Thomas Schleeh | Luxembourg Institute of Science and Technology (original) (raw)
Papers by Thomas Schleeh
Advanced materials and technologies, Apr 9, 2022
Carbohydrate Polymers, Mar 1, 2016
Biocompatibility and thickening properties predetermine alginates as ingredients in food, cosmeti... more Biocompatibility and thickening properties predetermine alginates as ingredients in food, cosmetic and pharmaceutical products. Further chemical modifications are often desired for a product optimization. The introduction of hydrophobic groups can be realized by employing organic tetrabutylammonium alginate (TBA-Alg) solutions. The synthesis of alginic acid alkyl amides from TBA-Alg with 2-chloro-1-methylpyridinium iodide (CMPI) as a coupling agent, however, has so far not resulted in a high degree of amidation. The analysis of the coupling reaction revealed the formation of mannuronic acid γ-lactone structures, which required a conformation change from (1)C4 to (4)C1. The opening of the γ-lactone required a high excess of butylamine. In the case of CMPI, triethylamine had to be added prior to the coupling agent in order to suppress the assumed alginic acid formation. The degrees of amidation achieved were up to 0.8, and for propylphosphonic anhydride as the coupling agent up to 1. The molecular weights of the alginic acid butyl amide were ≥35kDa.
Macromolecules, Feb 1, 1993
The synthesis and characterization of side-chain liquid crystal polymers baaed on atactic polysty... more The synthesis and characterization of side-chain liquid crystal polymers baaed on atactic polystyrene and derivatized with differing mesogenic groups are described. These groups are cyano-, methoxy-, nitro-, and fluoroazobenzene and cyanobiphenyl. In each caw a butyl spacer is used to link the mesagenic group to the backbone. The cyano-and nitro-substituted azobenzenes exhibit a partially interdigitated smectic A phase, whereas the methoxy-and fluoro-substituted azobenzenes exhibit a smectic A phase in which the side chains overlap to a considerably greater extent. The dependence of the clearing temperaturea on the molecular structure of the mesogenic unit was found to be in accord with the behavior obaerved for low molar mass mesogens and other side-chain polymers having differing backbones. In contrast, the dependence of the glass transition temperature on the chemical nature of the mesogenic moiety appears to be influenced by the structure of the backbone. OMe Azo-OMe with phenol to yield 4-hydro~y-4~-subntituted ambenzene, 1, was performed by a standard method.# 4Cyano-4f-hydroxybiphsnyl was used as received from American Tokyo Kaaei, Inc. W other matariala were used as received from Aldrich Chemical Co.
Carbohydrate Polymers, Dec 1, 2014
The adaptation of alginates to food and pharmaceutical specifications is limited to aqueous chemi... more The adaptation of alginates to food and pharmaceutical specifications is limited to aqueous chemistry due to the insolubility of sodium alginate (Na-Alg) and the insufficient solubility of tetrabutylammonium alginate (TBA-Alg) in organic solvents. In the present investigation, these restrictions were resolved by optimizing the solubility of TBA-Alg by improving its synthesis from Na-Alg via heterogeneous acidification with hydrochloric and formic acid, followed by neutralization with tetrabutylammonium hydroxide. The best acidification results were achieved with formic acid, because the reaction controlling solubility of the by-product in the acidic solvent was improved in comparison to hydrochloric acid. The solubility of TBA-Alg in polar aprotic organic solvents improved by increasing the degree of TBA substitution (DS TBA), decreasing the molecular weight of TBA-Alg and increasing the relative permittivity of the solvent. The best TBA-Algs, with DS TBA = 0.95 and relative high molecular weights, gave optically clear solutions with a turbidity of about 1 NTU.
