Methacrylic polymers containing permanent dipole azobenzene chromophores spaced from the main chain: Synthesis and characterization

Three photochromic monomers containing a permanent dipole photochromic azob enzene group separated from the methacryloyl moiety by a polymethylene spac er, namely 4-(4-oxy-4'-cyanoazobenzene)but-1-yl methacrylate, 6-(4-oxy-4'-c yanoazobenzene)hex-1-yl methacrylate, and 8-(4-oxy-4'-cyanoazobenzene)oct-1 -yl methacrylate, were synthesized in three steps starting from 4-cyanoanil ine. These monomers were homopolymerized and copolymerized with an opticall y active monomer, (-)-menthyl methacrylate, in the presence of AIBN as a ra dical initiator. The polymeric materials, having a molar content of photoch romic units comprised between 5 and 100% and molecular weights of about 150 00, were characterized by an almost random distribution of monomeric units and a glass transition temperature ranging from 35 to 131 degrees C. Polyme r samples having a content of aromatic units larger than 75% were character ized by a thermotropic liquid crystalline structure, as evidenced by optica l microscopy, X-ray diffraction and DSC measurements. Two-dimensional corre lations spectroscopy (COSY) allowed an appreciable contribution by intramol ecular charge transfer mesomers to the electronic distribution of the azobe nzene chromophore to be highlighted. (C) 1998 Society of Chemical Industry.