Date of Award

5-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Chemistry

Advisor

Smith, Jr, Dennis W

Committee Member

Creager , Stephen

Committee Member

DesMarteau , Darryl

Committee Member

Wagener , Earl

Abstract

Over the last decades Nafion¨ has emerged as the polymer of choice for the fabrication of Proton Exchange Membranes (PEM)s, due to its excellent proton conductivity and long-term stability. However, high temperatures and low relative humidity decrease fuel cell efficiency, due to the highly hydrated conditions required for proton conductivity. To overcome these issues, different types of sulfonated polymers have been proposed as promising substitutes for Nafion ¨, these include; Poly(arylene ether sulfones) (PAES) and Perfluorocyclobutyl (PFCB) aryl ether polymers among others.
Chapter 2 of this thesis describes the synthesis of a new class of sulfonated PAESs containing the perfluorocyclobutyl (PFCB) unit. These polymers have been prepared by the polycondensation of a unique bis-phenol (Bisphenol -T) with dichlorodiphenylsulfone (DCDPS) and sulfonated dichlorodiphenylsulfone (SDCDPS) under nucleophilic substitution conditions. Three different molar ratios of Bisphenol -T: DCDPS: SDCDPS were used: 1:1:0, 1:0:1 and 1:0.68:0.32, (P1, P2 and P3, respectively). The degree of incorporation of the sulfonated repeat unit into the copolymers was determined by 1H NMR. The resulting polymers show solubility in polar organic solvents such as DMAc and DMSO. The incorporation of SDCDPS into the backbone of the polymer decreased the mechanical strength of the membranes. Solution casting of the unsulfonated polymer P1 yielded tough, flexible films with a glass transition temperature of 138 oC. and catastrophic weight loss in N2 at 350-450 oC. Sulfonation of polymers P2 and P3 resulted in lower molecular weight brittle films and lower stability and mechanical properties. Chapter 3 describes the incorporation of zirconia into PFCB aryl ether polymers. The complex surface of zirconia aerogel was modified by complexation with p-trifluorovinyloxy phenyl phosphoric acid. PFCB polymers with different Ionic Exchange Capacity values were obtained by sulfonation with ClSO3H (P4, P5, P6). Sulfonated PFCB polymers showed a reproducible increase in the Ionic Exchange Capacity (IEC) after the addition of 10 wt % modified zirconia, whereas unmodified zirconia resulted in lower IEC membranes. Polymers P4 and P5 improved their thermo-oxidative stability. The use of modified zirconia proved to be a simple yet valuable tool towards the fabrication of more efficient PEMs.

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