Stability of Quadruple Hydrogen Bonds in an Ionic Liquid Environment

• Published in: Macromolecular rapid communications. 2024-01, Vol.45 (2), p.e2300464-n/a
• Main Authors: Li, Chenming, Bhandary, Rajesh, Marinow, Anja, Bachmann, Stephanie, Pöppler, Ann‐Christin, Binder, Wolfgang H.
• Format: Article
• Language: English
• Subjects: Bonding strength; Dimers; High temperature; Hydrogen Bonding; Hydrogen bonds; Infrared spectroscopy; Ionic liquids; Ionic Liquids - chemistry; Low molecular weights; Magnetic resonance spectroscopy; Microenvironments; Molecular weight; NMR spectroscopy; polymeric ionic liquids; Polymers - chemistry; Rheological properties; Rheology; Solvents - chemistry; Spectroscopy, Fourier Transform Infrared; Spectrum analysis; Stability; ureidopyrimidinone
• ISSN: 1022-1336; 1521-3927
• DOI: 10.1002/marc.202300464

Hydrogen bonds (H‐bonds) are highly sensitive to the surrounding environments owing to their dipolar nature, with polar solvents kown to significantly weaken H‐bonds. Herein, the stability of the H‐bonding motif ureidopyrimidinone (UPy) is investigated, embedded into a highly polar polymeric ionic liquid (PIL) consisting of pendant pyrrolidinium bis(trifluoromethylsulfonyl)imide (IL) moieties, to study the influence of such ionic environments on the UPy H‐bonds. The content of the surrounding IL is changed by addition of an additional low molecular weight IL to further boost the IL content around the UPy moieties in molar ratios of UPy/IL ranging from 1/4 up to 1/113, thereby promoting the polar microenvironment around the UPy‐H‐bonds. Variable‐temperature solid‐state MAS NMR spectroscopy and FT‐IR spectroscopy demonstrate that the UPy H‐bonds are largely present as (UPy‐) dimers, but sensitive to elevated temperatures (>70 °C). Subsequent rheology and DSC studies reveal that the ILs only solvate the polymeric chains but do not interfere with the UPy‐dimer H‐bonds, thus accounting for their high stability and applicability in many material systems. Hydrogen bonds (H‐bonds) are sensitive to the local microenvironments often weakened in polar surroundings to change the properties of materials they are embedded into. Herein, the presence of stable dimers of the quadruple H‐bonding motif ureidopyrimidinone (UPy) is proven in a polymeric ionic liquid as evidenced by solid‐state NMR and FT‐IR spectroscopy.