Main-chain breakage

In this method the amount of wool capable of being dissolved with a solution, which rupture the disulphide cross-links, is determined. Essentially it is a test which detects main chain breakage caused, most often, by action of acids on wool [21,22]. 

If the answer is yes, then would you expect the P.T.F.E. molecule to go through a transition f1uorine/meta1 state (as tentatively hypothesized in my paper yesterday for n 5Fi2/clean ion interactions) as a precursor to main chain breakage stimulated by metal catalytic activi ty ... 

Washino K, Denk O, Schnabel W (1983) OH-radical-induced main-chain scission of poly(ribonucleic acids) under anoxic conditions. Z Naturforsch 38c 100-106 Washino K, Katsikas L, Schnabel W (1984) Radiation-induced strand breakage in poly(riboadenylic acid). A pulse radiolysis study on the protective action of cysteamine under anoxic conditions. IntJRadiat Biol 46 747-758... 

It is well known that ESR is a sensitive eiqierimental technique to detect selectively free radicals having broken bonds or unpaired electrons. Therefore, one obtains direct experimental evidence for chemical bond scission, whenever an ESR spectrum was observed from a fractured polymer material. ESR studies on mechanical destruction give us a decisive answer to the question whether the macroscopic fracture of polymers results in breakage of main chains of the polymer molecules. And also ESR may provide interesting information which is helpful for crarelating phenomraiolopcal results with breaking of chemical bonds. 

A free radical formed by side-chain breakage can also induce main-chain scission according to... 

The effect of heat on the performance of a polymeric system can be studied by thermal ageing. During ageing, scission of the main chain, crosslink formation or crosslink breakage can take place. Sometimes, existing crosslinks may be replaced by more stable crosslinks. All these factors contribute to the properties of the aged samples. 

The main chain backbone should be free of weak links which could be the site of unwanted chain breakage (chain scission). 

The influence of NO2 on the mechanical properties of polyamidoimide films has been considered at 323 K and F(N02) = 13 kPa [23]. The temperature dependences of the storage modulus E and loss modulus E" have been obtained for various times of NO2 exposure. A nonmonotonic decrease of E was observed at 473 K, but the maximum of the E temperature dependence appears at approximately the same temperature. Samples exposed to NO2 for eight days show an increase in E at the glass transition temperature (563 K). The phenomenon is assoeiated with chain breakage and the recombination of macroradicals giving rise to crosslinking. Chain breakage is supported by results obtained by the present authors. The ESR spectra of polyamidoimide exposed to an NO2 atmosphere show the formation of iminoxyl radicals with spectral parameters that are close to those of PVP iminoxyl radicals. The possible mechanism of their formation includes the main-chain decomposition step as follows ... 

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