Tham khảo tài liệu 'optoelectronics materials and techniques part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 200 Optoelectronics - Materials and Techniques wvwvwvwwv WWWVWWYW X ƠNQ Y Derivative Main chain X Y C1 polymethacrylate CH2 n NO2 C2 polyacrylate CH2 N NO2 C3 polymethacrylate CH2 2 1 1 ỷp 9 C4 polymethacrylate CH3 O N 2 CN C5 polymethacrylate 9 ộ -A y CN C6 polyphosphazene CH2 3 N ÍÌ . N c 2 NO2 C7 polymethylsiloxane CH2 3 C _ C COOR cN C8 polyvinyl CH2 0 C CO DR1 CN C9 polyvinyl CH2 0 C _ C COORi cN C10 epoxy resin ch2 N z X 2 NO2 cr Fig. 19. Chemical structure of side-chain carbazole-azoaromatic polymers The first report concerning this class of materials appeared in 1996 Ho et al. 1996 dedicated to the synthesis and optical properties of the methacrylic polymer obtained by Side-Chain Multifunctional Photoresponsive Polymeric Materials 201 polymerization of N-hydroxyethyl carbazole methacrylate bearing the p-nitro phenylazo moiety linked to the position 3 of carbazole ring C1 n 2 . This material proved to be suitable to produce optically induced birefringence surface gratings and photorefractivity. Subsequently polymethacrylates prepared similarly with various spacer length n 3-6 810 and Tg values ranging gradually from 127 to 65 C were investigated Barrett et al. 1998 C1 n 3-6 8-10 Fig. 19 confirming the previous findings and that the orientational order photoinduced in the material is higher with the derivatives possessing lower spacer length. Relevant thermal stability of the photoinduced surface gratings and high stability of the birefringence was also observed in polyimides bearing the carbazole group in the main chain linked to pendant azo chromophore . Chen et al. 1999 . An investigation on a series of copolymeric polyacrylates constituted by butyl acrylate and various monolithic chromophores including azocarbazole C2 Fig. 19 with molar composition photorefractive monomer butyl acrylate 1 suggested that the photorefractivity was strongly dependent on the NLO property of the chromophore rather than photoconductivity and additionally that the
