Glass Transition Temperature of Conjugated Polymers by Oscillatory Shear Rheometry

Renxuan Xie, Youngmin Lee, Melissa P. Aplan, Nicholas J. Caggiano, Christian Müller, Ralph H. Colby, Enrique D. Gomez

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

The stiff backbones of conjugated polymers can lead to a rich phase behavior that includes both crystalline and liquid crystalline phases, making measurements of the glass transition challenging. In this work, the glass transitions of regioregular poly(3-hexylthiophene-2,5-diyl) (RR P3HT), regiorandom (RRa) P3HT, and poly((9,9-bis(2-octyl)-fluorene-2,7-diyl)-alt-(4,7-di(thiophene-2-yl)-2,1,3-benzothiadiazole)-5′,5″-diyl) (PFTBT) are probed by linear viscoelastic measurements as a function of molecular weight. We find two glass transition temperatures (Tg's) for both RR and RRa P3HT and one for PFTBT. The higher Tg, Tα, is associated with the backbone segmental motion and depends on the molecular weight, such that the Flory-Fox model yields Tα = 22 and 6 °C in the long chain limit for RR and RRa P3HT, respectively. For RR P3HT, a different molecular weight dependence of Tα is seen below Mn = 14 kg/mol, suggesting this is the typical molecular weight of intercrystal tie chains. The lower Tg (TαPE ≈ -100 °C) is associated with the side chains and is independent of molecular weight. RRa P3HT exhibits a lower Tα and higher TαPE than RR P3HT, possibly due to a different degree of nanophase separation between the side chains and the backbones. In contrast, PFTBT only exhibits one Tg above -120 °C, at 144 °C in the long chain limit.

Original languageEnglish (US)
Pages (from-to)5146-5154
Number of pages9
JournalMacromolecules
Volume50
Issue number13
DOIs
StatePublished - Jul 11 2017

Fingerprint

Conjugated polymers
Molecular weight
Thermoplastic elastomers
Glass transition
Crystalline materials
Thiophenes
Thiophene
Phase behavior
Glass transition temperature
Liquids

All Science Journal Classification (ASJC) codes

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

Cite this

Xie, Renxuan ; Lee, Youngmin ; Aplan, Melissa P. ; Caggiano, Nicholas J. ; Müller, Christian ; Colby, Ralph H. ; Gomez, Enrique D. / Glass Transition Temperature of Conjugated Polymers by Oscillatory Shear Rheometry. In: Macromolecules. 2017 ; Vol. 50, No. 13. pp. 5146-5154.
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Glass Transition Temperature of Conjugated Polymers by Oscillatory Shear Rheometry. / Xie, Renxuan; Lee, Youngmin; Aplan, Melissa P.; Caggiano, Nicholas J.; Müller, Christian; Colby, Ralph H.; Gomez, Enrique D.

In: Macromolecules, Vol. 50, No. 13, 11.07.2017, p. 5146-5154.

Research output: Contribution to journalArticle

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AB - The stiff backbones of conjugated polymers can lead to a rich phase behavior that includes both crystalline and liquid crystalline phases, making measurements of the glass transition challenging. In this work, the glass transitions of regioregular poly(3-hexylthiophene-2,5-diyl) (RR P3HT), regiorandom (RRa) P3HT, and poly((9,9-bis(2-octyl)-fluorene-2,7-diyl)-alt-(4,7-di(thiophene-2-yl)-2,1,3-benzothiadiazole)-5′,5″-diyl) (PFTBT) are probed by linear viscoelastic measurements as a function of molecular weight. We find two glass transition temperatures (Tg's) for both RR and RRa P3HT and one for PFTBT. The higher Tg, Tα, is associated with the backbone segmental motion and depends on the molecular weight, such that the Flory-Fox model yields Tα = 22 and 6 °C in the long chain limit for RR and RRa P3HT, respectively. For RR P3HT, a different molecular weight dependence of Tα is seen below Mn = 14 kg/mol, suggesting this is the typical molecular weight of intercrystal tie chains. The lower Tg (TαPE ≈ -100 °C) is associated with the side chains and is independent of molecular weight. RRa P3HT exhibits a lower Tα and higher TαPE than RR P3HT, possibly due to a different degree of nanophase separation between the side chains and the backbones. In contrast, PFTBT only exhibits one Tg above -120 °C, at 144 °C in the long chain limit.

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