Ammonium salts, alkyl quaternary, thermal stability

The onset temperature of decomposition of alkyl quaternary ammonium-modified montmorillonite, in nonoxidative thermal degradation, is about 180°C. Initial degradation of the surfactant follows either a Hoftnann elimination or an Sn2 nucleophilic substitution mechanism. Both mechanisms can affect the performance of high-processing-temperature nanocomposites and, in general, the thermal stability and combustion behavior of nanocomposites. In particular, Hofmann elimination generates acidic sites on the layered silicate that can act as a protonic acid catalyst on polymer decomposition. " Imidazolium and phosphonium salts exhibit improved thermal stability compared to ammonium salts.Alkylimidazolium salt-modified layered silicates were used successfully to prepare organoclays that exhibit an onset of decomposition temperature up to 392°C. 

Cationic antistats are generally long-chain alkyl quaternary ammonium, phosphonium, or sulfonium salts with, for example, chloride counterions. They perform best in polar substrates, such as rigid PVC and styrenics, but normally have an adverse effect on the resin s thermal stability. These antistat products are usually not approved for use in food-contact applications. Furthermore, antistatic effects comparable to those obtained from other internal antistats such as ethoxylated amines are only achieved with significantly higher levels, typically, five- to tenfold. 

Awad et al. reported extensive studies on the various imidazolium salts and montmo-rillonites modified with these salts [37]. The imidazolium salts included l,2-dimethyl-3-propylimidazolium, l-butyl-2,3-dimethylimidazolium, 1 -decyl-2,3-dimethylimidazolium, l,2-dimethyl-3-hexadecylimidazolium, l,2-dimethyl-3-eicosylimidazolium, 1,2-dimethyl-3-ethylbenzene imidazolium, and l-ethyl-3-methylimidazolium. The authors investigated the effect of counterion, alkyl chain length, and structural isomerism on the thermal stability of the imidazolium salts and compared their behavior with that of the conventional quaternary ammonium ions using a number of characterization techniques. It was reported that... 

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