Novel diphenylacetylene-based room-temperature liquid crystalline molecules with alkylthio groups, and investigation of the role for terminal alkyl chains in mesogenic incidence and tendency

<p>In this study, we offer a new family of alkylthio-containing diphenylacetylene-based liquid crystalline molecules (the so-called tolanes) showing nematic phases stable down to room temperature and high birefringence, with insights into the role for terminal alkyl chains in mesogenic incidence and tendency. A number of asymmetric tolane homologues having various alkyl chain lengths in the alkylthio and alkyl groups at each <i>p-, p’-</i>position were synthesised, and their phase transition behaviour was investigated by polarising optical microscope observation, differential scanning calorimetry and wide-angle X-ray diffraction measurement. Consequently, several homologues exhibited monotropic nematic or highly ordered smectic (soft crystal) phases stable down to room temperature. It is found that a long alkyl group on the side opposite to an alkylthio group is prerequisite for mesogenic incidence. In addition, a nematogenic homologue exhibited a higher birefringence value of 0.20 compared to that of 0.19 for an alkoxy counterpart.</p

Stereocomplex Crystallization of Star-Shaped Four-Armed Stereo Diblock Poly(lactide) from the Melt: Effects of Incorporated Linear One-Armed Poly(l‑lactide) or Poly(d‑lactide)

Star-shaped four-armed stereo diblock poly­(lactide) (4-LD) and <i>linear one-armed</i> PLLA or PDLA (1-L or 1-D) having a molecular weight similar to that of 4-LD [higher molecular weight 1-L­(H) or 1-D­(H)] and that of one block of 4-LD [lower molecular weight 1-L­(L) or 1-D­(L)] were synthesized, and the effects of incorporated 1-L or 1-D on the isothermal and nonisothermal crystallization of 4-LD blends from the melt were investigated. Solely stereocomplex crystallites were formed in unblended 4-LD and 4-LD blends incorporated with 1-L or 1-D during isothermal and nonisothermal crystallization. Incorporated 1-L or 1-D increased normalized stereocomplex crystallinity and accelerated cold nonisothermal crystallization and isothermal crystallization. The accelerating effect became higher with decreasing the molecular weight of 1-L or 1-D. The crystalline growth mechanism was not altered by the incorporation of 1-L and 1-D, whereas the crystalline growth geometry changed from line to sphere or circle, depending on the type of sample and <i>T</i>_c. The difference in crystallization half time and cold crystallization temperature between 4-LD/1-L­(H) and 4-LD/1-D­(H) blends or 4-LD/1-L­(L) and 4-LD/1-D­(L) blends was explained by the difference in radial growth rate and spherulite density, which was further discussed considering the <i>non-interpenetrating</i> and <i>interpenetrating models</i>

Stereocomplex Crystallization of Linear Two-Armed Stereo Diblock Copolymers: Effects of Chain Directional Change, Coinitiator Moiety, and Terminal Groups

Two-armed poly­(l-lactide) (PLLA)-<i>b</i>-poly­(d-lactide) (PDLA) (2-LD) copolymers with a wide-range of molecular weight were synthesized and the effect of coinitiator moiety, which functions as impurity and causes chain directional change in the middle of molecules (Effect A), and/or the additional effect of types of terminal groups (Effect B) on crystallization behavior of 2-LD copolymers were studied, in comparison with that reported for one-armed PLLA-<i>b</i>-PDLA (1-LD) copolymers. Formation of only stereocomplex (SC) crystallites in 2-LD and 1-LD copolymers indicates that neighboring PLLA and PDLA blocks facilitated SC crystallization and neither Effect A nor B affected the crystalline species. Effect A and/or B (both hydroxyl terminal groups) disturbed cold SC crystallization of 2-LD copolymers compared to that of 1-LD copolymers. Crystalline growth morphologies of 2-LD and 1-LD copolymers during cold SC crystallization were spherical and solid sheaf, respectively, exhibiting that crystalline growth morphology was influenced by Effects A and/or B. The melting temperature or crystalline thickness of SC crystallites were determined by number-average molecular weight per one block and not affected by Effect A or B. Maximum radial growth rates of spherulites of 2-LD copolymers compared to those of 1-LD copolymers were largely decreased by Effect A and/or B (both hydroxyl terminal groups)

Stereocomplex Crystallization and Homocrystallization of Star-Shaped Four-Armed Stereo Diblock Poly(lactide)s with Different l‑Lactyl Unit Contents: Isothermal Crystallization from the Melt

The effects of l-lactyl unit content on star-shaped four-armed stereo diblock poly­(lactide) (4-LD) polymers and star-shaped four-armed poly­(l-lactide) (4-L) on the isothermal crystallization from the melt were investigated. Solely stereocomplex (SC) crystallites were formed in equimolar 4-LD polymer with l-lactyl unit content of about 50%, irrespective of crystallization temperature (<i>T</i>_c) values. 4-L and 4-LD polymers with l-lactyl unit contents of 100 and 93% formed only homocrystallites, regardless of <i>T</i>_c, whereas only SC crystallites with traceable amounts were formed in 4-LD polymers with l-lactyl unit contents of 72 and 31% at a limited narrow <i>T</i>_c range of 110–120 °C, when crystallization was continued for as long as 24 h. About 20% deviation of l-lactyl unit content from 50% dramatically decreased the spherulite growth rate (<i>G</i>) values of SC crystallites, whereas a 7% decrease of l-lactyl unit content from 100% significantly decreased the <i>G</i> values of homocrystallites and largely decreased the overall homocrystallization rates. Branching architecture rather than diblock architecture hindered the simultaneous formation of SC and homocrystallites of non-equimolar 4-LD polymers

