Investigating hydrogen bonding in poly(vinyl butyral) copolymers near glass-transition temperature under uniaxial...

Understanding hydrogen bond dynamics and mechanical behavior in amorphous polymers remains a significant challenge. In this work, we selected poly(vinyl butyral) (PVB) copolymers as a model system and employed coarse-grained molecular dynamics (CGMD) simulations to investigate the evolution of hydrogen bonding networks, hydrogen bond dynamics and mechanical response near glass-transition temperature (T_g) under uniaxial tensile stress. We systematically studied the effects of vinyl alcohol (VA) content, blockiness parameter, and strain rate on hydrogen bonding networks, hydrogen bond dynamics, and the mechanical properties of PVB copolymers. Our results demonstrate that amorphous PVB experiences chain slippage during deformation, which disrupts intramolecular hydrogen bonds while facilitating the formation of intermolecular hydrogen bonds. Notably, mechanical stress induces a net reduction in total hydrogen bonds prior to fracture, followed by post-fracture relaxation that facilitates hydrogen bond reorganization through coupled mechano-thermal effects. Further analysis of the radius of gyration and hydrogen bond dynamics indicates that PVB copolymers with higher VA content exhibit enhanced chain rigidity. This molecular-level rigidity enables significant chain unfolding during deformation, which directly influences the lifetime of hydrogen bonds.