GLASS TEMPERATURE OF POLYMER RING-SYSTEMS

The glass temperatures of polymer ring systems are predicted from first principles and then compared to four sets of experimental data. In all four cases the glass temperatures rise with decreasing molecular weight as predicted by the theory. The glass transition is assumed to occur when the configurational entropy reaches a critically small value as the temperature is lowered. An attempt is made to keep the large number of parameters to a minimum by (1) estimating the number of flexible bonds per monomer through knowledge of chemical structure, (2) estimating the number of beads per monomer through considerations of volume, (3) estimating the intermolecular (hole) energy by means of the thermal expansion coefficient DELTA-alpha, and (4) fixing the lattice coordination number at the same value (z = 4) for all materials. The stiffness parameter DELTA-epsilon is determined by a fitting to the infinite molecular weight glass temperature. With these constraints the fit to data is only qualitative. Although the theory is compared to experimental data only for glass temperature vs molecular weight, approximate formulas are obtained for ring glass temperature variation with plasticizer and with blend composition when at least one of the two blend components is a ring.