Synthesis, phase transitions and birefringence of novel liquid crystalline 1,4-phenylene bis(4-alkylthio benzoates) and insights into the cybotactic nematic behaviour

<p>We synthesised a novel family of liquid crystalline 1,4-phenylene bis(4-alkylthio benzoates), of which homologues with different alkyl chain lengths of 1–8 were designed, to investigate the structure–property relationship. The mesogenic incidence and tendency were found to be strongly dependent on the carbon numbers in the terminal alkyl chains. Even members formed widely monotropic or enantiotropic nematic (N) phases compared to odd members that showed either none or monotropic-narrower ones. The temperature dependence of birefringence (Δ<i>n</i>) for the hexylthio homologue was evaluated and compared to that for a hexyloxy counterpart. It was found that the hexylthio homologue exhibited higher Δ<i>n</i> values than the hexyloxy counterpart over the entire range of near <i>T</i>_IN–<i>T</i>. In addition, wide-angle X-ray diffraction measurements, using magnetically aligned specimens, found enhanced cybotactic nematic tendency with smectic (Sm) A-like temperature dependence for the hexylthio analogue, due to the intermolecular attractive S···S interaction, in comparison with the hexyloxy analogue exhibiting N phase with clear Sm C-type clusters. We revealed the actual benefits of alkylthio groups in the fluid N phase.</p

Ternary Stereocomplex and Hetero-Stereocomplex Crystallizability of Substituted and Unsubstituted Poly(lactic acid)s

The ternary stereocomplex (TSC) crystallizability of ternary substituted and unsubstituted poly­(lactic acid) blends composed of poly­(d-2-hydroxy-3-methylbutanoic acid) [P­(D-2H3MB)], poly­(l-2-hydroxy-3-methylbutanoic acid) [P­(L-2H3MB)], and poly­(l-2-hydroxybutanoic acid) [P­(L-2HB)] or poly­(l-lactic acid) (PLLA), together with heterostereocomplex (HTSC) crystallizability of binary blends composed of P­(D-2H3MB) and PLLA, were investigated for solvent evaporated and precipitated samples. For the solvent evaporated P­(D-2H3MB)/P­(L-2H3MB)/P­(L-2HB) (50/25/25) (mol/mol/mol) blend, formation of TSC crystallites with a very small amount of P­(D-2H3MB) and/or P­(L-2H3MB) homocrystallites was observed, whereas in the precipitated P­(D-2H3MB)/P­(L-2H3MB)/P­(L-2HB) (50/25/25) blend, P­(D-2H3MB)/P­(L-2HB) HTSC crystallites, P­(D-2H3MB) and/or P­(L-2H3MB) homocrystallites, and P­(L-2HB) homocrystallites were formed without formation of TSC crystallites. This is the first report for TSC crystallization of all substituted PLAs with linear and branched side chains. In contrast, in both solvent evaporated and precipitated P­(D-2H3MB)/P­(L-2H3MB)/PLLA (50/25/25) (mol/mol/mol) blends, P­(D-2H3MB)/P­(L-2H3MB) homostereocomplex crystallites, P­(D-2H3MB) and/or P­(L-2H3MB) homocrystallites, and PLLA homocrystallites were formed without crystallization of TSC crystallites. It was confirmed that HTSC between P­(D-2H3MB) and PLLA is not formed in both solvent evaporated and precipitated P­(D-2H3MB)/PLLA (50/50) (mol/mol) blends. Based on reported and present results, we proposed the rule for TSC and HTSC crystallization of, respectively, binary and ternary substituted and unsubstituted poly­(lactic acid)­s, wherein all the optically active polymer components are included in the same SC crystalline lattice. The difference in carbon numbers of side chains between the two polymers with different chemical structures and opposite configurations is one

Deuterated Liquid Crystals - design and synthesis of deuterium labelled 4,4ʺ-dialkyl-2′,3′-difluoro-[1,1′:4′,1ʺ]terphenyls using batch and continuous flow systems

The high interest of isotopically labelled compounds is induced by two important factors: (i) improvement of highly sensitive and precise analytical methods for isotope identification and (ii) development of new synthetic approaches for isotopically labelled compounds. However, there is still a lack of efficient and cheap methods for the design of deuterium labelled liquid crystalline materials. Herein, the continuous flow system was adapted for the synthesis of deuterated Liquid Crystals using the H-Cube Pro reactor, where deuterium gas was generated in situ from heavy water. We designed and developed the synthesis of homologous series of 4,4ʺ-dialkyl-2′,3′-difluoro-[1,1′:4′,1ʺ]terphenyls where deuterium atoms are placed at carbon α and carbon β positions or only at carbon α positions of alkyl terminal chains. The synthetic strategy involves mainly selective deuteration reactions of C≡C bonds as well as reduction of carbonyl groups C=O using batch or continuous flow conditions. Theoretical calculation and experimental study show that deuterium labelled Liquid Crystals exhibit increased photochemical stability compared to protonated ones. Moreover, the comparison of physicochemical properties between deuterium labelled and non-labelled 4,4ʺ-dialkyl-2′,3′-difluoro-[1,1′:4′,1ʺ]terphenyls is presented. This work provides efficient methods to obtain deuterated liquid crystalline materials with much better photochemical stability compared to their fully protonated isotopologues.</p