Rotational reorientation dynamics of nonlinear optical chromophores in rubbery and glassy polymers: a-relaxation dynamics probed by second harmonic generation and dielectric relaxation. Dhinojwala, Ali; Wong, George K.; Torkelson, John M. Dep. Chem. Eng., Northwestern Univ., Evanston, IL, USA. Macromolecules (1993), 26(22), 5943-53. CODEN: MAMOBX ISSN: 0024-9297. Journal written in English. CAN 119:204233 AN 1993:604233 CAPLUS

Second harmonic generation (SHG) is used to monitor rotational, reorientation dynamics of C.I. Disperse Red 1 (I) doped at 2 wt.% in poly(iso-Bu methacrylate) (II) and poly(Et methacrylate) (III). A delay-trigger approach is employed in conjunction with conventional measurements to monitor dynamics from 10-4 s to as long as necessary, permitting characterization of rotational reorientation above and below the glass temp. (Tg). The dynamics of the orientation component of the second-order macroscopic susceptibility, c(2), is sensitive to ácos Qñ (Q is the angle between the direction vector of the applied d.c. field and that of the chromophore dipole moment). Both in poling-onset-mode and temporal decay expts., the time dependence of the orientational component of c(2) can be represented by a Kohlrausch-Williams-Watts equation, from which av. rotational reorientation time consts.(t) may be detd. By comparison of SHG and dielec. relaxation measurements in II, which exhibit only an a-relaxation, and III, which exhibit distinct a- and b-relaxations at temps. T £1.15-1.17Tg, the rotational, reorientation dynamics of I are coupled with the a-relaxation dynamics in these polymers. The t values are obtained over a 7-decade range and fit well to WLF equations above Tg but deviate below Tg; scaling the t data using the reduced variable Tg/T reveals good overlap for the two polymers, indicating similarity in the cooperativity of the a-relaxations in II and III. The implications of the coupling of nonlinear optical dopant reorientation to the polymer a-relaxation for the design of temporally stable SHG polymeric materials are discussed.