146 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



data, and the activation energy of 11.2 kilocalories per mole is obtained 

 in a similar manner. 



Due to the closeness of the surrounding polyisobutylene molecules, 

 one would expect that the relaxation frequencies would not have discrete 

 values but would be spread about the center value in some sort of a 

 Gaussian distribution. If we approximate this by representing each 

 region by two relaxations, one-half, and the other twice the frequency 

 of the mean value, as shown by the dotted lines of Fig. 17, the agree- 

 ment with the measured values of Fig. 15 is considerably better as 

 shown by Fig. 19. A wider distribution yet is indicated. 



For molecular weights greater than 2,000. the shortest chain segment 

 viscosity begins to diverge from the static viscosity indicating that 

 there are other relaxations for these longer chains. Some data for the 

 three longest chain polymers, F, G and H have been obtained by the 

 torsional rod method and the results are given in Table II. These data 

 are plotted on Fig. 20 as a ratio of dynamic to static viscosity plotted 



a 



< 109 



tl08 



20 25 30 35 40 45 



TEMPERATURE IN DEGREES CENTIGRADE 



Fig. 18 — Variations of high frequency shear stiffness and 

 stiffness plotted as a function of the temperature. 



'entanglement" 



