Synthesis of well defined, linear-dendritic, end-functionalised poly N-vinyl pyrrolidone additives via reversible addition-fragmentation transfer polymerisation for use in polymer electrolyte membrane fuel cells

Abstract

An ongoing challenge in polymer science is the preparation of materials with specific surface properties that differ from the bulk, whilst retaining the advantageous mechanical properties of the bulk polymer. We have explored the use of multi-end functionalised polymer additives, which undergo rapid spontaneous adsorption to a surface or interface, as an efficient method of modifying surface properties. These materials are of potential use in tailoring the hydrophobicity of the gas diffusion layer (GDL) in a polymer electrolyte membrane fuel cell (PEMFC), and hence optimising fuel cell efficiency.
In this research, reversible addition-fragmentation transfer (RAFT) polymerisation has been used to synthesise a range of well-defined, low molecular weight, end-functionalised poly N-vinyl pyrrolidone (PVP) polymer additives bearing aryl-ether end groups containing up to three, low surface energy, C8F17 fluoroalkyl chains. Polymer end-functionality is introduced via the design of functionalised RAFT chain transfer agents (CTAs).
Three novel CTAs have been made in addition to their corresponding end-functionalised PVP additives, in a range of molecular weights. Thin films have been prepared comprised of polymer blends of unfunctionalised PVP and varying percentages of each end-functionalised PVP additive, and these films have been analysed by contact angle measurements, ion beam analysis and atomic force microscopy in order to investigate effects of additive concentration, additive molecular weight, matrix molecular weight, design of functional group and annealing. We have shown that modest amounts of additive (<2.5%) can render the surfaces of bulk PVP hydrophobic and lipophobic.