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Willem Jacobus Dr Mijs - One of the best experts on this subject based on the ideXlab platform.
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Phase transitions of hydroxy-telechelic side-chain liquid crystalline polyethers and polyurethane networks derived thereof
Macromolecular Chemistry and Physics, 1996Co-Authors: Johannes B. Reesink, Arend J. Witteveen, Stephen J. Picken, Willem Jacobus Dr MijsAbstract:Hydroxy-telechelic polymers with side-chain mesogenic groups have been prepared from epoxy monomers using a BF 3 /1,6-hexanediol initiating system. Homopolymers showed either nematic or smectic A and C phases, depending on the length of the alkoxy substituent on the aromatic mesogenic group. In copolymers both nematic and smectic phases could be observed, depending on composition. Liquid crystallinity was found to be retained after crosslinking with a triisocyanate at Temperatures below the Clearing Temperature of the mixture. On the other hand, the mesophase was found to disappear on rapid cooling after a certain degree of crosslinking above the Clearing Temperature, only to reappear after a period of heating above the glass transition Temperature.
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Phase transitions of hydroxy‐telechelic side‐chain liquid crystalline polyethers and polyurethane networks derived thereof
Macromolecular Chemistry and Physics, 1996Co-Authors: Johannes B. Reesink, Arend J. Witteveen, Stephen J. Picken, Willem Jacobus Dr MijsAbstract:Hydroxy-telechelic polymers with side-chain mesogenic groups have been prepared from epoxy monomers using a BF 3 /1,6-hexanediol initiating system. Homopolymers showed either nematic or smectic A and C phases, depending on the length of the alkoxy substituent on the aromatic mesogenic group. In copolymers both nematic and smectic phases could be observed, depending on composition. Liquid crystallinity was found to be retained after crosslinking with a triisocyanate at Temperatures below the Clearing Temperature of the mixture. On the other hand, the mesophase was found to disappear on rapid cooling after a certain degree of crosslinking above the Clearing Temperature, only to reappear after a period of heating above the glass transition Temperature.
Johannes B. Reesink - One of the best experts on this subject based on the ideXlab platform.
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Phase transitions of hydroxy-telechelic side-chain liquid crystalline polyethers and polyurethane networks derived thereof
Macromolecular Chemistry and Physics, 1996Co-Authors: Johannes B. Reesink, Arend J. Witteveen, Stephen J. Picken, Willem Jacobus Dr MijsAbstract:Hydroxy-telechelic polymers with side-chain mesogenic groups have been prepared from epoxy monomers using a BF 3 /1,6-hexanediol initiating system. Homopolymers showed either nematic or smectic A and C phases, depending on the length of the alkoxy substituent on the aromatic mesogenic group. In copolymers both nematic and smectic phases could be observed, depending on composition. Liquid crystallinity was found to be retained after crosslinking with a triisocyanate at Temperatures below the Clearing Temperature of the mixture. On the other hand, the mesophase was found to disappear on rapid cooling after a certain degree of crosslinking above the Clearing Temperature, only to reappear after a period of heating above the glass transition Temperature.
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Phase transitions of hydroxy‐telechelic side‐chain liquid crystalline polyethers and polyurethane networks derived thereof
Macromolecular Chemistry and Physics, 1996Co-Authors: Johannes B. Reesink, Arend J. Witteveen, Stephen J. Picken, Willem Jacobus Dr MijsAbstract:Hydroxy-telechelic polymers with side-chain mesogenic groups have been prepared from epoxy monomers using a BF 3 /1,6-hexanediol initiating system. Homopolymers showed either nematic or smectic A and C phases, depending on the length of the alkoxy substituent on the aromatic mesogenic group. In copolymers both nematic and smectic phases could be observed, depending on composition. Liquid crystallinity was found to be retained after crosslinking with a triisocyanate at Temperatures below the Clearing Temperature of the mixture. On the other hand, the mesophase was found to disappear on rapid cooling after a certain degree of crosslinking above the Clearing Temperature, only to reappear after a period of heating above the glass transition Temperature.
Stephen J. Picken - One of the best experts on this subject based on the ideXlab platform.
