Investigating the Effects of Hydrogen Bonding on Mechanical and Electrical Properties of n-Type Semicrystalline Polymers

Abstract

Designing conjugated polymers with both excellent electrical properties and mechanical robustness is a prerequisite for their application in wearable and portable electronics. However, many of the efficient conjugated polymers are mechanically brittle due to their strong semicrystallinity, and only the limited amorphous parts contribute to the overall tensile properties. Here, we have incorporated monomers with hydrogen bonding (H-bonding) functionalized side chains (Qx-thymine and T-diaminopyrimidine) into the backbone of the naphthalene diimide-based semicrystalline polymer, N2200, to yield electroactive polymers with high electrical properties and stretchability, facilitated by dynamic bonding-assisted intermolecular assembly. To elucidate the impact of H-bonding on polymer properties, we systematically compare the mechanical and electrical properties, among the reference N2200 polymer, N2200-based terpolymers (Qx10 and Ester10) having side chains without H-bonding, and N2200-based terpolymers (Thy10 and Dap10) having Q(X)-thymine and T-diaminopyrimidine side chains. Interestingly, introducing H-bonding units into polymers promotes the formation of intermolecular assembly while reducing the critical molecular weight (M-c) of the polymer chain, thus facilitating the formation of tie-molecules and entanglement networks. Specifically, Thy10 polymers, with a weight-average molecular weight (M-w) of 133 kg mol(-1), achieve a significantly higher stretchability with crack-onset strain (COS) = 49.3% compared to those of the N2200 (M-w = 180 kg mol(-1), COS= 3.2%) and Qx10 polymers (M-w = 144 kg mol(-1), COS = 23.7%) with comparable M-w. Furthermore, Thy10 exhibits superior crystalline properties and more efficient charge transport compared with Qx10, highlighting the utility of H-bonding-capable conjugated polymers in wearable electronics.