Synthesis, characterization and polymerization of mesogenic salicylaldimine compounds

Liquid crystals which have unusual physical, electro-optical and thermal properties represent a combination of fluidity and anisotropy. These materials exhibit a variety of mesophases as a result of different molecular structure and interactions between molecules. Among new mesogens, salicylaldimines and their derivatives have special interest due to their structure-property relationships. These compounds exhibit mono- or polymorphism depending on the type of terminal groups such as alkly or alkyloxy chain, perflorinated chain and oligosiloxane unit. The strong phase seperation of oligosiloxane from hydrocarbon chain segments and also to rigid aromatic core gives rise to the formation of new liquid crystalline mesophases.Oligosiloxane liquid crystals are new class of materials which have great potential to show some properties such as mechanical properties of polymers and fast electro-optic response of classic low molar mass liquid crystals. Side chain liquid crystalline polymers (SLCP) which represent a combination of liquid crystalline behaviours and polymer properties have been the subject of intensive research during last years. Side chain liquid crystal homopolymers can be synthesized by low-molar mass calamitic liquid crystals.The aim of this study is to design, synthesis, characterization of the new salicyaldimine based thermotropic liquid crystalline compounds and to investigate their mesogenic properties. Three new series of calamitic liquid crystalline compounds (salicylaldimine mesogens, trisiloxane-terminated salicylaldimine mesogens and salicylaldimine based liquid crystalline homopolymers) were synthesized.The structure of new mesogenic compounds were characterized by using of classical spectroscopic methods (UV-Vis, FT-IR, 1H-NMR, 13C-NMR, 29Si-NMR, MS) and elemental analysis. Salicylaldimine based homopolymers were confirmed with FT-IR and 1H-NMR. The molecular weight of the homopolymers were detected by using gel permeation chromatograpy (GPC).The mesogenic behaviours of the all synthesized compounds were examined with differential scanning calorimetry (DSC) and polarized optical microscopy (POM).Key words: Thermotropic liquid crystals, Calamitic liquid crystals, Salicylaldimine based liquid crystalline homopolymers, Oligosiloxane-terminated liquid crystals.