Synthesis and polymerization of amphiphilic methacrylates containing permanent dipole azobenzene chromophores

New amphiphilic photochromic methacrylates with the structures of 4-[ω-methacryloyloxyoligo(ethyleneglycol)]-4′-cyanoazobenzene (MEn) and 4-methacryloyloxy-4′-{2-cyano-3-oxy-3-[ω-methoxyoligo (ethyleneglycol)]prop-1-en-1-yl}azobenzene (MEnMe) and oligo(oxyethylene) segments of different lengths were synthesized. These methacrylates were characterized by the presence of permanent dipole azobenzene chromophores and hydrophilic oligo (oxyethylene) segments. The methacrylates were obtained with six-step and five-step synthetic sequences, respectively, in 12-47% overall yields. The radical polymerization of the MEn monomers afforded a 50% yield of the corresponding polymers as orange solids with a number-average molecular weight of about 40 kD. No solid polymer was obtained from the radical polymerization of the MEnME compounds. Two-dimensional NMR spectra allowed the unequivocal assignment of the NMR signals and demonstrated a significant contribution of internal charge transfer to the electronic distribution of the azobenzene chromophore. Relaxation time measurements confirmed that the flexible polyether segment effectively decoupled photochromic groups from the polymer backbone. Optical microscopy, differential scanning calorimetry analysis, and X-ray diffraction data demonstrated the presence of interdigitated smectic mesophases. The stability of mesophases showed a significant dependence on the chemical structure of the analyzed compounds. The glass-transition temperatures of the polymers were rather low because of the plasticizing effect of the spacers. The monomers and polymers were used for the deposition of Langmuir films and Langmuir-Blodgett-Kuhn multilayers. A strong influence of the macromolecular structure on the film properties was observed. The photoresponsive properties of monomers and polymers were investigated with irradiation at different wavelengths. Isomerization kinetics were independent of both molecular weight and spacer length.