Abstract
The future availability of synthetic polymers is compromised due to the continuous depletion of fossil reserves; thus, the quest for sustainable and eco-friendly specialty polymers is of the utmost importance to ensure our lifestyle. In this regard, this study reports on the use of oleic acid as a renewable source to develop new ionomers intended for proton exchange membranes. Firstly, the cross-metathesis of oleic acid was conducted to yield a renewable and unsaturated long-chain aliphatic dicarboxylic acid, which was further subjected to polycondensation reactions with two aromatic diamines, 4,4′-(hexafluoroisopropylidene)bis(p-phenyleneoxy)dianiline and 4,4′-diamino-2,2′-stilbenedisulfonic acid, as comonomers for the synthesis of a series of partially renewable aromatic-aliphatic polyamides with an increasing degree of sulfonation (DS). The polymer chemical structures were confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (1H, 13C, and 19F NMR) spectroscopy, which revealed that the DS was effectively tailored by adjusting the feed molar ratio of the diamines. Next, we performed a study involving the ion exchange capacity, the water uptake, and the proton conductivity in membranes prepared from these partially renewable long-chain polyamides, along with a thorough characterization of the thermomechanical and physical properties. The highest value of the proton conductivity determined by electrochemical impedance spectroscopy (EIS) was found to be 1.55 mS cm−1 at 30 °C after activation of the polymer membrane.
Highlights
Sustainable development is commonly defined as the growth and satisfaction of current needs without compromising the scope of subsequent generations to meet their own needs [1,2,3]
The chemical structure of the renewable and unsaturated long-chain aliphatic monomer was successfully confirmed by Fourier transform infrared (FTIR) and NMR, which were in agreement with previously reported data [29]
The dicarboxylic acid (DA) monomer is considered as fully renewable because it is obtained from a raw material that is not exhausted at its source and that can be generated again naturally over time at a speed higher than that of its consumption
Summary
Sustainable development is commonly defined as the growth and satisfaction of current needs without compromising the scope of subsequent generations to meet their own needs [1,2,3]. The hydrophilic–hydrophobic behavior of a polyionic material aimed as a proton exchange membrane (PEM) for fuel cell applications could be subject to a more sustainable approach by incorporating long-chain aliphatic segments derived from natural compounds into the polymer structure In this sense, it is known that the use of long-chain aliphatic dicarboxylic acids provides characteristics such as hydrophobicity, ductility, and high impact strength to the polymer backbones [27]. These novel oleic acid-based ionomers are aimed as a sustainable alternative to specialty synthetic polymers commonly employed as PEM and whose future availability is compromised due to the continuous depletion of fossil reserves To accomplish this goal, we first conducted the cross-metathesis of oleic acid to yield a renewable and unsaturated long-chain aliphatic dicarboxylic acid. This research represents an important basic scientific contribution to the green chemistry field and alternative energies as well, since it provides a more sustainable route to obtain specialty polymeric products that are used to satisfy the energy requirements of our society
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