150 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



109 





10' 



yt 1.0 



<Oo.6 

 ^^ ^ . 



UL U 



t- 2 4 6 ,q6 2 4 6 ,q7 2 4 6 ,q6 2 4 



PRODUCT OF FREQUENCY TIMES STATIC VISCOSITY 



Fig. 21 — Calculated values of stiffness and viscosity obtained by adding a 

 single "configurational" relaxation frequency to the two short chain relaxations 

 obtained from high frequency measurements. 



mechanisms which show up as discrete relaxations in long chain mole- 

 cules in solution. 



Some measurements have also been made to determine the effect 

 of chemical substitutions in the polymer chains. In a previous paper,* 

 the high frequency properties of poly-a-methyl styrene were discussed. 

 This material has the polyisobutylene chain but with one methyl re- 

 placed by a phenyl so that its chain becomes 



H CH3 



1 I 



C C— 



H 



For low molecular weights this material is liquid. The shear stiffness of 

 this liquid is somewhat higher than for polyisobutylene but has about 

 the same change with temperature. The variation of the high-frequency 

 viscosity, however, is much larger for poly-a-methyl styrene than for 

 polyisobutylene, and corresponds to an activation energy of 23.6 kilo- 

 calories. The relaxation region for the shortest chain motion is much 



* See footnote on page 132. 



