Abstract
Thermomechanical properties of conjugated polymers (CPs) are greatly influenced by both their microstructures and backbone dynamics. In the present work, to investigate the effect of the side-chain branch position on the backbone's mobility and molecular packing structure, four poly (3-alkylthiophene-2,5-diyl) derivatives (P3ATs) with different side chains, either branched or linear, were synthesized by a quasi-living Kumada catalyst transfer polymerization (KCTP) method. The side-chain branch position greatly influences the glass transition temperature (Tg) of the backbone of P3ATs as well as the melting temperature (Tm), as measured by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) respectively. Placing the branching point closer to the conjugated backbone leads to increased backbone Tg and Tm. Also, according to grazing incidence wide-angle X-ray scattering (GIWAXS) results, branching closer to the backbone causes tighter packing in the side-chain direction. The tighter packing along the side-chain direction coresponds with the higher Tm, which decreases the free volume of the polymer system and subsequently increases the Tg at the same time. This work provides the first in-depth understanding of branch point influences on the thermal properties of poly(3-alkylthiophenes). It would provide guidance to the future development of side-chain engineering on next-generation CPs with desirable thermomechnical properties for stretchable and wearable electronics.
| Original language | English |
|---|---|
| Pages (from-to) | 517-526 |
| Number of pages | 10 |
| Journal | Polymer Chemistry |
| Volume | 11 |
| Issue number | 2 |
| DOIs | |
| State | Published - Jan 14 2020 |
| Externally published | Yes |
Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Science under award number of DE-SC0019361. The authors thank Peter V. Bonnesen (CNMS) for assistance during the NMR experiment. Part of the research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. L. G. acknowledges the financial support from NSF-DGE NRT program #1449999. We also thank Prof. Zhenan Bao for help during OFET device fabrication and test.