LIQUID-GLASS TRANSITION IN AMORPHOUS POLYMERS

The purpose of the present work is to present a survey of the behaviour of amorphous polymers through the glass-rubber transition range. In the first part, the main points are reviewed; from experimental data, beyond the universal character of several properties, the kinetic and relaxational aspects of the glass transition seem to be dominant. In the second part, a new theory of the glass transition is described on the basis of a model of molecular mobility. The structure of the amorphous condensed polymeric matter is described in terms of regular packing of repeat units in which there are sites with disorder, i.e. with excess of entropy and enthalpy. The concentration of such sites, here after called "defects", is calculated through thermodynamic arguments, usual in physical metallurgy. The concept of hierarchical correlated movements is, then, developed and applied to molecular displacements supposed to occur only in defects: thus, the characteristic time for the molecular mobility is calculated and is founded to be very dependent on the concentration of defects. The kinetic and relaxational aspects of the glass transition appear to be the consequence of the concentration evolution of different types of defects. The third part is devoted to the comparison between numeric simulations of the behaviour of amorphous polymers near T9 based on this theory, and experimental results concerning different properties such as entropy, enthalpy (i.e. C(p)), specific volume, dynamic modulus and viscosity. Those results are discussed in relation with the main theoritical aproaches mentioned in the literature.