Oxidative stability of urethane

H. J. Fabris, Thermal and Oxidative Stability of Urethanes in "Advances in Urethane Science and Technology," Volume 4, Technomic Publishing Co., Westport, Connecticut (1976). 

In order to address these issues, a brief discussion of thermal, oxidative, and hydrolytic stability of urethanes will be offered, so as to aid the adhesion scientist in designing a urethane adhesive with the desired durability. 

There appear to be conflicting reports regarding the degradation of urethanes. For example, some urethanes are reported to have relatively poor hydrolysis resistance and good biodegradability [77], while other urethanes are reported to be so hydrolytically stable that they have been successfully used as an artificial heart [78]. Both reports are correct. It will be shown that the thermal, oxidative, and hydrolytic stability of urethanes can be controlled, to some degree, by the choice of raw materials used to make the urethane. 

Polyurethanes are sensitive to strong acids, strong alkalis, aromatics, alcohols, hot water, hot moist air and saturated steam. The hydrolytic stability of polyurethanes in applications must be considered carefully. However, polyurethanes are resistant to weak acids, weak alkalis, ozone, oxygen, mineral grease, oils and petroleum. There are doubts for the oxidation stability of polytetramethylene ether glycol based polyurethanes. Polycarbonate urethane is a promising substitute with good oxidation stability. 

Oxidative stability is highly important because it deals with the degradation of polymers under actual performance conditions. Oxidative stability, as applied to urethanes, refers to the combination of oxygen and heat or oxygen and light that causes degradation of urethanes. 

Modification of poly(carbodiimide) foams with polyols afford hybride foams containing urethane sections. However, the thermal stabilities of the poly (urethane carbodiimide) foams are lower. Using isocyanate trimerization catalysts, such as l,3,5-tris(3-dimethylaminopropyl)hexahydro-s-triazine, in combination with the phospholene oxide catalyst gives poly(isocyanurate carbodiimide) foams with improved high temperature properties. The cellular poly(carbodiimide) foams derived from PMDI incorporate six-membered ring structures in their network polymer structure. ... 

Antioxidants inhibit oxidation and are usually employed in combination with UV absorbers. Most antioxidants used for urethane coatings fall into the following classes substituted phenols, aromatic amines, condensation products of aminophenols with aldehydes, thio compounds, and phosphites. Often combinations of antioxidants from the above categories exhibit a synergistic effect. More recently Mathur et al. (125) carried out an extensive study involving the use of one to six stabilizers, selected from the above antioxidants and UV stabilizers, employing several independent test methods, to study the thermooxidation of urethane and urethane-urea films. 

Uses Reactant in high polymers of the polyamide, polyester, and urethane types defoamer in food-contact coatings, paper/paperboard food pkg. adhesives, coatings, paper, cellophane, polymers Features Polymer grade exc. oxidation stability, color stability Regulatory FDA21CFR 175.105,175.300,175.320,176.170,176.200,... 

Sometimes in polyols small amounts of unsaturation are present which affect the light and thermal stability of the urethane hence detection and estimation of this unsaturation is desirable. Carbon-carbon unsaturated compounds in the sample are reacted with mercuric acetate and methanol in a methanolic solution to produce acetoxy-mercuricmethoxy compounds and acetic acid. The amount of acetic acid released in this equimolar reaction, which is determined by titration with standard alcoholic potassium hydroxide, is a measure of the unsaturation originally present. Because the acid cannot be titrated in the presence of excess mercuric acetate due to the formation of insoluble mercuric oxide, sodium bromide is added to convert the mercuric acetate to the bromide, which does not interfere. 

A diol containing a phosphine oxide structure was shown to be useful in urethane coatings, adhesives, and rigid foams (204). Advantages included shelf stability of the amine catalysl>-polyol mixture, low smoke, and good resistance to humidity (205). 

Fare S, Petrini P, Motta A, Cigada A, Tanzi M. Synergistic effects of oxidative environments and mechanical stress on in vitro stability of poly(ether urethanes) and poly(carbonate urethanes). J Biomed Mater Res 1999 45(1) 62—74. 

Salacinski HI, Tai NR, Carson RJ, et al. In vitro stability of a novel compliant polyfcar-bonate-urea)urethane to oxidative and hydrolytic stress. J Biomed Mater Res February 2002 59(2) 207-18. 

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