Highly birefringent polymer films from the photo-crosslinking polymerisation of bistolane-based methacrylate monomers

<div><p>The photo-polymerisation of mixtures of mono- and di-methacrylates, containing a bistolane moiety with a central fluorine-substituted benzene ring, resulted in the formation of highly birefringent polymer films (Δ<i>n</i> = 0.40), which were obtained in a nematic liquid crystal (NLC) phase. While the dimethacrylate forms enantiotropic NLCs at <i>T</i> = 110–138°C, smectic phases at <i>T</i> = 50–138°C and crystallises at <i>T</i> = 50°C, whereas the monomethacrylate forms NLCs at a wider temperature range (<i>T</i> = 98–185°C) and crystallises at a lower temperature (<i>T</i> = 98°C). These methacrylates were infinitely miscible and a 20/80 (w/w) mixture of the dimethacrylate/monoacrylate was able to form an NLC phase over a broad temperature range (<i>T</i> = 73–179°C). The mixed NLC phase exhibited a Δ<i>n</i> value of 0.36, even though the Δ<i>n</i> values of the mono- and di-methacrylates were determined as 0.35 and 0.25, respectively, suggesting that the Δ<i>n</i> of the mixture follows an additivity rule. Furthermore, the Δ<i>n</i> of the NLC phase could be increased to 0.40 by photo-polymerisation.</p></div

Synthesis of new wide nematic diaryl-diacetylenes containing thiophene-based heteromonocyclic and heterobicyclic structures, and their birefringence properties

<div><p>New monocyclic and bicyclic thiophene-based diaryl-diacetylene liquid crystal (LC) materials were synthesised and demonstrated to exhibit wide enantiotropic nematic phases. One thiophenyl-benzene derivative, in particular, displayed a stable nematic phase across a temperature range of over 100°C. The birefringence properties of the compounds were measured using a multiple-beam interference (MBI) method, with the highest value found to be for the same thiophenyl-benzene molecule (Δ<i>n</i> = 0.57, 550 nm) at 10°C above the crystal-to-nematic transition temperature. Furthermore, the effects of the cyclic structure on the mesomorphic behaviours, transition temperatures, and birefringence properties were investigated in detail from both experimental and theoretical viewpoints.</p></div

Thermotropic Behavior of Syndiotactic Polymethylenes with ω‑[4‑(<i>trans</i>-4-Pentylcyclohexyl)phenoxy]alkyloxycarbonyl Side Chains

A series of syndiotatic P5CP<i>n</i> polymethylenes was prepared with 4-(trans-4-pentylcyclohexyl)­phenoxy moieties linked to each backbone carbon atom via an alkyloxycarbonyl spacer and with even numbers of alkyl carbons <i>n</i> ranging from 2 to 14, and their thermotropic behaviors were investigated. The P5CP<i>n</i>, except P5CP2, formed smectic phases in which the rod-like polymethylene backbones were arranged in rectangular lattices, and the side-chain mesogens were aggregated into layers parallel to the shorter sides of the rectangular lattices. The packing of the mesogens changed with decreasing temperature from smectic C-like to smectic I-like (SmI-like) for <i>n</i> = 4–8 and from smectic A-like to SmI-like for <i>n</i> = 10–14. In the SmI-like phases, each mesogen along the main-chain axis was connected to every sixth backbone carbon atom, revealing a correlation between the packing of the mesogens and the main-chain conformation of a 3/2 helix. Conversely, P5CP2 formed a smectic phase with the main chains arranged in rows and with the mesogens barely aggregated into layers due to the short spacers