If there exists such relation, then why is this so?
If such relation doesn't exist, than which molecular factors contribute to endurance limit of polymers?
The image of Stress vs Fatigue cycle is from Callister's materials science and engineering. Both Nylon (polyamide) and PET (polyester) are condensation polymers, while rest in the example are addition polymers. I do not think this connection can be obvious- entrapped condensation products and water-induced hydrolysis may also have some role. Or is there any stress-dependent irreversible reaction going on for condensation polymers?
Dear Sumit Bhowmick, I don't think it has a link with whether addition or step-growth polymerizations, especially for polyesters and polyamides, as these laters may be obtained by both modes of polymerization. Fatigue is a matter of chain architecture and demensions, it is a function of the chemistry and the physical properties, and the stress type, conditions and intensity. All this contribute to the relaxation behavior of a given polymer. My Regards
Sumit Bhowmick
According to the theory of SN Zhurkov, the destruction of the polymer is associated with the rupture of the chemical bonds of the main chain. This position has been experimentally proven by the EPR method, since rupture of macromolecules leads to the formation of free radicals. Mechanical stress reduces the activation energy for breaking the chemical bonds of the main chain to a value, which leads to an increase in the rate of crack growth.
Therefore, to increase the durability of polymers, free radical inhibitors are added to it.
http://polymsci.ru/static/Archive/1959/VMS_1959_T1_3/VMS_1959_T1_3_485-486.pdf
Dear Sumit,
No, there is not such relationship. The fatigue endurance limit is exclusively a function of the polymer material structure and molar mass, not a function of the mode of polymer (material) preparing. (One can prepare it by polyaddition or polycondensation of monomer(s), or by polymer modification or vulcanization (cross-linking), or by partial polymer degradation, or by curing the polymer precursors etc.). More important usually is the polymer material processing which often strongly affects the material supramolecular structure, degree of crystallinity and overall morphology.
Kind regards, Jiri V.
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