Synthesis and characterization of liquid crystalline copolymethacrylates,copolyacrylates, and copolysiloxanes containing 4-methoxy-4′-hydroxy-α-methylstilbene and 4-hydroxy-4′-methoxy-α-methylstilbene constitutional isomers as side-groups

The synthesis of methacrylates and acrylates containing 4-methoxy-4′-hydroxy-α-methylstilbene and 4-hydroxy-4′-methoxy-α-methylstilbene constitutional isomers attached to the polymerizable group through flexible spacers containing 11, 8, 6, 3, and respectively 2 methylenic units is described. The radical copolymerization of a 1/2 or 2/1 mole ratio of the two constitutional isomeric monomers led to thermotropic side-chain liquid crystalline polymers in all cases. The synthesis of copolysiloxanes based on the same constitutional isomeric mesogens as side groups, and flexible spacers containing 11, 8, 6, 5, and respectively 3 methylenic units is also described. All polymers were characterized by differential scanning calorimetry and optical polarization microscopy. The polymers containing 11 methylenic units in the spacer exhibit S_c mesomorphism, while the other polymers are nematic. Copolymethacrylates do not undergo side-chain crystallization. Only the copolyacrylate containing 11 methylenic units in the spacer exhibits side-chain crystallization. All the copolysiloxanes display side-chain crystallization. The number of melting transitions seen for these polymers decreases with increasing spacer length. Copolysiloxanes containing dissimilar spacer length were also prepared. Only the copolymer synthesized with highly dissimilar spacer lengths, i.e., containing 3 and 11 methylenic units, does not undergo side-chain crystallization. These results have demonstrated that while the type of mesophase is dictated only by the spacer length, the degree of decoupling of the motion of the side-groups from the motion of the main chain is strongly dependent on the nature of the polymer backbone. For the same mesogenic unit and spacer length, the thermal stability of the mesophase is also dictated by the nature of the polymer backbone. The use of constitutional isomers of mesogenic units as side groups in liquid crystalline polymers provides at least qualitative information on the degree of decoupling of the side groups from the polymer main chain.     

Synthesis and thermal behavior of side-chain liquid crystalline polymethacrylates containing tolane-based mesogenic side groups

The synthesis and characterization of nine polymethacrylates containing 4-alkoxy-4′-trifluoromethyltolane, 4-alkoxy-4′-cyanotolane, and 4-alkoxy-4′-nitrotolane side groups were described in this study. The phase behavior of the prepared monomers and polymers was characterized by differential scanning calorimetry, optical polarizing microscopy, and x-ray diffraction. All of the obtained monomers exhibit no mesophase, while most of the synthesized polymers reveal enantiotropic mesomorphism. The polymethacrylate containing 4-propanyloxy-4′-nitrotolane side groups was the only one which shows no mesomorphic behavior. Both the spacer length and the nature of terminal groups have profound influence on the phase transition temperatures and thermal stability of the mesophase. The polymers with longer spacers tend to form a more ordered mesophase with a wider temperature range. Among three polymers with the same spacer length, the polymer with a trifluoromethyl terminal end group is inclined to form a more ordered mesophase than the other two polymers. No side chain crystallization occurred for all obtained polymers. © 1994 John Wiley & Sons, Inc.     

Synthesis and characterization of side-chain liquid crystalline polysiloxanes containing oligooxyethylene spacers and benzyl ether based mesogenic groups

The synthesis of side-chain liquid crystalline polysiloxanes containing oligooxyethylene spacers and 4-methoxyphenyl benzyl ether and 6-cyano-2-naphthyl benzyl ether based mesogenic groups is presented. The phase behavior of both monomeric and polymeric liquid crystals was characterized by differential scanning calorimetry and optical polarized microscopy. All synthesized polysiloxanes present smectic mesomorphism. The insertion of oxygen atoms into the flexible aliphatic spacers leads to decrease in both glass transition and isotropization temperatures of the resulting side-chain liquid crystalline polymers.     

Synthesis and characterization of side-chain liquid crystalline polysiloxanes containing 4-alkanyloxyphenyl trans-4-alkylcyclohexanoate side groups

The synthesis and characterization of nine polysiloxanes containing 4-alkanyloxyphenyl trans-4-alkylcyclohexane side groups are described. Six monomers which contain a pentenyloxy of a hexenyloxy flexible spacer display a nematic mesophase, while the other three monomers which contain an undecenyloxy flexible spacer display nematic, smetic A and smectic E mesophases. All synthesized polymers present two smectic mesophases except one containing 4-hexanyloxyphenyl trans-4-n-butylcyclohexanoate side groups presents one smectic mesophase and one containing 4-undecanyloxyphenyl trans-4-n-pentylcyclohexanoate side groups presents three smectic mesophases. Trans-cis isomerization of mesogens and side chain crystallization did not occur for any of the synthesized polymers.     

