Synthesis and phase behavior of nematic liquid‐crystalline elastomers derived from smectic crosslinking agent

Abstract

ABSTRACT:A mesogenic crosslinking agent M-1 was synthesized to minimize the perturbations of nonmesogenic crosslinking agent for liquid-crystalline elastomers. The synthesis of side-chain liquid-crystalline elastomers containing a rigid mesogenic crosslinking agent M-1 and a nematic monomer M-2 was described by a one-step hydrosilylation reaction. The chemical structures of the obtained monomers and network polymers were confirmed by Fourier transform infrared and 1 H-NMR spectroscopy. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction measurements. The influence of the crosslinking units on the phase behavior was discussed. The liquid-crystalline elastomers containing less than 15 mol % of the crosslinking units showed elasticity, reversible phase transition, and threaded texture. The experimental results demonstrated that isotropic temperature and liquid-crystalline range of polymers P-1-P-7 decreased a little as the concentration of crosslinking agent M-1 increased, and the use of mesomorphic crosslinking agent M-1 promotes the arrangement of liquid-crystalline units from P-1 to P-5.

Wheat straw hemicellulose films as affected by citric acid

“…A possible explanation for this apparently inconsistent behavior is that citric acid might act as a flexible crosslinker. Some previous studies (Hu, Song, Liu, & Zhang, 2010;Jia, Zhang, He, & Ning, 2005;Zhang, Hu, Jia, & Du, 2003) have described that, although chemical crosslinking usually imposes constraints on the motion of chain segments, a flexible crosslinking agent may act similarly to a plasticizer. The flexibility of citric acid crosslinking might then explain why it was effective in reducing the film solubility and WVP while impairing the overall tensile properties.…”

Wheat straw hemicelluloses added with cellulose nanocrystals and citric acid. Effect on film physical properties

“…A possible explanation is that glycerol may act as a crosslinking extender to citric acid (Jiang, Reddy, Zhang, Roscioli, & Yang, 2013;Yao, Wang, Ye, & Yang, 2013), which may provide flexibility to the crosslinking (Yao et al, 2013). Although chemical crosslinking usually restrict the mobility of polymer chains, a flexible crosslinking agent may act similarly to a plasticizer (Hu, Song, Liu, & Zhang, 2010;Jia, Zhang, He, & Ning, 2005;Zhang, Hu, Jia, & Du, 2003). The flexibility of a glycerol-extended citric acid crosslinking might thus explain why the crosslinking reduced the film solubility while impairing tensile strength and modulus.…”

Synthesis and Phase Behavior of Polysiloxane Nematic Liquid Crystal Elastomers

“…In this study, nematic liquid crystal monomer, 4-((4-(allyloxy)benzoyl)oxy)phenyl 4-butylbenzoate (M), was prepared according to our previous paper [14], and the flexible crosslinking agent C was synthesized by esterification reaction of hexane-1,6-diol and undec-10-enoic acid in the presence of catalyst concentrated sulfuric acid. The elastomers were prepared by a one-step reaction, in which the nematic monomer M and the dienes crosslinking agent C were simultaneously attached to the flexible main chain of polymethylhydrosiloxane (PMHS, n=7) with the H 2 PtCl 6 catalyst.…”