Effect of the Main/Side Chain Ratio on Mechanical Properties of Palm-Oil-Based H-Bond-Toughened Bottle-Brush Polymers Studied by MD Simulation

Bottle-brush polymers, consisting of rigid main chains and flexible long side chains, have attracted extensive attention due to their low chain entanglement, low melt viscosity, and high softness. In this study, molecular dynamics simulations were employed to investigate the multiscale mechanism by which the main/side chain ratio affects the mechanical properties of palm-oil-based H-bond-toughened bottle-brush polymers, with acrylic acid as the main chain and palm oil-based vinyl monomer (POFA-EA) as the side chain. Simulation results show that as the main chain ratio increases from 0.5:1 to 5:1, the average radius of gyration of single polymer chains increases by 65.4%, while the conformational fluctuation amplitude decreases by 79.4%, indicating a more extended and stable chain conformation. At the polymer aggregate scale, the hydrogen bond density increases from 1.4 to 4.9 nm-3, the free volume fraction decreases from 16.5% to 14.2%, and the diffusion coefficient decreases from 5.3 × 10-4 to 2.2 × 10-4 Å2/ps. Stronger hydrogen bonding, a more compact structure, and greater stability within the aggregates contribute to enhanced tensile strength. Furthermore, during stretching of the polymer aggregates, as the main/side chain ratio increases, the relative displacement of polymer centers of mass becomes smaller, indicating that the viscous deformation behavior of the material weakens and the material tends to be more brittle. Experimental results show that increasing the main chain ratio raises the tensile strength from 0.21 to 6.7 MPa, while the elongation at break decreases from 1059% to 51%, showing qualitative agreement with the simulation trends. Cross-scale correlation analysis reveals strong positive correlations between the main/side chain ratio and hydrogen-bond functional group density, the extension degree of single polymer chains within aggregates, and the tensile strength of the aggregates. This study provides insights into the cross-scale regulation mechanism of the main/side chain ratio on the mechanical properties of palm-oil-based H-bond-toughened bottle-brush polymers and offers a theoretical basis for the design and optimization of such materials.