Polymer strength and chain conformation

Abstract

It is found that the expected maximum strength of polymers is not proportional to the number of polymer chains per unit area. Under uniaxial stressing only part of polymer chains, i.e., overstressed chains, contribute to the strength of the polymer. The number of overstressed chains obtained here for some polymers is consistent with the results of electron paramagnetic resonance and stress-Fourier-transform IR measurements: (a) Polymers with all-trans conformation of their chains have more overstressed chains than those with helix conformation; (b) in the case of polymers with helix conformation, those with smaller side groups have more overstressed chains. Under uniaxial stress, the polymer chains change their conformation from gauche to trans which results in a relief of stress. Polymer with helix conformation thus have less overstressed chains and, hence, lower strength than polymers with all-trans conformation.