Designing dual-domain thermoplastic elastomers from ABA triblock copolymers: introducing bond-exchangeable subdomains into B-block strands

Abstract

Here, we propose dual domain thermoplastic elastomers (TPEs) with bond exchangeable subdomains. A simple poly(styrene)-b-poly(butadiene)-b-poly(styrene) (SBS) triblock copolymer is chemically modified to attach pyridine groups in the middle block, followed by cross-linking via pyridine quaternization with diiodo molecules. In this design, the network structure comprises both main domains of glassy poly(styrene) blocks and subdomains of self-aggregated quaternized pyridines within the middle block matrix, according to the scattering data. The scattering measurement at high temperatures reveals that the presence of subdomains significantly enhances the thermal stability of the micro-phase separated network. This fact eventually results in a thermally stable rubbery plateau region in the temperature-ramp rheology even at temperatures higher than the glass transition temperature of poly(styrene). In addition, the formation of subdomains affects the tensile properties, especially the Young's modulus and the recovery ratio in cyclic load–unload tests. Since the quaternized pyridines in the subdomains enable trans-N-alkylation bond exchange at high temperatures, the stress relaxation and other useful functions of TPEs, such as reprocessability and recyclability, are exhibited. Thus, the present system can lead to a new methodology to create functionalized TPEs composed of triblock copolymers. We also discuss the important role of the fraction of quaternized pyridine units and the unique relaxation behaviors in these dual domain bond exchange materials.