Synthesis and characterization of liquid crystalline polyacrylates and polymethacrylates containing benzyl ether and diphenyl ethane based mesogens

The synthesis and radical polymerization of a novel series of acrylates and methacrylates containing p-cyanophenyl-p-hydroxybenzyl ether, p-methoxyphenyl-p-hydroxybenzyl ether, and 1-(p-cyanophenyl)-2-(p-hydroxyphenyl) ethane groups attached to the polymerizable group through aliphatic spacers containing 11 and 6 methylenic units is described. The resulting polymers were characterized by differential scanning calorimetry and optical polarization microscopy. All polymers exhibited enantiotropic mesomorphism. Low molar mass compounds based on benzyl ether or diphenyl ethane units exhibit only monotropic or virtual transitions. This demonstrates that the “polymer effect” stabilizes mesophases obtained from “mesogenic units” which do not contain rigid interconnecting groups.     

Synthesis of α-hydroxy-β-lactams

A convenient synthesis of α-hydroxy-β-lactams has been devised that involves the annelation of an inline with benzyloxyacetyl chloride and triethylamine and subsequent hydrogenolysis in the presence of palladium on carbon. In most cases a cis-β-lactam was obtained. A thioimidate can also be used as the imino component in the annelation reaction but the hydrogenolysis step fails. The annelation of the appropriate thiazoline to a 6-epi-penicillin derivative occurred much more readily with benzyloxyacetyl chloride than with azidoacetyl chloride.     

Synthesis and characterization of liquid crystalline polysiloxanes containing benzyl ether mesogens

Side chain liquid crystalline polysiloxanes were synthesized by the hydrosilation of poly(methylhydrosiloxane) with p-(1-undecenyl-11-oxy) benzyl ethers of 4-cyanophenol (IM), 4-methoxyphenol (IIM), 4-cyano-4′-hydroxybiphenyl (IIIM), 4-methoxy-4′-hydroxybiphenyl (IVM), and 2-cyano-6-hydroxynaphthalene (VM). The phase behavior of both monomeric and polymeric liquid crystals was characterized by differential scanning calorimetry and optical polarization microscopy. IM is a monotropic liquid crystal, IIM is crystalline, and IIIM and IVM are enantiotropic liquid crystals, whereas VM presents two virtual liquid crystalline transitions and crystalline polymorphism. All the synthesized polysiloxanes present enantiotropic smectic mesomorphism.     

Preparation and characterization of side chain cholesteric liquid crystalline polysiloxanes containing two chiral groups

A series of liquid crystalline (LC) polysiloxanes containing diosgeninyl and menthyl groups (from monomers M ₁ and M ₂, respectively) were synthesized. The chemical structures of the monomers and polymers obtained were confirmed by elemental analysis, Fourier transform infrared spectroscopy, proton NMR and carbon‐13 NMR. The LC properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction. Monomer M ₁ showed cholesteric oily‐streak and spiral textures. Copolymers P ₂–P ₅ exhibited cholesteric phases. With increasing concentration of M ₂ units, the glass transition and clearing temperatures decreased. Experimental results demonstrated that a flexible polymer backbone and a long flexible spacer tended to favour a lower glass transition temperature, higher thermal stability, and wider mesophase temperature range.     

Preparation and characterization of side chain cholesteric liquid crystalline polysiloxanes containing two chiral groups

A series of liquid crystalline (LC) polysiloxanes containing diosgeninyl and menthyl groups (from monomers M₁ and M₂, respectively) were synthesized. The chemical structures of the monomers and polymers obtained were confirmed by elemental analysis, Fourier transform infrared spectroscopy, proton NMR and carbon-13 NMR. The LC properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction. Monomer M₁ showed cholesteric oily-streak and spiral textures. Copolymers P₂-P₅ exhibited cholesteric phases. With increasing concentration of M₂ units, the glass transition and clearing temperatures decreased. Experimental results demonstrated that a flexible polymer backbone and a long flexible spacer tended to favour a lower glass transition temperature, higher thermal stability, and wider mesophase temperature range.     

