Elucidating the hydrogen bonding location effect on morphology, mechanical and electrical properties of conjugated polymer/elastomer composites*

Developing stretchable semiconducting polymers plays an essential role with the growing demand for electronic skins, wearable, and implanted devices, sensors, etc. Hydrogen bond, a dynamic bond (HB), was reported able to effectively improve the stretchability of semiconductors when introduced either in pure conjugated polymers (CPs) or elastomer matrix of CP/elastomer composites. In this work, we combined these two methods that we introduced amide groups into both DPPTVT CP (DPPTVT-A) and elastomer matrix (amide-polyisobutylene, PIB-A) to fabricate dual hydrogen bond-crosslinked DPPTVT-A/PIB-A composites, and carefully studied the non-covalent hydrogen bonding location effect on morphology, electrical and mechanical properties. Their non-hydrogen bonding counterparts, DPPTVT and PIB, were selected as comparative reference fabricating uni-HB-crosslinked composites DPPTVT-A/PIB, DPPTVT/PIB-A and non-HB-crosslinked DPPTVT/PIB composites. Dual hydrogen bond-crosslinked composite DPPTVT-A/PIB-A showed micro-phase separation on the order of ~30 nm due to a combination of inter- and intramolecular HB interactions. In contrast, others show two-size phase separation, including macro-phase separation and fibril-like CP aggregation, characterized by the AFM-IR technique. However, the micro-phase separation morphology wasn’t beneficial to electrical properties. DPPTVT-A/PIB-A showed the lowest charge carrier mobility (0.03 cm²/V s), whereas DPPTVT/PIB-A, with the most fibril aggregation, showed the highest mobility (0.08 cm²/V s). The composite with PIB-A as elastomer matrix showed higher modulus due to the crosslink of elastomer. All composites showed high stretchability (crack onset strain >200%) originating from elastomers' high stretchability. This work provides a complete understanding of HB-crosslink effect on morphology and further influence on mechanical and electrical properties of CP/elastomer composite, which will guide the design of future stretchable semiconductors.