CHAPTER 3: Newly Synthesized Photocrosslinkable Liquid-Crystalline Polymers and their Properties

This chapter deals with a hitherto unreported newer root of synthesis of photocrosslinkable polymers containing pendant chalcone moieties with different substituents. The main aim of present research work is to synthesis photocrosslinkable polymers containing pendant chalcone moiety that exhibits both liquid-crystalline and photocrosslinking properties. The polymers were synthesized with various substituents in their terminal position to pendant chalcone unit and acrylic unit. All the five polymers P1–P5 were synthesized by the free-radical polymerization method. The predetermined quantities of monomers were dissolved in THF solvent and AIBN was used as initiator. The polymerization was carried out under nitrogen (inert) atmosphere for 48 h. The number (M_n) and weight average (M_w) molecular weight of the polymers were obtained by the gel permeation chromatography (GPC) method. The thermogravimetric analysis (TGA) results indicate that the polymers show good thermal stability, since the phenyl group in the case of polymers P1, P2 and P4 gives better thermal and thermal oxidative stability required for a negative photoresists. Liquid-crystalline behavior of polymers were identified by DSC thermogram and confirmed by hot-stage polarized optical microscope images. Photocrosslinking behavior of all the polymers were investigated by UV-Vis spectroscopy, the cross linking of all the polymers proceed via cyclobutane ring formation during 2π+2π cycloaddition reaction on irradiation with 254-nm UV light. The surface morphology studies of both virgin and photocrosslinked polymers were investigated by scanning electron microscope (SEM) analysis. The photocrosslinked polymer sample confirms the loosely held dispersion of polymeric material, while virgin polymer exhibits compact stringent dispersion of the polymeric surface.