Synthesis and characterisation of tough and permeable macroporous polymers

Abstract

Emulsion templating using high internal phase emulsions is an effective route to prepare low density, high porosity macroporous polymers known as polyHIPEs (poly(high internal phase emulsion)). Conventional polyHIPEs, synthesised from surfactant stabilised w/o (water-in-oil) emulsions, have low permeabilities and poor mechanical properties. This thesis describes an investigation into developing and characterising one type of tough and permeable macroporous polymers via emulsion templating. Increasing the continuous phase volume from HIPEs (high internal phase emulsion) to MIPEs (medium internal phase emulsion) is an effective way to improve the mechanical properties of resulting macroporous polymers. The influence on morphology and physical properties of the resulting macroporous polymers caused by the usage of different initiators and surfactants in MIPEs was initially discussed to optimise the formulation of MIPEs based on styrene and divinylbenzene (DVB). The MIPEs based on styrene and DVB used azobis(isobutyronitrile) (AIBN) as initiator produced macroporous polymers possessing desired open porous interconnected pore structure no matter which surfactant (surfactant mixture) was used while potassium persulfate (KPS) and redox initiator system cannot produce open porous macroporous polymers from MIPEs consisting of styrene and DVB. Then tough and permeable low density polymers were developed, produced by polymerising the continuous phase of emulsion templates, which contained styrene, polyethyleneglycoldimethacrylate (PEGDMA) and silylated silica particles. PEGDMA and the silylated silica particles acted as crosslinker. The functionalised silica particles were incorporated into the polymer, which resulted in a significant improvement of the mechanical properties of the polyHIPEs without affecting the interconnected and permeable pore structures. The physical and mechanical properties of the tough and permeable macroporous polymers were characterised. Especially the mechanical properties, including shear properties and fracture toughness (mode II) were investigated using the Arcan fixture. Both the shear properties and fracture toughness (mode II) increased significantly with increasing the organic phase volume in emulsion templates and the further improvements can be obtained by the incorporation of silica filler in the emulsion templates. Finally, approaches to directly synthesise hydrophilic macroporous polymers based on styrene and DVB were presented since most of macroporous polymers produced from HIPEs are hydrophobic and need modification after polymerisation to improve the surface wettability. The incorporation of silylated silica particles in the emulsion templates improved the wettability of the resulting macroporous polymer but not the water uptake. The water uptake of macroporous polymers can be increased by the introduction of methacrylic acid (MA) and dimethylaminoethyl methacrylate (DMAEMA) into the aqueous phase of emulsion templates as additional monomers in order to synthesise hydrophilic polymer/polymer macroporous composites.