Synthesis and phase behaviour of a homologous series of polymethacrylate-based side-chain liquid crystal polymers

The homologous series of side chain liquid crystal polymers, the poly[ω-(4-methoxyazobenzene-4′-oxy)alkyl methacrylate]s, has been prepared in which the length of the flexible alkyl spacer has been varied from 3 to 11 methylene units. All the polymers exhibit liquid crystalline behaviour. The propyl and butyl members show exclusively nematic behaviour. The pentyl, hexyl, octyl and decyl members show a nematic and a smectic A phase while the heptyl, nonyl and undecyl homologues exhibit only a smectic A phase. The smectic A phase has been studied using X-ray diffraction and assigned as a smectic A1 phase in which the side chains are fully overlapped and the backbones are confined to lie between the smectic layers. For the nonyl member an incommensurate smectic phase is observed. The dependence of the transition temperatures on the length of the flexible spacer is understood in terms of the average shapes of the side chains.

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► Report the phase behaviour of a homologous series of photo sensitive SCLCPs.
► Increasing spacer length promotes smectic behaviour relative to nematic behaviour.
► A fully interleaved smectic A1 phase is seen with incommensurate smectic behaviour.
► Smectic phase formation is driven by packing efficiency.
► Transition temperatures interpreted in terms of the average shape of the side chains.