(131g) A Tunable, Particle-Based Model for the Diverse Conformations Exhibited By Chiral Block Polymers

Chirality occurs across many length scales such as molecular and conformational chirality found in biomolecules, and structural chirality formed from hierarchical self-assembly. Chiral block copolymers are one such model system, capable of exhibiting chirality at the conformational length scale and also self-assembles into a variety of chiral morphologies (e.g. helices, single gyroid, undulating lamellae, rosettes, etc.). Recent studies have also shown that the conformational chirality affects the thermodynamics and microstructure of non-chiral morphologies. Despite theoretical studies that qualitatively capture the phase diagrams of these model molecules, mechanistic insights at the molecular level are missing in the literature. Therefore, we developed a tunable, particle-based model of a chiral polymer and performed extensive characterization to map out the polymer physics. We varied the energetic parameter K in the angular and dihedral potentials, the angular setpoint θ0, and the dihedral setpoint φ0-π. The resulting chain conformations for a single molecule were characterized quantitatively using helicity, pitch, persistence length, and mean-squared end-to-end distance. Resulting correlations allow for the model to be tuned to match an appropriate experimental system. As a sample calculation, we used experimental data on polypeptoid-based chiral polymers (Rosales et al., 2012; Yu et al., 2021) using the ratio of the persistence length between the chiral and disordered polymer chains and identified parameters in our model to reproduce experimental values. Using this model, we further studied the behavior of a melt of chiral block copolymers in the lamellar morphology. We found that the interfacial constraints of the morphology produced non-ideal conformations in the chiral block. Beyond the current study, we envision that such a tunable model can be used to study the thermodynamic origins of chirality transfer.

References:

1. Rosales, A. M., Murnen, H. K., Kline, S. R., Zuckermann, R. N., & Segalman, R. A. (2012). Determination of the persistence length of helical and non-helical polypeptoids in solution. Soft Matter, 8(13), 3673–3680. https://doi.org/10.1039/c2sm07092h
2. Yu, B., Li, R., & Segalman, R. A. (2021). Tuning the Double Gyroid Phase Window in Block Copolymers via Polymer Chain Conformation near the Interface. Macromolecules, 54(12), 5388–5396. https://doi.org/10.1021/acs.macromol.1c00048