Thermal degradation structural changes

MALDI - Pyrolyzates with much higher molecular weight can be detected. - Observation of the thermally induced structural changes in the polymer samples. - Fast time of analysis. - MWD determination by SEC-MALDI. - Matrix interference - no low-molecular-weight detection (below miz 500). - Difficulties to analyse unsoluble or apolar polymers. - Indirect method - only the degradation products most thermally stable will survive. - Suppression of degradation products present in trace. - Only quahtative analysis. 

Thermal degradation occurs when heat causes compounds to undergo structural changes, leading to the formation of simpler species. For example, many organophosphorus esters isomerize when heated... 

Poly(a-phenylethyl isocyanide), however, yields complex products distinguishable from monomer upon thermal degradation at 20 mm Hg (13). At 300° C a viscous condensate is produced which is free of isocyanide absorption in its infrared spectrum and appears very similar to the recently synthesized oligo-isocyanides, a,co-dihydrotri(a-phenylethyl isocyanide) and a,co-dihydrohexa(a-phenylethyl isocyanide) (15). Pyrolysis at 500° C produces an intense broad infrared absorption band in the range about 3300 cm-1, which is the range of associated N il bonds. Pyrolysates obtained at 700° C reveal nitrile absorption at 2270 cm"1, that becomes more intense in pyrolysates produced at temperatures up to 1300° C. A slow pyrolysis at 200-300° C is indicated for the study of primary structural changes in poly(a-phenylethyl isocyanide). Pyrolysates of poly(<7-... 

With an inert carrier gas in this system, the acyl groups of the lipid classes are split from the backbone structures and identified as the [RCOOH + 1]+ and [RCO]+ ions. Since the products of the backbone structures of the lipid classes are produced by thermal degradation, their formation does not appear to be affected by the change to an inert gas. 

Studies on the thermal degradation of the cellulose structure have shown that oxidation reactions at 160-180 °C are more important than decarboxylation, but that this state may change at 190 °C (28). 

Both thermal and photochemical processes take the form of a dehydrochlorination reaction which leads to discolouration as well as extensive changes in the internal structure of the polymer which has an unfavourable effect on the desirable electrical and mechanical properties. It has become apparent that considerable similarity exists between the two degradation processes and that it is neither easy nor desirable to make a vigorous distinction between the two. Information gained from e eriments on thermal degradation are often directly relevant to the analogous photochemical process. 

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