Synthesis of POSS-functionalized liquid crystalline block copolymers via RAFT polymerization for stabilizing blue phase helical soft superstructures

Abstract

A series of POSS-functionalized liquid crystalline block copolymers (LC BCPs), PHEMAPOSS-b-P6CBMA, containing a crystalline polyhedral oligomeric silsesquioxane (POSS) block and a mesogenic cyanobiphenyl block, were prepared via reversible addition–fragmentation transfer (RAFT) polymerization for the first time and utilized to stabilize blue phase (BP) liquid crystals through facile doping. Using the advantages of both the POSS and polymer, a new strategy, which is distinct from the commonly adopted strategy for polymer stabilization of the BP, has been established. This new BP system with a wide BP range covering the typical room temperature range (i.e. 25–30 °C) leaps over intricate processing barriers, which are inevitable in conventional photo-induced polymer stabilization. In particular, improved electro-optical (E-O) properties of the BP, including lower driving voltage, lower hysteresis and a higher Kerr constant (K) compared with the common BP stabilized via photopolymerization, were obtained by optimizing the concentration of the doped LC BCP. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were employed to evaluate the thermal properties of the LC BCPs, and the results indicated that the introduction of POSS enhanced the thermostabilities of the copolymers effectively. Such an ingenious strategy provides a brilliant and easy way to form large size BP displays and other devices that are incompatible with UV light exposure during the working process.