Solvents ozone attack

Processing ndProperties. Neoprene has a variety of uses, both in latex and dry mbber form. The uses of the latex for dipping and coating have already been indicated. The dry mbber can be handled in the usual equipment, ie, mbber mills and Banbury mixers, to prepare various compounds. In addition to its excellent solvent resistance, polychloroprene is also much more resistant to oxidation or ozone attack than natural mbber. It is also more resistant to chemicals and has the additional property of flame resistance from the chlorine atoms. It exhibits good resiUence at room temperature, but has poor low temperature properties (crystallization). An interesting feature is its high density (1.23) resulting from the presence of chlorine in the chain this increases the price on a volume basis. 

Like NR, SBR is an unsaturated hydrocarbon polymer. Hence unvulcanised compounds will dissolve in most hydrocarbon solvents and other liquids of similar solubility parameter, whilst vulcanised stocks will swell extensively. Both materials will also undergo many olefinic-type reactions such as oxidation, ozone attack, halogenation, hydrohalogenation and so on, although the activity and detailed reactions differ because of the presence of the adjacent methyl group to the double bond in the natural rubber molecule. Both rubbers may be reinforced by carbon black and neither can be classed as heat-resisting rubbers. 

Amorphous non-polar polymers and crystalline solvents This situation is identical to the previous one and occurs, for example, when paraffin wax is mbced into rubber above its melting point. On cooling the paraffin wax tends to crystallise, some of it on the surface of the rubber. Such a bloom is one way of protecting a diene rubber from ozone attack. 

Natural rubber is resistant to dilute mineral acids, alkahes, and salts, but oxidizing media, oils, and most organic solvents will attack it. Hard rubber is made by adding 25 percent or more of sulfur to natural or synthetic rubber and, as such, is both hard and strong. Chloroprene or neoprene rubber is resistant to attack by ozone, sunlight, oils, gasoline, and aromatic or halogenated solvents but is... 

Nitrile rubbers have high resistance to oils and organic solvents, and, although their mechanical properties are not as good as those of natural rubber, they are subject to much less deterioration in the presence of oils and solvents. They are not resistant to ozone attack. 

Solvents as well as solids must be inert against ozone attack, which some are not (e. g. if the material contains C-C-double bonds they will be readily destroyed by ozone) ... 

Although the distribution among these products varies, depending on the reaction conditions, particularly on the solvent used, it is evident from the data in Table II that the latter type of products in which the double bond has been immunized towards further ozone attack comprises in each case a significant part (between 22 and 30% ) of the total product mixture. This is perhaps the most remarkable result of the present investigation. In contrast to the ozonolysis of hydrocarbon olefins, the ozonolysis of this dibromosubstituted double bond cannot be viewed primarily as a double bond cleavage reaction. 

The amount of ozone used for ring attack is not accounted for in our expressions therefore the values for b and c in Experiments 1 and 2 will be erroneous. The large discrepancy in consumed ozone and ozygen yield when ozonizing in ethyl or methyl acetate at — 78°C (Experiments 3-5, 22, and 26) cannot be accounted for by any of our schemes. The possibility of ozone attack on the solvents cannot be excluded. However, we have not been able to discover any product arising from oxidation of the solvent. Ozonation of ethyl acetate was shown by Price and Tumolo to be nonquantitative while ozone is quantitatively absorbed at —78°C when p-nitro-N,N-dimethylaniline (IVc) is dissolved in ethyl acetate. This problem has to be left open at this stage of our research. 

The best known of these is the ozonation of tertiary amines to amine oxides (II) (i). Henbest and Stratford (11) and Shulman (17) have shown that competing with this is an ozone attack on the alpha position of an alkyl side chain to produce various decomposition products of III. Henbest (11) showed that amine oxide formation is favored in chloroform and methanol, while side chain oxidation is predominant in hydrocarbon solvents. Also of considerable interest are the reported conversions, during ozonation, of phenylenediamines to Wursters salts (VII) (8, 14), of liquid ammonia to ammonium ozonate (VA) at a low temperature 18), and of amines to amine hydrochlorides (VB) in chlorinated hydrocarbon solvents 17, 19), Finally, an early report states that azobenzene and quinone are obtained upon ozonation of aniline (15). 

With polycyclic aromatic hydrocarbons, the site of ozone attack may be dependent upon substrate stmcture and reaction solvent (eq 21). ... 

Weather Resistance Many rubbers are affected adversely by outdoor exposure, particularly by the traces of ozone, which are always present in the atmosphere and which cause rapid cracking of lightly stressed rubber articles. Nitrile rubber is no exception and thus it is not suitable for use in exposed conditions. However, the incorporation of a proportion of PVC (Polyvinyl chloride) into the nitrile compound results in improved resistance until, with a blend of 70/30 nitrile/PVC, a material with almost complete resistance to ozone attack is produced. The presence of PVC produces stiffer compounds, with lower resiliance and inferior low temperature properties, but the oil and solvent resistance is enhanced. 

Note Ozone attacks the respiratory system and reacts explosively with organic solvents at room temperature. All work with ozone and ozonides should therefore be conducted in a fume cupboard, protective goggles should be worn and only smM amounts used. 

Fluoroelastomers excel compared to all other elastomers in heat, chemical, flame, weathering, fuel, and ozone resistance. In addition oil, oxygen, and water resistance are very good. The fluoroelastomers, however, are attacked by amines and some highly polar solvents. The abrasion resistance and low temperature properties are adequate for most applications. 

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