Peter Krajnc

High Internal Phase Emulsion Templating – A Path To Hierarchically Porous Functional Polymers

Recently, a series of new monomers and polymerization mechanisms has been applied to the templating of high internal phase emulsions (HIPEs) providing a route to hierarchically porous materials with a range of functionalities and applications. The high degree of control over the pore size is another attractive feature of these materials. Usually, the continuous phase contains monomers, the droplet phase is used to template the large, primary pores, which are interconnected by secondary pores. The addition of nonpolymerizable components to the continuous phase can result in phase separation during polymerization and tertiary pores. Applications include polymer supports for catalysis and synthesis, separation and filtration, cell culture media, enzyme supports, and structural and isolation applications.

Ultra‐High Surface Area Functional Porous Polymers by Emulsion Templating and Hypercrosslinking: Efficient Nucleophilic Catalyst Supports

4-Dimethylaminopyridine (DMAP) is a highly efficient and important organocatalyst used for a variety of organic reactions, including the acylation and silylation of hindered alcohols, the Baylis–Hillman reaction and the ringopening polymerisation of lactide and other lactones. Heterogeneous versions supported on soluble and crosslinked polymers as well as inorganic nanoparticles have been described. Soluble catalysts and nanoparticles can show high activities but require extra isolation steps for catalyst recycling. On the other hand, catalysts supported on insoluble polymer beads, whilst being simple to recycle, tend to suffer from a drop in activity compared to the homogeneous catalyst. Furthermore, the performance of catalysts supported on gel-type polymer beads is limited by solvent-dependent access to the reactive sites inside the beads. The use of permanently porous (often referred to as macroporous ) polymer beads overcomes these solvent limitations, however reactions with these supports can be slow as mass transfer to the active sites on the internal surface of the porous bead occurs by diffusion only. The mass transport limitations of permanently porous beads can be overcome by using emulsion-templated porous polymers (polyHIPEs), which possess very large pores (1– 100 mm) permitting mass transfer by convection rather than diffusion. PolyHIPE materials are produced from high internal phase emulsions (HIPEs), where the dispersed phase occupies >74 % of the emulsion volume. PolyHIPEs have been prepared from either oil-in-water (o/w) or water-in-oil (w/o) emulsions and have been used in a flow through manner as scavengers, reagents, solid-phase synthesis supports and chromatography media. For polyHIPEs to function as a heterogeneous catalyst support, a high surface area is required. PolyHIPE materials with surface areas up to 690 m g 1 can be prepared by the addition of an organic porogen to the monomer phase together with careful choice of HIPE stabilising surfactant. However the resulting materials are rather weak mechanically. An alternative approach to introducing high surface areas is the hypercrosslinking method. Hypercrosslinked polymers contain a very high density of crosslinks together with molecular-sized pores (micropores), and exhibit important properties such as an ultra-high surface area (up to 2000 m g ) and the ability to sorb large amounts of both thermodynamically good and poor solvents, due to high matrix rigidity and a much reduced degree of chain entanglement. Hypercrosslinked polystyrene, in the form of beads, can be prepared by Lewis acid catalysed post polymerisation crosslinking of poly(4-vinylbenzyl chloride) (pVBC) (Scheme 1). High surface area polyHIPE materials for gas storage have recently been prepared by this method. Hypercrosslinked polyHIPE is a potentially attractive catalyst support material due to the combination in one material of an interconnected network of macropores, facilitating access of reagents to the surface, with an ultra-high surface area produced by the hypercrosslinking induced microporosity. Furthermore, hypercrosslinking VBC polyHIPEs to less than full conversion would leave residual chloromethyl functionality for the attachment of catalysts. In this work, we demonstrate proof of this concept; the hypercrosslinking of VBC polyHIPEs is controlled to leave unreacted benzyl chloride moieties with which to anchor DMAP, leading to a highly efficient, recyclable nucleophilic catalyst (Scheme 1). [a] J. Wall, Prof. N. R. Cameron Department of Chemistry and Biophysical Sciences Institute Durham University South Road, Durham, DH1 3LE (UK) Fax: (+44) 191-3844737 E-mail : n.r.cameron@durham.ac.uk [b] Dr. I. Pulko, Prof. P. Krajnc Faculty of Chemistry and Chemical Engineering University of Maribor Smetanova 17, 2000 Maribor (Slovenia) Fax: (+386)2-2527-774 E-mail : peter.krajnc@uni-mb.si [c] Dr. I. Pulko Polymer Technology College Pod gradom 4, 2380 Slovenj Gradec (Slovenia) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200903043.

Inherently reactive polyHIPE material from dicyclopentadiene

A simple formulation of a stable high internal phase emulsion of dicyclopentadiene which is cured by using properly selected ring opening metathesis polymerization initiators yields highly porous monolithic materials with paramount mechanical properties and the possibility of easy functionalisation.

