ORIENTATION MOTION IN GLASSY-POLYMERS

We present a theory of orientation Brownian motion of a polar particle frozen-in in a polymer glass. The theoretical problem is then one of orientation dynamics in a viscoelastic medium. The glassy material pro vides, at a short-time scale, an elastic force that returns the orient ation to that at time t=0. On larger time scales, this privileged orie ntation diffuses due to thermal motion. A cascade of orientation motio ns at all time scales results in a stretched-exponential behavior of t he nonlinear optical response function and of other moments of the ang ular distribution function.