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.

KEYWORDS:

• Chemical adhesion
• IR external reflection absorption spectroscopy
• Methylene diphenyl diisocyanate
• Native metal surfaces
• Polypropylene ether triol

ACKNOWLEDGMENT

This work was kindly supported by Bayer MaterialScience AG, Germany and by the National Research Fund, Luxembourg.

Notes

One of a Collection of Papers honoring Wulff Possart, the recipient in February 2012 of The Adhesion Society Award for Excellence in Adhesion Science, Sponsored by 3M.