Thermoplastic elastomers (TPEs) are widely used in electronics, clothing, adhesives and automotive components due to their high processability and flexibility. ABA triblock copolymers, in which A represents glassy endblocks and B the rubbery midblock, are commercially available TPEs. The most commonly used triblock copolymer TPEs contain glassy polystyrene endblocks and rubbery polydiene midblocks. However, commercial TPEs are derived from petroleum. The manufacturing and disposal of petroleum-derived products have undesired environmental impacts, which promotes development of TPEs from sustainable sources. Vegetable oils and their fatty acid derivatives are attractive alternatives to petroleum due to their abundancy and low cost. Our group has previously reported replacing polydienes in commercial TPEs with sustainable polyacrylates derived from fatty acids. However, polymers with bulky constituents, such as the long alkyl side-chains of fatty acid-derived polymers, typically exhibit poor mechanical performance due to lack of entanglements in the rubbery matrix. To improve mechanical performance, a transient network was incorporated into the fatty-acid derived midblock through incorporation of ionic interactions. ABA triblock copolymers were synthesized with poly(lauryl methacrylate–<i>co</i>–methacrylic acid) copolymer midblocks (with alkyl chain length n = 12) and poly(methyl methacrylate) endblocks, in which the acid was neutralized with sodium to induce ionic interactions. Enhancement of tensile strength and strain at break in these systems with varying acid and ion content showed a collapse onto a master curve when plotted vs. relaxation time of the rubbery midblock. However, when all acid sites were neutralized, there was a strong deviation from the master curve. This implies a crucial role of free acid sites in the stress relaxation mechanism in ion containing triblock copolymers.

Sustainable thermoplastic elastomers with ionic interactions

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ACS Fall 2022

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