Elucidating the Role of Hydrogen Bonds for Improved Mechanical Properties in a High-Performance Semiconducting Polymer

Incorporation of hydrogen bond moieties into the backbone or side chain of conjugated polymers is an effective strategy to enhance mechanical performance, facilitate morphological organization, and promote self-healing ability. However, the understanding of hydrogen bonds, particularly the effect of bond strength and directionality, on thermomechanical and optoelectronic performance is still in its infancy due to the competing influence of morphology, glass transition phenomena, and the measurement process itself. Here, we compare the influence of statistically incorporated amide and urea moieties on the mechanical properties of DPP-TVT parent polymers. We observed a profound difference in ductility; amide functionalization increases the strain at failure by over 100% relative to the pure DPP-TVT polymer, while urea functionalization results in a loss of strain at failure by 50%. This is attributed to the crystalline behavior of functionalized conjugated polymers that is promoted by intermolecular interactions of urea groups, which we elucidated via an in-depth investigation of the swelling, crystalline packing, thermal behavior, and strain-dependent charge transport. Furthermore, we employed a novel free-standing tensile test to validate our mechanical measurements supported on a water surface. Our results demonstrated that hydrogen bond moieties must be carefully chosen to achieve a delicate balance of morphological control and mechanical performance, as simply increasing the hydrogen bond strength can result in detrimental mechanical and electrical performance.