Synthesis and Characterization of Proton Conducting, Fluorine-Containing Block Copolymers

Fuel cells are being investigated as environmental-friendly, highly efficient alternative power sources. Proton conducting membranes play a central role in proton exchange membrane fuel cells (PEMFCs), serving as both electrolyte and fuel separator. This thesis addresses the design, synthesis and characterization of novel fluorinecontaining block copolymers, and the preparation and investigation of sulfonated block copolymers as model proton exchange membranes (PEMs). Poly([vinylidene difluoride-co-hexafluoropropylenel-b-styrene), P[VDF-co- HFPI-b-PS, block copolymers have been prepared by a combination of chain transfer radical polymerization and atom transfer radical polymerization. The strategy of producing trichloromethyl-terminated vinylic polymers by chain transfer polymerization has proven useful for the synthesis of macroinitiators for subsequent preparation of novel fluorine-containing block copolymers. Another class of block copolymer, based on bisphenol A polysulfone and poly(viny1idene fluoride), (PSF-b-PVDF), has also been prepared by polycondensation of a,dihydroxy bisphenol A polysulfone precursors and a,dibromo polyvinylidene fluoride. Both families of block copolymers, (P[VDF-co- HFPI-b-PS) and (PSF-b-PVDF), were subsequently sulfonated and acidified to yield several series of model proton exchange membranes that were used to examine the effect of fluorous blocks on membrane morphology and proton conductivity. One of the key findings of this work is that the conductivity of block copolymer membranes is significantly higher than that of random copolymer membranes indicating that block structures facilitate proton conductivity. Additionally, the conductivity of partially sulfonated P[VDF-co-HFPI-b-PS block copolymer membranes is higher than that of non-fluorous block copolymer membranes. The fluoropolymer block segments induce formation of connected ion channels which results in enhanced proton transport.