Impact of Backbone Rigidity on the Thermomechanical Properties of Semiconducting Polymers with Conjugation Break Spacers

Abstract

There remains a lack of fundamental understanding in the role of backbone rigidity on the thermomechanical properties of conjugated polymers. Here, we provide the first holistic approach to understand the fundamental influence of backbone rigidity on an n-type naphthalene diimide-based conjugated polymer, denoted by PNDI-Cx, through insertion of a flexible conjugation break spacer (CBS). CBS lengths are varied from fully conjugated with zero alkyl spacer (PNDI-C0) to a seven-carbon alkyl spacer (PNDI-C7), with the CBS engineered into each repeat unit for systematic evaluation. Solution small-angle neutron scattering and oscillatory shear rheometry were employed to provide the first quantitative evidence of CBS influence over conjugated polymer chain rigidity and entanglement molecular weight (M e), demonstrating a reduction in the Kuhn length from 521 to 36 Å for fully conjugated PNDI-C0 and PNDI-C6, respectively, as well as a nearly consistent M e of ∼15 kDa upon the addition of CBS. Thermomechanical properties, such as elastic modulus and glass-transition temperature, were shown to decrease with an increasing length of CBS. An extraordinary ductility, upwards of 400% tensile strain before fracture, was observed for high-molecular-weight PNDI-C4, which we attribute to a high number of entanglements and disruption of crystallization. Furthermore, the deformation mechanism for PNDI-Cx was studied under strain through X-ray diffraction, polarized UV–vis spectroscopy, and atomic force microscopy. Overall, this work sheds light on the important role of backbone rigidity in designing flexible and stretchable conjugated polymers.

Mixed Conduction in an N‐Type Organic Semiconductor in the Absence of Hydrophilic Side‐Chains

“…BBL chains exhibit large persistence lengths of up to ≈153 nm (limited by the overall chain length), [ 45 ] whereas the persistence length of the NDI‐T2 backbone appears to be limited to ≈26 nm, regardless of the overall chain length. [ 46 ] We suggest that rigid long chains of BBL extend across amorphous regions connecting multiple crystallites. Although dry AFM and TEM images showed no porosity for BBL in the length scales that we could investigate, we postulate that these inter crystallite disordered regions have enough void space to allow electrolyte intercalation, as evidenced by GISAXS.…”

High‐Performance All‐Polymer Solar Cells with a Pseudo‐Bilayer Configuration Enabled by a Stepwise Optimization Strategy

“…Among the above‐mentioned approaches, achieving suitable microstructure in all‐PSCs plays a vital role in improving device performance. [ 3,6,20–22 ] However, some major problems, related to the blend morphologies of P D s and P A s, namely the bulk heterojunction (BHJ), which is generally formed during P D ‐ P A mixture solution casting, have been identified in all‐PSCs, including large‐scale demixing of P D / P A domains, [ 8,21 ] unoptimized P D / P A ordering, [ 23,24 ] and misaligned molecular orientation at P D ‐ P A interfaces. [ 25,26 ] Thus, reasonable use of different morphology control strategies, such as modification of molecular structures, [ 5,9,21,27 ] selection of solvent and additive, [ 6,20,28 ] thermal annealing, [ 6,22 ] and so on, to modify domain size and phase purity in all‐PSCs is critical.…”

Perfluoroalkylated alternating copolymer possessing solubility in fluorous liquids and imaging capabilities under high energy radiation

“…2a). As previous studies have demonstrated that the T g increases with increasing chain stiffness, 22 this explains how the P(R F Mi-St) can have a T g Fig. 1 (a) Synthesis of R F Mi (3).…”