Mechanical properties including the failure behavior of physically assembled gels or physical gels are governed by their network structure. To investigate such behavior, we consider a physical gel system consisting of poly(styrene)‐poly(isoprene)‐poly(styrene)[PS‐PI‐PS] in mineral oil. In these gels, the endblock (PS) molecular weights are not significantly different, whereas, the midblock (PI) molecular weight has been varied such that we can access gels with and without midblock entanglement. Small angle X‐ray scattering data reveals that the gels are composed of collapsed PS aggregates connected by PI chains. The gelation temperature has been found to be a function of the endblock concentration. Tensile tests display stretch‐rate dependent modulus at high strain for the gels with midblock entanglement. Creep failure behavior has also been found to be influenced by the entanglement. Fracture experiments with predefined cracks show that the energy release rate scales linearly with the crack‐tip velocity for all gels considered here. In addition, increase of midblock chain length resulted in higher viscous dissipation leading to a higher energy release rate. The results provide an insight into how midblock entanglement can possibly affect the mechanical properties of physically assembled triblock copolymer gels in a midblock selective solvent. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.
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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 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 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.
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- Award ID(s):
- 1906009
- PAR ID:
- 10548159
- Publisher / Repository:
- ACS Journals
- Date Published:
- Journal Name:
- Macromolecules
- Volume:
- 57
- Issue:
- 17
- ISSN:
- 0024-9297
- Page Range / eLocation ID:
- 8306 to 8319
- Subject(s) / Keyword(s):
- Ionomer Midblock, Fatty Acid, Vegetable Oil, Transient Interactions, Supramolecular Interactions, Supramolecular Network, Dynamic Crosslinks, Long-Chain Polyacrylates, Hydrogen Bonding
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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