Synthesis and characterisation of novel side-chain chiral liquid crystalline elastomers with long dimer mesogens

ABSTRACT

In this work, novel nematic monomer (M₁), chiral monomer (M₂) and crosslinker (CL) have been synthesised to form a series of side chain chiral liquid crystalline elastomers (ChLCEs) LCE₁-LCE₇ by graft copolymerisation with poly(methylhydrogeno)siloxane backbone. M₁ and M₂ were both dimer type with great length, and the chiral 2-octyl terminal group was seldom used in liquid crystal elastomer system. The chemical structures, thermal stability and LC phase behaviours of monomers, crosslinker and ChLCEs were examined by different experimental techniques. The helical structure of combining the chiral and achiral liquid crystalline side chains endowed the obtained ChLCEs with chiral nematic liquid crystalline properties. By changing the dosages of the crosslinker, the mesomorphic properties of ChLCEs could be adjusted. The mesophase-isotropic phase range of the ChLCEs were slightly broadened with increasing addition of CL according to the differential scanning calorimetry (DSC). The synthesised ChLCEs exhibited excellent thermal stability from thermal analysis (TG) results. The effective crosslink density (_c) of the ChLCEs was characterised by swelling experiments showing the molecular weight between the crosslinking points decreasing with the increase of the CL. The FT-IR imaging system indicates the functional groups of all the ChLCEs are well distributed.

Graphical Abstract

KEYWORDS:

• Liquid crystal
• elastomer
• chiral
• dimer
• crosslinker

Acknowledgements

The authors are grateful to the National Nature Science Foundation of China (31560268), Yunnan Science and Technology Project (2015FB156) and Foundation of Yunnan Education Department (2015Z153) for financial support of this work. The authors also would like to thank Zirui Lin of the Research Centre for Molecular Science and Engineering, Northeastern University, for his technical support during the experiments.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Additional information

Funding

This work was supported by the National Nature Science Foundation of China [31560268]; Yunnan Science and Technology Project [2015FB156]; Foundation of Yunnan Education Department [2015Z153].