Orientation of liquid crystals (LC) on a polymer surface irradiated with polarized UV light was observed as early as in the beginning of 90s and this effect promised wide applications in LCDs technology. Nevertheless, despite evident advantages of photoalignment technology, insufficient photosensitivity, low anchoring energy and strong sticking effect prevent a wide application of photoalignment in LCD industry and this technique is used just in scientific laboratories. Therefore, the development of new photoalignment materials is an issue of great importance. Our previous studies showed promising features of photoaligning polymers that contain derivatives of cinnamic acid in the side fragments of a cellulose main chain [1]. Here we report on development of new photosensitive polymers (PG1 and PG2) based on cellulose backbone containing cinnamate groups and additional C=C bonds to improve photosensitivity and thermostability of the materials. The additional C=C fragments participate at photodimerization of cinnamate moieties that results in the increasing of crosslink density in the polymer films. We found that the developed materials possess enhanced photosensitivity and thermostability, rather high anchoring and extremely low sticking image effect. Photosensitivity of the materials (UV dose D, necessary to get the same aligning quality as of commercial polyimide materials) is about 75 mJ/cm² that is in an order less than of popular polyvinyl-cinnamate materials. Thermostability of the alignment quality and pretilt angle is not worse than 100 ^oС. Azimuthal anchoring energy achieves the maximum value W_a > 10^-2 erg/cm² after irradiation dose about 30 s. Zenithal anchoring (measured by the team of Prof.Nobili, Monpellier, France), W_z ~ 0.1 - 0.3 erg/cm². Rather high anchoring energy of the developed polymers results extremely low image sticking effect in the cells with PG1, PG2 materials. The sticking parameters, S - 1 % is the same order as the value S of commercial polyimide materials. To elucidate mechanisms of photoalignment of nematic LC on PG-materials, IR absorption spectra and their modification after UV irradiation were studied. Cross-linking of the side fragments and their trans-cis isomerization are supposed to be the main photochemical processes leading to UV light-induced anisotropy of the polymers. The results obtained show that the complex of the main characteristics of PG materials makes them promising candidates for LCD applications.

[1] I.Gerus, A.Glushchenko, Yu.Kurioz, Yu.Reznikov, O.Tereshchenko. Opto-Electronics Review. 12(3), 281 (2004).