CHROMOPHORE-FUNCTIONALIZED GLASSY-POLYMERS WITH LARGE 2ND-ORDER NONLINEAR-OPTICAL RESPONSES - TRANSIENT DYNAMICS AND LOCAL MICROSTRUCTURE OF POLY(P-HYDROXYSTYRENES) AS ASSESSED BY IN-SITU 2ND-HARMONIC GENERATION TECHNIQUES

Microstructural relaxation of thin films of the poled, chromophore-fun ctionalized amorphous polymer 4-nitrophenyl)-(S)-prolinoxypoly(p-hydro xystyrene) has been studied by in-situ second harmonic generation (SHG ) techniques. The temporal and temperature dependence of the SHG inten sity decay has been analyzed as a function of poling and processing pa rameters within the framework of the Kohlrausch-Williams-Watts (KWW '' stretched exponential'') model. The average SHG relaxation time, tau, increases rapidly upon reduction of the applied poling field strength, with increasing poling time (physical aging), and with decreasing fil m temperature. The other KWW parameter, beta, which reflects the distr ibution of relaxation times, decreases (the distribution broadens) mod erately with increases in the applied electric field strength and stro ngly with increases in poling time (physical aging). The observed valu e of beta increases (the distribution narrows) with increasing film te mperature. These trends and the variation in KWW parameters yield info rmation regarding reorientation dynamics of the tethered chromophore m olecules within the polymer matrix and thus on the nature of the syste m subspace which is explored during relaxation. Both parameters reveal a strikingly narrower distribution of relaxation times/reduced rotati onal mobility versus chromophore-doped, ''guest-host'' systems and cla ssify the present materials as Angell ''intermediate'' glasses. The te mperature dependence of the second harmonic signal decay after poling field cessation can be divided into two distinct regions: (i) above T- g, where the dynamics are characteristically nonlinear and best descri bed by the Williams-Landel-Ferry (WLF) equation; (ii) below T-g, where the behavior is linear and modeled adequately by the Arrhenius equati on. Analysis of the growth of the second harmonic signal as the poling field is applied yields a similar picture; however, limiting SHG valu es at temperatures significantly above T-g appear to be influenced by both thermal disruption of chromophore alignment and ion conduction/sp ace charge effects.