A method for reproducible preparation of chiral polysiloxanes with regular repeat units as stationary phases for capillary gas chromatography

Trifluoroethyl ester-functionalized polysiloxanes can be prepared by block condensation of 3-dichloromethylsilyl-2-methylpropionic acid 2′,2′,2′-trifluoroethyl ester with 1,5-bis(diethylamino)hexamethyltrisiloxane or with disodium tetramethyldisiloxane-1,3-diolate. The functionalized polysiloxanes may serve as supports for a variety of selector groups; for instance, nucleophilic displacements with L-valine-t-butylamide or L-α-naphthylethylamine lead to chiral polysiloxanes in high yields and with high reproducibility. Imidazole accelerates the rate of nucleophilic displacement. Capillary columns coated with such chiral polysiloxanes exhibit high enantioselectivity and thermostability.     

Cyclocholates as Chiral Selectors for Capillary Gas Chromatography – Effect of Temperature Conditioning on the Chromatographic Behavior of the Stationary Phase

The suitability of cyclocholates as chiral selectors in gas chromatography has been evaluated. We present the synthesis and characterization of two cyclocholates, viz. 3α,7α-diacetoxycyclo[3]cholate and 3α,7α-diacetoxycylo[4]cholate. Mixtures of these new selectors with polysiloxanes were tested as chiral stationary phases in capillary gas chromatography. Several enantiomer separations of common racemates were achieved with the 3α,7α-diacetoxycyclo[3]cholate at 10% in OV-1701 (w/w). It was shown that column efficiency was strongly dependent on temperature and that enantioselectivity was very sensitive to column conditioning. This chromatographic behavior suggested that cyclocholates were only dispersed in polysiloxane. Thus, it was assumed that chiral discrimination occurred via enantioselective adsorption interactions of enantiomers at the surface of the solid chiral selector dispersed in the polysiloxane matrix OV-1701.     

Thermal immobilization of carboxy functionalized polysiloxanes: Practice and mechanism

Summary The thermal immobilization of polysiloxanes bearing carboxyalkyl functional groups has been investigated. Under conditions of reduced carrier-gas flow, in particular with water vapour saturated, carrier-gas, high degrees of immobilization could be achieved at moderate temperatures (<200°C). The mechanism of immobilization is shown two involve condensation of carboxyl groups of the polysiloxane with silanol groups either originally present in the polymer or formed during the immobilization process. Other polysiloxane stationary phases could also be immobilized under similar conditions when mixed with carboxyalkyl polysiloxanes. In particular, cyanoalkyl silicones which are otherwise difficult to crosslink, are amenable to this form of immobilisation.     

Polysiloxanes with chlorobenzyl groups as precursors of new organic‐silicone materials

Various polysiloxanes bearing chlorobenzyl side groups were synthesized by the hydrolytic polycondensation of the 73:27 mol/mol mixture of [2‐(4‐chloromethylphenyl)ethyl] methyldichlorosilane and [1‐(4‐chloromethylphenyl)ethyl] methyldichlorosilane followed by the cationic equilibration or coequilibration with octamethylcyclotetrasiloxane, D₄. 1,3‐Divinyltetramethyl‐disiloxane was used as the chain end blocker to obtain a vinyl–Si ended chlorobenzyl‐substituted polysiloxane. In some cases, the polymer was additionally treated with dimethylvinylchlorosilane to achieve full substitution of chain ends by the vinyl group. Cohydrolysis of the chlorobenzylic monomer mixture with dimethyldichlorosilane was also practiced. Multiblock copolymers were obtained by polyhydrosilylation of the α,ω‐divinylsilyl chlorobenzyl‐substituted polysiloxanes with α,ω‐dihydrosilyl polydimethylsiloxanes. All these polymers and copolymers containing reactive chlorobenzylic groups were demonstrated to be convenient precursors of functional polysiloxanes of potential practical use. Some specific functional groups, such as quaternary ammonium salt groups of biocidal activity or azobenzene groups making the polymer sensitive to external stimuli by light, may be readily generated on polysiloxane under mild conditions. The chlorobenzylic substituted polysiloxanes may be also used as macroinitiators of the atom transfer radical polymerization, to obtain polysiloxanes with grafted organic polymers, such as styrene, 4‐chloromethylstyrene, and n‐butylacrylate. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1682–1692, 2004     

