicarboximide (II) were prepared. The thermoxidative stability of the copolymers was evaluated by measuring the exotherm temperature exhibited by finely ground polymer heated in an oxygen atmosphere in a differential scanning calorimeter. The results reported in Table 1 illustrate the effectiveness of providing oxidative stability to a cyclic olefin polymer by incorporating therein a minor amount, e.g. about 5 %, of a cyclic olefin oxidation inhibitor. The results also

illustrate the high temperature oxidation stability afforded by copolymers comprising higher levels, e.g. 10 to 33%, of cyclic olefin oxidation inhibitor.

TABLE 1

EXAMPLE 4 This example illustrates the preparation of polybutadiene grafted with N-(3,5-di-t-butyl-4- hydroxy)phenyl norbornene dicarboximide. About 0.1 ml of t-butylperoctoate was added to solution of 5 g of polybutadiene and 0.5 g of N-(3,5- di-t-butyl-4-hydroxy)phenyl norbornene dicarboximide dissolved in 200 ml of toluene. The solution was mixed at about 80"C for 2 hours with an increase in viscosity indicating some crosslinking. The reaction product was diluted with chloroform and oxidation stabilized polybutadiene was recovered in methanol.

EXAMPLE 5 This example illustrates the stabilization of polybutadiene by addition of monomeric N-(3,5-di- t-butyl-4-hydroxy)phenyl norbornene dicarboximide. Antioxidant was removed from polybutadiene (PB, as received) by dissolving polybutadiene in toluene and recovering in methanol. Purified polybutadiene (PB, purified) and N-(3,5-di-t-butyl-4-hydrox )phenyl norbornene dicarboximide (at 2% and 5%) were dissolved in ethylene chloride; after mixing the solvent was allowed to evaporate. The thermoxidative stability of

the stabilized polybutadiene compositions were evaluated by measuring the exotherm temperature exhibited by the polymer heated in an oxygen atmosphere in a differential scanning calorimeter. TABLE 2

COMPOSITION Exotherm ( ^β C)

PB, as received 206

PB, purified 195

PB + 2% 212 PB + 5% 238

EXAMPLE 6 This example illustrates the preparation of a copolymer oxidation inhibitor. Using the catalysts and procedures of

Example 2, but using 100 parts by weight of N- cyclohexyl norbornene dicarboximide (I) and about 10 parts by weight N-(3,5-di-t-butyl-4-hydroxy)phenyl norbornene dicarboximide (II) , an oxidatively stable cyclic olefin copolymer was prepared. The thermoxidative stability of the copolymer was evaluated by measuring the exotherm temperature exhibited by finely ground polymer heated in an oxygen atmosphere in a differential scanning calorimeter. The results reported in Table 3 illustrate the effectiveness of providing oxidative stability to a cyclic olefin polymer by incorporating therein a minor amount, e.g. about 10%, of a cyclic olefin oxidation inhibitor. TABLE 3

MONOMER I MONOMER II Exotherm (°C) 100 0 204

90 10 268

While specific embodiments of the invention have been described, it should be apparent to those skilled in the art that various modifications thereof

can be made without departing from the true spirit and scope of the invention. Accordingly, it is intended that the following claims cover all such modifications within the full inventive concept.