Isocyanate Reactions

Isocyanates reactions are critical building blocks for high performance polyurethane-based polymers that make up coatings, foams, adhesives, elastomers and insulation. Concerns over exposure to residual isocyanates led to new limits for residual isocyanates in new products. Traditional analytical reaction methods for measuring the residual isocyanate (NCO) concentration using offline sampling and analysis raise concerns with:

• Long wait times for offline analytical results, making it impossible to make real-time decisions, leading to inconsistent product quality and reduction in production capacity
• Sufficient process knowledge lacking at any given time point
• Exposure to NCO samples increasing the risk of sensitization and human health risks

In situ monitoring with process analytical technology addresses these challenges. Specifically, in situ mid-IR spectroscopy with an attenuated total reflectance (ATR) sensor is an ideal choice due to its selectivity and sensitivity. Inline FTIR spectroscopy offers a straight-forward way to monitor reaction initiation, progression, conversion, intermediate (transient and/or highly reactive) formation, and endpoint in real time. FTIR spectroscopy can quantify NCO, polyol, by-products, and pre-polymer concentrations under reaction conditions, without taking samples for offline analysis. This enables manufacturers and formulators to ensure that product quality specifications, personnel safety, and environmental regulations are met.

In this example, a diisocyanate reacts with a polyol.  Several critical process parameters may affect the residual diisocyanate in the product, including temperature of the reaction, quality of the incoming starting material, feed rates, reaction kinetics, and reaction time.

To track reaction progression, an in situ FTIR spectroscopy probe is inserted directly into the vessel for the duration of the batch. Mid-infrared spectra are recorded every 60 seconds and plotted over time creating a three dimensional waterfall graph as shown to the right.  This plot depicts how a decrease in reactants is concurrent with an increase in the product as time progresses.  Results can also be depicted via reaction progression, displaying a plot of the relative concentration of each reaction component as a function of reaction time.

The mid-infrared absorbance values of the diisocyanate component trend are correlated to the ASTM titration method.  If a trend deviates from expected values, the in situ measurement can immediately detect the change from optimum or expected, and provide engineers and plant operators with the opportunity to make the necessary corrections during development or manufacture of the prepolymer.  This actionable information available in real-time reduces or eliminates the need to re-work batches that do not meet quality standards; this ensures residual NCO concentration meets specifications, while optimizing production capacity and lowering operating costs.

In situ monitoring with PAT provides process understanding to quantify isocyanate (NCO), polyol, by-products, and pre-polymer concentrations in real-time.  In this paper, in situ mid-infrared spectroscopy was applied to ensure product quality, personnel safety, and environmental regulations were met.

Infrared spectroscopy is widely used to improve the control of residual isocyanates (NCO).  Researchers in academia and industry employ in situ mid-FTIR spectroscopy routinely to provide comprehensive information rich experimental data that is used to advance research.

In situ ReactIR FTIR spectroscopy provides continuous monitoring of key reaction species and reaction progression. ReactIR provides specific information about reaction initiation, conversion, intermediates, and endpoint - even under challenging conditions that make offline sample and analysis difficult. Combining automated synthesis reactors with in situ analytical tools provides an additional level productivity by controlling and recording all reaction parameters 24 hours a day.

• Chemical Reaction Kinetics Studies
• Hydrogenation
• Sampling for Impurity Profiling
• Chemical Synthesis
• Continuous Flow Chemistry