Characterisation of grafted weak anion-exchange methacrylate monoliths

A weak ion-exchange grafted methacrylate monolith was prepared by grafting a methacrylate monolith with glycidyl methacrylate and subsequently modifying the epoxy groups with diethylamine. The thickness of the grafted layer was determined by measuring permeability and found to be approximately 90nm. The effects of different buffer solutions on the pressure drop were examined and indicated the influence of pH on the permeability of the grafted monolith. Protein separation and binding capacity (BC) were found to be flow-unaffected up to a linear velocity of 280cm/h. A comparison of the BC for the non-grafted and grafted monolith was performed using beta-lactoglobulin, bovine serum albumin (BSA), thyroglobulin, and plasmid DNA (pDNA). It was found that the grafted monolith exhibited 2- to 3.5-fold higher capacities (as compared to non-grafted monoliths) in all cases reaching values of 105, 80, 71, and 17mg/ml, respectively. It was determined that the maximum pDNA capacity was reached using 0.1M NaCl in the loading buffer. Recovery was comparable and no degradation of the supercoiled pDNA form was detected. Protein z-factors were equal for the non-grafted and grafted monolith indicating that the same number of binding sites are available although elution from the grafted monolith occurred at higher ionic strengths. The grafted monolith exhibited lower efficiency than the non-grafted ones. However, the baseline separation of pDNA from RNA and other impurities was achieved from a real sample.

Ring opening metathesis polymerisation of emulsion templated dicyclopentadiene giving open porous materials with excellent mechanical properties

Surfactant stabilized emulsions of dicyclopentadiene and 50%, 60%, 70% or 80% of water were cured using ring opening metathesis polymerisation. All formulations gave open porous architectures featuring excellent mechanical properties which change upon oxidation.

Emulsion templated open porous membranes for protein purification.

Approximately 25 cm×25 cm large sheets of crosslinked highly porous poly(glycidyl methacrylate-co-ethyleneglycol dimethacrylate-co-ethylhexyl methacrylate) membranes with an average thicknesses between 285 and 565 μm were prepared by casting a high internal phase emulsion (HIPE) containing monomers onto glass substrates and subsequent polymerisation. Open cellular porous polyHIPE type membranes were obtained with large pores (cavity) sizes between 3 and 10 μm while interconnecting pores were between 1 and 3 μm. The percentage of ethylhexyl acrylate and ethyleneglycol dimethacrylate influenced the flexibility and morphology of the resulting membranes. Porous membranes were chemically modified with diethylamine to yield functionalised supports for ion exchange chromatography. Cylindrical housings were used for positioning of the membranes and allowing flow of the mobile phase. Pulse experiments were used to study the flow characteristics and a homogeneous flow through the entire area of the membrane was found. Bovine serum albumin was purified by a 8 ml column containing functional membrane in modular shape; dynamic binding capacity was measured to be as high as 45 mg/ml.

On the mechanical properties of HIPE templated macroporous poly(dicyclopentadiene) prepared with low surfactant amounts

Reducing the surfactant amount below generally accepted values in polyHIPE chemistry allowed for distinctly improving the mechanical properties of ROMP derived HIPE templated poly(dicyclopentadiene) without compromising the open cellular structure of the scaffold rendering the preparation of a ductile polymer foam with 80% porosity and a Youngs modulus of 110 MPa possible.

Open cellular reactive porous membranes from high internal phase emulsions

High internal phase emulsions (HIPEs) incorporating styrene, 4-vinylbenzyl chloride, divinylbenzene and ethylhexyl acrylate were applied to prepare reactive, cross-linked porous membranes with open cellular architecture and thicknesses between 30 and 500 microm.

Hierarchically Porous Materials from Layer-by-Layer Photopolymerization of High Internal Phase Emulsions

A combination of high internal phase emulsion (HIPE) templating and additive manufacturing technology (AMT) is applied for creating hierarchical porosity within an acrylate and acrylate/thiol-based polymer network. The photopolymerizable formulation is optimized to produce emulsions with a volume fraction of droplet phase greater than 80 vol%. Kinetic stability of the emulsions is sufficient enough to withstand in-mold curing or computer-controlled layer-by-layer stereolithography without phase separation. By including macroscale cellular cavities within the build file, a level of controlled porosity is created simultaneous to the formation of the porous microstructure of the polyHIPE. The hybrid HIPE-AMT technique thus provides hierarchically porous materials with mechanical properties tailored by the addition of thiol chain transfer agent.

The Use of an Emulsion Templated Microcellular Poly(dicyclopentadiene-co-norbornene) Membrane as a Separator in Lithium-Ion Batteries

The preparation of open-cell macroporous membranes made by the ring opening metathesis polymerization (ROMP) of a mixture of norbornene and dicyclopentadiene, and their basic applicability as separators in lithium-ion batteries, is discussed. Cyclic voltammetry (CV) measurements of negative electrodes (graphite) and positive electrodes (LiCoO2 ) are performed and the results prove the absence of parasitic decomposition reactions within the membrane at high oxidative or reductive potentials. Furthermore, LiCoO2 /Li half cell cycling studies of 100 charging/discharging cycles reveal that the newly disclosed separator and conventional commercial polyolefin based separators have similar performance. These results demonstrate that a potential weakness in the newly disclosed separator, namely residual double bonds present in the polymer network, does not limit the use of this material as a separator in lithium-ion batteries.