Abstract
Thermomechanical properties of polymers highly depend on their glass transition temperature (Tg). Differential scanning calorimetry (DSC) is commonly used to measure Tg of polymers. However, many conjugated polymers (CPs), especially donor–acceptor CPs (D–A CPs), do not show a clear glass transition when measured by conventional DSC using simple heat and cool scan. In this work, we discuss the origin of the difficulty for measuring Tg in such type of polymers. The changes in specific heat capacity (Δcp) at Tg were accurately probed for a series of CPs by DSC. The results showed a significant decrease in Δcp from flexible polymer (0.28 J g−1 K−1 for polystyrene) to rigid CPs (10−3 J g−1 K−1 for a naphthalene diimide-based D–A CP). When a conjugation breaker unit (flexible unit) is added to the D–A CPs, we observed restoration of the Δcp at Tg by a factor of 10, confirming that backbone rigidity reduces the Δcp. Additionally, an increase in the crystalline fraction of the CPs further reduces Δcp. We conclude that the difficulties of determining Tg for CPs using DSC are mainly due to rigid backbone and semicrystalline nature. We also demonstrate that physical aging can be used on DSC to help locate and confirm the glass transition for D-A CPs with weak transition signals.
| Original language | English |
|---|---|
| Pages (from-to) | 1635-1644 |
| Number of pages | 10 |
| Journal | Journal of Polymer Science, Part B: Polymer Physics |
| Volume | 57 |
| Issue number | 23 |
| DOIs | |
| State | Published - Dec 1 2019 |
Funding
This work is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Science under award number of DE‐SC0019361 for Z. Qian, Z. Cao, and X. Gu S. Zhang also acknowledge NSF for partial supported through office of integrative activities (OIA) by NSF OIA‐1757220. L. Galuska thanks NSF NRT for providing support with grant no. 1449999. W. W. McNutt and J. Mei acknowledge NSF grant no. 1653909 for the support of conjugated polymer synthesis. S. Rondeau‐Gagné thanks the Natural Sciences and Engineering Research Council of Canada (NSERC) for financial support (RGPIN‐2017‐06611 and NETGP‐508526‐17). M. U. Ocheje thanks NSERC for a doctoral scholarship. R. B. Goodman thanks NSERC for an undergraduate student research award. Part of the polymers was synthesized at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. J. Xu acknowledges the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, and supported by the U.S. Department of Energy, Office of Science, under Contract No. DE‐AC02‐06CH11357. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE‐AC02‐76SF00515. The instrument used in this work was acquired with support from ERDC. This work benefited from the use of the SasView application, originally developed under NSF award DMR‐0520547. SasView contains code developed with funding from the European Union's Horizon 2020 research and innovation programme under the SINE2020 project, grant agreement No 654000. The authors would like to thank Eric King at the University of Southern Mississippi for assisting on the nuclear magnetic resonance measurement on poly(3‐hexylthiophene) (P3HT) and gel permeation chromatography measurement on P3HT and PNDI‐C0. The authors would also like to thank Brian N. Turner from Mettler‐Toledo, Inc. and Madhusudhan R. Pallaka at Texas Tech University for the great discussion about Sapphire method, Matthew Hartline at the University of Southern Mississippi for conforming the T of polystyrene with TA Instruments DSC Q200. Finally, the authors would like to thank Guorong Ma at the University of Southern Mississippi for assisting on the absolute heat capacity measurement of P3(2EB)T. g This work is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Science under award number of DE-SC0019361 for Z. Qian, Z. Cao, and X. Gu S. Zhang also acknowledge NSF for partial supported through office of integrative activities (OIA) by NSF OIA-1757220. L. Galuska thanks NSF NRT for providing support with grant no. 1449999. W. W. McNutt and J. Mei acknowledge NSF grant no. 1653909 for the support of conjugated polymer synthesis. S. Rondeau-Gagn? thanks the Natural Sciences and Engineering Research Council of Canada (NSERC) for financial support (RGPIN-2017-06611 and NETGP-508526-17). M. U. Ocheje thanks NSERC for a doctoral scholarship. R. B. Goodman thanks NSERC for an undergraduate student research award. Part of the polymers was synthesized at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. J. Xu acknowledges the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, and supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The instrument used in this work was acquired with support from ERDC. This work benefited from the use of the SasView application, originally developed under NSF award DMR-0520547. SasView contains code developed with funding from the European Union's Horizon 2020 research and innovation programme under the SINE2020 project, grant agreement No 654000. The authors would like to thank Eric King at the University of Southern Mississippi for assisting on the nuclear magnetic resonance measurement on poly(3-hexylthiophene) (P3HT) and gel permeation chromatography measurement on P3HT and PNDI-C0. The authors would also like to thank Brian N. Turner from Mettler-Toledo, Inc. and Madhusudhan R. Pallaka at Texas Tech University for the great discussion about Sapphire method, Matthew Hartline at the University of Southern Mississippi for conforming the T g of polystyrene with TA Instruments DSC Q200. Finally, the authors would like to thank Guorong Ma at the University of Southern Mississippi for assisting on the absolute heat capacity measurement of P3(2EB)T.
Keywords
- conjugated polymers
- glass transition
- heat capacity
- organic electronics
- specific heat capacity