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Conjugated polymers have been widely investigated where ladder-type conjugated polymers receive more attention due to their rigid backbones and extraordinary properties. However, the understanding of how the rigid conformation of ladder polymers translates to material properties is still limited. Here, we systematically investigated the solution aggregation properties of a carbazole-derived conjugated ladder polymer (LP) and its analogous non-ladder control polymer (CP) via light scattering, neutron scattering, and UV-vis absorption spectroscopy characterization techniques, revealing a highly robust, temperature-insensitive aggregation behavior of the LP. The experimental findings were further validated by computational molecular dynamics simulations. We found that the peak positions and intensities of the UV spectra of the LP remained constant between 20 °C and 120 °C in chlorobenzene solution. The polymer also showed a stable hydrodynamic radius measured by dynamic light scattering from 20 °C to 70 °C in the chlorobenzene solution. Using small-angle neutron scattering, no Guinier region was reached in the measured q range down to 0.008 Å −1 , even at elevated temperature. In contrast, the non-ladder control polymer CP was fully soluble in the chlorobenzene solvent without the observation of any notable aggregates. The Brownian dynamics simulation showed that during polymer aggregation, the entropy change of the LP was significantly less negative than that of the non-ladder control polymer. These findings revealed the low entropy nature of rigid conjugated ladder polymers and the low entropy penalty for their aggregation, which is promising for highly robust intermolecular interactions at high temperatures. Such a unique thermodynamic feature of rigid ladder polymers can be leveraged in the design and application of next-generation electronic and optoelectronic devices that function under unconventional high temperature conditions. 

Persistence length is commonly used to quantitatively describe the chain rigidity of macromolecules, which represents an important structural parameter governing many physical properties of polymers. Although the mathematical models and experimental measurements on the chain rigidity of conventional single stranded polymers have been well explored and documented, those of the more rigid yet highly intriguing multiple stranded polymers, especially conjugated ladder polymers, are yet not well established. This article introduces the fundamental concepts on macromolecular chain rigidity, as well as the corresponding experimental methods, models, and simulations. Subsequently, representative examples of works done on the chain rigidity of nonladder conjugated polymers and conjugated ladder polymers are reviewed. Last but not least, it provides outlooks on the challenges with respect to the less‐investigated chain rigidity of conjugated ladder polymers, including new models to describe and predict chain conformation, synthetic control on structural defects, and insights into the correlation of rigidity and applications.