Epoxy-based photosensitive polymers with two different cinnamoyl side groups (cinnamoyl group and 4-octyloxy cinnamoyl group) were prepared by functionalization of the polymer precursor (BP-AN).Two kinds of photo-sensitive molecules including cinnamoyl groups were also prepared:hydroquinone dicinnamate obtained by reaction between hydroquinone and cinnamoyl chloride

while hydroquinone di(4-octyloxyl)cinnamate synthesized through reaction between hydroquinone and 4-octyloxy cinnamoyl chloride.All chemicals were characterized by necessary spectroscopic methods including 1H-NMR and FTIR

which indicated their accurate molecular structures had matched our target molecules.The photo-sensitive molecules were doped into corresponding photo-sensitive polymers in different proportions respectively

and photo-alignment layers were prepared based on the spin-coated films of the polymers

which were irradiated under LPUV (linearly polarized ultra violet) and then used to assemble LC cells filled with nematic liquid crystal 5CB.The photo-alignment behavior of the doped polymers was characterized by the microscopic observation and comparing the numerical value of Tmax/Tmin in sinusoid-curves of LC cells.The results showed that

below a certain doping point (about 10%)

increasing the concentration of the photo-sensitive molecules would result in a better photo-alignment performance.Since the photo-dimerization reaction of cinnamoyl groups happens only when two cinnamoyl groups stand in properly spatial positions to form a tetra-atomic ring.Doped molecules greatly added up the amount of cinnamoyl pairs with adequate steric relations

thus created greater chance for cinnamoyl groups to crosslink and improved the LC-alignment performance.By doping different amount of photo-sensitive molecules we found the ideal doping point would be around 10%(np:nm).Doping content going up higher than that would lead to a worse alignment effect

with the presence of irregular patterns and luminous points under light microscope

and decreased contrast too.Luminous points were probably caused by the limited compatibility between the polymer and the doped molecules

and doped photo-sensitive molecules cumulated and became crystallized.As for irregular patterns

they are surely caused by the weak photo-alignment ability of the doped polymer.On one hand

tiny crystals would disturb the uniformity of the surface;on the other hand

it is possible that the existence of excess amount of cinnamoyl groups would both enhance photo-dimerization and photo-isomerization reactions

which are competitive reactions and lead to opposite alignment directions:photo-dimerization would align the LC molecules parallel to the polarization direction of LPUV

while photo-isomerization would align them perpendicular to the polarization direction of LPUV.At the same time

we found that LC cells doped with 4-octyloxy cinnamoyl groups showed a higher increase in photo-alignment performance

which indicated that the effect of doping varied for different systems

and this method could be rather useful for certain polymers.In a word

we’ve synthesized two novel photo-sensitive molecules and doped them into epoxy polymers to enhance the alignment ability of the material with success.In our case

the contrast could be doubled or even tripled by doping adequate amount of photo-sensitive molecules.The optimum doping amount found is around 10%

regardless of the assortments of epoxy polymers.