1. The structure of the products obtained from the reaction of NR latex with peracetic acid depends on the reaction conditions. 2. Under controlled conditions, specific levels of epoxidized NR (ENR) can be obtained. A random epoxide distribution has been observed. These materials undergo strain crystallization and hence exhibit good strength properties, although at high levels of epoxidation there is a decrease in the degree of crystal-unity. Other properties, e.g., hysteresis, air permeability, and oil resistance, change systematically with the level of epoxidation. These properties indicate that ENR has the potential to become an extremely useful commercial polymer. 3. At higher acid concentrations and/or temperatures, ring opening of the epoxide groups occurs, and even low levels of ring-opened structures have been found to adversely affect the properties of ENR. 4. The nature of the ring-opened structures depends on the degree of epoxidation. At low levels of epoxidation, where the majority of epoxide groups are isolated, simple diols and hydroxyacetates are formed. However, at higher epoxide levels, where blocks of epoxide predominate, the major product is a five-membered cyclic ether. At 100 mole% modification, a white amorphous thermoplastic product was obtained consisting almost entirely of furan structures.
1. Vulcanization by sulfur alone is faster and more efficient for ENR than for NR because isolated double bonds react more rapidly than contiguous double bonds. This vulcanization may be accelerated by sodium carbonate, which also protects the cured rubber against the subsequent effect of oxidative aging, and the scorch time may be increased by the addition of CTP. 2. The CBS-accelerated sulfur vulcanization of ENR is essentially similar to that of NR, although ENR reacts with MBT formed during the process. 3. The poor aging of sulfur vulcanizates of ENR is due to acid-catalyzed ring-opening reactions of the epoxide groups with the formation of ether crosslinks. The acids are produced by the thermal decomposition of oxidized sulfides. 4. The addition of a suitable base confers excellent resistance to oxidative aging upon conventional, semi-efficient, and efficient vulcanizates of ENR.
Treatment of 6-chloro-4-dialkylamino-5-nitropyrimidines (la-d) under acidic conditions resulted in ring cleavage and formation of 3-amino-3-dialkylamino-2-nitroacrylonitriles (llla-d).Similar treatment of 4-amino-or 4-alkylamino-6-chloro-5-nitropyrimidines also gave acrylonitriles (I1 le-i) but 4-aminoor 4-alkylamino-5-nitropyrimidin-6(1H)-ones (Ile-i) were formed a t the same time.The relative proportions of ring cleavage and simple nucleophilic substitution varied with the 4-substituent and with the pH, Under near neutral conditions only the pyrimidinone (11) was formed, even when the 4-substituent was dialkylamino.lH N.m.r., u.v., and i.r. spectra are tabulated
The discovery that C-nitrosoanilines react with olefins to give p-phenylenediamines has made possible the synthesis of powerful antioxidants from a wide range of naturally occurring and synthetic unsaturated compounds. Simple alkenes, vegetable oils, and factices may be converted to antidegradants whose behavior parallels that of commercially available materials. The reaction of 4-nitrosoanilines or 4-nitrosophenols with natural and synthetic rubber or latices gives rubber-bound antioxidants which are completely resistant to extraction by water or organic solvents. No major modification of technological processing or fabrication techniques is necessary, and the reaction takes place conveniently during vulcanization. Attachment of the protective group to the rubber molecule does not affect its antioxidant activity, but reduces its effectiveness when migration to the surface is required, e.g., in protection against ozone. Although faster at elevated temperatures, the nitroso-olefin reaction will occur at room temperature, and this allows the preparation of chemically modified raw rubbers by carrying out the reaction in latex before coagulation and drying.
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