Melting Temperatures as a Function of the Strain of Oriented Polymer Networks

Abstract The reduction in conformational entropy on stretching elastomers causes an increase in melting point of the temperature-induced crystallisation. The dependence of the melting point on degree of deformation is relatively weak. The high melting points of the strain-induced crystallites must be caused by regions whose orientation is markedly higher than that which corresponds to the macroscopic strain. Such a bimodal orientation distribution is explained by an inhomogeneous deformation of the rubber. There exist either regions in the specimen which do not participate in the deformation or regions with very low strength. Stretching leads to an affine deformation of a part of the specimen. If one lets this crystallize, temperature-induced crystallites find themselves in surroundings whose orientation is describable with the assumption of a Gaussian network. Correspondingly, the increase in melting point as a function of strain can be calculated with the aid of the statistical theory of entropy elastic...