ISSN 1560�0904, Polymer Science, Ser. B, 2011, Vol. 53, Nos. 7–8, pp. 431–434. © Pleiades Publishing, Ltd., 2011.

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1 INTRODUCTION

Organic polymeric monolithic column, recognizedas a new generation of stationary phases, has been afield of extensive research in recent years [1, 2]. It hasbeen used in numerous fields, including pharmaceuti�cal [3], environmental [4], and especially proteomicand genomic applications [5–9].

Compared to traditional stationary phases, whichconsist of packed particles, the monolithic columnshows significantly greater chromatographic efficien�cy, especially in separating bio�macromolecules suchas proteins, peptides, nucleotides, and oligonucle�otides [10–12]. It is mainly resulted from its appropri�ate pore structure which has a pronounced effect oncolumn performance. Because there are no interpar�ticulate voids in the monolith, all the mobile phaseflowing through the separation medium and the vol�ume availability of the column are thus significantlyimproved. Larger throughpores in the beds allow fasterseparations under lower backpressure, which permitsrapid separations on relatively longer columns. In ad�dition, the unique pore structure produces convectivemass transfer between the stationary phase and ana�lytes, thus alleviating the restricted mass transfer and

1 The article is published in the original.

reducing significantly the band broadening. Hence themonolithic column has been investigated as a possibletool for reducing separation time in reversed phaseHPLC without significantly sacrificing efficiency orresolution. Besides, the avoidance of particle packingand retaining frit fabrication during the preparationprocess makes column preparation a straightforwardprocess and thus ensures higher reproducibility.

To date, poly(styrene�co�divinylbenzene) (PSt�DVB)based monolith is regarded as one of the most impor�tant kinds of organic polymer monoliths. In additionto the common advantages described above, the com�pelling merits of the monolith lie in its adequate me�chanical robustness and stability under high pressureand in strong acidic/basic conditions [7, 8], and itstolerable swelling in the organic mobile phases mostcommonly used. Therefore, research on PSt�DVB�based monoliths is mainly focused on preparation. In1999, Horvath, together with his coworkers, preparedporous�layer open�tubular columns or monolithiccolumns by in situ polymerization of vinylbenzyl chlo�ride and divinylbenzene (DVB) in the presence of asuitable porogen [13, 14]. Macroporous PSt�DVBmonolithic columns were prepared in fused silica cap�illaries of 100 µm id by in�situ copolymerization of

Synthesis of Monolithic Columns Based

on Poly(styrene�co�divinylbenzene)

with the Capillary�like Flow�through Pore Diameter

by Template Method1

Yuan Yuan and Xin�Cai Xiao

School of Pharmacy, South�Central University for Nationalities, Wuhan, 430074, Chinae�mail: xcxiao71@yahoo.com.cn

Received June 7, 2010; Revised Manuscript Received February 1, 2011

Abstract—Poly(styrene�co�divinylbenzene) (PSt�DVB) is one of the most important kinds of organic poly�meric monolithic columns. In order to improve its efficiency, it is necessary that the column has regularmicrostructure. In this research, hollow and ordered PSt�DVB columns were successfully prepared throughradical polymerization using crystal structure of dimethyl sulfoxide as template. Different initiation types,times and storing temperatures were mainly investigated. The results showed PSt�DVB prepared at a temper�ature lower than the melting point of DMSO had regular and oriented structure. And longer initiating timeand higher storing temperature helped polymer forming.

DOI: 10.1134/S1560090411070086

INVESTIGATIONPROCEDURES

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styrene with divinylbenzene in the presence of pro�pan�1�ol and formamide as the porogen system [15].

An efficient way to form porous structures is to usecrystals of a frozen solvent as the porogen to avoid in�troducing new chemicals in the system. This cryopoly�merization technique is based on the formation of apolymeric structure in a frozen system in which sol�vent crystals act as the porogen. When the solvent isfrozen, the dissolved substances containing monomersand initiators are expelled from the growing ice crys�tals [16] and concentrated in small unfrozen regions,so�called “liquid microphase” [17]. As the volume ofthe unfrozen liquid microphase is much less than thatof the solid phase, the local monomer concentration ismuch higher than that in the initial reaction mixture,which is known as cryoconcentration [18]. The poly�merization proceeds in the cryoconcentrated unfro�zen liquid phase surrounding the ice crystals; thus, adense polymer is formed around these crystals. Whenthe system is defrosted, the ice crystals melt and amacroporous interconnected network, complementa�ry to the ice crystals, is formed.

In some applications, however, a mode with capil�lary�like flow�through pore diameter is preferred. Un�fortunately, until very recently, little attention has beenpaid to this type. In this study, a PSt�DVB�based col�umn with regular and oriented structure was preparedin one step for the first time by introducing the cryopo�lymerization technique, which provides a new ideaand opens a new road for systematic study of large�scale production of hollow and ordered polystyrene.

