Structure–Property Relationship between Hard Segments of Shape Memory Polyurethane Copolymers and Interchain Hydrogen Bonds: A Comprehensive Theoretical Study

Shape memory polymers have received increased interest from the scientific community, because of their extraordinary properties. Interchain hydrogen bonds play an important role in the shape memory property of polyurethane copolymers. This paper provides a comprehensive description of the interchain interactions' network of Hard Segments within shape memory polyurethane copolymers. Model systems included Hard Segments of different chemical compositions, mainly based on hexamethylene diisocyanate (HDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), toluene-2,4-diisocyanate (TDI), and diphenylmethane-4,4'-diisocyanate (MDI). <i>Ab initio</i> molecular dynamics was used to describe the reorganization of interchain hydrogen bonds, while the character and strength of hydrogen bonds were determined with the help of interaction energy decomposition (ETS) as well as analysis of the IR spectrum data. HDI- and MDI-based Hard Segments showed the formation of interchain hydrogen bonds of the highest strength, while the TDI-based Hard Segments formed the weakest interactions. The HMDI-based Hard Segments showed medium performance. The paper also demonstrates a direct relationship between the character of interchain hydrogen bonds of the studied hard-segmented models and thermal and mechanical experimental properties of polyurethane copolymers containing corresponding fragments.