10~1 234 5cm. for the calculation. The sharp peaks are a result of the discontinuous change from 9X to S2 at the boundaries. If our model had varying continuously between 9X and 02 then the barrier would have been rounded. The linearity of the sides of the barriers shows that the first term in eq. II-ll predominates.

A major objective in polymer rheology is to predict a fluid's response to a general deformation from molecular information. A method has been developed which allows one to predict the viscoelastic properties of polymer melts from a limited amount of rheological and molecular data for the polymer. The input parameters are: (a) zero-shear viscosity; (b) molecular weight distribution; (c) temperature and density; and (d) constants relating Graessley's relaxation time to the Rouse relaxation time. The technique then "simulates" a discrete relaxation spectrum using G' and G" data from the Rouse theory and finally requires that a continuum model of polymer viscoelasticity be fit to shear viscosity data predicted by Graessley's theory. Examples of the utility of the procedure are given to illustrate the role of molecular weight and weight distribution in determining rheological behavior.

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SYNOPSISMolecular motions in the bulk polycarbonates of bis(4-hydroxyphenyl)-2,2-propane, bis(4-hydroxyphenyl)hexafluoro-2,2-propane, and bis(4-hydroxyphenyl)1,3-dichloro, tetrafluoro-2,2-propane have been studied by wide-line nuclear magnetic resonance techniques. Magnetic resonance information obtained over a broad temperature range from both H' and F' nuclei has been used to assign various mobility phenomena to specific segments of the macromolecules. Furthermore, because of the close similarity in size of the fluorine and hydrogen atoms, F' resonance information yields some further insights on molecular motions in BPA polycarbonate. The rotation of -CF3 groups, which begins at 283"K, is apparently cooperative with the motion of the adjacent phenyl groups. The effect of the -CF3 groups on the restricted motion of the adjacent phenyl groups is the same as that of -CH3 groups. Furthermore, it is inferred that in BPA polycarbonates the restricted motion of the phenyl groups occurs cooperatively with the carbonyl group and that this mode of motion is the principal contributor to the dielectric and mechanical loss peaks observed near 170°K. The glass transition temperature of the dichlorotetrafluoro compound is only 5°C higher than the hexafluoro compound. Nevertheless, the reorientation of the -CF*CL groups and the phenyl groups in the dichlorotetrafluoro compound occurs 100°C higher than the corresponding motions in the hexafluoro compound. 0 1970 by John Wiley & Sons, Inc.