New side chain liquid crystalline polysiloxanes containing 1,3-dithiane or 1,3-dioxane rings as mesogenic side groups

New liquid crystal materials: 2-\[p-(9-decenyloxy)phenyl]-5-(p -alkoxyphenyl)-1,3-dioxane( 11 ) and 2-\[p-(9-decenyloxy)phenyl]-5-(p -alkoxyphenyl)-1,3-dithiane( 12 ) were synthesized. The mesomorphic behaviour of these compounds was determined. Though the 1,3-dioxane-type monomer exhibited both SmA and nematic phases, the 1,3-dithiane-type monomer only exhibited a nematic phase. By the hydrosilylation of poly(methylhydrosiloxane) and these monomers, side chain polysiloxanes were synthesized. For the monomers, the transition temperatures of the nematic to isotropic transitions of 1,3-dioxane-type compounds are higher than those of the corresponding 1,3-dithiane-type compounds. However, in the polysiloxane polymer this relation reversed.     

Synthesis and characterization of chiral liquid‐crystalline polysiloxanes containing fluorinated units and sulfonic acid groups

Chiral side‐chain liquid‐crystalline polysiloxanes ( PS‐1 , PS‐2 , PS‐3 , PS‐4 , PS‐5 , PS‐6 ) bearing fluorinated units and sulfonic acid groups were synthesized with poly(methylhydrogeno)siloxane, cholest‐5‐en‐3‐ol(3β)‐4‐(2‐propenyloxy)benzoate, and 3‐trifluoromethyl‐phenyl 3‐sulfo‐4‐undec‐10‐ enoyloxy‐benzoate. The effects of fluorinated units and sulfonic acid groups on characteristic of liquid‐crystalline properties were studied. PS‐1 , PS‐2 , and PS‐3 exhibited both smectic and cholesteric mesophases, while PS‐4 , PS‐5 , and PS‐6 exhibited only cholesteric mesophase. As the polymers contained more fluorinated units and sulfonic acid groups, segregation of the fluorinated segment to the surface and aggregation of hydrogen bonding should occur. Therefore, the highly ordered lamellar mesogen–siloxane matrix systems should be disturbed severely, suggesting that PS‐4 , PS‐5 , and PS‐6 show no smectic phase. The maximum reflection bands become broad and shifted slightly to long wavelength from PS‐1 to PS‐6 . Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and X-ray investigation of liquid crystalline polymers containing laterally methyl-substituted tolane-based mesogenic side groups

A series of polymethacrylates containing laterally methyl-substituted 4-alkoxy-4-nitrotolane, 4-alkoxy-4'-cyanotolane, and 4-alkoxy-4'-trifluoromethyltolane as mesogenic side groups are presented. The thermal behaviours of the prepared compounds were characterized by differential scanning calorimetry, optical polarized microscopy and X-ray diffraction. All of the obtained methacrylate monomers exhibit no mesophase, while most of the synthesized polymers reveal enantiotropic mesomorphism. The polymer containing 4-propyloxy-2'-methyl-4'-nitrotolane side groups was the only one to show no mesomorphic behaviour. The spacer length and the nature of terminal group have a profound influence on the type of mesophase formed and the thermal stability. Incorporation of a lateral methyl-substituent into the mesogenic groups reduces the thermal stabilities of the mesophases. X-ray diffraction reveals that polymers with a smectic A or smectic E phase have the inclination to form a bilayer structure. Increasing the temperature within the smectic phase range, the intermolecular spacing increases while the layer spacing decreases. On the other hand, introducing a lateral substituent into the mesogenic side groups leads to increase in both layer and intermolecular spacing.     

Synthesis, structure and characterization of side chain cholesteric liquid crystalline polysiloxanes

A series of liquid crystalline homopolysiloxanes and copolysiloxanes were synthesized. The chemical structures of the monomers M₁-M₇ were confirmed by FTIR and ¹H NMR spectroscopy. The structure-property relationships of the monomers and polymers are discussed; their phase behaviour and optical properties were investigated by differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscopy. All the monomers, except M₂ and M₇ showed smectic and nematic phases; the copolymers P₈-P₁₅ displayed cholesteric phases. The homopolymers P₁-P₇ exhibited smectic phases. The selective reflection of cholesteric monomers and copolymers shifted to longer wavelengths with increasing length of the rigid mesogenic core, with decreasing length of the flexible spacer, or with increasing content of nematic units. Experimental results demonstrated that a flexible polymer backbone, a rigid mesogenic core and a long flexible spacer tended to produce a lower glass transition temperature, higher thermal stability, and wider mesophase temperature range.     

