326 



THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1952 



viscosity of the polymer has relatively little to do with the actual values 

 of dynamic viscosities. These would be at frequencies where the response 

 of the polymer liquid to the mechanical field is determined only by 

 motions within the local fixed arrangements mentioned above. 



Fig. 7 illustrates this, where on one scale the macroscopic viscosity is 

 plotted according to the familiar log-log relation with molecular weight. 

 Two extremes of average molecular weight, M,, and M„ are used for the 

 liquids, to show that the molecular weight distribution does not alter 

 the general conclusions. (M, is an upper limit weight average figure.) 

 On the other scale, the dynamic viscosity /x', ii^ this case for a single 

 element frequency-dependentYoigt model, shows low values and marked 

 curvature. These betoken the relaxation in which molecular weight, 

 through its effect on free volume and other structural factors, is signif- 



2.0 



Z 0.8 

 < 



8 0-^ 



,^ 4 



55 2 



O 



2.4 2.6 2.8 3.0_ 3.2 3.4 3.6 3.B 4.0 



LOG M;^ AND LOG Mn 



Fig. 7 — Comparison of steady flow and dynamic viscosities (at 25°C and 8 mc) 

 of polyisobutj'lene liquids of different molecular weights. 



