Sustainability through blockcopolymers: novel ion exchange cathode membranes and soybean oil based thermoplastic elastomers

Abstract

<p>This work studies the sustainable use of blockcopolymers (BCPs) in aims to reduce dependency in oil. This work focused on the design and development of new materials that can provide "green" substitutes to petroleum based products. Our two main areas of interest are: alternative power sources, more specifically polymer electrolyte fuel cells (PEFCs), and the synthesis of vegetable oil based thermoplastic elastomers. Research on PEFCs focused on developing a new cathode catalyst layer membrane comprised of a mesoporous block copolymeric nanocomposite that will satisfy (1) electrical conductivity, (2) proton conductivity, (3) oxygen transport in, (4) and water transport out via the self-assembly of BCPs. The proposed design is highly tunable in that many of the parameters (<em>e.g. </em> pore diameter, ionomer content) are independently adjustable. To attain this we made use of BCPs containing charged species, <em>e.g. </em> the sulfonic acid (SO^-₃) group, giving the membrane the ability to possess ion exchange (proton conductivity) capabilities. Furthermore we examined the thermodynamic behavior of diblock copolymers representing the binary pairs of the ternary system:</p> <p>poly(dimethylsiloxane)/poly(ethylene-<em>stat</em>propylene)/poly(styrene-<em>ran</em>-styrene sulfonic acid), D/E_P/S_S in lieu of understanding the interaction an be able to predict a desired molecular architecture. SWNTs were noncovalently attached, using a phase inversion method, to the BCPs to serve for electron conductivity.</p> <p>Lastly S_S/E_P/D triblock copolymers were synthesized to locate their different molecular architecture along the triphase diagram. We employ small angle x-ray scattering, electron microscopy, and rheology to characterize the order-to-disorder transition temperature T_ODT and lamellar period <em>d</em> of 28 materials with varying molecular weights and sulfonation extents.</p> <p>Research on thermoplastic elastomers focused on creating a replacement for the Styrene-Butadiene-Styrene (SBS) petroleum based BCP with the use of a vegetable oil, <em>e.g.</em> soybean oil (SBO). We present --for the first time-- two distinct controlled radical polymerization techniques of a vegetable oil. To date, moderate success has been achieved through the application of traditional cationic and free radical polymerization routes to vegetable oils to yield thermoset plastics. The success of the technology on vegetable oils such as soybean oil is surprising, as conventional radical polymerization typically brings the polymerization of triglycerides into thermoset materials, whereas our present research successfully</p> <p>controls the polymerization of triglyceride so that it terminates at a desired molecular weight and block composition and produces thermoplastic polysoybean oil. Different methods of synthesizing</p> <p>elastomeric block copolymers using acrylated epoxidized soybean oil (AESO) and styrene are discussed: <em>i.e.</em> Atom Transfer Radical Polymerization (ATRP) and Reversible Addition-Fragmentation chain Transfer (RAFT). Each technique was able to individually create diblock and triblock copolymers, resulting in polymers that are predominantly non-crosslinked linear or with lightly branched chains. These materials behave as elastomers/rubbers at room temperature but are susceptible to common processing techniques at elevated temperatures, making them suitable for a wide range of applications. Elastic properties of the final polymers outperformed the petroleum based Kraton®.</p>