The effect of side-chain branch position on the thermal properties of poly(3-alkylthiophenes)

• Published in: Polymer chemistry 2019-10, Vol.11 (2)
• Main Authors: Cao, Zhiqiang, Galuska, Luke, Qian, Zhiyuan, Zhang, Song, Huang, Lifeng, Prine, Nathaniel, Li, Tianyu, He, Youjun, Hong, Kunlun, Gu, Xiaodan
• Format: Article
• Language: English
• Subjects: INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
• ISSN: 1759-9954; 1759-9962

Thermomechanical properties of conjugated polymers (CPs) are greatly influenced by both their microstructures and backbone dynamics. In the present work, to explore 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 offers 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.