Thermal degradation mechanisms

There have been many studies on the thermal and thermo-oxidative degradation of PMMA.23 24 It is well established that the polymer formed by radical polymerization can be substantially less stable than predicted by consideration of the idealized structure and that the kinetics of polymer degradation are dependent on the conditions used for its preparation. There is still some controversy surrounding the details of thermal degradation mechanisms and, in particular, the initiation of degradation.31... 

Applications Desorption chemical ionisation has proven potential in the analysis of thermally labile, nonvolatile and polar compounds [40,67,68], for the identification of unknown polymers and the study of the thermal degradation mechanisms of polymers. Considering the overall ease of DCI operation, the capability of analysing nonvolatile compounds, and the selectivity provided by choosing different reagent gases, DCI has found surprisingly few practitioners in the analysis of polymer additives. 

Figure 11.3 Proposed PTT thermal degradation mechanism through the Mc-Clafferty rearrangement and the formation of acrolein and allyl alcohol...

Liquid chlorinated paraffins are the main halogen-containing fire-retardant additives used for poly(vinyl chloride) often in combination with a phosphate ester. In this case, the chlorinated paraffins have the secondary function of plasticizers. The thermal degradation mechanism of chlorinated paraffins is similar to that of poly(vinyl chloride), so in this case poly(vinyl chloride) stabilizers have also the secondary function to stabilize chlorinated paraffins. 

Although population balance methods are relatively undeveloped for interesting polymers, the author believes they have great potential. Each of the four distinct thermal degradation mechanisms mentioned earlier will be analyzed in detail and examples involving specific polymers will be discussed wherever possible. Furthermore, some relevant combinations of mechanisms (such as combined random scission and end-chain scission) will also be discussed. 

One important thermal degradation mechanism of cellulose fibres (cotton, rayon, linen, etc.) is the formation of the small depolymerisation product levoglucosan (Fig. 8.7). Levoglucosan and its volatile pyrolysis products are extremely flammable materials and are the main contributors to cellulose combustion. Compounds that are able to hinder levoglucosan formation are expected to function as flame retardants for cellulose. The crosslinking and the single type of esterification of... 

G. Montaudoa, C. Puglisib and F. Samperi Primary thermal degradation mechanisms of PET and PBT, Polym. Degrad. Stab., 42, 13-28 (1993). 

G. Montaudo and C. Puglisi, Thermal degradation mechanisms in condensation polymers. In Developments in Polymer Degradation, N. Grassie (ed.). Applied Science Pubhshers, London, 1987. 

Two additional phenomena contribute to the thermal degradation mechanism and can determine the formation of the relative maximum and minimum in the characteristic surface of the gaseous MWD as shown in Fig. 1. In the backbiting process, the end of polymer chain can also react to form gaseous products with a non-random distribution through a sequence of isomerization and /1-scission reactions. Finally, monomer units can also be released by an unzipping process through /1-scission of the terminal radicals. 

Hence, a zero percent residue from our TGA of the silicone OH fluids were obtained. GC/MS studies of the decomposed volatiles which were collected by a liquid nitrogen trap have confirmed the presence of these cyclic siloxanes. (A proposed thermal degradation mechanism is listed in Figure 4). Since oxidation... 

Figure 7. Photocrosslinking and thermal degradation mechanism of OHMSS or MOPSS-containing polymers.

Isothermal methods have generally been used for the study of thermal degradation mechanisms and the determination of kinetic parameters. In recent years, however, dynamic thermogravimetric analysis (TGA) has been developed. In this case, polymer samples are weighed in a... 

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