Synthesis Of Novel Polyimides With Variety Side Chains End Capped By Alkoxy And Study On Their Surface Morphology And Characters

Liquid crystal display(LCD) was the important component ofelectronic products, and its essential technology is how to control thealignment of liquid crystal(LC) molecules that contacted with alignmentfilm surface, the arrangement of LCs directly affect the performance ofLCD e. g. contrast ratio, chroma and so on. Polyimide (PI) films are widelyused as liquid crystal alignment layers for liquid crystal molecules inadvanced liquid crystal display (LCD) devices owing to their outstandingand excellent properties.Focusing on the applied requirements of PI alignment film, two noveldiamides, containing nonpolar alkoxy and aryl ester groups, named 4-((4'-(butoxy) phenoxy) carbonyl) phenyl 3" ,5" - diaminobenzoate (BCDA)and 4-((4'-(octyloxy) phenoxy) carbonyl) phenyl 3'',5''-diaminobenzoate (OCDA) were synthesized. And the chemical structureswere confirmed by FTIR and ~1H-NMR. PI-BCDAx/OCDAx with aromatic ester sidechain end-capped by aliphaticoxy group were prepared by one-step solutionpolycondensation of BCDA/OCDA and ODPA.All the copolyimides with side chains had good solubility; TGAresults reveal that all PIs loss weigh in three-step, the first step isowing to the decomposition of alkoxy group in side chain, the second stepis owing to the break of ester bond on side chain that far away from main chain, and the last step is because of the break of the last ester bondon side chain and the degradation of main chain.Comparing with the pretilt angle of PI-OCDAx, the pretilt angle ofPI-BCDAx were bigger when they had the same side chain content, thereinto,the biggest one was the pretilt angle of I-BCDAO. 5, reached 13.2°, andthe biggest pretilt angle of PI-OCDAx was PI-OCDAO. 5's too, whichreached 7.2°.According to the result of surface tension(γc) test, theprobable reason is that, the reciprocity between side chain on PI'ssurface and LC molecules caused the LCs tilt. With the increasing of sidechain on PI surface, they arranged more compact, that lead the reciprocitybetween side chain and LC molecules weaklier, so the pretilt anglepresents the change tendency which after first changes in a big wayreduces.The surface morphology of PI alignment films was characterized byAFM, XPS, ATR-FTIR. The result of XPS, ATR-FTIR indicated that, alkoxygroup transferred to surface when side chain content of copolyimides waslow, but when the content of side chain rezched 50%, this transferringprocess would slow down and the increasing of side chain only owing tothe composition difference.AFM result indicated that microgroove, which along with the rubbingdirection, wide 30-100nm and height was about 18nm, appeared on thesurface of PI alignment layers after rubbing.Finally, a preliminary theory was studied on the aligning mechanismof liquid crystal molecules induced by rubbed PI alignment films in thispaper. We consider that, amyl of 5CB lap over the alkyl on side chainof alignment film, and the biphenyl group of 5CB lap over the aryl estergroup which is mesomorphic group too, thereby, forces the liquid crystalmolecules to align regularly and pre tilt.