PEO-based brush-type amphiphilic macro-RAFT agents and their assembled polyHIPE monolithic structures for applications in separation science

Aminreza Khodabandeh,Fotouh R Mansour,R Dario Arrua,Emily F Hilder,Stuart C Thickett

doi:10.1038/s41598-017-08423-x

Abstract

Polymerized High Internal Phase Emulsions (PolyHIPEs) were prepared using emulsion-templating, stabilized by an amphiphilic diblock copolymer prepared by reversible addition fragmentation chain transfer (RAFT) polymerization. The diblock copolymer consisted of a hydrophilic poly(ethylene glycol) methyl ether acrylate (PEO MA, average Mn 480) segment and a hydrophobic styrene segment, with a trithiocarbonate end-group. These diblock copolymers were the sole emulsifiers used in stabilizing “inverse” (oil-in-water) high internal phase emulsion templates, which upon polymerization resulted in a polyHIPE exhibiting a highly interconnected monolithic structure. The polyHIPEs were characterized by FTIR spectroscopy, BET surface area measurements, SEM, SEM-EDX, and TGA. These materials were subsequently investigated as stationary phase for high-performance liquid chromatography (HPLC) via in situ polymerization in a capillary format as a ‘column housing’. Initial separation assessments in reversed-phase (RP) and hydrophilic interaction liquid chromatographic (HILIC) modes have shown that these polyHIPEs are decorated with different microenvironments amongst the voids or domains of the monolithic structure. Chromatographic results suggested the existence of RP/HILIC mixed mode with promising performance for the separation of small molecules.

Highlights

Macroporous polymer materials with interconnected structures represent a useful class of polymers used in different fields including separation science in the last decades[1]
PolyHIPEs with a hydrophilic surface are able to be produced through several different methods: post-synthesis modification of hydrophobic polyHIPEs from water-in-oil (w/o) HIPEs26–28, the synthesis of inverse high internal phase emulsion (HIPE) (using an oil-in-water (o/w) template) in which the monomer is placed in aqueous phase[29,30,31,32], or the synthesis of bi-continuous hydrophobic polyHIPEs wherein a hydrophilic co-monomer is placed in the aqueous phase of an internal phase in w/o HIPEs33–36
Targeting a high hydrophilic-lipophilic balance (HLB) number (HLB ~16), amphiphilic macro-reversible addition fragmentation chain transfer (RAFT) agents were synthesized to investigate the effect of the length of the P(PEO MA) and P(Sty) of the macro-RAFT agent with regards to the stability of the inverse HIPE

Summary

Introduction

Macroporous polymer materials with interconnected structures represent a useful class of polymers used in different fields including separation science in the last decades[1]. A cellular monolithic structure, commonly with interconnected pores and an open cellular network is produced, referred to as a poly(HIPE)[2,3,4,5,6,7] These materials have been applied extensively to different applications[8] including membrane separator for batteries[9,10,11,12], electro-chemical sensors[13], tissue engineering[14,15,16,17], supported catalysis[18], water purification[19, 20], and separation science[21,22,23,24]. In our previous study[39], an amphiphilic copolymer (a “macro-RAFT agent”) was used as an anionic emulsifier in an inverse HIPE approach This method offers attractive possibilities for the development of special coatings of the resultant hydrophilic polyHIPE after the curing step while the RAFT-end group remained at the surface. We hypothesize that the PEO-based brush-type amphiphilic macro-RAFT agents with appropriate wettability will be adsorbed at the toluene–water interface, in a similar fashion as polymeric surfactant, and will provide stability against coalescence of the oil droplets, while the PEO block anchoring assists the attachment of these polymeric surfactants to the surface of the obtained polyHIPE upon polymerization (Fig. 1)

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Conclusion