Quantitative Rational Predictions of the Long-Term Temporal Decay Properties of Second-Order Nonlinear Optical Polymers from the Analysis of Relaxation Dynamics
An accelerated method of testing has been developed which allows quantitative, rational prediction of the temporal decay properties of second-order nonlinear optical (NLO) polymers under conditions of technological interest but which are experimentally inaccessible. This is accomplished by using a novel delay-trigger technique to monitor the reorientation of NLO chromophores doped and labeled in amorphous polymers over 12 decades in time (10-6 to 106 sec). By fitting the time-dependent orientational component of the second-order macroscopic susceptibility, χ(2), to the Kohlrausch-Williams-Watts expression, an average reorientation relaxation time, <τ>, is determined in both the glassy and rubbery states. The reorientation dynamics of Disperse Red 1 (DR1) above Tg, is coupled to the α-relaxation of polystyrene (PS) and poly(isobutyl methacrylate) (PIBMA). The temporal stability of χ(2) can be enhanced by physically aging the sample or by covalent attachment of the chromophore. However, increases in <τ> at a given temperature for the methacrylate-based copolymers with increasing functionalization is due to the increasing Tg of the copolymer with greater chromophore content. Finally, the issue of poling method and conditions are considered in terms of correctly interpreting the temporal behavior of SHG properties in NLO polymers.