Synthesis and polymerization of amphiphilic methacrylates containing permanent dipole azobenzene chromophores

New amphiphilic photochromic methacrylates with the structures of 4-[omega -methacryloyloxyoligo(ethyleneglycol)]-4 ' -cyanoazobenzene (MEn) and 4-met haeryloyloxy-4 '-[2-cyano-3-oxy-3-[omega -methoxyoligo (ethyleneglycol)]pro p-1-en-1-yl)azobenzene (MEnMe) and oligo(oxyethylene) segments of different lengths were synthesized. These methacrylates were characterized by the pr esence of permanent dipole azobenzene chromophores and hydrophilic oligo (o xyethylene) segments. The methacrylates were obtained with six-step and fiv e-step synthetic sequences, respectively, in 12-47% overall yields. The rad ical polymerization of the MEn monomers afforded a 50% yield of the corresp onding 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 azobenzen e chromophore. Relaxation time measurements confirmed that the flexible pol yether segment effectively decoupled photochromic groups from the polymer b ackbone. Optical microscopy, differential scanning calorimetry analysis, an d X-ray diffraction data demonstrated the presence of interdigitated smecti c mesophases. The stability of mesophases showed a significant dependence o n the chemical structure of the analyzed compounds. The glass-transition te mperatures of the polymers were rather low because of the plasticizing effe ct of the spacers. The monomers and polymers were used for the deposition o f Langmuir films and Langmuir-Blodgett-Kuhn multilayers. A strong influence of the macromolecular structure on the film properties was observed. The p hotoresponsive properties of monomers and polymers were investigated with i rradiation at different wavelengths. Isomerization kinetics were independen t of both molecular weight and spacer length. (C) 2001 John Wiley & Sons, I nc.