Nitrogen, curing

However, the curves in Figure 2 shows that while the nitrogen cure shows a vitrification temperature of the sulfone resin at 208°C the corresponding air scan vitrification temperature is 222 >C. 

Figure 4. Percent reaction vs. time for BA-DAB-BA (neat) and BA-DAB-BA (with 1% initiator) at 177°C, isothermal nitrogen cure.

The first-order decomposition rates of alkyl peroxycarbamates are strongly influenced by stmcture, eg, electron-donating substituents on nitrogen increase the rate of decomposition, and some substituents increase sensitivity to induced decomposition (20). Alkyl peroxycarbamates have been used to initiate vinyl monomer polymerizations and to cure mbbers (244). They Hberate iodine quantitatively from hydriodic acid solutions. Decomposition products include carbon dioxide, hydrazo and azo compounds, amines, imines, and O-alkyUiydroxylarnines. Many peroxycarbamates are stable at ca 20°C but decompose rapidly and sometimes violently above 80°C (20,44). 

Novolaks. Novolak resins are typically cured with 5—15% hexa as the cross-linking agent. The reaction mechanism and reactive intermediates have been studied by classical chemical techniques (3,4) and the results showed that as much as 75% of nitrogen is chemically bound. More recent studies of resin cure (42—45) have made use of tga, dta, gc, k, and nmr (15). They confirm that the cure begins with the formation of benzoxazine (12), progresses through a benzyl amine intermediate, and finally forms (hydroxy)diphenyknethanes (DPM). 

Both urea— and melamine—formaldehyde resins are of low toxicity. In the uncured state, the amino resin contains some free formaldehyde that could be objectionable. However, uncured resins have a very unpleasant taste that would discourage ingestion of more than trace amounts. The molded plastic, or the cured resin on textiles or paper may be considered nontoxic. Combustion or thermal decomposition of the cured resins can evolve toxic gases, such as formaldehyde, hydrogen cyanide, and oxides of nitrogen. 

Oxidation has also been cited as occurring in the cure of polymethyUiydrosiloxane [9004-73-3] (PMHS) on cellulose acetate fibers. Investigation of the cured, cross-linked siUcone shows no evidence of the Si—H bond. The same compound under an atmosphere of nitrogen does not cure and retains the Si—H bonds (99). 

Polished steel substrates primed with plasma polymerized acetylene films were immersed into a stirred mixture of these materials at a temperature of 155 5°C to simulate the curing of rubber against a primed steel substrate. During the reaction, the mixture was continuously purged with nitrogen to reduce oxidation. At appropriate times between 1 and 100 min, substrates were removed from the mixture, rinsed with hexane ultrasonically for 5 min to remove materials that had not reacted, dried, and examined using RAIR. The RAIR spectra obtained after reaction times of 0, 15, 30, and 45 min are shown in Fig. 13. 

NaN02, in addition to its use with nitrates in heat-transfer molten-salt baths, is much used in the production of azo dyes and other organo-nitrogen compounds, as a corrosion inhibitor and in curing meats. 

Novolac network degradation mechanisms vary from tiiose of resole networks due to differences in crosslinking metiiods. Nitrogen-containing linkages must also be considered when HMTA (or other crosslinking agent) was used to cure novolac networks. For example, tribenzylamines, formed in HMTA-cured novolac networks, decompose to cresols and azomethines (Fig. 7.50). 

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