Liquid-crystalline side chain polymers have recently been used to store optical data by a local optical heating of a preoriented polymer film into the isotropic phase. The resulting macroscopically unoriented light scattering spots were frozen-in by subsequent cooling. This technique is referred to as thermorecording'**).In our studies we found a completely different method for optical data storage in liquid-crystalline polymers. It consists in inducing optically a birefringence pattern in a layer of such a polymer. A phase object results due to spatial refractive index modulation. The stored optical information is therefore invisible to the naked eye. fX-@; !--~12~-. f g 43 sA 94 n 104 i N c e N = N + A 1The liquid-crystalline polyester 1 with transitions glassy to smectic A, nematic, and isotropic as indicated (in "C), containing mesogenic groups of the azobenzene type in the side chain was used as storage medium. Its dielectric anisotropy is strongly positive due to the cyano dipoles linked to the mesogenic units. This offers the possibility to orient the liquid-crystalline polymers 1 with the director parallel to an externally applied electric field. Experimental partThe liquid-crystalline polymer 13) was oriented with the director parallel to an externally applied electric field. A cell, consisting of two conductive glass plates, separated by 7 prn polyimide spacers, was prepared and the polymer was subsequently filled-in. A uniform homeotropic orientation was achieved by applying an appropriate electric field at temperatures above the glass temperature of the polymer. A completely clear monodomain film resulted in each case.

Recently, self-healing polymers based on disulfide compounds have gained attention due to the versatile chemistry of disulfide bonds and easy implementation into polymeric materials. However, the underlying mechanisms of disulfide exchange which induce the self-healing effect in poly(disulfide)s remain unclear. In this work, we elucidate the process of disulfide exchange using a variety of spectroscopic techniques. Comparing a model exchange reaction of 4-aminophenyl disulfide and diphenyl disulfide with modified reactions in the presence of additional radical traps or radical sources confirmed that the exchange reaction between disulfide compounds occurred via a radical-mediated mechanism. Furthermore, when investigating the effect of catalysts on the model exchange reaction, it could be concluded that catalysts enhance the disulfide exchange reaction through the formation of S-based anions in addition to the radical-mediated mechanism.

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We present a novel method of preparing highly efficient and stable second-order nonlinear optical (NLO) polymers via chemical cross-linking induced vitrification under electric field. In this method a soluble prepolymer is first prepared that contains cross-linking sites attached to the NLO-active groups. Upon preparing samples of desired thicknesses, the prepolymer is heated (precured) to enable some chemical cross-linking and thus to increase the glass transition temperature (Tg) to an optimum for poling. The precured polymer is then heated above its Tg and subjected to a high electric field to obtain the desired alignment of NLO moieties. Subsequent chemical cross-linking (curing) under electric field continues to advance the Tg and hence leads to in situ vitrification of the polymer that stabilizes the electric-field-induced orientation of the NLO moieties. Detailed results of thermal, linear optical, poling kinetics, and NLO properties are described for the polymer system prepared from tetrafunctional 4-nitro 1,2-phenylenediamine and bifunctional Bisphenol-A diglycidylether as the starting monomers. The polymer which has been cured finally at 140 °C under a very high corona field exhibits d33≂14 and d31≂3 pm/V, determined from the Maker-fringe experiments. Most significant, however, is the fact that this polymer shows no detectable decay in second harmonic generation for over 500 h under ambient conditions and no tendency of relaxation even at 85 °C.