Photopolymerization of Reactive Mesogenic Schiff Bases and Related Metallomesogens

Abstract

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.

Visible light‐induced photopolymerization of an in situ macroporous sol–gel monolith

“…Thermally initiated polymerization in the presence of Iragacure 784 occurs above 1408C [20]. Figure 1 presents the separation abilities for a sample of six APKs in four columns containing different vis-PSG monoliths.…”

Synthesis and characterization of reactive liquid crystalline Schiff bases, Rh(I) complexes, and their derived polymers

“…Reactive and model Schiff bases were obtained by condensing an aldehyde and an aniline in 96% ethanol using acetic acid as a catalyst. 16 The process for the synthesis of the required aldehydes has been reported previously 8,17 and 4-decyloxyaniline was synthesized in accordance with reported procedures, 18 as well. Other anilines were obtained by a reduction of nitro derivatives using SnCl 2 .…”

“…Free-radical polymerization in solution has been reported to succeed for cyclopalladated azobenzene acrylates 23 and has failed for Cu(II)-, Pd(II)-and Zn(II)-containing salicylaldimine acrylates. 8 However, successful photoinduced polymerization of several metalcontaining Schiff bases has been reported for Pd(II) and Zn(II) complexes but not for Cu(II) analogs. 8,24 Given these precedents, both methods were tested.…”

“…8 However, successful photoinduced polymerization of several metalcontaining Schiff bases has been reported for Pd(II) and Zn(II) complexes but not for Cu(II) analogs. 8,24 Given these precedents, both methods were tested. Polymerization in toluene using 1% AIBN was attempted without success.…”

“…6 However, the preparation of polymers such as polyacrylates with pendant metallomesogenic units not only requires asymmetrically substituted metallomesogenic monomers of low accessibility but demands suitable polymerization methods in which the metal does not interfere. [7][8][9] The most general approach to overcoming this problem involves modification with metal ions of a polymer that contains coordination centers. This alternative has been applied to both main-chain 10 and sidechain 9,11-13 ortho-hydroxyl Schiff-base polymers, although in most cases the final polymeric system is a crosslinked material that is difficult to process because of insolubility or infusibility, especially those systems with higher metal contents.…”