The influence of spacer composition on thermomechanical properties, crystallinity, and morphology in ionene segmented copolymers
Date
2021-05-04
Authors
Liesen, Nicholas
Wang, Meng
Lee, Jae Sang
Montazami, Reza
Hall, Lisa M.
Green, Matthew D.
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Royal Society of Chemistry
Abstract
A series of segmented ammonium ionenes with varying weight fractions of 2000 g mol−1 poly(ethylene glycol) (PEG) or poly(tetramethylene oxide) (PTMO) soft segments were synthesized, and a simplified coarse-grained model of these materials was implemented using molecular dynamics simulations. In addition to varying soft segment type (PTMO vs. PEG), charge density and soft segment content were varied to create a comprehensive series of segmented ammonium ionenes; thermogravimetric analysis reveals that all segmented ionenes in the series are thermally stable up to 240 °C. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) show the formation of phase separated microdomains at low soft segment content. In particular, DSC shows that the hard and soft domains have distinct glass transition temperatures. Similarly, simulations show that reduced soft segment content induces stronger microphase separation, reduces soft segment mobility, and increases ionic aggregate connectivity and size. These increased ionic associations result in elastomeric behavior, as evidenced by the higher rubbery plateau moduli observed at lower soft segment contents through DMA. Moreover, simulations show that ionic aggregation increases when switching from PEG to the less polar PTMO repeat units, which is consistent with DMA results showing higher plateau moduli for PTMO-based ionenes relative to PEG ionenes. DSC and X-ray diffraction determined that the degree of crystallinity increased with soft segment content regardless of segment type. Overall, these results suggest a semi-crystalline microphase-separated morphology strongly influenced by charge density, the degree of ionic aggregation, and the resulting level of confinement and mobility of the soft segments.
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This is a manuscript of an article published as Liesen, Nicholas T., Meng Wang, Mehrnoosh Taghavimehr, Jae Sang Lee, Reza Montazami, Lisa M. Hall, and Matthew D. Green. "The influence of spacer composition on thermomechanical properties, crystallinity, and morphology in ionene segmented copolymers." Soft Matter 17, no. 22 (2021): 5508-5523.
DOI: 10.1039/D1SM00501D.
Copyright 2021 The Royal Society of Chemistry.
Posted with permission.