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Liquid crystalline solutions of cellulose acetate in phosphoric acid
Polymer, 2001Co-Authors: H. Boerstoel, Stephen J. Picken, H. Maatman, R Remmers, J.b. WesterinkAbstract:Abstract The influence has been studied of both the acid strength of phosphoric acid and the degree of substitution of cellulose acetate on the formation of an anisotropic phase. The solvent composition is expressed as a P2O5 concentration. It was found that the Clearing Temperature increases strongly with decreasing amount of water in the solvent. The influence of the degree of substitution (DS) was studied on a series of samples with a DS ranging from 0.23 to 2.89. It was found that over the entire range good solubility occurred in anhydrous phosphoric acid. The DS hardly affected the Clearing Temperature in the process of dissolving a constant number density of polymer chains. However, the birefringence of the solution was strongly influenced by the DS, due to the intrinsic birefringence of the polymer chains.
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Phase transitions of hydroxy-telechelic side-chain liquid crystalline polyethers and polyurethane networks derived thereof
Macromolecular Chemistry and Physics, 1996Co-Authors: Johannes B. Reesink, Arend J. Witteveen, Stephen J. Picken, Willem Jacobus Dr MijsAbstract:Hydroxy-telechelic polymers with side-chain mesogenic groups have been prepared from epoxy monomers using a BF 3 /1,6-hexanediol initiating system. Homopolymers showed either nematic or smectic A and C phases, depending on the length of the alkoxy substituent on the aromatic mesogenic group. In copolymers both nematic and smectic phases could be observed, depending on composition. Liquid crystallinity was found to be retained after crosslinking with a triisocyanate at Temperatures below the Clearing Temperature of the mixture. On the other hand, the mesophase was found to disappear on rapid cooling after a certain degree of crosslinking above the Clearing Temperature, only to reappear after a period of heating above the glass transition Temperature.
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Phase transitions of hydroxy‐telechelic side‐chain liquid crystalline polyethers and polyurethane networks derived thereof
Macromolecular Chemistry and Physics, 1996Co-Authors: Johannes B. Reesink, Arend J. Witteveen, Stephen J. Picken, Willem Jacobus Dr MijsAbstract:Hydroxy-telechelic polymers with side-chain mesogenic groups have been prepared from epoxy monomers using a BF 3 /1,6-hexanediol initiating system. Homopolymers showed either nematic or smectic A and C phases, depending on the length of the alkoxy substituent on the aromatic mesogenic group. In copolymers both nematic and smectic phases could be observed, depending on composition. Liquid crystallinity was found to be retained after crosslinking with a triisocyanate at Temperatures below the Clearing Temperature of the mixture. On the other hand, the mesophase was found to disappear on rapid cooling after a certain degree of crosslinking above the Clearing Temperature, only to reappear after a period of heating above the glass transition Temperature.
Dumitru Pavel - One of the best experts on this subject based on the ideXlab platform.
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poly 4 vinylpyridine based hydrogen bonded side chain liquid crystal polymers
Reactive & Functional Polymers, 2008Co-Authors: Subing Zhang, Robe A Shanks, Dumitru PavelAbstract:Abstract Novel liquid crystalline (LC) poly(4-vinylpyridine) (PVP)-based side-chain polymers were prepared from PVP and cyanobiphenyl (HOC n B) derivatives through intermolecular hydrogen-bonding between hydroxyl groups of the cyanobiphenyl derivatives and the nitrogen of PVP. PVP was used as a hydrogen bond acceptor polymer. A series of HOC n B having a linear alkoxy chain HOC n H 2 n + 1 O–( n = 2–6) have been used as H-bond donor. The existence of H-bonding was confirmed using FTIR spectroscopy. The polymeric complexes behave as LC polymers and exhibit stable mesophases. DSC and optical microscopy were used to investigate LC behaviour. All PVP–LC-complexes exhibited stable and homogeneous nematic phases. On increasing spacer length or concentration of the hydrogen bonded mesogenic unit in the complex, the Clearing Temperature and the Temperature range of the nematic phase increased. The binary phase diagram of the polymeric complexes PVP–HOC n B showed complete miscibility over the entire range of composition. Molecular interactions of self-assembled SCLCP presented the idea that various LC-complexes could be prepared through mixing a functionalised polymer with various low molar mass mesogens.
