Thermoplastic elastomers (TPEs) are widely used in electronics, clothing, adhesives and other applications 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. However, commercial TPEs are derived from petroleum and thus contribute towards negative environmental impacts due to their manufacturing and disposal. This lack of sustainability strongly motivates the development of TPEs from sustainable sources. Vegetable oils and their fatty acid derivatives are attractive alternatives due to their abundancy and low cost. Our group has previously reported using sustainable polyacrylates derived from fatty acids for TPEs, however, polymers with bulky constituents, like 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 with poly(n-alkyl acrylate) midblocks with varying alkyl chain length n: poly(lauryl acrylate) (n=12), and poly(n-butyl acrylate) (n=4), were synthesized. A comonomer of either methacrylic acid or acrylic acid was used to incorporate ionic interactions in the midblock after sodium neutralization. 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 for n=12 samples. 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.

Structure-property relationships in ion-containing sustainable thermoplastic elastomers

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