Synthesis of multifunctional liquid crystalline epoxy resin embedded cyclic-siloxane chain with T_g-less behavior and enhanced toughness

Abstract

A novel tetrafunctional mesogenic epoxy monomer with a cyclic-siloxane chain as a central part was successfully synthesized and characterized by proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, differential scanning calorimetry, and polarized optical microscopy. The transition temperature and liquid crystallinity of cyclic-siloxane type mesogenic epoxy were compared with those of linear-siloxane type mesogenic epoxy. Moreover, epoxy thermosets were prepared based on the cyclic- and linear-siloxane type mesogenic epoxy monomers and 4,4′-diaminodiphenylethane. The effects of epoxy backbone moiety on thermal and mechanical properties were investigated in detail. As a result, the cyclic-siloxane type mesogenic epoxy thermoset shows glass transition temperature-less behavior and low coefficient of linear thermal expansion without a decrease in toughness.

Advancements in The Cross-Linking and Morphology of Liquid Crystals

“…While the inclusion of siloxane chains enhances the material's hardness in comparison to aliphatic chains, they tend to rotate freely, thereby reducing their thermal properties. Addressing this issue, Harada et al in the publication [30] propose a solution consisting of introducing cyclic tetrasiloxane integrated with four liquid crystal epoxy structures. This resulted in the formation of a larger molecule in which free rotation was stopped and the melting point was lowered.…”

Reactivity, processability, and thermal stability of tetrafunctional glycidyl ether cyclic siloxane epoxy hybrid networks

“…The enhanced performance of the cyclic epoxy resin was attributed to the additional thermal stability provided by the higher crosslink density afforded by the cyclic motif and was suggested as an ideal candidate as an LED encapsulant. Harada et al 18 also synthesized a tetrafunctional glycidyl ether cyclic siloxane and compared it to linear siloxane resins. In this case, the epoxy groups incorporated mesogenic bis‐aryl imines which had a profound impact upon the mechanical and thermal properties of the cured network.…”

Colorfully Patterned Epoxy Resin Films with a Cholesteric Structure Prepared through a Photopolymerization Approach

“…Epoxy resins with LC structures are able to be prepared through cationic polymerization, which does not suffer from oxygen inhibition. − Moreover, epoxy LCs have low shrinkage before and after polymerization. , The epoxy resins show high mechanical strength , and heat resistance. − Despite these advantages, epoxy resin films with LC structures have been rarely reported. ,− This is mainly caused by the low polymerization rate of epoxy monomers. For instance, Shen et al reported epoxy-based polymer-stabilized liquid crystals prepared by the photoinitiated cationic polymerization for 2 h, which limits its industrial production.…”