Relaxation processes in nonlinear optical modified polyimide polymers
with side-chain azo chromophores having glass transition temperatures
in the range of 140 < T-g < 170 degrees C have been studied. The relax
ational mechanisms of the side-chain chromophores in these polymers ha
ve been investigated above and below the glass transition by second-ha
rmonic decay, dielectric relaxation, and differential scanning calorim
etry measurements. The nonexponential relaxation in both the time and
frequency domains was modeled by the Kohlrausch-Williams-Watts (KWW) f
unction. The nonlinear relaxational behavior of these polymers can be
modeled in terms of the Tool-Narayanaswamy description of glassy state
behavior. It allows for the nonlinear extension of the liquid equilib
rium state behavior into and below the glass transition region with an
accurate prediction of the relaxation times over more than 15 orders
of magnitude in time. Time-temperature scaling of the relaxation times
with (T-g - T)/T as the relevant scaling parameter is observed below
the glass transition.