Exploring the impact of weak interaction on conformational flexibility in polyborosiloxane

Weak interactions are ubiquitous and critically modulate the conformational flexibility of polymers. Here, we investigate polyborosiloxane (PBS), a supramolecular polymer renowned for its shear-stiffening behavior. A series of PBS samples with varying molecular weights were synthesized via a condensation reaction and characterized by GPC and FTIR spectroscopy. The nearly identical molecular weights of PBS and its PDMS precursor confirm the absence of significant side reactions. The trends observed in Si-O-B infrared band intensities correlate with the hydroxyl group content in PDMS, verifying the successful formation of PBS. These experimental results guided the construction of initial structural models. Low-energy conformers were identified through a multi-level computational approach combining high-temperature molecular dynamics sampling, semi-empirical pre-screening, and high-level DFT single-point energy calculations. Frequency calculations confirmed all optimized structures as true minima. Weak interactions were comprehensively characterized via advanced wavefunction analyses, including IRI based on AIM theory, energy decomposition analysis, atomic charge calculations, and ESP mapping. These analyses reveal that intramolecular hydrogen bonds are crucial for PBS conformational flexibility. Thermodynamic calculations further confirmed the stability of energetically favorable conformers. A key innovation lies in the integrated, multi-perspective visualization of weak interactions. Our findings provide fundamental insights into the physicochemical properties of PBS isomers and establish a robust protocol for studying complex polymer systems.