Polymer destruction

Compelling evidence suggesting that the breakdown of hydroperoxyl groups is not related to polymer destruction, at least in the initial period of oxidation at temperatures below 400 K, comes from experiments on the initiated oxidation of polymers. It was found that the destruction of polymers develops in parallel with their oxidation from the very onset of the process, but not after a delay related to the accumulation of a sufficient amount of hydroperoxyl groups [129]. These experiments also demonstrated that it is free macroradicals that undergo destruction. Oxidation of polymers gives rise to alkyl, alkoxyl, and peroxyl macroradicals. Which radicals undergo destruction can be decided based on the kinetics of initiated destructive oxidation. 

Alkoxyl radicals can result from the isomerization of peroxyl radicals of oxidized PP (see above 13.1.6). If alkoxyl radicals cause polymer destruction, then, as they are produced from alkyl radicals, their accumulation and quasistationary concentration must decrease with increasing p02. However, despite varying p02, vs = const, in the oxidized PE and PP and, therefore, alkoxyl radicals essentially do not contribute to the oxidative destruction of polymers. At moderate temperatures, alkoxyl radicals eliminate hydrogen atoms from PH more rapidly than they undergo degradation. 

This reaction is very exothermic (A// —180 to —200kJ mol-1) and, therefore, seems to be very probable from the thermochemical point of estimation. The pre-exponential factor is expected to be low due to the concentration of the energy on three bonds at the moment of TS formation (see Chapter 3). To demonstrate that this reaction is responsible for the oxidative destruction of polymers, PP and PE were oxidized in chlorobenzene with an initiator and analyzed for the rates of oxidation, destruction (viscosimetrically), and double bond formation (by the reaction with ozone) [131]. It was found that (i) polymer degradation and formation of double bonds occur concurrently with oxidation (ii) the rates of all three processes are proportional to v 1/2, (iii) independent of p02, and (iv) vs = vdbf in PE and vs = 1.6vdbf in PP (vdbf is the rate of double bond formation). Thus, the rates of destruction and formation of double bonds, as well as the kinetic parameters of these reactions, are close, which corroborates with the proposed mechanism of polymer destruction. Therefore, the rate of peroxyl macromolecules degradation obeys the kinetic equation ... 

During processing polypropylene melts under the action of transverse strain there occur strain-chemical conversions which can result in both decrease and increase in their molecular masses the mechanical effect on the rapidity and level of the occurring processes is considerably more prominent than the mere contribution of thermal and thermal-oxidative breakdown. These data necessitate studying the process of polymer destruction. For this purpose it would be most effective to apply the criterion of assessment of the intensity with which destructive processes happen in polymer melts. 

Figure 6.8 Photo-resist technology. A metal substrate (s) deposited on an insulator base (b) is protected by the resist (r). Irradiation of the resist through a mask (m) results in photoinduced polymerization or polymer destruction...

Viscosity of dissolved polymers drops irreversibly under acoustic treatment65 A8). The depolymerization process us rather fast during the first minutes of the treatment and then it becomes slow and ceases completely when the equilibrium molecular mass (MM) M is reached. The higher the polymer s initial molecular mass N0, the higher the rate of destruction. The majority of authors associate polymer destruction in solution with cavitation effects occurring under acoustic treatment. 

Developed in works [47-50] idea of application of EPR-tomography method for investigation of polymers destruction processes lies in the following. 

We shall not carry out kinetic analysis of obtained results in this work we shall only notice that EPR-spectroscopy is more sensitive method for polymers destruction investigation than traditional methods such as method of IR-spectroscopy [47, 50],... 

Presented in this work results allow concluding that method of EPR-tomography is perspective and very promising method of investigation of polymers destruction processes. 

V.A. Belyakov et al. Biological activity of a new technogenic particle, a product of polymer destruction displaying antiradical properties, Dokl. /L4V 336 (1994) 124-126. 

Great attention in literature is paid to stabilizers - spatially difficult amines and then-derivatives [10, 70] which act as inhibitors of radical processes of polymer destruction. Difficult piperidines and their nitroxyl radicals are among them ... 

At samples heating in the presence of oxy gen of the air exothermic and endothermic effects, corresponding to oxidation reactions and polymer destruction, are seen on DTA curves. In our case, much more differences than in melting region are observed on DTA curves in the region of 400-500 °C where complex process of oxidation and PETP decay take place. 

IV International conference on achievements in the field of stabilization and control over the processes of polymer destruction//Highmolecular compounds (1933), A-35, No 2, 663-664 (in Russian). 

N.R. Prokopchuk Definition of activation energy of polymer destruction according to the data of dynamic thermogravimetry. Plastic masses (1983), No 10, 24-25 (in Russian). 

Application ultrasound has been used for the synthesis of materials, coating carbon nanotubes and noble metals, destruction and fragmentation of contrast agents, gas release, polymer destruction, and in drug delivery. i Ultrasound application has effect on permeability of PEC microcapsules. 

The polymer strength depends on both the probability of destruction of the polymer chains and the recombination of the free macroradicals formed. The potential barrier to restore a terminated chain increases the stress. A liquid with which the free radic ds react without secondary chemical reactions further decreases the probability of the recombination of macroradic ds. In this case one may consider the medium to be the catalyst of the polymer destruction process. 

N. Grassi, Chemistry of Processes of Polymer Destruction [Russian Translation], Moscow, Foreign Literature Press, 1959. 

Rubber reinforeement is a process of mechano-chemical nature, consisting of elastomer structuration from the crude mixture under the action of the meehanical forces. It depends both by the polymer destruction degree and mechanical regime applied during the processing. The absence of radical acceptors in the reaction medium, espeeially of the oxygen, does not modify the nature of the transformations produced on the properties of mechanically processed crude mixtures. 

Polymer destruction initiated by ionizing radiation is accompanied by the formation of double bonds and by the evolution of gaseous products (hydrogen, low-molecular-weight hydrocarbons, hydrochloric acid, tetrafluoroethylene, etc.). In the presence of oxygen, oxidized structures such as hydroperoxides. 

Novikova ND, Zalogoyev SN (1985) Formation of volatile substances during polymer destruction by Pseudomonas aeruginosa (in Russian) Kosmicheskaya Biologi) i Aviakosmicheskaya Medistina 19 74—76... 

The mechanism of autoxidation of solid polyolefins RH has many common features with hydrocarbon oxidation polymers are oxidized by the chain route the chain develops as alternation of acts of R- with O2 and RO with RH in the absence of an inhibitor and at a sufficiently high [O2] in polymer, chain oxidation occurs with autoacceleration because the hydroperoxide groups that formed are a source of initiation. However, there are several substantial distinctions. As already mentioned in Chapter 6, reactions resulting in polymer destruction play an important role. In initiated oxidation the main source of destruction is reactions of peroxide radicals, whereas in autoxidation the contribution of alkoxy radicals, which decompose in the reaction of the type... 

The more hydroperoxide groups were accumulated in the polymer, the higher is the rate of RO- formation and their contribution to polymer destruction. 

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