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Differentiating urethane and urea bond activation in polyurethane foam acidolysis
Madeleine Davis1, Kelsey Richardson2, Zach Westman2
1Department of Chemistry and Biochemistry, University of California Santa Barbara Santa Barbara CA 93106-9510 USA.
Chemical Science
|December 12, 2025
Summary
Chemical recycling of polyurethane foams (PUFs) is advanced by distinguishing urea and urethane bond acidolysis rates. Urethane bonds cleave rapidly, while urea bonds react slower and depend on acid structure, enabling efficient PU foam recycling strategies.
Area of Science:
- Polymer Chemistry
- Sustainable Materials Science
- Chemical Engineering
Background:
- Polyurethane (PU) is a widely produced plastic, often as flexible foam (PUF), posing recycling challenges.
- Chemical recycling of PUFs, particularly acidolysis, offers a sustainable method to recover valuable polyols.
- Previous research has not differentiated the acidolysis rates of urea and urethane linkages in PUFs.
Purpose of the Study:
- To distinguish and quantify the relative acidolysis rates of urea and urethane bonds in polyurethane.
- To investigate the influence of acid structure on the depolymerization kinetics of PUFs.
- To provide insights for designing more recyclable polyurethane materials and optimizing chemical recycling processes.
Main Methods:
- Acidolysis of polyurethane foams using benzoic acid and its analogues.
- Monitoring depolymerization via gas evolution, Gel Permeation Chromatography (GPC), and Nuclear Magnetic Resonance (NMR) spectroscopy.
- Employing Density Functional Theory (DFT) calculations to elucidate reaction mechanisms and transition states.
Main Results:
- Polyurethane acidolysis exhibits biphasic kinetics, with faster urethane bond cleavage and slower urea bond cleavage.
- Urethane bond acidolysis rates are unaffected by electronic modifications of the carboxylic acid.
- Urea bond acidolysis rates show a strong correlation with the electronic structure of the acid (Hammett ρ = 3.00 ± 0.01).
- DFT calculations reveal transition state differences contributing to the observed reactivity disparities.
Conclusions:
- The distinct reactivity of urea and urethane bonds in acidolysis is quantified, revealing urethane's higher susceptibility.
- The sensitivity of urea bond cleavage to acid electronics provides a basis for tuning recycling conditions.
- Findings support the development of more efficient chemical recycling strategies for polyurethanes and the design of inherently recyclable PU foams.
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