Synthesis and characterization of polymerizable β-diketone-based liquid crystalline metal chelates

Two novel square-planar palladium chelating liquid crystals, bis(p-n-(l-undecenoxyphenyl-3-dodecyloxyphenyl)-propane-1,3-dionato)palladium(II) (Pd-C₁₁-C₁₂) and bis(1,3-di(p-n-tetradecyloxphenyl)-propane-1,3-dionato) palladium (II) (Pd-C₁₄-C₁₄) have been synthesized. Moreover, the copper chelating liquid crystal bis(p-n-(l-undecynoxylphenyl-3-dodecyloxylphenyl)-propane-1,3-dionate)copper (II) (Cu-Cu₁₁-C₁₂) has been synthesized by heterogeneous ligand-exchange reaction. These β-diketone metal chelates have been characterized by elementary analysis, differential scanning calorimetry, polarizing microscopy, X-ray diffraction analysis and temperature-variable IR. It was found that these chelates were discotic lamellar-(D_L) mesophase liquid crystals. In particular, the temperature-variable IR study indicates that the central chelating ring and the surrounding benzene rings would form a co-planar conjugated structure in the liquid crystalline (LC) state.     

Synthesis and characterization of new chiral liquid crystalline polyacrylates from L-isoleucine

The synthesis of chiral side chain liquid crystalline polyacrylates with a two-stereogenic centre from L-alpha-aminoacid is described. The chiral tail is 2-chloroalcohol obtained from L-isoleucine and the spacer group has either four or eleven methylene units. The mesogenic moiety is derived from phenyl benzoate. The stereochemistry of the key intermediate (2 S ,3 S )-(+)-4- [1-(2-chloro-3-methyl)pentyloxy]phenyl benzoate ( 6 ) obtained by a Mitsunobu reaction was established by single crystal X-ray analysis. This result indicates that the nucleophilic displacement of chiral diazonium salts proceeds with overall retention of configuration. The liquid crystalline behaviour of polyacrylates P 13 and P 14 was investigated by DSC, optical microscopy, small angle X-ray scattering and depolarized light scattering. The polyacrylate P 13 , with eleven methylene units in the spacer, exhibits a chiral smectic A phase whereas the polyacrylate P 14 , with a spacer containing four methylene units, displays a chiral nematic phase.     

Synthesis and characterization of new chiral liquid crystalline polyacrylates from L-isoleucine

The synthesis of chiral side chain liquid crystalline polyacrylates with a two-stereogenic centre from L-α-aminoacid is described. The chiral tail is 2-chloroalcohol obtained from L-isoleucine and the spacer group has either four or eleven methylene units. The mesogenic moiety is derived from phenyl benzoate. The stereochemistry of the key intermediate (2S,3S)-(+)-4- [1-(2-chloro-3-methyl)pentyloxy]phenyl benzoate (6) obtained by a Mitsunobu reaction was established by single crystal X-ray analysis. This result indicates that the nucleophilic displacement of chiral diazonium salts proceeds with overall retention of configuration. The liquid crystalline behaviour of polyacrylates P13 and P14 was investigated by DSC, optical microscopy, small angle X-ray scattering and depolarized light scattering. The polyacrylate P13, with eleven methylene units in the spacer, exhibits a chiral smectic A phase whereas the polyacrylate P14, with a spacer containing four methylene units, displays a chiral nematic phase.     

Synthesis,characterization, and properties of hydroxyl‐terminated copolysiloxanes containing γ‐cyanopropyl groups

A series of random copolysiloxanes (PCDMS) containing various amount of γ‐cyanopropyl groups are prepared by a new method under mild conditions. Structures of the synthesized polymers are fully characterized by FTIR, ¹H NMR, ²⁹Si NMR, and GPC. Rheological properties of PCDMS are tested by cone and plate rheometer, and thermal properties by differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). Damping properties as well as fuel resistance of the cured PCDMS elastomers are also tested. The correlation between chemical structure, content of cyanopropyl group and properties are discussed. With the increasing amount of polar cyanopropyl group introduced, glass transition temperatures (T_g) of the synthesized PCDMS gradually increases from ?121 to ?65 °C, residual weight increases from 0 to 36% at 800°C, loss factor reaches as high as 1.74, mass increase under fuel immersion for 14 days can be as low as 3.6%. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1408–1421