In-situ study of the nonlinear optical responses and dynamics for crosslinked and uncrosslinked polymers

We performed the in-situ experimental study of rionlinear optical responses and dynamics for crosslinked- and uncrosslinked-polymers by changing the poling and relaxation profiles. In the characterization both second harmonic generation and photoinduced birefringence were employed. Two newlysynthesized polymer structures, P(MMA-Co-MMCN)(0.7:0.3) with chromophores(A) arid P(MkI.4-Co- IP0)(0.5:0.5) without, chrornophore(B) were adopted as representative polymeric systcriis. Whcii tlic dipoles in the two polymeric systems (A) and (B) were thermally crosslinked to the polynier main chaiii along tie electric field, the rotational mobility of dipoles were found to be suppressed, resulting in the iniprovernent of thermal stability. In order to understand the higher thermal stability of the crossli:iketl polymer system, we investigated thc in-situ second harmonic generation response at vaiious teniperatures. At the temperature of 1OO'C the amount of dipole alignment in crosslinked polymer system was considerably larger than that of the uncrosslinked polymer system. This behavior is understood to be from the increased moment of inert,ia of dipoles in the crosslinked polymer system(l1. That is, because the moment of inertia of crosslinked dipoles IT is greater than that of the uncrosslinlced dipoles 11, thc angular lhermal fluctuation of crosslinked dipoles < 68 >= fl is smaller than that of uncrosslinked diploma. <δ θ>=√KT/I_f.