Journal of Polymer Science Part A, Jun 1, 1993
A series of new side-chain liquid-crystalline copolymers has been prepared, and the thermal prope... more A series of new side-chain liquid-crystalline copolymers has been prepared, and the thermal properties of the individual copolymers have been determined. These copolymers are derived from atactic polystyrene and contain both 4-methoxyazobenzene and 4-nitroazobenzene mesogens; these are linked through octyl spacers to the polystyrene backbone. All the copolymers exhibit a smectic phase that has been assigned smectic A on the basis of polarizing microscopy and x-ray diffraction studies. The glass transition temperatures of the polymers exhibit a linear dependence on composition, whereas the clearing temperatures and the associated entropies show significant deviations from such behavior. The smecticisotropic transition temperatures of the copolymers are higher than those of the compositionweighted averages for the corresponding homopolymers, whereas the entropies of transition are lower than expected. X-ray diffraction studies of fiber samples revealed that the director of the mesophase is oriented perpendicular to the fiber axis. The liquid-crystalline polystyrene containing 25 mol % nitro-substituted mesogen shows an unusual &-phase WAXS pattern. The copolymers were investigated further by 13C CP /MAS NMR spectroscopy, and the observed changes in the spectra are analyzed in terms of chemical composition and local electronic environment. The application of the interrupted decoupling technique revealed that the spacer contains a number of gauche defects. These observations lead us to suggest possible microstructural arrangements in the smectic phase.
Advanced materials and technologies, Aug 1, 2022
Colloid and Polymer Science, Mar 1, 1992
An unusual continuous film formation process of lateral pentyloxy substituted poly(p-phenylene te... more An unusual continuous film formation process of lateral pentyloxy substituted poly(p-phenylene terephthalate)s (s-PPPT) and poly(carbonate) (PC) is observed. A liquid film of polymer solution creeps over the surface of water dropped into the polymer solution. By vaporization of the solvent a solid polymer film is formed on the water surface and can be removed. The driving force for the film formation mechanism is assumed by the reduction of the surface tension of water. Experiments verify this mechanism by increasing the film formation speed using a gas stream, by reducing the formation speed through lowering the surface tension by rinsing agents, and by lowering the solubility of the polymer. As expected, no effects are found by variation of the pH-value of water. Necessary conditions for the film formation process are: good solubility of the polar polymers in organic solvents having a high vapor pressure, complete phase separation, solution density higher than water density, and a surrounding gas phase unsaturated with solvent vapor. The thickness of the mechanically stable films is less than 0.5/lm. The films are amorphous by microscopical, FT-IR, x-ray, and DTA investigations.
Advanced Materials Technologies
Advances in Polymer Technology, 2003
ABSTRACT
Food & Function
Proteins differentially affect carotenoid bioaccessibility and physicochemical characteristics of... more Proteins differentially affect carotenoid bioaccessibility and physicochemical characteristics of the digesta and constituents, depending on carotenoid and protein species/concentration.
Advanced materials and technologies, Apr 9, 2022
Carbohydrate Polymers, Mar 1, 2016
Biocompatibility and thickening properties predetermine alginates as ingredients in food, cosmeti... more Biocompatibility and thickening properties predetermine alginates as ingredients in food, cosmetic and pharmaceutical products. Further chemical modifications are often desired for a product optimization. The introduction of hydrophobic groups can be realized by employing organic tetrabutylammonium alginate (TBA-Alg) solutions. The synthesis of alginic acid alkyl amides from TBA-Alg with 2-chloro-1-methylpyridinium iodide (CMPI) as a coupling agent, however, has so far not resulted in a high degree of amidation. The analysis of the coupling reaction revealed the formation of mannuronic acid γ-lactone structures, which required a conformation change from (1)C4 to (4)C1. The opening of the γ-lactone required a high excess of butylamine. In the case of CMPI, triethylamine had to be added prior to the coupling agent in order to suppress the assumed alginic acid formation. The degrees of amidation achieved were up to 0.8, and for propylphosphonic anhydride as the coupling agent up to 1. The molecular weights of the alginic acid butyl amide were ≥35kDa.
Macromolecules, Feb 1, 1993
The synthesis and characterization of side-chain liquid crystal polymers baaed on atactic polysty... more The synthesis and characterization of side-chain liquid crystal polymers baaed on atactic polystyrene and derivatized with differing mesogenic groups are described. These groups are cyano-, methoxy-, nitro-, and fluoroazobenzene and cyanobiphenyl. In each caw a butyl spacer is used to link the mesagenic group to the backbone. The cyano-and nitro-substituted azobenzenes exhibit a partially interdigitated smectic A phase, whereas the methoxy-and fluoro-substituted azobenzenes exhibit a smectic A phase in which the side chains overlap to a considerably greater extent. The dependence of the clearing temperaturea on the molecular structure of the mesogenic unit was found to be in accord with the behavior obaerved for low molar mass mesogens and other side-chain polymers having differing backbones. In contrast, the dependence of the glass transition temperature on the chemical nature of the mesogenic moiety appears to be influenced by the structure of the backbone. OMe Azo-OMe with phenol to yield 4-hydro~y-4~-subntituted ambenzene, 1, was performed by a standard method.# 4Cyano-4f-hydroxybiphsnyl was used as received from American Tokyo Kaaei, Inc. W other matariala were used as received from Aldrich Chemical Co.
