Azo compounds for free radical crosslinking of polysiloxane stationary phases

SummaryThe preparation of wide bore (320 pm) and narrow bore (50 pm) fused silica capillary columns is described for immobilized cyanopropyl substituted silicones containing 60 and 88% substitution. The effect of high temperature deactivation with cyanopropylcyclosiloxanes was studied with a special test mixture. Curing was achieved with dicumyl peroxide or azo-tenbutane.The columns were evaluated and compared in terms of efficiency, activity, polarity, and temperature stability. Different coating methods were compared for the narrow bore columns. The activity of the 60% cyanopropyl columns that had been immobilized with dicumyl peroxide was significantly larger than for azo-ten-butane immobilized columns. The polarity of polar columns appeared to depend greatly on column temperature and is completely different for wide and narrow bore columns.

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“…The phase was cured at 22OOC for 1 h as described by Richter et a/. [13], after heating from room temperature with a programming rate of 4Olmin.…”

Section: Crosslinking Methodsmentioning

confidence: 99%

“…-Filling of columns (13,14). The column was pushed through the septum via the inner side of the syringe needle provided with the column to a certain depth above the coating solution (cf.…”

Section: Coating Proceduresmentioning

confidence: 99%

Preparation, evaluation, and comparison of wide bore (320 μm) and narrow bore (50 μm) cyanosilicone‐coated capillary columns for gas chromatography

Aerts

Rijks

Bemgård

et al. 1986

J. High Resol. Chromatogr.

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“…40 The stationary phases were cross-linked with dicumyl peroxide. 41 Both columns were conditioned at 300°C overnight under a nitrogen flow until a stable baseline was obtained at the maximum sensitivity of the instrument.…”

Section: Gc Column Fabrication and Testingmentioning

confidence: 99%

Synthesis of High Temperature Mesomorphic Polysiloxanes and Their Use as Stationary Phases for High Resolution Gas Chromatography

Lin

Hsu

1993

Polym J

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ABSTRACT:Two new liquid crystalline polysiloxanes with very wide mesomorphic temperature range have been prepared. One containing 4-[(S)-2-methyl-l-butoxy]phenyl 4-hexanyloxybiphenyl-4'-carboxylate side groups displays enantiotropic smectic A, chiral smectic C and smectic B phases. The other containing (S)-2-methyl-l-butyl 6-(4-undecanyloxybiphenyl-4'-carbonyloxy)-2-naphthalenecarboxylate side groups exhibits only an enantiotropic cholesteric phase. Both mesomorphic polysiloxanes were used as stationary phases in gas chromatography capillary columns. They show very unique separating properties for various isomeric halogenated naphthalene compounds, methylanthracene compounds, fatty acid methyl esters and polycyclic aromatic compounds.KEY WORDS Liquid Crystalline Polymers / Mesomorphic Polysiloxanes / Gas Chromatography / Liquid Crystal Stationary Phases / Thermotropic side-chain liquid crystalline polysiloxanes were first synthesized by Finkelmann and Rehage. 1 Since then, nematic, smectic and cholesteric liquid crystalline polymers, and elastomeric liquid crystalline networks containing polysiloxane backbone 2 -11 have been synthesized. Some of the synthetic works summarized above has been already reviewed. 12 -15 Interest in the polysiloxane backbone for the preparation of side-chain liquid crystalline polymers (LCPs), comes from the low glass transition temperature and high thermostability exhibited by this class of polymers.Recently, high temperature mesomorphic polysiloxane "solvents" have demonstrated excellent potential as stationary phases in gas chromatography (GC) because of their superior properties with regard to chromatographic efficiency and thermal stability. 16 -29 The use * To whom all correspondences should be addressed.of liquid crystals as stationary phase in GC was first reported by Kelker in 1963. 30 · 31 This field has been extensively reviewed. 32 -34 Unlike conventional stationary phases that provide separation based on solute vapor pressure and/or different solubility arising from specific energetic interactions, liquid crystal stationary phase yield separation based upon differences in solute molecular shape. Although the properties exhibited by many monomeric liquid crystals are good from the point of view of GC requirements, polymeric liquid crystals are attracting growing attention because they offer significant improvements in column efficiency as well as thermal stability over monomeric liquid crystals.In this work, the synthesis of a new chiral smectic and a new cholesteric liquid crystalline polysiloxanes which can be used as GC stationary phase over a wide temperature 153

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“…Immobilization of the stationary phase is generally achieved by bonding the polymer chain to the support. This immobilization process is initiated by free radicals which are produced by heat [1][2][3][4][5] , chemical initiators such as azocompounds [6][7][8] , peroxides [9][10][11][12][13] or ozone 14,15 , and ionizing radiation such as electrons 16 , gamma radiation 17,18 and low-temperature plasmas 19 . All these methods have been successfully applied to produce immobilized nonpolar silicone phases within capillary columns.…”

Section: Introductionmentioning

confidence: 99%

Preparation of thermostable poly(ethylene glycol) using thermal treatment in sealed system

Cardoso¹,

Copetti²,

Schwerz³

et al. 2000

J. Braz. Chem. Soc.

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O trabalho descreve um método rápido para a preparação de Carbowax 20M imobilizada sobre suporte, através do uso de tratamento térmico em forno convencional. O processo de extração com solventes remove a fase estacionária não imobilizada de poli(etileno glicol) (PEG) do suporte e a diferença de massa antes e após a extração fornece o percentual extraído e, consequentemente, o percentual total imobilizado. O tratamento térmico a 250 °C por 10 horas mostrou que a imobilização reduziu a atividade do material e aumentou o número de pratos (N) e a resolução (Rs), enquanto o fator de retenção (k) reduziu. Desta forma, a separação na coluna com material tratado é mais rápida e mais eficiente. A rapid method is described for preparation of support -bonded Carbowax 20M columns packing using a conventional furnace to heat the packing. Solvent extraction of the stationary phase removes the non-immobilized poly(ethylene glycol) (PEG) from the support and the difference between final and initial weight provides the total percent extracted and, consequently, the total percent immobilized. Treatment of the packing material at 250 °C for 10 h. reveals that the immobilization reduces the material activity and increases the plates number (N) and resolution (Rs) while the retention factor (k) is decreased. Thus, separations with this treated column are faster and display higher efficiency.

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Azo compounds for free radical crosslinking of polysiloxane stationary phases

Cited by 79 publications

References 18 publications

Preparation, evaluation, and comparison of wide bore (320 μm) and narrow bore (50 μm) cyanosilicone‐coated capillary columns for gas chromatography

Preparation, evaluation, and comparison of wide bore (320 μm) and narrow bore (50 μm) cyanosilicone‐coated capillary columns for gas chromatography

Synthesis of High Temperature Mesomorphic Polysiloxanes and Their Use as Stationary Phases for High Resolution Gas Chromatography

Preparation of thermostable poly(ethylene glycol) using thermal treatment in sealed system

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