結晶性高分子の粘弾性論

Abstract

The remarkable difference in rheological properties between the crystalline polymers and the amorphous ones is represented by the relaxation time spectra H(τ), τ being the relaxation time. In amorphous polymers it is well known that the intrachain relaxation gives rise to the wedge type spectrum with the slope of -1/2 in the log H-logτ plot. Here is discussed about the molecular characteristics in case of the crystalline polymers. We consider in the linear viscoelastic range and at temperatures above the glass transition point.The peculiarities in crystalline polymers, such as the rotation of crystallites, the slipping of chain segments in or on the surface of crystallites, and the spacial heterogeneity in friction constants for chain segments do not change the spectrum in amorphous polymers significantly.The crystalline polymers owe their crystallinity intrinsically to the high regularity in the molecular structure and the strong intermolecular interaction. Therefore, even in the amorphous region of the crystalline polymer, we can expect many crystalline nuclei or physical secondary bonds, under frequent dissociation and reconstruction. Then the movement of a molecular chain is inevitably accompanied by the cooperative movement of neighbouring chains. It is a main aim of this paper to study how these characteristics influence the above mentioned wedge type spectrum.Accordingly, in treating a molecular chain by the normal coordinate method for Bueche's vibrating string model, it is suggested to assume that the normal mode with the longer wave length suffers the larger frictional resistance. Under the assumption, it can be shown that the spectrum in crystalline polymer has a smaller slope and a larger spread than in amorphous polymers.To proceed more quantitatively, a tentative assumption is made such that, in order to excite a normal mode, a constant fraction of the secondary bonds should be cut off within a sphere, say the cooperative sphere, with radius equal to a quarter of the wave length characterisitic of the mode. Then we have in fact log H=const. -(1/4)logτ, being in qualitative accord with the spectrum for Teflon.The theoretical viewpoints at present, however, are far from the final stage, and the critical review on the experimental situations is much desired, especially as to whether the rheological properties are studied experimentally at temperature higher than the glass transition point.