Molecular Dynamics investigation on the sites of acetylation of advanced polyurethanes

Polyurethane (PU) -chitosan (CHI) composite systems are of interest because of their modified thermal and mechanical properties with respect to polyurethane, besides providing the system with anti-microbic ones. This makes this system a candidate for biomedical applications. [1][2] The molecular behavior of PU–CHI composite systems was investigated using atomistic simulations, focusing on chitosan oligomers with a fixed acetylation degree (8:2) and varying acetyl group positions along the oligomer backbone. A series of PU+CHI systems was constructed in which acetyl groups were systematically located at different sites within the chitosan repeat units (e.g., chain termini or internal positions), while preserving overall chemical composition. All-atom molecular dynamics simulations were used to analyze how acetyl positioning influences thermal response, supramolecular interactions, and mechanical-related properties. Glass transition behavior was assessed through thermal annealing simulations, while hydrogen-bond networks were quantified in terms of interfacial connectivity and bonding efficiency. Chain mobility and mechanical response proxies were evaluated using dynamic and deformation-based descriptors. The results show that acetyl group position affects system behavior despite identical acetylation levels. Different acetyl distributions lead to distinct hydrogen-bond topologies, altering both the strength and spatial organization of PU–CHI interactions. These differences translate into measurable variations in glass-transition trends, chain mobility, and mechanical response. Systems with acetyl groups located at specific backbone positions promote more effective interfacial bonding, whereas other configurations enhance self-association within the chitosan phase. Overall, the simulations demonstrate that acetyl positional patterning represents an important molecular parameter governing the emergent physical properties of PU–CHI composites, highlighting the sensitivity of supramolecular polymer systems to fine chemical details beyond global composition. This project has received funding from the European Union's Horizon Europe research and innovation programme under grant agreement No 101178590 and MUR Bando PRIN 2022 with No “PRIN202225EDELF_01”. References [1] https://doi.org/10.1007/s10973-020-09283-w. [2] https://doi.org/10.3390/polym12051205.