In this study, we synthesized hydroxypropyl cellulose (HPC) derivatives possessing alkyl ether side chains through Williamson ether synthesis. Such HPC ether derivatives exhibited thermotropic cholesteric liquid crystals (CLCs) with Bragg reflection. The temperature dependence of reflection wavelength could be controlled by changing the side chain lengths and etherification degrees in the HPC derivatives. Moreover, the thermal stability of both HPC ester and ether was evaluated before and after heating at 60 ºC for 20 days. The reflection peak of HPC ester shifted to the longer wavelength upon the heating treatment due to the hydrolysis of ester linkage. On the other hand, we found that the reflection peak of HPC ether can be robustly preserved even after the prolonged heating treatment, arising from the thermal stability of ether linkage. The rational approach addressed here provides promising clues to fabricate the stable photonic CLC devices with refection features by exploiting anti-hydrolysis of the cellulose ether derivatives.

Previously, we have reported on the preparation of hydroxypropyl cellulose (HPC) ether derivatives by the Williamson ether synthesis as SN2 reaction. In this article, we carried out the optimization of synthesis conditions to obtain the completely etherified HPC derivatives tethering hexyl ethers in the side chains (HPC-HeEt).By adopting N-methyl-2pyrrolidinone (NMP) as a reaction solvent, as-synthesized HPC-HeEt showed high substitution degree of hexyl ethers, probably arising from high solubility of NaOH in NMP. Moreover, this optimized reaction condition enabled to apply the synthesis of completely etherified HPC derivatives with different length of alkyl chains. These HPC ether derivatives showed thermotropic cholesteric liquid crystal (CLC) phase with visible Bragg reflection. As a result, their reflection properties would be stable against humidity due to the robust bonding of ether group rather than ester.