Retardation of rotational reorientation dynamics in polymers near the glass transition: a novel study over eleven decades in time using second-order non-linear optics. Dhinojwala, Ali; Hooker, Jacob C; Torkelson, John M. Department of Chemical Engineering, Northwestern University, Evanston, IL, USA. J. Non-Cryst. Solids (1994), 172-174(Pt. 1), 286-96. CODEN: JNCSBJ ISSN: 0022-3093. Journal written in English. CAN 121:231741 AN 1994:631741 CAPLUS

A novel protocol has been developed using second harmonic generation to quantify the rotational, reorientation dynamics of second-order non-linear optical chromophores in amorphous polymers. Dynamics are monitored over 11-12 decades in time, from microseconds onwards, allowing characterization both well above and below the glass transition temp., Tg. The time dependence of the orientational component of the second-order macroscopic susceptibility, c(2), can be represented by a Kohlrausch-Williams-Watts equation from which av. rotational reorientational time consts., átñ, are detd. For the Disperse Red 1-poly(iso-Bu methacrylate) (PIBMA) system studied here, átñ is coupled to the a-relaxation dynamics of PIBMA. Retardation of these dynamics is investigated by phys. aging (below Tg) and covalent attachment to the polymer (above and below Tg). Phys. aging for several days near Tg can result in two orders of magnitude increase in átñ, above the value obtained for the quenched state. Covalent attachment of Disperse Red 1 chromophores also increases átñ relative to the doped-chromophore systems; this effect is due to the increase in Tg for the cases of 1 and 6 mol% attachment. The implications of these effects for the design of temporally stable SHG polymeric materials are discussed.