EXPERIMENTAL

Materials

The styrene (St), divinylbenzene (DVB) were pur�chased from Tianjin Guangfu Fine Chemical Institute(Tianjin, China) and used after washed with 10% w/vaqueous sodium hydroxide to remove the inhibitorsbefore use. The initiator ammonium persulfate (APS),the accelerator N,N,N',N'�tetramethylethylene di�amine (TEMED), the cross�linker N,N'�methyleneb�

isacrylamide (MBA), sodium hydroxide, dimethylsulfoxide (DMSO) and acetone were of analyticalgrade and used as supplied by Shanghai Chemical Co.(Shanghai, China) without any further purification.Double�distilled water was used in all the synthesisprocesses.

Optimum Polymerization

PSt�DVB were prepared by free radical polymer�ization in DMSO and a typical preparation processwas involved: monomer styrene (St, 1 ml), crosslinkerdivinyl�benzene (0.5 ml) and initiator ammoniumpersulfate (APS, 10 mg) were dissolved in DMSO atroom temperature (22°C) in a glass tube of 10 mm ininternal diameter. Subsequently polymerization initi�ated by adding 100 µl TEMED or heating at 70°C for5 or 6 h, and the reaction glass bottles were sealed andplaced at 0°C or –20°C to carry out the copolymer�ization reaction for at least 72 h. Experimental param�eters are listed in the table.

After polymerization, the prepared polymer wasseparated from the glass tube. Washed five times withacetone, adsorbed DMSO and unreacted compoundswere then removed from the surface of the system. Af�ter drying in vacuo at room temperature, the finalproduct was obtained.

Characterization of the Samples

Morphology is a critical factor in analyzing the fi�nal result. In this research, the polymers were cut intopieces in both the cross section and the vertical sectionfor further studies after drying in vacuo at room tem�perature. The microstructures of these dried polymerswere studied by an anatomical lens. The morphologiesof PSt�DVB and the crystal structures under differenttemperatures were observed by digital camera (CanonIXY DIGITAL 40, Japan).

Conversion is another factor. It is commonly ex�pressed as the weight percentage of the dried productformed from the monomer.

RESULTS AND DISCUSSION

Selection of the Template

Some solvents such as DMSO and water becomeglacial when the environmental temperature is lowerthan their melting points. When these solvents areused as polymerization template, polymer will formamong the icicles. After the solvents melt, the finalpolymer with regularly oriented micromatrix will beobtained. Because the solubility of a solute usually de�creases when the temperature decreases, it is necessaryto choose a suitable solvent for polymerization in ex�periment in order to establish a reaction system whichcan not only guarantee the formation of different crys�

Experimental parameters for preparation of PSt�DVB

Number Initiation Initiating time, h

Storing tem�perature, °C

Conver�sion, %

1 redox 0 0 49.00

2 heat 5 0 55.32

3 heat 6 0 78.50

4 heat 6 –20 22.73

5 heat 1 –20 0

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SYNTHESIS OF MONOLITHIC COLUMNS BASED 433

tal structures, but also dissolve as much solute as pos�sible under the circumstance. Because monomer Stand crosslinker DVB are not dissoluble in water andthe melting point of DMSO is 18°C, DMSO was cho�sen as template in this project.

Preparation of the Columns

In order to explore the preparation of polymer, re�agent initiating, heat initiating and different initiatingtimes were adopted. The results are shown in Fig. 1and the table. Sample 1 is the polymer obtained by re�dox initiating and storing immediately at 0°C, andothers are the ones obtained by heat initiating in dif�ferent durations and storing at 0°C or –20°C. In Fig. 1,all tubes show crystal structure and present bulk poly�mers except sample 5. In theory, sample 5 should havefragments of polymer instead of bulk polymers be�cause the speed of polymerization often becomes slowand even stops when the polymerizing temperatureand the initiating time are low. The conversions inthe table display the yield, compared with those insamples 2 and 3, increases with initiating time and ini�tiating temperature increasing, and it, compared withthose in samples 3 and 4, decreases with storing tem�

perature decreasing. Compared with samples 4 and 5,the table also demonstrates that the yield can be in�creased by prolonging initiating time. And a compari�son between the dynamics of yields because of the freeradical resulting from redox and heat cleavage will beinvestigated in a further research.

As mentioned above, polymer will form among theicicles below melting point. After the melting ofDMSO at room temperature, many pores would beformed in the spaces that were originally occupied bysolvent crystals. Figure 2 shows the images of sample 1in cross section (a) and vertical section respectively, inan anatomical lens. In Fig. 2a, series of light�spotsforming can be seen by the lamp traversing through thepores of the sample. In fact, these pores are somegrooves with very regular and oriented having the samedirection, which is testified by Fig. 2b, which demon�strates that the samples have porous and regular mi�crostructure.

ACKNOWLEDGMENTS

This work was financially supported by NaturalScience Foundation of Hubei Province(No. 2009CDB161).

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0°C, 0 h

[1]

0°C, 5 h

[2]

0°C, 6 h

[3]

−20°C, 6 h

[4]

−20°C, 1 h

[5]

Fig. 1. Photographs of samples prepared in DMSO at different initiation types, time and storing temperature. The sample numberis defined in the table.

2 mm(a) 2 mm(b)

Pore

Fig. 2. Images of sample 1 of (a) cross section and (b) ver�tical section (scale bar = 2 mm).

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