A new recyclable crosslinked polymer combined polyurethane and epoxy resin

Eco-Friendly Epoxy-Terminated Polyurethane-Modified Epoxy Resin with Efficient Enhancement in Toughness

Polyurethane is widely used to toughen epoxy resins due to its excellent comprehensive properties and compatibility. However, some demerits of polyurethanes limit their applications, such as the harsh storage condition of isocyanate-terminated polyurethane (ITPU), the limited amount of ITPU in epoxy resin, and using solvents during the preparation of polyurethane-modified epoxy resins. To address these issues, in this study, we reported a facile and green approach for preparing epoxy-terminated polyurethane (EPU)-modified epoxy resins with different EPU contents. It was found that the toughness of the epoxy resin was significantly improved after the addition of EPU. When the EPU content was 30 wt%, the elongation at break and toughness were improved by 358.36% and 73.56%, respectively. In comparison, the toughening effect of EPU outperformed that of ITPU. Moreover, the high content of EPU did not significantly decrease the glass transition temperature and had little effect on the thermal stability of the epoxy resin.

Improving Epoxy Resin Performance Using PPG and MDI by One-Step Modification

The toughening modification of epoxy resin by polyurethane prepolymer (PU) can effectively solve the disadvantage of high brittleness in its application. In this study, a convenient way to toughen epoxy resins was explored, and the monomers PPG and MDI for the synthesis of polyurethane prepolymers were used for a one-step modification of epoxy resins. The test results of viscosity and elongation at break showed that P-M reduced the viscosity of the epoxy resin and improved the toughness. Especially when the content of P-M was 25%, the elongation at the break of the modified EP reached 196.56%. From a thermogravimetric and pyrolysis kinetic analysis, the P-M modification had better thermal stability than the PU modification. These findings have particular implications for the toughening and engineering applications of epoxy resins.

Oxime - Urethane Structure-based Dynamically Crosslinked Polyurethane with Robust Reprocessing Property

Crosslinked polyurethane with excellent mechanical property, solvent resistance and transparency has become one of the most widely used materials. However, the presence of chemical crosslinks makes it difficult to be reprocessed once moulded, which largely restricts its recycling and reusing, resulting in the serious waste problems. Therefore, it is of great significance to prepare a new type of crosslinked polyurethane with reprocessing function. In this work, a novel reprocessable polyurethane (DOPUs) based on reversible dibutanone oxime-carbamate bonds was facilely prepared. The gel fraction of DOPUs is all higher than 95%, endowing it with excellent solvent resistance. Meanwhile, the visible light transmittance of DOPUs can reach up to 97.48%. After four thermal recycles, the tensile strength and elongation at break of recycled DOPUs can still remain at 3.21 MPa and 219.09%, respectively. Importantly, the synthesized DOPUs exhibit excellent elastic shape memory and permanent shape reconstruction properties under thermal stimulation. The dibutanone oxime-carbamate bonds can also be degraded under UV irradiation, making this material easily degradable. Hence, this material has potential applications in coatings, elastomers and some other fields. This article is protected by copyright. All rights reserved.

Trends in the Diels-Alder reaction in polymer chemistry

The Diels-Alder (DA) reaction is regarded as quite a useful strategy in organic and macromolecular syntheses. The reversibility of this reaction and the advent of self-repair technology, as well as other applications in controlled macromolecular architectures and crosslinking, have strongly boosted the research activity, which is still attracting a huge interest in both academic and industrial research. The DA reaction is a simple and scalable toolbox. Though it is well-established that furan/maleimide is the most studied diene/dienophile couple, this perspective article reports strategies using other reversible systems with deeper features on other types of diene/dienophile pairs being either petro-sourced (cyclopentadiene, anthracene) or bio-sourced (muconic and sorbic acids, myrcene and farnesene derivatives, eugenol, cardanol). This review is composed of four sections. The first one briefly recalls the background on the DA reactions involving cyclodimerizations, dienes, and dienophiles, parameters affecting the reaction, while the second part deals with the furan/maleimide reaction. The third one deals with petro-sourced and bio-sourced (or products becoming bio-sourced) reactants involved in DA reactions are also listed and discussed. Finally, the authors' opinion is given on the potential future of the crosslinking-decrosslinking reaction, especially regarding the process (e.g., key temperatures of decrosslinking) or possibly monocomponents. It presents both fundamental and applied research on the DA reaction and its applications.

Probing the glass transition in reversible cross-linked polymer composites

Understanding the nature of glass transition is still a great challenge.