SYNTH ETIC KlBBEIi KESEAKCII 



377 



method. Branched copolymers show inordinately high concentrated solu- 

 tion viscosities. The latter may therefore be employed as a measure of 

 degree of branching or approach to gelation when supplemented by dilute 

 solution viscosity measurements. Furthermore, the power required to 

 maintain the armature stationary as measured by the current {)assing 

 through the magnet furnishes data useful in predicting how a given co- 

 ])olymer sample will process. 



Fig. 9.— Apparatus employed to effect the solution of synthetic rubber prior to the 

 determination of concentrated solution viscositv. 



Application of Sol-Gel Methods to Control Processing 



In addition to their application to the control of synthetic rubber in 

 production, the sol-gel methods of characterizing the copolymer which have 

 been briefly described above are of very great use in elucidating what 

 happens during the processing of the rubber^^. By the term "processing" 

 is meant the operations which are carried out on the copolymer subsequent 

 to its manufacture and prior to its vulcanization into its fmal form. These 

 operations involve working the rubber on machinery (plastication) in order 

 to render it soft and satisfactory for mixing in pigments and for extrusion 



