Physical and mechanical properties of phosphonium based poly(ionic liquids)

Currently for applications in materials science, there is a growing interest in Ionogels i.e. polymers with ionic liquids (ILs) integrated such that they retain their specific properties within the polymer/gel environment. However one disadvantage of ionogels is the leaching of the IL in the liquid phase1. To overcome this, ‘poly (ionic liquids) PILs, are gaining momentum in the literature. Interesting applications for the incorporation of PILs into polymers have been published such as ultrasensitive and selective chemiresistive CO2 sensors2, and potential applications in fuel cell technology as some reported PIL films, display very high ionic conductivities (exceeding 90 mS cm-1 at 100 oC and 75% relative humidity)3. However the range of possible monomeric IL structures is far greater than has so far been explored4 In recent years functional materials have been developed to respond to a wide variety of stimuli, but their use in practical macro-scale devices has been hindered by slow response times arising mainly due to the diffusion processes that typically govern polymer swelling/contraction. The scaling-down to microfluidic devices should improve response times, due to the improved surface-to-volume ratios of these actuators. At these dimensions, stimuli-responsive PIL materials could dramatically enhance the capabilities of micro-fluidic systems by allowing self-regulated flow control. In this study we synthesis, characterise and photopattern a family of PILs, Tributyl 4-Vinylbenzylphosphonium ([P4,4,4,4VB]+ ), Trihexyl 4-Vinylbenzylphosphonium ([P6,6,6,4VB]+) and Trihexyl-allyl phosphonium [P6,6,6,allyl]+ cations coupled with commonly found anions in the ionic liquid literature (chloride, dicyanamide and bis(trifluoromethylsulfonyl)imide). As one might expect varying the anion of the PIL gave varying behaviour (thermal stability and electrochemically). The resulting polymer gels from the PILs also gave drastic mechanical stability differences. Finally the synthesised polymer gels have been photo-structured to submicron resolution as both planar and 3D patterns employing both single and multi- photon polymerisation (MPP) techniques. These materials will form a platform for the next generation of sensors & actuators currently being developed