350 



THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1952 



Fig. 27 — Effect of microgel molecules in synthetic rubber on smoothness of 

 extruded wire insulation. Rough covering is fi-om high-speed extrusion of GR-S 

 without microgel. 



weights of chain molecules. Further, accompanying the extremely high 

 average molecular weight of the microgel (18.6 X 10 ), the [/s] per 

 average molecule is 42 X 10~ " dyne cm or about twenty-five times that 

 of the polyisobutylene with M, = 3.9 X 10 . Also, the temperature 

 coefficient for ms of polybutadiene microgel is low. 



Of course, polybutadiene, as chams or as microgel molecule segments, 

 has many double bonds. These will surely influence the m , or internal 

 rotation mechanism. Further work remams to show just what is their 

 effect in the microgel case. But, it is interesting to compare ms values 

 for Hevea rubber chains with those for, say, polyisobutylene, which has 

 only single bonds in the chain. 



=3. 



..OJ 



^2 



10 Q 2000 

 5? 



D 



30 35 40 45 50 55 



TEMPERATURE IN DEGREES CENTIGRADE 



Fig. 28— Rigidity of 0.5 per cent solution in cyclohexane of polybutadiene 

 microgel {Mw = 18.6 X lO^) at 20kc. 



