In-situ study of the nonlinear optical responses and dynamics for a crosslinkable polymer-pair

The nonlinear optical responses of crosslinked and uncrosslinked polymer-pa irs were characterized by using in-situ second-harmonic-generation measurem ents. When the molecular dipoles were thermally crosslinked to the polymer- pair main chain along the electric field, the rotational mobility of the mo lecular dipoles was found to be suppressed, resulting in improved rotationa l relaxation. This is understood to be from the increased moment of inertia of the molecular dipoles attached to the crosslinked polymer system, which also give an increased second-harmonic-generation signal. From the second harmonic generation measurement, the second-order nonlinear optical coeffic ients, d(31) = 1.7 pm/V and d(33) = 6.6 pm/V, were obtained. On the other h and, the transient dynamics of molecular alignment was investigated for bot h crosslinked and uncrosslinked polymer-pairs at various temperatures. At t emperatures above T-g - 50 degrees C, the double exponential and Dissado-Hi ll model fit the relaxation data well while at temperatures below T-g - 50 degrees C, the double exponential and stretched exponentials provided a goo d fit. This finding suggests that two relaxation times can characterize the relaxation behavior of the polymer-pairs over the temperature range from r oom temperature to the glass-transition temperature.