Photopolymerization of reactive mesogenic Schiff bases and related metallomesogens

Mesomorphic salicylaldimines and related Cu(II), Pd(II), Zn(II), and VO(IV) complexes modified with acrylate groups have been synthesized. The liquid crystalline properties of the acrylic monomers are reported and, except for the Zn(II) complex, all are mesogenic. Their free-radical polymerization has been undertaken under several conditions, in solution, by using a thermal initiator or a photoinitiator. Use of visible light and a fluorinated diaryltitanocene photoinitiator (Irgacure 784-DC from Ciba-Geigy) have been proved the most adequate conditions to polymerize either the organic or the metal-containing acrylate Schiff bases. The light induced polymerization has been investigated by optical microscopy, DSC, and in cells, and only Cu(II) inhibits the process. The process has been applied to the preparation of metal-containing elastomers and networks, but the change of mesophase during polymerization and the high transition temperatures of diacrylates have limited the preparation of macroscopically oriented films. Light-activated polymerization has also been attempted for related vinyl-ether Schiff bases but it was unsuccessful.