Quantitative assessment of tie chains for charge transport in conjugated polymers

Intercrystallite molecular connections are widely recognized to greatly impact the macroscopic properties of semicrystalline polymers. Because it is challenging to directly probe such connections, theoretical frameworks have been developed to quantify their concentrations and predict the mechanical properties accordingly. Tie-chain connectivity similarly impacts the electrical properties in semicrystalline conjugated polymers. Yet, its quantitative impact has eluded the community. Here, we applied the Huang-Brown model, a framework commonly used to describe the structural origins of mechanical properties in polyolefins, to quantitatively elucidate the effect of tie chains on the electrical properties of a model conjugated polymer. We found that a critical tie-chain fraction of 10E-3, below which intercrystallite connectivity limits macroscopic charge transport, and above which intracrystallite disorder is the bottleneck. It follows that tensile straining polymer films with tie chains above percolation threshold reorients the interconnected crystallites, leading to charge-transport anisotropy in the films. Our study shows the importance of connected crystalline domains by tie chains for efficient charge transport and implicates the importance of long and rigid polymer chains.