MECHANICAL PROPERTIES OF POLYMERS 



153 



109 



ujci: 





10° 

 1.0 

 0.8 

 0.6 



0.4 



0.2 



0.1 

 0.08 

 0.06 



O 



5 0.04 

 < 



z 



Q 0.02 



O 0.008 

 p 0.006 



10"* 



PRODUCT OF FREQUENCY TIMES STATIC VISCOSITY 



Fig. 22 — Ratio of dynamic to static viscosity and the shear stiffness for four 

 polj'mer liquids plotted against product of frequency and static viscosity. 



the 4.8 kilocalories for polyisobutylene. This presumably indicates that 

 there is more of a difference between the viscosity flow segment and the 

 shortest chain segment in these materials than in polyisobutylene. Since 

 no measurements are available over a range of molecular weights, no 

 direct evidence has been obtained for the various chain lengths. 



B. Longitudinal Wave Measurements in Liquid Polymers 



Since the increase in shear elasticity for the highest relaxation fre- 

 quency is so large, it should also appear in longitudinal wave measure- 

 ments. Fig. 23 shows a calculation for the 5590 molecular weight liquid 

 of the longitudinal velocity assuming that the Lame X elastic constant 

 is independent of frequency and that all the variation occurs in the shear 



