ULTRASONIC-WAVES - A TOOL FOR GELATION PROCESS MEASUREMENTS

The attenuation of high frequency ultrasonic waves ( greater than equivalent to 100 MHz) is very different depending on the phase, sol or gel, of a polymeric melt in course of gelation, and its measurement is a sensitive and nondestructive method for monitoring the sol-gel transition: the gelation point is accurately determined and the growing of the gel fraction is followed during the progress of the reaction. With assumptions about the friction coefficient between polymer and solvent, the measurements give the critical coefficient beta of the gel fraction S// infinity : beta equals 0. 5.