Synthesis and characterization of polyoxetanes containing 4-cyanobiphenyl-based side groups for nonlinear optical applications .2. Synthesis, characterization and polymerization of 3,3-bis(4-cyano-4'-biphenylyloxymethyl) oxetane

3,3-Bis(4-cyano-4'-biphenylyloxymethyl)oxetane was prepared by reaction of 3,3-bis(chloromethyl)oxetane with the sodium salt of 4-cyano-4'-hydroxybiphenyl. With highly purified dichloromethane, single crystals could be prepared. The X-ray patterns could be indexed in terms of a monoclinic cell a = 13,87 Angstrom, b = 14,74 Angstrom, c = 13,91 Angstrom and beta = 118,68 degrees. Some experiments were carried out to determine the cationic polymerization behavior of this oxetane. The initiating system BF3 . Et(2)O/dichloromethane was used and it was shown that unusually high initiator concentrations were necessary to observe polymerization. By means of steric exclusion chromatography and NMR spectroscopy, the formation of cyclic oligomers was evidenced. Upon heating, all the polymers showed a nematic phase. Some preliminary Corona poling experiments were performed and the second harmonic generation coefficients d(31) and d(33) were measured. It was shown that one can gain in net polar ordering by starting with a liquid crystalline system. The ratio d(33)/d(31) was found to be much larger than 3 in agreement with the molecular statistical models for electric field poling of liquid crystals.