Polymers 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. 

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. 

A complete picture of polymer thermal degradation is clouded because multiple reaction mechanisms can be operable for a single polymer at a single temperature, leading to a host of volatile products and residues. Therefore, one has to consider the relative rates of these competing reactions to establish an optimized and controlled binder burnout. 

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. 

The main purpose of these process analysis activities is to evaluate goal achievement in terms of polymer product properties. For example, the residence time as well as the deformation history of a single particle is an indication for the polymers thermal and mechanical degradation. 

The interest here is focused mainly on heavy hydrocarbons feedstocks, as in the case of certain refinery processes, and on polymer thermal degradation. A radical chain mechanism is also involved in the liquid- or condensed-phase pyrolysis. This is once again characterized by initiation, radical recombination... 

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. 

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... 

Py-GC/MS is one of the most powerful techniques to study the thermal degradation mechanism of polymers. In particular, the use of isotope-labeled polymer samples is often effective for such investigation. Here the detailed... 

In a similar maimer, thermal degradation mechanisms of fully aromatic polyesters were investigated in detail by Py-GC/MS using a partially deuterated polymer sample. Moreover, the mechanisms of reactive pyrolysis of the same aromatic polyester in the presence of tetramethylammonium hydroxide (TMAH) was also studied by Py-GC/MS. In this case, the contribution of solvent (methanol) to the reaction was confirmed by use of a deuterated methanol solution of TMAH. 

Sueoka, K., Nagata, M., Ohtani, H., Nagai, N., and Tsuge, S., Thermal Degradation Mechanisms of Liquid Crystalline Aromatic Polyester Studied by Pyrolysis-Gas Chromatography/Mass Spectrometry, /. Polym. Sci Part A, 29,1903,1991. 

In the following, we will discuss some examples, which better illustrate the applications of the DPMS and the power of this technique in die assessment of the thermal degradation mechanisms of polymers. 

In this respect, DPMS has the advantage of allowing the detection of high mass pyrolysis products that are crucial in defining structures and thermal degradation mechanisms of aromatic polymers bearing large repeat units. 

Trityl-2,3-di-0-methylcellulose, 6 Polymer 6 gave satisfactory elemental analysis (Table 1), however, the conversion of polymer 4 to 5 resulted in a drop in the average DPw from 353 to 251 anhydroglucose units. While many mechanisms can be postulated to explain DP loss upon reactions with base, acids, organometals, and the like, none are satisfactory. Therefore, in this article we report DP loss upon reaction, but do not attempt to explain it. The polymer thermally degraded above 224 C, and we were imable to generate films for DMA analysis. 

McNeill, I.C. and Leiper, H.A. (1985) Degradation studies of some polyesters and polycarbonates 2. Polylactide Degradation under isothermal conditions, thermal degradation mechanism and photolysis of the polymer. Polymer Degradation and Stability, 11,309-326. 

Linear-temperature controlled pyrolysis with subsequent analysis of the pyrolysates (volatiles and residues) by FTIR spectroscopy can provide information on the thermal degradation mechanisms of polymers including aromatic polyesters (325). Thermal analysis of PS, poly-p-methylstyrene and poly-a-methylstyrene was carried out using evolved-gas IR analysis (302). 

The fundamental degradation chemistry of PET and PEN should be very similar. Actually, thermal degradation studies show strong similarities in the degradation behavior of these related polymers. Identical primary and secondary thermal degradation mechanisms have been proposed [63]. 

Liang and Shi [1] used Fourier-transform infrared spectroscopy and direct pyrolysis -mass spectrometry to elucidate the thermal degradation mechanism of these polymers. 

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