Local Chain Alignment via Nematic Ordering Reduces Chain Entanglement in Conjugated Polymers

Renxuan Xie, Melissa P. Aplan, Nicholas J. Caggiano, Albree R. Weisen, Tang Su, Christian Müller, Mo Segad, Ralph H. Colby, Enrique D. Gomez

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


Chain entanglements govern the dynamics of polymers and will therefore affect the processability and kinetics of ordering; it follows that through these parameters chain dynamics can also affect charge transport in conjugated polymers. The effect of nematic coupling on chain entanglements is probed by linear viscoelastic measurements on poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and poly((9,9-dioctylfluorene-2,7-diyl)-alt-(4,7-di(thiophene-2-yl)-2,1,3-benzothiadiazole)-5′,5″-diyl) (PFTBT) with varying molecular weights. We first verify the existence of nematic phases in both PFTBT and PCDTBT and identify nematic-isotropic transition temperatures, T I N , between 260 and 300 °C through a combination of differential scanning calorimetry, polarized optical microscopy, temperature-dependent X-ray scattering, and rheology. In addition, both PCDTBT and PFTBT show a glass transition temperature (T g ) and T I N , whereas only PFTBT has a melting temperature T m of 260 °C. Comparing the molecular weight dependence of T I N with theoretical predictions of nematic phases in conjugated polymers yields the nematic coupling constant, α = (550 ± 80 K)/T + (2.1 ± 0.1), and the long-chain limit T I N as 350 ± 10 °C for PFTBT. The entanglement molecular weight (M e ) in the isotropic phase is extracted to be 11 ± 1 kg/mol for PFTBT and 22 ± 2 kg/mol for PCDTBT by modeling the linear viscoelastic response. Entanglements are significantly reduced through the isotropic-to-nematic transition, leading to a 10-fold increase in M e for PFTBT and a 15-fold increase for PCDTBT in the nematic phase.

Original languageEnglish (US)
Pages (from-to)10271-10284
Number of pages14
Issue number24
StatePublished - Dec 26 2018

All Science Journal Classification (ASJC) codes

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


Dive into the research topics of 'Local Chain Alignment via Nematic Ordering Reduces Chain Entanglement in Conjugated Polymers'. Together they form a unique fingerprint.

Cite this