Carbohydrate Polymers, Dec 1, 2014
The adaptation of alginates to food and pharmaceutical specifications is limited to aqueous chemi... more The adaptation of alginates to food and pharmaceutical specifications is limited to aqueous chemistry due to the insolubility of sodium alginate (Na-Alg) and the insufficient solubility of tetrabutylammonium alginate (TBA-Alg) in organic solvents. In the present investigation, these restrictions were resolved by optimizing the solubility of TBA-Alg by improving its synthesis from Na-Alg via heterogeneous acidification with hydrochloric and formic acid, followed by neutralization with tetrabutylammonium hydroxide. The best acidification results were achieved with formic acid, because the reaction controlling solubility of the by-product in the acidic solvent was improved in comparison to hydrochloric acid. The solubility of TBA-Alg in polar aprotic organic solvents improved by increasing the degree of TBA substitution (DS TBA), decreasing the molecular weight of TBA-Alg and increasing the relative permittivity of the solvent. The best TBA-Algs, with DS TBA = 0.95 and relative high molecular weights, gave optically clear solutions with a turbidity of about 1 NTU.
Journal of Polymer Science Part A, Jun 1, 1993
A series of new side-chain liquid-crystalline copolymers has been prepared, and the thermal prope... more A series of new side-chain liquid-crystalline copolymers has been prepared, and the thermal properties of the individual copolymers have been determined. These copolymers are derived from atactic polystyrene and contain both 4-methoxyazobenzene and 4-nitroazobenzene mesogens; these are linked through octyl spacers to the polystyrene backbone. All the copolymers exhibit a smectic phase that has been assigned smectic A on the basis of polarizing microscopy and x-ray diffraction studies. The glass transition temperatures of the polymers exhibit a linear dependence on composition, whereas the clearing temperatures and the associated entropies show significant deviations from such behavior. The smecticisotropic transition temperatures of the copolymers are higher than those of the compositionweighted averages for the corresponding homopolymers, whereas the entropies of transition are lower than expected. X-ray diffraction studies of fiber samples revealed that the director of the mesophase is oriented perpendicular to the fiber axis. The liquid-crystalline polystyrene containing 25 mol % nitro-substituted mesogen shows an unusual &-phase WAXS pattern. The copolymers were investigated further by 13C CP /MAS NMR spectroscopy, and the observed changes in the spectra are analyzed in terms of chemical composition and local electronic environment. The application of the interrupted decoupling technique revealed that the spacer contains a number of gauche defects. These observations lead us to suggest possible microstructural arrangements in the smectic phase.
Advanced materials and technologies, Aug 1, 2022
Colloid and Polymer Science, Mar 1, 1992
An unusual continuous film formation process of lateral pentyloxy substituted poly(p-phenylene te... more An unusual continuous film formation process of lateral pentyloxy substituted poly(p-phenylene terephthalate)s (s-PPPT) and poly(carbonate) (PC) is observed. A liquid film of polymer solution creeps over the surface of water dropped into the polymer solution. By vaporization of the solvent a solid polymer film is formed on the water surface and can be removed. The driving force for the film formation mechanism is assumed by the reduction of the surface tension of water. Experiments verify this mechanism by increasing the film formation speed using a gas stream, by reducing the formation speed through lowering the surface tension by rinsing agents, and by lowering the solubility of the polymer. As expected, no effects are found by variation of the pH-value of water. Necessary conditions for the film formation process are: good solubility of the polar polymers in organic solvents having a high vapor pressure, complete phase separation, solution density higher than water density, and a surrounding gas phase unsaturated with solvent vapor. The thickness of the mechanically stable films is less than 0.5/lm. The films are amorphous by microscopical, FT-IR, x-ray, and DTA investigations.
Advanced Materials Technologies
Advances in Polymer Technology, 2003
ABSTRACT
Food & Function
Proteins differentially affect carotenoid bioaccessibility and physicochemical characteristics of... more Proteins differentially affect carotenoid bioaccessibility and physicochemical characteristics of the digesta and constituents, depending on carotenoid and protein species/concentration.