Cyclolinear polysiloxanes. I. Synthesis and characterization

The synthesis and characterization of two novel cyclic siloxanes, diacetoxydiethyltetramethylcyclotetrasiloxane and diacetoxytriethylpentamethylcyclopentasiloxane, and cyclolinear polymers synthesized from these monomers are presented. The cyclic siloxanes were synthesized from tetramethylcyclotetrasiloxane and pentamethylcyclopentasiloxane, respectively, by acetylation followed by ethylation. The cyclic monomers were characterized with ¹H NMR spectroscopy. Subsequently, the cyclic siloxanes were self‐condensed into cyclolinear polysiloxanes and cocondensed (extended) with silanol‐terminated polydimethylsiloxane into high‐molecular‐weight polymers containing cyclic units withlinearpolydimethylsiloxane spacers (extended cyclolinear polysiloxanes). The molecular weights of both the cyclolinear polysiloxanes and extended cyclolinear polysiloxanes were determined. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4039?4052, 2006     

Studies on the Syntheses and Properties of UV-sensitive Organosilicon Monomers and Polymers

Photosensitive organosilicon monomers and polymers containing furylacrylate, cinnamate or methacrylate groups were synthesized. The chemical structure of these organosilicon monomers were confirmed by 1H NMR and elemental analysis.The curing rates of these photosensitive polysiloxanes were also determined, all of them show a good UV-sensitivity. The UV-sensitivity of polysiloxanes containing pendent furylacrylates are comparable to that of polysiloxanes with either pendent cinnamate or pendent methacrylate groups.     

Polysiloxane cationic biocides with imidazolium salt (ImS) groups, synthesis and antibacterial properties

Novel polysiloxanes with pendant biocidal N,N′-dialkylimidazolium salt (ImS) groups were synthesized and compared with polysiloxanes bearing conventional biocidal quaternary ammonium salt (QAS) groups. The bacteriostatic power of these polymers was tested and compared under the same conditions in aqueous solution against two common strains of Gram positive bacteria and three strains of Gram negative bacteria. These new ImS containing polymers exhibited high antibacterial potency against all bacteria studied, similar to those substituted with QAS groups. The advantage of the imidazolium substituted polysiloxane stems from its higher thermal stability, as compared with the quaternary alkylammonium functionalized polymer, as demonstrated by thermogravimetric studies.     

Liquid crystalline polyaniline and phthalocyanine-based polysiloxanes bearing lateral fluoro-substituted benzoic acid groups

A series of novel liquid crystalline polymers (PI, PII, PIII and PIV) containing lateral fluoro-substituted benzoic acid groups was synthesised using cholesteryl 4-(2-propenyloxy)-benzoate, 4-(allyloxy)-3-fluorobenzoic acid and poly(methylhydrogeno)siloxane. PI and PII showed smectic phase, but PIII and PIV showed chiral nematic phase due to more lateral fluoro-substituted benzoic acid groups in the polymer systems. Liquid crystalline polyaniline (PAN) and phthalocyanine (Pc)-based polysiloxanes showing chiral nematic phase were prepared by use of Pc, PAN and these liquid-crystalline polymers via hydrogen bond. PAN-based polysiloxanes showed different liquid crystalline behaviours from Pc-based polysiloxanes due to the difference of molecular structure. PAN-based polysiloxanes showed greater d-spacings between the side mesogenic groups than Pc-based polysiloxanes due to long rod-like geometrical shapes. Hydrogen bond based on lateral fluoro-substituted benzoic acid groups was formed to different geometrical shapes (strip or roundness) between PAN and Pc-based polysiloxanes.     

Study on retention behavior of cyclic siloxanes by high resolution pyrolysis-gas chromatography with a fused silica capillary column

The general gas chromatographic retention behavior of cyclic methylsiloxanes partially substituted with phenyl or 2-cyanoethyl groups has been systematically studied, with pyrolysis-gas chromatography being utilized to form the cyclic siloxanes from the corresponding polysiloxanes at a temperature of 600°C. Kovats retention indices (KI) were determined for the cyclic siloxanes by use of the retention data of the pyrolyzates from polyethylene as standards. The effect of phenyl and 2-cyanoethyl substituents in the cyclic siloxanes on retention behavior has also been considered.     

