Effect of flexible spacer length on the mesophase structures of main-chain/side-chain liquid crystalline polymers based on ethyl cellulose

Abstract

Main-chain/side-chain liquid crystalline polymers (MCSCLCPs) based on ethyl cellulose (AzomEC, m¼2,4,6, where m is the length of the spacer between the main chain and mesogens) were successfully synthesized by N,N¢-dicylcohexylcarbodiimide (DCC) coupling. Molecular characterizations of the resultant polymers with different spacer lengths were performed by proton nuclear magnetic resonance, Fourier transform-infrared spectroscopy and gel permeation chromatography. The phase transitions and liquid crystalline (LC) behaviors of these polymers were investigated by differential scanning calorimetry, polarized optical microscopy and wide-angle X-ray diffraction. The results indicate that spacer length has a tremendous effect on the LC behavior of the polymer. The glass transition temperatures, phase transition temperatures and the corresponding enthalpy of transitions decreased as the flexible spacer length increased. The mesophase structures of polymers consisted of a large-scale ordered lamellar structure composed of the EC main chain and a relatively small-scale ordered structure formed by azobenzene side chains. All the polymers form a similar lamellar structure on a large scale; however, the small-scale ordered structure becomes relatively disordered, that is, from crystal (m¼2) to smectic B (m¼4) to smectic A (m¼6) at low temperatures.

Cellulose-Based Liquid Crystalline Photoresponsive Films with Tunable Surface Wettability

“…It is important to stress that the purification of the AzoAPC was an issue that needed special attention due to the formation of ureas, a byproduct of the coupling agent carbodiimide, during the reaction. In the literature − the cellulose derivative used was ethylcellulose (EC) which, after azo substitution, is precipitated in methanol. Because of its intrinsic solubility, APC is soluble in methanol (even after azo substitution) so the precipitation must be preformed in water.…”

Competition and Promotion between Two Different Liquid-Crystalline Building Blocks: Mesogen-Jacketed Liquid-Crystalline Polymers and Triphenylene Discotic Liquid Crystals

“…Altering the calamitic mesogen from biphenyl to azobenzene results in a similar hierarchical supramolecular structure . Calamitic mesogens have also been introduced to other polymer backbones with a rod-like nature, such as polypeptides and ethyl cellulose (EC), to construct functional hierarchical ordered structures. − Hence, combining rod-like LC main chains and calamitic mesogen-containing side chains can provide LCPs with hierarchical ordered structures. However, discotic mesogens have completely different self-assembling tendencies compared with the calamitic mesogens.…”

Synthesis and properties of poly(norbornene)s with lateral aramid groups

“…This behaviour is possibly due to the reduction of internal plasticization. 19 By decreasing the amount of the flexible EHNI spacers, the rigid components are closer to each other and hence interactions are more likely to occur. Furthermore, it must be noted, that the increasing molecular weight does not significantly affect the T g .…”