Preparation and characterisation of poly(high internal phase emulsion) methacrylate monoliths and their application as separation media

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Abstract

Poly(glycidyl methacrylate-co-ethyleneglycol dimethacrylate) monolithic supports were prepared by radical polymerisation of the continuous phase of water in oil high internal phase emulsions. Morphology of monolithic materials was studied by scanning electron microscopy and mercury intrusion porosimetry. The ratio of phase volume and the degree of crosslinking influenced the void size and pore size distribution of resulting polymers. Void sizes between 1 and 10 μm were observed and average pore sizes around 100 nm. Polymers with 60, 75, 80 and 90% pore volume were prepared and even samples with highest pore volume showed good mechanical stability. They were modified to bear weak-anion exchange groups and tested on the separation of standard protein mixture containing myoglobin, conalbumine and trypsin inhibitor. Good separation was obtained in a very short time similar to the separation obtained by commercial methacrylate monoliths. However, higher dispersion was observed. Bovine serum albumin dynamic binding capacity for monolith with 90% porosity was close to 9 mg/ml.

Introduction

Monolithic chromatographic supports are nowadays used in many different areas, from microchips up to preparative purifications [1]. The main reason is their advantageous features over conventional particle shaped chromatographic supports. Columns filled with bead shaped particles suffer from channeling of the solution and therefore the efficiency of the support can be reduced [2]. This is not the case with the monoliths since they consist of a single block of highly porous material. Besides, convection based transport and very high dynamic porosity are two of the most outstanding properties. Monolithic supports can be prepared by different methods and with various chemistries [1]. Silica based monolithic columns exhibit the highest porosity, over 80%, and are mainly used for RP separation and purification of smaller molecules [3]. On the other hand, methacrylate based monoliths, were applied in a variety of shapes and separation modes for the purification of large molecules like proteins, polynucleotides or even viruses [4]. Usual way of preparing methacrylate monoliths is via bulk polymerisation in the presence of porogenic solvents. In such a manner materials with porosities up to 65% are prepared. Beyond this value, their mechanical stability becomes poor.

An alternative method for the preparation of highly porous monolithic polymer material is polymerisation of the continuous phase of a high internal phase emulsion (HIPE).1 Typically, the yielding polymer has an open cellular structure with interconnects, which is the result of the internal phase being trapped inside the continuous phase during the polymerisation. After the extraction of internal phase, the porous structure remains. Such monolithic polymers, termed PolyHIPE [6] were initially prepared as styrene/divinylbenzene copolymers and applied as precursors for reactive species [7], as biocatalysts supports [8] and as supports for filtration [9]. With the addition of 4-vinylbenzyl chloride as a monomer, a reactive PolyHIPE monolith was produced, functionalized and utilized as a scavenger in a flow through mode [10]. The porosity of such a material can be further enhanced by adding a porogenic solvent to the continuous phase and monoliths with surface area up to 700 m2/g were prepared in such manner [11].

Open cellular structure of PolyHIPE monolithic materials suggests the possible applications of such monoliths as a separation media. We were therefore intrigued by the possibility of preparing glycidyl methacrylate based PolyHIPE monoliths. Despite the fact that methacrylates posses very attractive chemistry for chromatographic supports, due to their high mechanical and chemical stability, we have found no reports of such a material, while the preparation of poly(glycidyl methacrylate) grafted PolyHIPE material was recently published [12].

In this work, the preparation of poly(glycidyl methacrylate–co-ethyleneglycol dimethacrylate) PolyHIPE monolithic material, its characterization and the application as a chromatographic support for protein separation are described.

Section snippets

Chemicals

Glycidyl methacrylate (GMA; Aldrich, Steinheim, Germany) and ethylene glycol dimethacrylate (EGDMA; Aldrich) were washed with 5% NaOHaq to remove the inhibitors. Potassium persulfate (Fluka), calcium chloride hexahydrate (Merck, Darmstadt, Germany), the surfactant Synperonic PEL 121 (ICI Chemical, London, UK) and diethylamine (DEA; Fluka, Buchs, Switzerland) were used as received.

Polymerisation of GMA/EGDMA PolyHIPE

Organic phase, consisting of 14.51 g of GMA, 6.76 g of EGDMA and 4.28 g of synperonic PEL 121 was placed in a three

Results and discussion

While preparation of monolithic polymers via bulk polymerisation requires use of porogenic solvents to achieve permanent porosity, emulsions offer another way of porosity templation. However, emulsions are thermodynamically unstable systems and the addition of a surfactant is necessary for an emulsion to survive heating needed for the initiation of polymerisation. Most PolyHIPE materials so far have been prepared from hydrophobic monomers and a surfactant with an a hydrophilicity–lipophilicity

Conclusions

Emulsion polymerisation of glycidyl methacrylate showed good prospects as an alternative method for preparing highly porous monolithic supports for separation. Good mechanical properties of polymers with porosity as high as 90% is an important feature in the view of applications of porous monoliths, while epoxy groups in the polymer matrix offer possibilities of chemical modifications. Further experiments regarding the use of novel polymer supports as separation media but also as supports for

Acknowledgement

Support of this research through a project L2-5219 of the Ministry of Education, Science and Sport, and Ministry of Economy, Republic of Slovenia is gratefully acknowledged. We wish to thank Neil R. Cameron for valuable discussion and Jana Vidič for technical assistance.

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