Conformational elasticity theory of chain molecules

This paper develops a conformational elasticity theory of chain molecules, which is based on three key points: ( i) the molecular model is the rotatio nal isomeric state (RIS) model; (ii) the conformational distribution functi on of a chain molecule is described by a function of two variables, the end -to-end distance of a chain conformation and the energy of the conformation ; (iii) the rule of changes in the chain conformational states during defor mation is that a number of chain conformations would vanish. The ideal defo rmation behavior calculated tay the theory shows that the change in chain c onformations is physically able to make the upward curvature of the stress- strain curve at the large-scale deformation of natural rubber. With the the ory, different deformation behaviors between polymers with different chemic al structures can be described, the energy term of the stress in the deform ations can be predicted, and for natural rubber the fraction of the energy term is around 13%, coinciding with the experimental results.