Date of Award
Master of Science
Roberto S. Benson
Kevin Kit, Raymond Buchanan
The thermo-oxidative behavior of ether based fluorinated polyurethane elastomers was assessed. For achieving this goal, samples were exposed to high temperatures (118±3oC) for periods of up to eight weeks. The chemical structure changes were monitored through infrared spectroscopy and several other test methods such as mass retention, contact angle measurements and viscosity measurements. Thermo-gravimetric analysis was done for the unexposed samples, and the mechanical properties of these materials were monitored through a multi-frequency dynamic mechanical analyzer.
The polyurethanes supplied for this study are ether based polymers synthesized in a two step process where on the first step 4,4’-diphenyl methane diisocyanate (MDI) was coupled with polytetramethylene glycol (PTMG) or with polypropylene glycol (PPG) to form a pre-polymer. For the fluorinated polymers, this first step included a third component. This component is a perfluoro polyether diol (Mn=2000) and its proportion to the basic glycols defined the percentage of fluorination of the final polymer. On the second step, ethylene diamine (EDA) was used as a chain extender to generate polymers with molecular weight in the range of 130,000 (50% fluorinated) to MW 287,000 (0% fluorinated).
Results show that the presence of fluorinated groups changes the dynamics of the degradation process and it results in better thermo-oxidative resistance as well as better mechanical properties retention along the exposure times and poorer surface wettability, appreciable for most surface treatment applications. The fluorination of these polymers via substitutions of the polyglycol on the first step of polymerization accentuates some thermo-oxidative effects on the base polyurethanes, such as mass retention with exposure and yellowing, what could be attributed to smaller chain lengths of the fluorinated segments.
Tocchetto, Rogerio Silva, "Thermo-Oxidative Behavior of PTMG and PPG Based Polyurethane-Ureas With Varying Degree of Fluorination. " Master's Thesis, University of Tennessee, 2002.