RELAXATIONS OF THERMOSETS .8. BRILLOUIN LIGHT-SCATTERING DURING THE CURING OF DIGLYCIDYL ETHER OF BISPHENOL-A THERMOSETS

The kinetics of sol-gel-glass transformations have been studied in the thermosets of diglycidyl ether of bisphenol A cured with diamino diphenyl methane and diamino diphenyl sulfone, at different temperatures using Brillouin light scattering. The shape of the Brillouin peak is generally broad. This is attributed to the damping of elastic waves in the mixture of unpolymerized low-molecular weight fluid and the polymer chains forming the networks. The Brillouin peak becomes sharp and narrow at complete curing of the thermosets. The phonon velocity increases and the attenuation decreases with the curing time. These changes occur in two steps with the second step appearing near the gelling time of the thermosets. A semilogarithmic plot of the time for the velocity and attenuation to reach half of their total change against the reciprocal temperature yields a straight line with different slopes for the two thermosets. It is suggested that Brillouin light scattering is a useful non-destructive, in-line, method for control in the processing of epoxy thermosets.