MECHANICAL PROrEKTIES OF POLYMERS 



143 



cosities -qi and 772 assumed as a function of molecular weight is shown by 

 Fig. 16. The log of the viscosity starts proportional to the molecular 

 weight but above a molecular weight of 2,400 the increase is very slow 

 and becomes asymptotic to a value of 240 poises. An ecjuation which 

 fits the increase in viscosity with molecular weight is 



T' 11-8 tanh Z/2370 



Vd = Ac 



\\here Z is the molecular weight. The solid line shows a plot of this curve 

 and the circles are the assumed values to obtain a best fit to the meas- 



MOLECULAR WEIGHT 

 4000 6000 8000 



40 80 120 160 200 



NUMBER OF CHAIN ELEMENTS 



^ Fig. 15 — Mea.surpd values of high frequency shear viscosity and ehisticity for 

 25°C and three fretjuencies plotted against molecular weight. Solid lines are best 

 fit obtained by a two relaxation mechanism having the element values shown by 

 the figure. 