聚硅氧烷辐射效应研究进展

综述了聚硅氧烷在不同类型辐射下的辐射效应及其各种影响因素,并展望了提高聚硅氧烷耐辐射性能的途径。     

Synthesis of hybrid polysiloxane-MO<Subscript>2</Subscript> (M = Si,Ti, Zr) nanoparticles through a sol–gel route

Polysiloxanes in combination with metal oxides show interesting properties as nanocomposites for optical or medical applications. The formation of covalent connections between the metal oxide and the polysiloxane is an important method to overcome phase separation between the two components, but it also can have an influence on the morphology of the final materials. In this contribution we report a method for the synthesis of hybrid materials based on polysiloxanes and various metal oxides in which both components are tightly connected to each other. Alkoxysilane modified polysiloxanes were obtained by hydrosilation reactions between vinyl triethoxysilane and poly(dimethylsiloxane-co-methylhydrosiloxane) (PDMS-co-PMHS). The thus functionalized polymers were used in a sol-gel process applying Stöber conditions and hybrid nanoparticles were obtained. Following the same pathway, different metal alkoxides (M(OR)₄; M = Ti, Zr; R = ethyl, isopropyl) were coordinated to allyl acetoacetate (AAA) and the resulting complexes were applied in a hydrosilation reaction with PDMS-co-PMHS. Metal oxide hybrid nanoparticles were obtained through a sol–gel process.     

Chiral selectors based on C2-symmetric dicarboxylic acids

Bis-allylamides of rigid C₂-symmetric dicarboxylic acids, useful as precursors in the synthesis of liquid chromatographic chiral stationary phases via hydrosilylation reactions, have been prepared by two different approaches. One involved resolution of the dicarboxylic acid followed by reaction with allylamine via the acid chloride or by a carbodiimide-assisted condensation. The other route involved acetalization of N,N′-diallyl-l-tartardiamide (DATD) with aromatic aldehydes. Moreover, transformation of the enantiopure dicarboxylic acid used in the first route into the corresponding diamine permitted the synthesis of selectors possessing a reversed amide functionality. The enantiomer-discriminating properties of some of these selectors were studied by NMR.     

Synthesis and characterization of bis(methoxyl hydroxyl)-functionalized disiloxane and polysiloxane oligomers derivatives therefrom

With purpose to prepare waterborne polyurethane with improved performance, bis(methyoxyl hydroxyl)-functionalized polysiloxanes with different dimethylsiloxane segment length were prepared. The preparation includes three steps, the first is synthesis of 1,3-bis(glycidoxypropyl)tetramethyldisiloxane (compound I) via hydrosilylation of allylglycidyl ether with tetramethyldisiloxane, followed by a subsequent methoxylation of the resultant compound from the hydrosilylation to give 1,3-bis(3-(1-methoxy-2-hydroxypropoxy)propyl)tetramethyldisiloxane (compound II). Using this compound II and octamethylcyclotetrasiloxane (D₄), an equilibrium reaction was carried out to obtain the target Product III, i.e. bis(methoxyl hydroxyl)-functionalized polysiloxanes. The ratio of D₄/compound II was varied in order to prepare product III with different segment length consisting of dimethylsiloxane units. At each step, the outcome compounds were characterized through Infrared, ¹H NMR, ¹³C NMR as well as H-H and H-C Correlated Spectroscopy (COSY). The results showed that each step was successfully carried out and objective products were achieved. It was estimated that compound II was not exclusive in the methoxylation step. Characterizations of the compound II enabled us to give a reliable quantitative amount for the by-products for the first time. In addition, the molecular weights of the final product III with varying dimethylsiloxane length were estimated by hydroxyl group analysis, ¹H NMR and GPC, which showed a good agreement between the theoretical molecular weights and those from these tests.     

