Mesomorphic Behavior of Novel Photopolymerizable Carbazole Liquid Crystals and Photocuring for 4D Printing

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Four novel carbazole-based photopolymerizable liquid crystals (PLCs) incorporating diacrylates or nonconjugated dienes were designed and synthesized to study their mesomorphic behavior and photocuring properties, with a focus on future applications in 4D printing. A combined analysis protocol using polarized optical microscopy (POM), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS) revealed a favorably wide range of nematic phases near room temperature and a slow tendency to crystallize. This should be advantageous in applications requiring good surface-alignment of the reactive mesogen in the nematic phase. This behavior could be attributed to the effects of polymerization under prolonged high temperatures for acrylates and the high entropy of long, branched, flexible alkyl chains in dienes. The polymerization process induces a kinetic competition between LC ordering and network formation. This work establishes protocols for real-time phase monitoring during polymerization, resolving longstanding ambiguities in LC phase identification under thermal polymerization. Furthermore, photocuring tests of the acrylate and diene monomers demonstrated high photopolymerization efficiency and good thermal stability, particularly for the acrylate monomers.