Enhancing Mechanical Properties of Sustainable Thermoplastic Elastomers through Incorporating Ionic Interactions

The physical properties of an ABA triblock copolymer-based thermoplastic elastomer, containing a poly(lauryl methacrylate-co-methacrylic acid) midblock and poly(methyl methacrylate) endblocks, were enhanced through neutralization of the methacrylic acid (MAA) repeat units with NaOH to form ionic interactions in the midblock. Rheological properties of the midblock and mechanical properties of the triblock copolymer were investigated as functions of the acid (MAA) and ion content. Midblock relaxation times (τ) increased with increasing acid and ion content; however, the activation energy extracted from an Arrhenius analysis appeared constant for all acid and ion contents. Meanwhile, the factors of enhancement of the strain at break and tensile strength (as compared to the baseline polymer without ionic interactions or hydrogen bonding) collapsed onto master curves when plotted as functions of log τ, indicating that the mechanical behavior of the triblock copolymer could be tuned through varying the relaxation time of the midblock. The tensile strength increased by as much as a factor of 17 times greater than that of the baseline polymer. More moderate enhancements were observed in the strain at break, with the maximum strain at break occurring at intermediate relaxation times. This suggests that midblock chain dynamics are a governing factor for the mechanical property enhancements due to the effects of the ionic aggregates and chain mobility on stress dissipation under tensile deformation.