Adhesive Interactions of Polyurethane Monomers with Native Metal Surfaces

Abstract

Understanding of fundamental adhesion is a key issue for bonding, polymer composites, and coatings. In this study, diluted solutions of polyurethane monomers (methylene diphenyl diisocyanate isomer mixture-MDI, polypropylene ether triol-PPET) are exposed to the native surfaces of Au, Al, and Cu. The adsorption state of the molecules (from multi-to sub-monolayers) is investigated in situ by infrared external reflection absorption spectroscopy (IR-ERAS). A sequence of solvent rinsing steps helps to distinguish physisorbed from chemisorbed molecules. PPET sticks very weakly to the metals. The spectra reveal a bulk-like state. MDI adsorbs weakly on Au but the spectra differ significantly from the bulk state. On Al and Cu, MDI establishes strong adhesion. Rich new spectral features indicate a probably chemical nature of adhesion, and a specific structure in the neighboring adsorbate layer. However, detailed final conclusions on the adhesion mechanisms must not be derived without appropriate quantum mechanical modeling.

Silane Deposition via Gas-Phase Evaporation and High-Resolution Surface Characterization of the Ultrathin Siloxane Coatings

“…Three siloxane particle types were formed in a sol–gel reaction with H 3 PO 4 as a catalyst. ,,, The materials were analyzed in the isotropic bulk liquid with FTIR–ATR, and the resulting spectra of APS (Figure a,b), GPS (Figure c,d), and FOS (Figure e,f) are shown.…”

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.…”

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

“…Ultimately, 4,4′-MDI is supposed to form covalent bonds to an (oxidized) metal surface, which could suggest that it will also form strong covalent bonds to other molecules. Tetrahydrofuran (THF), C 4 H 8 O, can be used in rinsing the samples when 4,4′-MDI is adsorbed on some metal surface, 7 and therefore, it is of relevance to study the 4,4′-MDI−THF interactions. Alternatively, it may also be possible that two 4,4′-MDI molecules will form some complex.…”

“…Because the experimental studies on the 4,4′-MDI deposited on a substrate may not involve a single 4,4′-MDI molecule, we will also study how the properties change when the 4,4′-MDI molecule is interacting with some other molecule. This other molecule will be either a second 4,4′-MDI molecule or a single tetrahydrofuran (THF) molecule, C 4 H 8 O, that can be used in rinsing the samples when 4,4′-MDI is adsorbed on some metal surface . Also the consequences of modifying the 4,4′-MDI molecule on its structural and energetic properties will be studied whereby additional information on those properties of 4,4′-MDI is obtained.…”

“…This other molecule will be either a second 4,4′-MDI molecule or a single tetrahydrofuran (THF) molecule, C 4 H 8 O, that can be used in rinsing the samples when 4,4′-MDI is adsorbed on some metal surface. 7 Also the consequences of modifying the 4,4′-MDI molecule on its structural and energetic properties will be studied whereby additional information on those properties of 4,4′-MDI is obtained.…”