Surface/interfacial changes during polyurethane crosslinking: A spectroscopic study. V *

Abstract

Crosslinking reactions and stratification processes in polyurethane films were investigated using attenuated total reflectance (ATR) FTIR spectroscopy. The HDI trimer levels near the film–substrate (F–S) interface appear to increase at the early stages of reactions, and after reaching a maximum, decrease. This is attributed to solvent depletion and subsequent film shrinkage, thus causing local NCO concentration changes. At the later stages of crosslinking reactions, stratification of the 1,6‐hexamethylene diisocyanate (HDI) trimer occurs, with higher concentration levels at shallower penetration depths from the F–S interface. At the same time, NCO‐containing groups assume preferentially parallel orientation to the F–S interface. On the other hand, H‐bonded carbonyl groups tend to orient themselves in a perpendicular direction. Quantitative analysis indicates that at extended reaction times the amount of H‐bonded CO groups at shallower penetration depths increases and their orientation tends to be more random, which is correlated with migration toward the F–S interface. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2045–2054, 2001

Well-Ordered Self-Assembled Monolayers Created via Vapor-Phase Reactions on a Monolayer Template

“…RAIR spectra of the low-energy modes associated with the carbamate vibrations are shown in Figure . The lowest frequency modes at 1152 and 1060 cm -1 are attributed to the (O)C−O−C stretch and the C−O−C stretch, respectively. ,, The amide II peak, a C−N stretch coupled with an N−H bend, is located at 1548 cm -1 , and the amide III stretch is positioned at 1277 cm -1 . The amide III mode exhibits shoulders at ∼1304 and ∼1255 cm -1 , likely due to multiple environments of the buried carbamate groups .…”

Surface Phase Partitioning in Film Formation of Waterborne Polyurethanes. Monte Carlo Simulations and Internal-Reflectance IR Imaging

“…While laboratory measurements provide the opportunity to examine the effect of external and internal stimuli (temperature, molecular weight, reactivity of individual components, solubility, and others) on the film formation, [8][9][10] computer simulations offer other advantages in understanding the macroscopic properties evolving from the microscopic details in response to such stimuli. 11 For example, the effects of molecular weight, driving field, and temperature on the film formation can be studied effectively.…”

“…Understanding the film formation mechanisms, in particular for thermosetting polymeric systems, has attracted considerable interests of experimentalists − as well as theoreticians − in recent years. While laboratory measurements provide the opportunity to examine the effect of external and internal stimuli (temperature, molecular weight, reactivity of individual components, solubility, and others) on the film formation, − computer simulations offer other advantages in understanding the macroscopic properties evolving from the microscopic details in response to such stimuli . For example, the effects of molecular weight, driving field, and temperature on the film formation can be studied effectively. , This is particularly important when multicomponent systems are considered; even though there are difficulties associated with computational analysis because of the increased number of parameters and chemical reactivity of the system, computer simulations remain the useful theoretic tool to probe such a complex system.…”