Interphase synergistic effects of dynamic bonds in multiphase thermoplastic elastomers

Abstract

Enhancing the mechanical reliability of thermoplastic elastomers (TPEs) is a key issue for their application as a structural material. Here we systematically investigated the effects of dynamic bonds on the mechanical properties of ABA triblock copolymer-type TPEs. We prepared a series of TPEs having strong hydrogen-bonding side groups, ureidopyrimidinone (UPy), in either or both of the hard A blocks and soft B blocks. The TPEs formed microphase-separated structures consisting of spherical hard A domains surrounded by soft B matrices. When the dynamic bonds were introduced in the hard A blocks, the mechanical stability of the hard domains was improved. The stress in the tensile tests also increased but only at relatively large strains. Dynamic bonds in the soft B block served as transient crosslinks in the soft matrix that enhanced stress across the entire range of strain. The effect of introducing dynamic bonds in both the hard domains and soft matrix was more than just the sum of the effects of the dynamic bonds in both phases: a robust synergistic interaction existed between the dynamic bonding moieties in the two phases. This synergistic interaction enhanced the rigidity of the material (tensile stress ∼13 MPa) while maintaining high tensile toughness (∼58 MJ m⁻³). The dynamicity of the interactions in the different phases and its effect on fatigue recoverability in the large strain regime were also discussed using the classical theory of nonlinear viscoelasticity.