INTERACTION OF POLYMERS AND MECHANICAL WAVES 



323 



pcrature. While pure kinetic theory elasticity would give a modulus 

 increasing linearly with increasing temperature, these systems, like all 

 practical rubbers and plastics, actually grow softer with rising tempera- 

 ture when deformed dynamically. It is striking, nevertheless, that a 

 modulus of '^lO' dynes/cm" seems characteristic of the visco-elastic 

 energy storing of these simple polymer structures. As noted below this 

 is 10 less than the crystal-like, close-packed, stiffness found for these 

 same molecular frequencies above their second principal relaxation time. 



TEMPERATURE IN DEGREES CENTIGRADE 

 70 60 50 40 30 20 10 



200 XtO^ 



3.2 

 i/T X 10^ 

 Fig. 5 — Sheiir elasticities and viscosities of pol^yisohutyleiie li(iui(ls assuming a 

 Ma.wvell model with relaxation frequencies 10^-10<. (Lower dashed curves for fre- 

 iiuency-dependent models.) 



