INTFRACTIOX OF POLYMERS. AND MIX'HAXICAL WAVES 



315 



visoosit.v" arising from transfer of momentum among thermally agitated 

 chain segments, does not seem to have been considered in the theory of 

 perfect rubbers. As in gases, it would require an increase of viscosity 

 with temperature. 



In polyisobutylene, however, the dynamic viscosity leaps upward in 

 both magnitude and temperature dependence. It should be emphasized 

 that this is, again, for a cross-linked (Butyl) gum — an infinite network 

 like the hevea gum, with presumably infinite macroscopic viscosity. 

 The striking thing is that this internal viscosity is not greatly dependent 

 on the network, at the degrees of "cure" used in rubber technology. For 

 instance, recent studies over the frequency range 20-600 cycles, on high 

 molecular weight, M^ = 1.2 X 10^ linear polyisobutylene," give, at 

 2o°C and 100 cycles, n' = 4800 poises, although the steady flow viscosity 

 of this polymer at this temperature is greater than 3 X 10^ poises.^* 

 Then, the infinite network (Tjstea.iy now -^ °o ) Butyl polymer of Fig. 3 

 has at 27°C and 100 cycles n' = 8000 poises. At 1000 cycles agreement 

 ajjpears to be about the same, and is tolerable considering the several 



100,000 

 80,000^ 



60 ,000 



40,000 

 30,000 



VI 20,000 



10,000 

 8000 



4000 

 3000 



2000 



100 

 80 



1000 

 800 



w 200 rvj 

 2 5 



100 ^ 



z 60 z 



4 9 40 9 



100 200 400 600 1000 2000 4000 6000 10.000 



FREQUENCY irj CYCLES PER SECOND 



Fig. 4 — Vi-scosity and .shear iukIuIus of j)lasticizc(l cellulose nitrate. 



