Main-chain side-chain combined liquid crystalline polymers bearing azobenzene and biphenyl-based mesogens – segregation of the mesogens within two distinct layers

ABSTRACT

Two different mesogenic units, namely biphenyl and azobenzene, were installed centrally within the polymer backbone and pendant alkylene segments; the purpose was to examine if chain folding of the backbone occurs so as to segregate the azobenzene and biphenyl units in adjacent layers of a smectic-type ordering. Two sets of isomeric main-chain side-chain liquid crystalline polymers (MCSC-LCPs), namely SC-AzoCx-MC-BPCx and SC-BPCx-MC-AzoCx (x=6 or 10), were synthesised; the former series has biphenyl in the backbone and azobenzene in the side-chain, while their locations are switched in the latter. It was observed that all four polymers were semicrystalline at room temperature and exhibited a smectic mesophase upon melting. DSC and X-ray scattering studies revealed that switching the locations of the azobenzene and biphenyls had little effect on; the phase transition temperatures and smectic layer spacings. A second series, namely SC-AzoCx-MC-BPCy and SC-BPCx-MC-AzoCy, where the length of alkylene spacers in the side-chain (Cx) and backbone (Cy) is different, was also studied; this was done to examine the influence of unequal alkylene segment lengths on the mesophase structure and interlayer spacing, and importantly, whether the zigzag folding-induced formation of a layered structure is retained, despite their unsymmetrical nature.

Graphical abstract

KEYWORDS:

• Liquid crystalline polymer
• pendant mesogen
• mesogen segregation
• zigzag folded chains

Acknowledgments

We would like to thank the Department of Science and Technology, New Delhi, for the award of J C Bose fellowship (2016-2021) to SR. Authors would also like to thank Mr Amal Raj, NIIST, Thiruvananthapuram for carrying out XRD measurements. We would also like to thank Dr Krishna Prasad and Dr Shankar Rao from CeNS, Bangalore, for some insightful discussions. Mr Ogunsola and Mr Bej would like to thank Indian Institute of Science for the doctoral fellowship.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

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Additional information

Funding

This work was supported by the Science and Engineering Research Board [J C Bose Fellowship 2016-2021].