Phenomenology of Free Radical Formation and of Relevant Radical Reactions (Dependence on Strain, Time, and Sample Treatment)

Historically, the first ESR experiments with mechanically produced free radicals have been made in the Ioffe-Institute in Leningrad in 1959 [1] with ground or milled polymers, the samples being investigated after completion of the fracture process. To elucidate the effect of structural or environmental parameters on the kinetics of stress-induced free radical formation it is necessary to study — by ESR — highly stressed chains during the loading process. As outlined in Chapter 5 a notable energy elastic straining of a chain can only be achieved if the chain cannot relieve stresses internally by a change of conformation or externally by slippage against the field exerting the uniaxial forces. Vice versa the mechanical scission of a chain must be taken as an indication that at the time of chain rupture axial stresses ψ equal to the chain strength ψ_chad not only been reached but also maintained during the average lifetime period T_c of the chain segment.