Morphological origins of temperature and rate dependent mechanical properties of model soft thermoplastic elastomers

Abstract

Thermoplastic elastomers (TPEs) combine high elasticity with melt processability due to their structural features being based on physical associations rather than chemical crosslinking. Their mechanical properties are governed by the interplay of the different dynamics present in the system (i.e., hard block associations and soft block mobility) combined with their morphology. Irrespective of their exact chemical structure or type of association (crystals, hydrogen bonds, or glassy domains), many soft TPEs show a reduction in toughness at elevated temperatures. In this study, we investigate the high‐temperature mechanical properties of a model series of industrially relevant TPEs via systematically varying composition and molecular weight. The results show an increase in temperature resistance and in large‐strain stress response as chain length increases. We underline the key parameters that influence the mechanical behavior and explain the observed effect of molecular weight on both the temperature‐ and rate‐dependent large‐strain response. A physical network‐based model is presented that can explain the experimental findings assuming an improved network connectivity and extended lifetime of the entangled segments with increasing molecular weight.

Recent advances on the structure–properties relationship of multiblock copolymers

“…In Figure 8C, we adapted the work of Aime et al 173 showing yet, its dramatic impact on PBT-PTHF (or PEG) MBCs tensile properties. In their article, the authors manage to predict accurately the strain at failure of their PTHF-based MBC by modeling the kinetics of formation and breakage of physical bonds between through the Eyring's rate equation ) and strain rate (solid and dashed lines refer, respectively, to 0.17 and 0.0017 s À1 ) on the stress-strain curves of PBT-PTHF MBCs, adapted from Reference [88]. (E) Schematic representation of the corresponding MBC morphology upon increasing the strain.…”

“…(E) Schematic representation of the corresponding MBC morphology upon increasing the strain. (F) Schematic representation of the phenomenology rationalizing the stress-strain curves in corresponding MBCs (E and F are adapted from Reference [88])…”

“…Some of these aspects, notably concerning the role of the entanglements, have been considered by the same group in a more recent work dealing with welldefined PBT-PTHF MBCs. 88 In this paper, the authors explain the role of the molecular weight, the temperature and the strain rate through a new "mechanistic" model that describes the network from the molecular length scale. We adapted this work in Figure 8D-F showing, respectively: (8D) tensile experiments data measured from two MBCs (M ¼ 29 and 50 kg mol À1 ) at either _ ε ¼ 0:17 s À1 or 0:0017 s À1 at room temperature, (8E) a schematic representation of the microstructure upon stretching and (8F) a cartoon that emphasizes the various molecular mechanisms captured by the model.…”

“…(C) Effect of the temperature on the stress–strain curves of PBT‐PTHF MBCs, adapted from Reference [173]. (D) Effect of the chain length (red and brown refer, respectively, to 50 and 29 kg mol −1 ) and strain rate (solid and dashed lines refer, respectively, to 0.17 and 0.0017 s −1 ) on the stress–strain curves of PBT‐PTHF MBCs, adapted from Reference [88]. (E) Schematic representation of the corresponding MBC morphology upon increasing the strain.…”

“…Some of these aspects, notably concerning the role of the entanglements, have been considered by the same group in a more recent work dealing with well‐defined PBT‐PTHF MBCs 88 . In this paper, the authors explain the role of the molecular weight, the temperature and the strain rate through a new “mechanistic” model that describes the network from the molecular length scale.…”