Catalysis of isocyanate reaction with water by DMF and its use for fast preparation of uniform polyurea microspheres through precipitation polymerization

Toward Circular Recycling of Polyurethanes: Depolymerization and Recovery of Isocyanates

We report a depolymerization strategy to nearly quantitatively regenerate isocyanates from thermoplastic and thermoset polyurethanes (PUs) and then resynthesize PUs using the recovered isocyanates. To date, chemical/advanced recycling of PUs has focused primarily on the recovery of polyols and diamines under comparatively harsh conditions (e.g., high pressure and temperature), and the recovery of isocyanates has been difficult. Our approach leverages an organoboron Lewis acid to depolymerize PUs directly to isocyanates under mild conditions (e.g., ∼80 °C in toluene) without the need for phosgene or other harsh reagents, and we show that both laboratory-synthesized and commercially sourced PUs can be depolymerized. Furthermore, we demonstrate the utility of the recovered isocyanate in the production of second-generation PUs with thermal properties and molecular weights similar to those of the virgin PUs. Overall, this route uniquely provides an opportunity for circularity in PU materials and can add significant value to end-of-life PU products.

Application of molecular imprinting technology based on new nanomaterials in adsorption and detection of fluoroquinolones

Irrational use of fluoroquinolones (FQs) can lead to allergic reactions, adverse reactions to the heart and damage of the liver; thus, it is of great significance to establish rapid, sensitive and accurate detection methods for FQs. Molecularly imprinted polymers (MIPs) with specific structures synthesized by molecular imprinting technology (MIT) are widely used for the detection of FQs due to their high specificity, high sensitivity and stable performance. Recently, new functional nanomaterials with different morphologies and sizes, which can provide rich sites for surface chemical reactions, have attracted more and more attention of the researchers. Thus, the application status and development prospects of MIT based on new nanomaterials in the adsorption and detection of FQs were summarized in this study, providing a theoretical basis and technical guarantee for the development of new and efficient food safety analysis strategies based on MIPs.

Investigation of the Atmospheric Moisture Effect on the Molecular Behavior of an Isocyanate-Based Primer Surface

A primer coating is engineered to facilitate compatibility between products like adhesives, sealants, and potting compounds and targeted substrates. Prolonged exposure of isocyanate-based primer surfaces to the environment is known to negatively affect the interfacial adhesion between itself and the products subsequently applied on top of it. However, the molecular behavior behind this observed phenomenon remained to be further investigated. In this study, sum frequency generation (SFG) vibrational spectroscopy, a nonlinear optical spectroscopic technique, was applied to study the surface of an isocyanate-based primer exposed to different environments at the molecular level. Atmospheric moisture was considered to be a potential factor in impairing the adhesion performance of the primer, and thus, time- and humidity-dependent experiments were executed to monitor the molecular behavior at the primer surface using SFG. In addition, 180° peel testing experiments were conducted to measure the adhesion properties of primers after being exposed to the corresponding conditions to correlate to SFG results and establish a chemical structure-macroscopic performance relationship. This study on the changes at the primer surface in different environments with varied humidity levels as a function of time aims to provide an in-depth understanding of the moisture effect on isocyanate-based primers. These learnings may also be helpful toward exploring a broader range of coatings and surface layers and improving customer product use guidelines.

Fluorescent linear polyurea based on toluene diisocyanate: Easy preparation, broad emission and potential applications

In contrast to conventional fluorescent polymers featured by large conjugation structures, a new class of fluorescent polymers without above conjugations are gaining constant interest owing to their significant academic importance and promising applications in diverse fields. These unconventional fluorescent polymers are in general composed of heteroatoms (e.g. N, O, P, and S) under different forms. Here we report our recent study on polyurea, prepared by a very simple one step precipitation polymerization of toluene diisocyanate in a binary solvent of water-acetone. This polyurea, basically consisting of phenyl ring and urea group, shows fluorescent emission in a broad concentration range, from very low (10-5 mg/mL) to its solubility limit (50 mg/mL), and in a wide range of emission wavelength from UV to visible regions of up to 500 nm under varied excitation wavelength. The emission behaviors were fully studied under different concentrations and excitations. It was concluded that the emission in UV region was intrinsic due to the conjugation between the phenyl and the adjacent urea unit; while the emission in visible region, strongly excitation dependent, was caused by the cluster formation of the molecular chains, in accordance with the cluster-triggered-emission (CTE) mechanism. The formation of the cluster was tested through dynamic light scattering, FTIR and UV absorbance. Tested in presence of different metal ions, Fe3+ demonstrated a quenching effect with high selectivity. Based on this study, different paper-based sensors were designed to detect Fe3+, H2O2 in bioanalysis and for data encryption. This work provides a simple way to prepare a polyurea, a novel type of unconventional fluorescent polymer, with high emission performance distinct from its known analogues.

Highly Uniform and Porous Polyurea Microspheres: Clean and Easy Preparation by Interface Polymerization, Palladium Incorporation, and High Catalytic Performance for Dye Degradation

Owing to their high specific surface area and low density, porous polymer materials are of great importance in a vast variety of applications, particularly as supports for enzymes and transition metals. Herein, highly uniform and porous polyurea microspheres (PPM), with size between 200 and 500 μm, are prepared by interfacial polymerization of toluene diisocyanate (TDI) in water through a simple microfluidic device composed of two tube lines, in one of which TDI is flowing and merged to the other with flowing aqueous phase, generating therefore TDI droplets at merging. The polymerization starts in the tube while flowing to the reactor and completed therein. This is a simple, easy and effective process for preparation of uniform PPM. Results demonstrate that the presence of polyvinyl alcohol in the aqueous flow is necessary to obtain uniform PPM. The size of PPM is readily adjustable by changing the polymerization conditions. In addition, palladium is incorporated in PPM to get the composite microspheres Pd@PPM, which are used as catalyst in degradation of methylene blue and rhodamine B. High performance and good reusability are demonstrated. Monodispersity, efficient dye degradation, easy recovery, and remarkable reusability make Pd@PPM a promising catalyst for dye degradation.