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Synthesis and Characterisation of Side-Chain Liquid Crystalline Poly[1-({[(4-cyano-4′-biphenyl)oxy]alkyl}oxy)-2,3-epoxypropane]
Macromolecular Chemistry and Physics, 2004Co-Authors: Xiangen Han, Robert A. Shanks, Dumitru PavelAbstract:A new series of side-chain liquid-crystal polymers, the poly[1-({[(4-cyano-4'-biphenyl)oxy]alkyl}oxy)-2,3-epoxypropane], has been synthesized in which the spacer length is varied from 2 to 8 methylene units. The synthesis used for the chemical modification of polyepichlorohydrin (PECH) involved the phase transfer catalyzed etherification of the chloromethyl groups with sodium 4-cyano-4'-biphenoxide and lithium n-(4-cyano-4'-oxybiphenyl)-alkanoates. All the resulting polymers. (except polymers 7 and 8), including that without spacer, characterized by H-1 NMR, and IR, exhibit thermotropic liquid crystalline mesomophism. The thermal behavior of the polymers has been characterized using differential scanning calorimetry (DSC) and polarized light microscopy (POM) equipped with hot-stage. A more pronounced odd-even effect in the Clearing Temperatures is observed on increasing the spacer length in which the odd members display slightly higher values, which were also dependent on the substitution degree of PECH. The flexible PECH chain assists nematic LC formation compared with other more rigid backbone polymers where a smectic phase is often encountered with the same mesogen. A comparison of the thermal properties of the cyanobiphenyl based series reported here. Polyacrylate (PA) and poly(methacrylate)based (PMA) SCLCPs containing 4-cyanobiphenyl as the mesogenic unit are consistent with the general rule that increasing backbone flexibility for a given mesogenic unit and spacer length enhance the Clearing Temperature. This was not found from the PECH-based series, which show the lower Clearing Temperature than the PMA and PA series, even though they have more flexible backbone than PA and PMA series. So the Clearing Temperature is not solely determined by the flexibility of the backbone.
Madalena Dionísio - One of the best experts on this subject based on the ideXlab platform.
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dielectric relaxation studies and electro optical measurements in poly triethylene glycol dimethacrylate nematic e7 composites exhibiting an anchoring breaking transition
Liquid Crystals, 2008Co-Authors: Ana R. Brás, Olga García, María Teresa Viciosa, S. Martins, Roberto Sastre, Carlos J. Dias, João L. Figueirinhas, Madalena DionísioAbstract:Electric field driven anchoring breakage in poly(triethylene glycol dimethacrylate)/nematic E7 composites was studied using dielectric spectroscopy and transmittance measurements. The transmittance hysteresis observed on increasing and decreasing an applied electric field, associated with different alignment states of the liquid crystal (LC), was monitored through dielectric loss. Essential changes are felt mainly in the δ‐peak, i.e. the dielectric response of the nematic when the director lies parallel to the applied electric field. An irreversible effect persists after the field had exceeded a critical value, which was manifest in a higher transmittance and a higher dielectric strength of the δ‐peak in the OFF state. The initial scattering/opaque state of the sample can only be recovered by heating to the Clearing Temperature of the nematic LC. The effect referred, commonly called memory effect, is rationalized in terms of anchoring breakage of the LC at the polymer–LC interfaces. The electro‐optical re...
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Dielectric relaxation studies and electro‐optical measurements in poly(triethylene glycol dimethacrylate)/nematic E7 composites exhibiting an anchoring breaking transition
Liquid Crystals, 2008Co-Authors: Ana R. Brás, Olga García, María Teresa Viciosa, S. Martins, Roberto Sastre, Carlos J. Dias, João L. Figueirinhas, Madalena DionísioAbstract:Electric field driven anchoring breakage in poly(triethylene glycol dimethacrylate)/nematic E7 composites was studied using dielectric spectroscopy and transmittance measurements. The transmittance hysteresis observed on increasing and decreasing an applied electric field, associated with different alignment states of the liquid crystal (LC), was monitored through dielectric loss. Essential changes are felt mainly in the δ‐peak, i.e. the dielectric response of the nematic when the director lies parallel to the applied electric field. An irreversible effect persists after the field had exceeded a critical value, which was manifest in a higher transmittance and a higher dielectric strength of the δ‐peak in the OFF state. The initial scattering/opaque state of the sample can only be recovered by heating to the Clearing Temperature of the nematic LC. The effect referred, commonly called memory effect, is rationalized in terms of anchoring breakage of the LC at the polymer–LC interfaces. The electro‐optical re...