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The conversion of industrially produced greenhouse gases, like CO2, into value-added chemicals is economically beneficial to industry and vital for environmental conservation. However, the conditions for these conversions must themselves be sustainable. In this work, polyurethane (PU) was used to catalyze the formation of five-membered cyclic carbonates (5CCs) via cycloaddition of epoxides and CO2. Using optimized conditions, the representative epoxide, phenyl glycidyl ether, afforded the corresponding 5CC (PGE-5CC) in a quantitative yield with remarkable selectivity (>99%). The PU catalyst does not degrade during the reaction and is separable by simple filtration. In addition, PU could catalyze the 5CC synthesis at least 10 times without loss of catalytic activity and is applicable to a wide range of substituted epoxides. This study pioneers the utilization of polyurethane as an easily recycled catalyst in halogen-free and metal-free reactions for the repurposing of CO2 waste., ACS Sustainable Chemistry & Engineering, 8(11), pp.4337-4340; 2020

We have developed a synthetic methodology using poly(hydroxyurethane) as an organocatalyst for the chemical fixation of CO2 into epoxides, leading to the formation of five-membered cyclic carbonates with remarkably high selectivity and yields. The catalyzed reaction was applicable to various epoxides., Chemical Communications, 56(73), pp.10678-10681; 2020

We have demonstrated a hydrolysis reaction of polyurethane (PU) under high pressure of carbon dioxide (CO2) in water. We employed the PU sample, poly(methylene bis-(1,4-phenylene)hexamethylene dicarbamate), denoted as M-PU, which was synthesized from 4,4′-diphenyl methane diisocyanate and 1,4-butane diol (BD). The optimum hydrolysis reaction condition was 190 °C under CO2 pressures over 4.1 MPa in water medium, and 93% hydrolysis of M-PU was achieved. After the reaction, the water-soluble parts were obtained, and isolated by column chromatography. The isolated products were 4,4′-methylenedianiline (MDA) and 1,4-butane diol (BD), which were components of repeating unit of M-PU. In addition, the hydrolysis reaction gave no byproduct. This hydrolysis under high pressure of CO2 with water is a reaction by which M-PU is selectively hydrolyzed into MDA and BD by cleaving urethane linkage. Moreover, the resulting hydrolyzed products were easily obtained by evaporation of aqueous layer after the reaction, indicating an efficient chemical recycling of PU was achieved., Journal of Polymer Science Part A: Polymer Chemistry, 55(12), pp.2004-2010; 2017

In order to develop a chemical recycling system of polyurethanes (PUs), environment-friendly hydrolysis of two types of aliphatic PUs was studied under pressured CO2 in water, in which the carbonic acid generated from CO2 acted as an acid catalyst. Two PUs, namely H-PU or I-PU, were synthesized starting from 1,4-butanediol and 1,6-hexamethylene diisocyanate or isophorone diisocyanate, respectively. The hydrolysis of PUs depended on the experimental conditions, such as the temperature and CO2 pressure. As a result, 98% of H-PU and 91% of I-PU were successfully hydrolyzed under the typical conditions of 190?°C for 24 h at 8.0 MPa CO2. The reaction mixtures afforded 1,4-butanediol and diamines without the formation of any byproducts. Both of these raw materials generated from the originated PUs by selective hydrolytic cleavage of the urethane linkages, and they were easily isolated in high yields simply by evaporation of the water-soluble components within the reaction mixture. By comparing the results of the two aliphatic PUs with those of an aromatic PU (M-PU), the hydrolyzability was found to decrease in the order H-PU, I-PU, and M-PU. The difference can be ascribed to the hydrophilicity of the aliphatic or aromatic groups connected to the urethane moieties at the terminals of PUs., Journal of Applied Polymer Science

A chemical decomposition of polyurea (PUA) by hydrolysis under high pressure of carbon dioxide (CO2) was proposed. The hydrolysis of PUA was carried out at 190 °C for 2 h under 7.0 MPa of CO2 in the presence of water. The hydrolysis reaction gave white residual solid and water soluble compound. The white residual solid was characterized to be degraded PUA by FT-IR spectrum and elemental analysis. 1H-NMR spectra of the water soluble compound revealed that the hydrolysis of PUA produced diamine only from repeating unit of PUA, which was a component of PUA. This hydrolysis gave the corresponding diamine for quantitative yields., Polymer Bulletin, 74(3), pp.615?623; 2017