Degradation thermooxidative

Unlike thermal degradation, where polymer scission can occnr randomly and/or at the chain end, oxidative degradation is characterised by random scission in the polymer backbone. For instance, the addition of free-radical initiators to polyolefins dnring extrusion is used industrially to improve the mechanical properties of the polymer 864583. The most important issues in thermooxidative degradation of polymers are where oxidation takes place, which structure fragments are most vulnerable, how they should be protected, and what are the main principles of protection. 

However, very recently some authors [a.37] have proved that polyene sequences are formed at very low percentage of DHC and increase only their concentration (not their length) with degradation. Such sequences seem to be stabilised against the action of oxygen, at 

Features of the kinetics of the high-temperature oxidation of volatile polymer degradation products for some general classes of polymers and polymeric materials have been investigated [a.42]. For PMMA, isoprene and ethylene-propylene rubbers, the oxidation kinetics depended on the pyrolysis temperature and are in good correlation with the 

The change of tacticity during the thermal treatment of commercial PMMA at 200 °C in air was studied by the NMR technique 884331. The ratios of the three characteristic triads - isotactic, syndiotactic and heterotactic sequences - depend on the degradation time and approach a constant ratio of syndiotactic heterotactic isotactic = 3 4 3 at about 80% mass loss when starting with an initial ratio of syndiotactic heterotactic isotactic = 5 4 1. The correlation between the evaluated parameters and the degradation processes led to information on repolymerisation, which was dominant after about 50% 

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Thermal, Thermooxidative, and Photooxidative Degradation. Polymers of a-olefins have at least one tertiary C-H bond in each monomer unit of polymer chains. As a result, these polymers are susceptible to both thermal and thermooxidative degradation. Reactivity in degradation reactions is especially significant in the case of polyolefins with branched alkyl side groups. For example, thermal decomposition of... 

Fig. 9. Thermal and thermooxidative degradation of PS. Viscosity is for a 10% solution in toluene at 25°C.

Kovarskaya, Levantovskaya, and Yazvikova 86) recently studied the kinetics of thermooxidative degradation of PTHF of low molecular weight (1130) at 90—120° C. Hydroperoxides were formed at all stages of the oxidation. The rate of accumulation of peroxides reached a maximum of 2—2.3 millimoles/g at all temperatures. Kinetic curves of the oxidation revealed an auto-acceleration according to the formula ... 

Polymers of a-olefins are susceptible to thermal and thermooxidative degradation. Reactivity in degradation reactions is especially significant in the case of polyolefins with branched alkyl side groups,... 

Thermooxidative degradation of PMP is noticeable even at 140-l50°C, and its photooxidative degradation, especially at wavelengths below 400 mu, also proceeds at a relatively high rale, thus limiting some of its outdoor applications. 

Antonov, A., Yablokova, M., Costa, L., Balabanovich, A., Levchik, G., and Levchik, S. 2000. The effect of nanometals on the flammability and thermooxidative degradation of polymer materials. Mol. Cryst. Liquid Cryst. 353 203-210. 

Production and use of PVC occur in the presence of air, i. e. in the presence of oxygen. Therefore, it is surprising that the mechanistic details of thermooxidative degradation of PVC are still not fiilly revealed. The major reactions of this process are shown in Scheme 1. As indicated in this Scheme, thermal dehydrochlorination yields HCl and simultaneously sequences of conjugated double bonds (polyenes) in the chain. The reactive polyenes lead to peroxides in a reaction with oxygen followed by the formation of radicals. Subsequent chain reactions result in additional initiation of HCl loss and further oxidative processes (/, 8). 

CH3CHO and (CH3CH2)20. Other reports on PEG are also available in literature. These reports cover various conditions of decomposition, such as low-temperature pyrolysis [5], or thermooxidative degradation of the homopolymer with or without added salts. In thermooxidative degradation PEG forms similar products as in an inert atmosphere [6,... 

From the chemist s point of view, the keto defect sites can be formed during polymer synthesis as a consequence of incomplete monomer alkylation, as well as a result of photo-, electro-, or thermooxidative degradation processes occurring after polymer synthesis. Acting as low-energy trapping sites... 

T. Karstens, V. Rossbach, Thermooxidative degradation of polyamide-6 and polyamide-6,6. Structure of UV/VIS-activc chromophores//Afocrazwo/. Chem. (1990), v. 191, No 4, 757-771. 

The Course of Thermooxidative Degradation of LD- and HD- Polyethylene under Accelerated Testing Conditions... 

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