The ozonation products of a common rubber antiozonant, N,N′-di-(l-methylheptyl)-p-phenylenediamine (DOPPD), have been separated by liquid or gas chromatography. Molecular weights of about thirty LC separated components have been measured by field desorption mass spectroscopy. Elemental formulae have been determined by atomic composition mass spectroscopy. Other structural details have been elucidated by electron impact mass spectroscopy and attenuated total reflectance infrared spectroscopy. Two principal mechanisms appear to govern the ozonation of DOPPD. Amine oxide formation leads to observed nitrosoaryl and nitroaryl products. The second major mechanistic pathway is side chain oxidation. This leads to a number of low molecular weight components, including some that contain an amide moiety. A third (minor) mechanistic pathway involves a nitroxide radical intermediate and leads to the formation of a stable dinitrone species. The surface film formed on ozonation of a black loaded natural rubber sheet containing DOPPD has also been examined. The film contains appreciable quantities of unreacted DOPPD and many of the same low molecular weight components as observed in the ozonized liquid antiozonant. It is clear that DOPPD blooms to the rubber surface and acts as a scavenger for ozone. The results are consistent with a combined “scavenger-protective film” mechanism for antiozonant protection.
This work reports a direct surface analysis of ozonization of vulcanized NR compounds by ATR. On ozonization of a vulcanized NR compound without clay filler or AO a degraded rubber layer, which contains ozonides and carbonyl compounds, is formed on the surface. This reaction is considerably slower than that of raw NR. When clay filler is added, the first effect is a decrease of rubber on the surface and a corresponding increase in the surface concentration of clay. With further ozone exposure, ozonides and carbonyl compounds appear. When a compound containing N,N′-dioctyl-p-phenylenediamine AO is ozonized, a film is seen, which has an ATR spectrum essentially identical to that of the ozonized liquid AO. There is no evidence of ozonized NR products, or of complex reaction products between AO and ozonized NR. These results are consistent with a scavenger or protection-layer mechanism for antiozonant protection.
This work reports a direct surface analysis of ozonization of carbon black loaded NR compounds by ATR and SEM. On ozonization of raw NR or NR containing carbon black, a thick layer builds up consisting of ozonides and carbonyl compounds. It is suggested that this layer is composed principally of the reaction products of ozone with unsaturated fatty acids and unsaturated fatty acid esters found in NR. On ozonization of cured and uncured carbon black loaded NR compounds containing curatives, the NR is attacked causing a decrease of rubber on the surface and a corresponding increase in the surface concentration of carbon black. The thick ozonide/carbonyl layer did not form, probably due to the coordination of the fatty acids and esters with ZnO, which was added with the curatives. On ozonization of carbon black-loaded NR compounds containing N,N′-dioctyl-p-phenylenediamine antiozonant, a continuous film is seen by SEM which has an ATR spectrum essentially identical to ozonized antiozonant. There is no evidence of ozonized NR products, or of complex reaction products between antiozonant and ozonized NR. These results are consistent with a dual scavenger and protective layer mechanism for antiozonant protection.
Phenolic resins are added to rubber compounds to improve the tack (or autohesion) characteristics. These resins are generally oligomers of alkylated phenols and formaldehyde. Analytical characterizations of these resins are very limited and incomplete in the open literature. We have examined several types of resins using mass spectroscopy (principally field desorption, FD-MS), liquid chromatography (LC), and infrared spectroscopy (ATR-IR). Several oligomeric series were identified by FD-MS in t-octylphenol and t-dodecylphenol resins. ATR-IR analysis showed that the t-octyl groups are essentially completely p-substituted on the phenolic ring. LC was only of limited utility in obtaining analytical separations of resin oligomers. Higher molecular weight oligomers (≿1500) showed little if any LC resolution. Resins prepared under different manufacturing conditions showed additional series of oligomers. These were either “cyclic ethers” and/or amine-containing compounds, depending on the synthetic procedures used.
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