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

• Published in: Macromolecules Vol. 53; no. 22; pp. 10189 - 10197
• Main Authors: Zhang, Shuqing, Andre, John S, Hsu, Lorraine, Toolis, Amy, Esarey, Samuel L, Li, Bolin, Chen, Zhan
• Format: Journal Article
• Language: English
• Published: American Chemical Society 24.11.2020
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.0c01862

Polyurethane potting compounds and sealants, widely used as encapsulating and protective barriers, are usually applied to substrates after precoating substrate surfaces with primers. While the use of primers is known to improve adhesion properties of polyurethanes, fundamental mechanisms of adhesion enhancement are not fully understood due to the difficulties of direct observations at buried interfaces. Interfacial properties like adhesion are determined by interfacial molecular structures. In this study, sum frequency generation (SFG) vibrational spectroscopy was applied to investigate interfacial molecular structures in situ between a polyurethane potting compound and an isocyanate-based primer. The SFG signals of isocyanate groups from the primer initially were observed at the interface but disappeared after 16 h of polyurethane cure time. The following SFG experiments confirmed that interfacial reaction occurred at the interface between the polyurethane potting compound and the primer. Attenuated total reflectance (ATR)-FTIR spectroscopy and 180° peel tests were utilized as complementary techniques to support the SFG analyses. The results indicate that the formation of chemical bonds at the interface were responsible for the enhancement of adhesion. This study aims to help build on fundamental design principles toward the development of polymer materials with improved mechanical performance and other macroscopic interfacial properties.