Amphiphilic sorbents based on polysiloxanes crosslinked by an N,N′‐heterocycle

New amphiphilic sorbents have been synthesized by crosslinking of the chloromethyl side‐functionalized polysiloxanes with piperazine. Three structures, differing by the crosslinking degree, have been synthesized as potential sensitive materials for humidity sensors able to work at high humidity or as metal sorbents. Correlations between structure and morphology of the polymeric matrix, as well as their swelling capacity in solvents with different polarities, are discussed. Copyright © 2006 John Wiley & Sons, Ltd.     

A versatile synthetic path to thiol containing polysiloxanes

A synthetic strategy to polydimethylsiloxanes and polymethylsiloxanes containing thiol functions as end‐ or side‐groups, respectively, is presented. Such polymers are important starting materials for elastomeric networks and postpolymerization modifications. The synthesis starts either with vinyl end‐functionalized polydimethylsiloxanes or with polymethylvinylsiloxanes. The vinyl groups are reacted either with thioacetic acid or with a thioacetic acid/butanethiol mixture via a UV‐initiated thiol‐ene reaction to form the respective thioester quantitatively within few minutes. The thioesters are subsequently deprotected to the respective thiols by reduction with LiAlH₄. The resulting thiol containing polysiloxanes can be used for the formation of networks or another functionalization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2940–2948     

Dicyanobiphenyl polysioloxane stationary phases for capillary column gas chromatography

Summary The chromatographic performance of newly developed dicyanobiphenyl polysiloxane stationary phases were evaluated and compared with the performance of other polar stationary phases, including the previously reported monocyanobiphenyl polysiloxanes. Due to the unique combination of polarizable biphenyl and polar cyano functionalities in the side chains of the flexible polysiloxane backbone, and by virtue of their mild liquid crystalline properties, the new stationary phases provide excellent resolution of a wide variety of analytes, both polar and nonpolar, in both GC and SFC. They can be easily coated and cross-linked in open tubular columns, and the resultant columns demonstrate excellent efficiency and performance at temperatures up to 280–300°C. The new stationary phases exhibit enhanced selectivities for various types of isomeric compounds.     

Synthesis of chiral carbosilane dendrimers with l-cysteine and N-acetyl-l-cysteine on their surface and their application as chiral selectors for enantiomer separation by capillary electrophoresis

The synthesis of chiral carbosilane dendrimers functionalized with cysteine and N-acetylcysteine groups is presented. These dendrimers were obtained through thiol–ene addition reactions and their application as chiral selectors in capillary electrophoresis was investigated. Four drugs used as model compounds were analyzed under different experimental conditions observing that the use of a first generation dendrimer containing 4 terminal N-acetyl-l-cysteine groups enabled the enantiomeric discrimination of razoxane with a discrimination power similar to that obtained with other powerful chiral selectors such as cyclodextrins.     

Synthesis of carbohydrate‐segmented polydimethylsiloxanes by hydrosilylation

Carbohydrate‐modified polysiloxanes have been presented several times within the last decade. In this work, a new route to carbohydrate‐segmented polysiloxanes is presented. A series of allyl‐group‐containing bifunctional carbohydrate derivatives was synthesized and reacted with hydrodimethylsilyl‐terminated polysiloxane in hydrosilylation reactions with Speier's catalyst. The carbohydrate monomers and the resulting materials were fully characterized with ¹H and ¹³C NMR spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3814–3822, 2005     

Propylamido-Modified C18 Reversed-Phase for High-Performance Liquid Chromatography

The synthesis and chromatographic properties of a propylamido-modified C18 stationary phase are described. The propylamido-modified C18 phase was prepared by bonding stearic acid to 3-aminopropyl-silica gel. The synthesis was simple and reproducible through amide formation by using N-hydroxysuccinimide and dicyclohexylcarbodiimide. This prepared stationary phase exhibited excellent abilities to separate polycyclic aromatic hydrocarbons (PAHs), polysiloxanes and phenols by HPLC. The chromatographic results show that both the C3 moiety and the amido-group in this phase contribute significantly to the HPLC separation process. The chromatographic behavior of the prepared phase and commercial C18 phases was also compared in analyses of PAHs and phenols. Although the commercial C18 phases have been extensively used, both the unique selectivity and the highly reproducible synthesis of our prepared phase make it an excellent complement to ordinary C18 phases.