Energetic, Structural, and Vibrational Properties of 4,4′-Methylenediphenyl Diisocyanate with Relevance for Adhesion

Abstract

Through a polymerization process, the monomer 4,4'-methylenediphenyl diisocyanate can participate in glueing, whereby strong covalent bonds between the monomer and the substrates that will be glued have to be formed. In the present work, we use density functional theory (DFT) calculations to study a group of properties that are important for the initial steps of this process and for its experimental characterization. We focus on energetic and structural properties of a single monomer of 4,4'-methylenediphenyl diisocyanate as obtained using different theoretical approaches. We demonstrate that the molecule is chiral and that for each chirality, three different structures, differing in the orientations of the isocyanate groups, can be identified. The molecule is soft against certain geometry transformations and can, accordingly, easily take a structure that is optimal for the formation of covalent bonds with a substrate. Infrared spectroscopy may be used in identifying these covalent bonds, and therefore, these spectra were calculated, and we identify the most relevant vibrations in this context. Finally, changes in the properties when the monomer was modified or when it was allowed to interact with other molecules were studied, too.

Nondestructive In Situ Detection of Chemical Reactions at the Buried Interface between Polyurethane and Isocyanate-Based Primer

“…Recent studies provide insights by investigating adhesion mechanisms between isocyanates and different kinds of substrates, such as aluminum, gold, copper, steel, and epoxy resin surfaces. − Although both experimental tests and modeling have been utilized, most existing knowledge is established on selected model compounds and/or limited by the incapability of characterizing molecular structures directly and selectively at the buried interfaces. Thereby, the nature of a buried interface involving isocyanate functionality needs further investigation, especially for practical systems containing more diversified and multifunctional structures.…”

Physical behavior of electrostrictive polymers. Part 1: Polarization forces

“…at 300 K. This gives average dipole values of 1.18 Debye and 2.40 Debye for PTMO and MDI-BDO, respectively. There is also literature evidence of a larger dipole moment for MDI-BDO than for PTMO[42][43][44]. These calculations enable the HD and SD permittivities to be evaluated separately.…”