From Molecular Architecture to Performance: Structure–Property Correlations in Crosslinked SBR Explored through a Combined Experimental and Molecular Simulation Approach

Understanding how sulfur crosslinking architecture influences the properties of styrene–butadiene rubber (SBR) is critical for optimizing tire performance and durability. Our study employs all-atom molecular dynamics (MD) simulations and experimental validations to systematically investigate the impact of crosslinking density and sulfur crosslink types (monosulfide, disulfide, and polysulfide) on the structural, thermodynamic, dynamical, mechanical, and thermal properties of SBR. The computational framework is designed to enable precise control over network architecture, allowing the effects of crosslink length and density to be isolated─an approach not readily achievable in experimental settings. The models are validated by comparing simulated glass-transition temperatures (Tg) and densities with experimental data. An increase in Tg with crosslinking density and sulfur chain length was observed, consistent with reduced chain mobility. Thermodynamic properties such as thermal expansion coefficient, isothermal compressibility, adiabatic bulk modulus, and specific heat capacity were determined, revealing that higher crosslinking densities generally enhance thermal stability and mechanical rigidity, with subtle differences among crosslink types. Notably, the presence of intrachain crosslinks in polysulfide systems introduced additional constraints, affecting both thermal conductivity and chain dynamics. Stress–strain simulations indicated that mechanical strength primarily depends on crosslinking density, with minimal sensitivity to crosslink type. Our findings provide molecular level insights into how crosslinking architecture governs the macroscopic behavior of vulcanized SBR, offering valuable guidance for the rational design of advanced tire compounds.