Mechanism of Thermal Degradation

Cullis and Hirschler proposed a detailed study on the mechanism of the thermal degradation of polymers [2, 40], which consists of two distinct reactions occurring simultaneously in the reactor. One is a random scission of links, causing a molecular weight reduction of the raw polymer, and the other is a chain-end scission of C-C bonds, generating volatile products [40]. 

The decomposition mode mainly depends on the type of polymer (i.e., the molecular structure). 

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Mechanisms of thermal degradation of PVC, the structure of PVC and the stabilization of PVC have been the subject of many reviews. Those by Starnes,44 Endo45 and Ivan46 are some of the more recent. Defect structures in PVC arise during the propagation and chain transfer steps. As with PMMA, PVC formed by... 

The thermostability of siloxane-silazane copolymers of both random and block structure is found to be much higher (i.e. 100-200°C) with respect to polysiloxanes. This effect is brought about by introducing only a few silazane entities into the polymer chain. The reasons for the effect are not clear and the mechanism of thermal degradation of polysilazoxanes will require further experimental studies. 

Mechanisms of Thermal Degradation Chain Growth Polymers... 

Mechanism of Thermal Degradation of Fire-Retardant Melamine Salts... 

Lee, L-H. "Mechanism of Thermal Degradation of Phenolic Condensation Polymers" in Proceedings of Battelle Sym., on Thermal Stability of Polymers" Dec. 5,6, 1963. 

G. N. Richards and F. Shafizadeh, Mechanism of thermal degradation of sucrose. A preliminary study, Aust. J. Chem., 31 (1978) 1825-1832. 

The oxygen index increase was suggested to be due to a condensed phase mechanism and explained by taking into account the mechanism of thermal degradation of chloroparaffin and the interaction with the polymers. 

H. Sato, K. Kondo, S. Tsuge, H. Ohtani, and N. Sato, Mechanisms of thermal degradation of a polyester flame retarded with antimony oxide/brominated polycarbonate studied by temperature programmed analytical pyrolysis. Poly. Degr. Stab., 62, 41-48 (1998). 

The radical mechanism of thermal degradation of pristine PE has been widely discussed in a framework of random scission type reactions [14-22], It is known that PE decomposition products comprise a wide range of alkanes, alkenes and dienes. Branching of PE chains causes enhanced intermolecular hydrogen transfer and results in lowering thermal stability. The polymer matrix transformations, usually observed at lower temperatures and involving... 

One of the main interests of the polymer chemist is to develop new polymers that have good mechanical properties at high temperature and to improve the thermal stability of existing polymers. Extensive studies of the mechanism of thermal degradation of the presently available macromolecules are very helpful in this field. 

The use of many different analytical techniques is necessary for the determination of a mechanism of thermal degradation. The main experimental data required are... 

Main chain scission followed by depolymerization is a very frequently observed mechanism of thermal degradation. Kinetic treatments allowing... 

In order to obtain further evidence on the mechanism of thermal degradation of polystyrene, several workers have recently studied the decrease in molecular weight occurring below 300°C. In this temperature range, in fact, volatile formation is negligible and it was hoped that the degradation kinetics would be easier to interpret. 

The mechanism of thermal degradation of nornicotine is generally similar to nicotine although differences in thermostability exist (175, 17B25). Nornicotine is less stable than nicotine and the pyrrolidine ring fragments at temperatures below 400°C. At 400°C (in an inert atmosphere) myosmine and... 

The mechanism of thermal degradation of polyetheleneterephthalate (PET) has been studied over many years by off-line analysis of the pyrolysis products " and by Py-GC/MS studies. The results suggested a jS-CH hydrogen transfer process leading to the formation of oligomers with olefin and carboxylic end-groups (Eq. 5.4). 

Lee, L., Mechanisms of thermal degradation of phenolic condensation polymers. 

The mechanism of thermal degradation of plastics proceeds through a radical chain reaction pathway with hydrogen transfer steps. In secondary reactions, branched products were only formed as a result of the interaction between two radicals without any rearrangement reactions [48]. As a consequence, thermal cracking of polyolefins leads toward a broad distribution of hydrocarbons up to waxy products. More than 500 °C temperatures are needed to receive more oily products. In contrast, catalytic cracking takes place at lower temperatures and leads to the formation of smaller branched hydrocarbons. This catalytic cracking can potentially lower the costs and increase the yields of valuable products. 

It is well-established in organic chemistry that acids increase rates of halogen elimination. There is still no agreement on the mechanism of thermal dehydrochlorination of PVC but ionic mechanisms prevail in disputes. More detailed description is available in monographic sources which suggests polarization of H-C and C-Cl bonds to form carboanion or carbonium ion. If snch conrse of reaction is accepted then participation of acids is well-explained by the mechanism of thermal degradation. 

To establish new relationships which make it possible to develop general concepts of the mechanism of thermal degradations of polymers. 

The mechanisms by which such changes occur are many and it is important to know what these are and to be able to measure the rate of change of polymer structure and its dependence on temperature and time. Development of an understanding of the mechanisms of thermal degradation will help the chemist to develop materials with better thermal stability. This is particularly important in new er developments in engineering and aerospace. 

Developing an imderstanding of the mechanisms of thermal degradation will help the chemist to develop materials with better thermal stability. This is particularly important in newer developments in engineering and aerospace. 

The mechanism of thermal degradation of cellulose appears to include two reactions. The first reaction consists of dehydration and the second one of scission of C-O bonds in the chains between the rings or within the rings [457], This can give rise to levoglucosan [457] ... 

Wachen, O. Reichert, K.H. Kruger, R.P. Much, H. Schulz, G. Thermal decomposition of biodegradable polyesters-III. Studies on the mechanisms of thermal degradation of oligo-l.-lactide using SEC, LACCC and MALDI-TOF-MS. Polym. Degrad. Stabil. 1997, 55 (2), 225-231. 

Is important to emphasize that the fillers in the polymer matrix have as effect an increase in the thermal stability of the nanocomposite. Interactions between polymer and inorganic filler materials are powerful and increase the molecular cohesion energy and hence the heat needed to activate the mechanism of thermal degradation [73]. 

L. H. Lee, Mechanisms of Thermal Degradation of Phenolic Condensation Polymers. 1. Studies on the Thermal Stability of Polycarbonate, J. Polym. Sci., Part A 2 2859 (1964). 

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