Intramolecular Hydrogen Bonds in Low‐Molecular‐Weight Polyethylene Glycol

Abstract

We used static DFT calculations to analyze, in detail, the intramolecular hydrogen bonds formed in low-molecular-weight polyethylene glycol (PEG) with two to five repeat subunits. Both red-shifted O-H⋅⋅⋅O and blue-shifting C-H⋅⋅⋅O hydrogen bonds, which control the structural flexibility of PEG, were detected. To estimate the strength of these hydrogen bonds, the quantum theory of atoms in molecules was used. Car-Parrinello molecular dynamics simulations were used to mimic the structural rearrangements and hydrogen-bond breaking/formation in the PEG molecule at 300 K. The time evolution of the H⋅⋅⋅O bond length and valence angles of the formed hydrogen bonds were fully analyzed. The characteristic hydrogen-bonding patterns of low-molecular-weight PEG were described with an estimation of their lifetime. The theoretical results obtained, in particular the presence of weak C-H⋅⋅⋅O hydrogen bonds, could serve as an explanation of the PEG structural stability in the experimental investigation.

Dynamic tensile and shear storage moduli of PEG/silica‐polymorph composites

“…More weak bonding broke as a higher temperature was introduced. From a previous study, it was found that there were two weak intramolecular interactions, that is, O‐H···O and C‐H···O hydrogen bonds, which manage the flexibility of PEG . Therefore, in general, a storage modulus decrease at a temperature below the melting point of a polymer‐based composite is due to the breakage of weak bonds in the polymer.…”

Structural and dynamical aspects of PEG/LiClO4 in solvent mixtures via NMR spectroscopy

“…The observed downfield shifts of PEG in the PEG/LiClO 4 /D 2 O mixtures are because of the breaking of intermolecular and intramolecular ─HCH⋯OCH 2 hydrogen‐bonded structure, suggesting that the H‐bonded structure of PEG molecules are greatly perturbed when the temperature of the medium is increased. The conformational changes occurring in PEG are due to the reorganization of the strong O─H⋯O and weak C─H⋯O H‐bond, which is also in support of this statement . Increasing the temperature of the medium results in a breakage of these intermolecular and intramolecular hydrogen‐bonded networks and consequently increases the polymer interactions with the D 2 O molecules through the weak D 2 O⋯HCH─ and strong O─D⋯OCH 2 H‐bonding interactions …”

“…The conformational changes occurring in PEG are due to the reorganization of the strong O─H⋯O and weak C─H⋯O H‐bond, which is also in support of this statement . Increasing the temperature of the medium results in a breakage of these intermolecular and intramolecular hydrogen‐bonded networks and consequently increases the polymer interactions with the D 2 O molecules through the weak D 2 O⋯HCH─ and strong O─D⋯OCH 2 H‐bonding interactions …”

“…The conformational changes occurring in PEG are due to the reorganization of the strong O─H⋯O and weak C─H⋯O H-bond, which is also in support of this statement. [35,36] Increasing the temperature of the medium results in a breakage of these intermolecular and intramolecular hydrogenbonded networks and consequently increases the polymer interactions with the D 2 O molecules through the weak D 2 O⋯HCH─ and strong O─D⋯OCH 2 H-bonding interactions. [9,35,36] The increased dipole moment of the ─CH bond with an increase in the temperature of the medium also contributes to the downfield shift of the ─CH bond because of the solvent disordering, as observed from our earlier report of the LiClO 4 salt mixtures of ionic liquids in water.…”

“…[35,36] Increasing the temperature of the medium results in a breakage of these intermolecular and intramolecular hydrogenbonded networks and consequently increases the polymer interactions with the D 2 O molecules through the weak D 2 O⋯HCH─ and strong O─D⋯OCH 2 H-bonding interactions. [9,35,36] The increased dipole moment of the ─CH bond with an increase in the temperature of the medium also contributes to the downfield shift of the ─CH bond because of the solvent disordering, as observed from our earlier report of the LiClO 4 salt mixtures of ionic liquids in water. [25] An increased solvent disordering around the EO unit of polymers has also been observed, which leads to an increased dipole moment of the ─CH bond of EO units, which is also in support of our argument.…”