Sustainable Thermoplastic Elastomers with Ionic Interactions

Thermoplastic elastomers (TPEs) are ABA triblock copolymers, in which A represents glassy end-blocks and B a rubbery midblock. Commercial TPEs are derived from petroleum whose manufacturing and disposal have undesired environmental impacts, motivating the development of TPEs from sustainable sources. However, polymers with bulky constituents, such as the long alkyl side-chains of vegetable oil-derived polymers, exhibit poor mechanical performance due to lack of entanglements in the rubbery matrix. Transient networks were incorporated into the midblock through either hydrogen bonding or ionic interactions to improve mechanical performance. ABA triblock copolymers were synthesized with poly(n-butyl acrylate–co–acrylic acid) or poly(lauryl methacrylate–co–methacrylic acid) copolymer midblocks and poly(methyl methacrylate) endblocks. 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, it was seen that when all acid sites were participating in ionic interactions, there was strong deviation in enhancement from master curve. This implies crucial role of free acid sites in stress relaxation mechanism in ion containing midblocks.