Crystallinity thermal degradation

Phosphonium salts are typically stable crystalline soHds that have high water solubiUty. Uses include biocides, flame retardants, the phase-transfer catalysts (98). Although their thermal stabiUty is quite high, tertiary phosphines can be obtained from pyrolysis of quaternary phosphonium haUdes. The hydroxides undergo thermal degradation to phosphine oxides as follows ... 

Because of its fundamental role as a precursor of vitamin A and the availability of P-carotene standard in crystalline form, the thermal degradation of P-carotene in model systems has been a subject of intense research. 

Effect of Crystallinity and Additives on the Thermal Degradation of Cellulose... 

At very high temperatures, the chemical nature of the catalytic agents may be altered so that the catalytic activity is definitely lost. This type of thermal degradation is called solid-state transformation and can be seen as an extreme form of sintering, which leads to the transformation one crystalline phase into a different one. Phase transformations in the bulk washcoat and incorporation of an active metal into the washcoat may take place during solid-state transformation. 

For both polyethylene and its many copolymeric variants and polypropylene, the main thermal degradative routes follow initial random chain scission. These reactions are only slightly affected by the differences in the physical structure such as crystallinity, but are influenced by the presence of impurities. However, it is largely true that while these may influence the proces-sibility and long-term stability of respective polyolefins, they may have little or no effect on the flammability. 

Navarro [36] has reported several soluble, low transition temperature MCLC polymers containing ortho- or para-linked units and cinnamates or phenylene-fcis-acrylates in the main chain. One series of cinnamate-containing polymers is shown as 9. Some of the polymers seemed to be partially crystalline in the solid state. All had N and/or S mesophases which were retained in the solid glasses upon cooling to room temperature. Some of the polymers underwent thermal degradation and cross-linking above 300°C. Irradiation ( max = 300 nm)... 

Since the thermal degradation in phenylated polyphenyls of the type XXa is caused by the loss of pendant phenyl groups, and since the reported (4, 7, 9, 10, 11, 14, 15) properties of p-polyphenylenes are quite different from those of XXa, the synthesis of an unphenylated polyphenylene by this pathway was of considerable significance. Only a few results employing this reaction have thus far been obtained. [The p-poly-phenylenes reported are black or brown, insoluble, crystalline materials of lower thermal stability than XXa.]... 

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