The orientational decay of chemically and thermally stable high-temperature chromophores doped into thin films made from polyimides and a variety of other polymeric hosts has been investigated. The chromophores are aligned using electric field poling and second-harmonic generation (SHG) is used to probe the decay of the electric field poling induced alignment. The decay rate of the SHG signal from films poled using both a corona discharge and side-by-side in-plane electrodes was measured. When electrodes are chosen so that the effects of charge injection are minimized, little difference has been observed between the orientational decays from films poled using the two methods for either an amorphous preimidized polyimide host or a highly anisotropic film poled during imidization. The films imidized during poling showed significant orientational stability at 250 °C for over 15 h after a fast initial partial decay. In addition, the decay of the SHG signal was measured as a function of temperature below the glass transition in a wide variety of different polymer host systems. The temperature dependence of the decay was found to be non-Arrhenius, but could be strongly correlated with the glass transition temperature of the guest-host system using an empirical relationship similar to the Williams–Landel–Ferry or Vogel–Tamann–Fulcher equation.

The use of polymeric materials requires understanding of the underlying mechanisms responsible for the slow structural relaxation processes that result in changes in physical properties associated with aging. This is especially critical for second-order nonlinear optical polymers in which polar order has been created by electric field poling near the glass transition temperature. For application in frequency doubling or electrooptic devices, these poled polymers must maintain a substantial degree of poled order and associated bulk nonlinearity at operating temperatures at least as high as 80 "C and at processing temperatures that may exceed 250 "C for short periods of time.In this paper, relaxation of poled order is measured by following the decay of the second-harmonic generation signal in a variety of nonlinear optical polymer with glass transition temperatures varying from 90 to 225 "C. The nonlinear chromophores have been incorporated into the polymer hosts either as dissolved guests or by covalent attachment to the polymer backbone as a side chain. In the guest-host case, it will be shown that there is a strong correlation between the characteristic poled order relaxation time 7 at a particular temperature and the glass transition temperature Tg of the guest-host system. This relationship has been observed over 6 decades in 7 for several large chromophores and in a variety of polymer hosts. The poled order decay in side-chain polymers is consistent with this "universal relationship" over a limited temperature range just below Tg but deviates from it at lower temperatures.The guest chromophores and side-chain polymer systems used in this work are presented in Figure 1. The synthesis of and measurements on the lophines have been described previous1y.lI2 For the guest-host systems, the chromophores have been dissolved in the polymers at concentrations up to 26 wt % without any evidence of crystallization or phase separation. Host polymers used in this work are as follows: Ultem, an amorphous soluble poly(ether imide) (from General Ele~tric);~ poly (methy1 methacrylate) (PMMA; Aldrich, MW 90K); Bisphenol A polycarbonate (PC; Aldrich, M, = 20-25K); polystyrene (PS; Polysciences, M, = 250-3OOK); PIQ-2200, a soluble poly(amic acid)-polyimide precursor (from Hitachi). The side-chain polymers studied were DR1-PMMA and NAT-PMMA in which the chromophores Disperse Red 1 (DR1) and 4-amino-4'-nitrotolan (NAT) are covalently attached to the methacrylate as indicated in Figure 1 at a loading level of 10 76. The polymers were dissolved in appropriate solvents, and thin films were spun onto transparent 0024-9297 f 931 2226-3720$04.00/0 6 L1 NMT 6' L 2 NAT NAT-PMMA Figure 1. Chromophores and side-chain polymers used.conducting substrates. The films were then baked in a vacuum oven above Tg to give solvent free 1-4-pm-thick films. The films made from PIQ-2200 were imidized at 250 "C. The T i s of all the doped and cured films were determined by differential scanning calorimetry (DSC).The electric field poling and subsequent rel...

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Guest-host polymer systems with potential use in electro-optic devices are discussed. The polymer host is a polyimide and the guest chromophores are 2,4,5-triarylimidazoles (lophines). Poling stabilities have been obtained by extrapolating the second harmonic generation decay using a stretched exponential function and extrapolated lifetimes greater than a year at 80 °C have been obtained. In addition, an apparent relationship between the stability of poled order and the glass transition temperature is discussed.

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