Glass Transition Temperature of Conjugated Polymers by Oscillatory Shear Rheometry
Artikel i vetenskaplig tidskrift, 2017

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 (T g 's) for both RR and RRa P3HT and one for PFTBT. The higher T g , T α , is associated with the backbone segmental motion and depends on the molecular weight, such that the Flory-Fox model yields T α = 22 and 6 °C in the long chain limit for RR and RRa P3HT, respectively. For RR P3HT, a different molecular weight dependence of T α is seen below M n = 14 kg/mol, suggesting this is the typical molecular weight of intercrystal tie chains. The lower T g (T αPE ≈ -100 °C) is associated with the side chains and is independent of molecular weight. RRa P3HT exhibits a lower T α and higher T αPE 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 T g above -120 °C, at 144 °C in the long chain limit.

Författare

R. Xie

Pennsylvania State University

Y. Lee

Pennsylvania State University

M.P. Aplan

Pennsylvania State University

N.J. Caggiano

Pennsylvania State University

Christian Müller

Kemi och kemiteknik, Tillämpad kemi, Polymerteknologi

R.H. Colby

Pennsylvania State University

E.D. Gomez

Pennsylvania State University

Macromolecules

0024-9297 (ISSN) 1520-5835 (eISSN)

Vol. 50 5146-5154

Ämneskategorier

Polymerkemi

DOI

10.1021/acs.macromol.7b00712