Synthesis, Morphology and Thermal Properties of Side-chain Liquid Crystalline Polymers
Han Xiangen, Robert Shanks
RMIT University
Mel.

Keywords: Synthesis, Liquid Crystalline polymers, thermal properties


A series of side-chain liquid crystalline polymers (LCP) have been synthesised by substitution onto polyepichlorohdrin (PECH). PECH is a flexible polymer with labile chlorines that facilitate substitution with mesogen containing groups. The mesogens were chosen from diphenyl and azobenzene containing molecules. The mesogens were first connected to short chain alkoxy groups of varying lengths to act as spacer groups between the mesogen and the main-chain. The combination of mobility due to the spacer groups and main chain segments between substituents is needed to provide mobility for the mesogens to align. Mesogens were chosen to have an electron acceptor at one end of the molecule and the spacer group provided an electron donor, so that the LCP would have potential application in electro-optical devices.
The side-chain LCP synthesised were analysed by infrared and nuclear magnetic spectroscopy to confirm their structure and measure the degree of substitution. Hot stage polarised optical microscopy and differential scanning calorimetry (DSC) were used to study the liquid crystalline temperature region and morphology. Thread textured nematic phases and an abrupt change at the nematic-isotropic transition temperature were observed. The texture of the nematic phases was changed by shearing the LCP film on the hot stage. In general these LCP show directional but not positional order, that is they are all nematic. DSC showed the crystalline melting temperature followed by the nematic-isotropic transition temperature. The side-chain LCP were compared with polymer dispersed liquid crystals (PDLC) using similar mesogens. The PDLC more readily form nematic structures but the mesogens tend to phase separate at higher concentrations. The concentration of mesogenic groups was important for LC formation since at lower concentrations LC structure was absent.