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.

Trends in the Diels-Alder reaction in polymer chemistry.

Synergistic functionalization of h-BN by mechanical exfoliation and PEI chemical modification for enhancing the corrosion resistance of waterborne epoxy coating

4D printing of shape memory polymer composites: A review on fabrication techniques, applications, and future perspectives

[신간의 별자리iv] 세기의 겨울, 사냥꾼의 밤을 지나며_파국破局과 희망의 사이에서

Sustainable polymers are emerging fast and have received much more attention in recent years compared to petro-sourced polymers. However, they inherently have low-quality properties, such as poor mechanical properties, and inadequate performance, such as high flammability. In general, two methods have been considered to tackle such drawbacks: (i) reinforcement of sustainable polymers with additives; and (ii) modification of chemical structure by architectural manipulation so as to modify polymers for advanced applications. Development and management of bio-based polyurethanes with flame-retardant properties have been at the core of attention in recent years. Bio-based polyurethanes are currently prepared from renewable, bio-based sources such as vegetable oils. They are used in a wide range of applications including coatings and foams. However, they are highly flammable, and their further development is dependent on their flame retardancy. The aim of the present review is to investigate recent advances in the development of flame-retardant bio-based polyurethanes. Chemical structures of bio-based flame-retardant polyurethanes have been studied and explained from the point of view of flame retardancy. Moreover, various strategies for improving the flame retardancy of bio-based polyurethanes as well as reactive and additive flame-retardant solutions are discussed.

https://www.mdpi.com/2073-4360/12/6/1234/pdf

Flame Retardancy of Bio-Based Polyurethanes: Opportunities and Challenges.

An adhesive is a non-metallic substance used for the joining of two separate objects by applying it either on one side or both the sides of objects. One of the classifications of adhesives is based on the chemical nature, i.e. it can either be reactive or non-reactive, while the other segregates them depending upon the origin like natural or synthetic. The pressure-sensitive adhesives (PSAs) are one of the important classes following the mechanism of curing of the adhesive which do not undergo any chemical reaction or physical change during the adhesion process. PSAs are greatly replacing many conventional types of adhesive and are considered safe to use. The application of the hybrid polymers in the field of PSAs that consists of silane-curing organic compounds having wide formulation tolerance and outstanding mechanical properties is a major class in the upcoming PSA market. The present article discusses the various types of PSAs, their recent trends based on the various application properties with the structure–property relationship and their synthesis techniques.

Developments in pressure-sensitive adhesives: a review

Current research work focuses on the synthesis of phosphorus- and silicon-containing amine curing agent (PSA) for epoxy resins. PSA was synthesized using phenyl phosphonic dichloride and ethylenediamine as raw materials and further modification with 3-glycidoxypropyltrimethoxysilane. NMR, FTIR and amine value analysis were performed for the structure confirmation of the obtained product and intermediate. PSA was taken in different molar ratios for the crosslinking with epoxy resin before which the sol–gel technique was performed onto the product for self-crosslinking of the methoxy groups. The obtained formulations were applied onto the mild steel panels and cured in an oven. The thermal and mechanical properties of cured epoxy resins were analyzed by TGA, DSC, impact resistance, pencil hardness and flexibility. The thermal and mechanical properties were increased along with the heat resistance index temperature (THRI) toward the loading of PSA into the coating formulations. The flame retardant properties were also checked and found to be increased with respect to the increasing concentration of PSA because of the synergistic effect of P and Si atoms. The formulation with the highest amount of PSA showed the highest LOI as 29 with self-extinguishing behavior in the UL-94 test.

Phosphorus- and silicon-containing amino curing agent for epoxy resin

Cardanol derived P and Si based precursors to develop flame retardant PU coating

Shape memory polymers (SMPs) are among the main groups of smart materials widely used in smart textiles and apparels, intelligent medical devices, sensors & actuators, high-performance water–vapor permeability materials, morphing applications, and self-deployable structures in spacecraft. However, SMPs have some limitations: comparatively low tensile strength and stiffness, relatively low recovery stress, low thermal conductivity, inertness to electrical, light, and electromagnetic stimuli accompanied by slow responsibility and low recovery time during actuation, which often limits SMPs potential applications in high-performance field. In recent years, researchers have focused more on shape memory polymer nanocomposites (SMPNCs) than the classical composites to overcome this limitation of the SMPs, as nanofillers have a large surface area and strong interaction with polymers. This review thoroughly examines the progress in SMPNCs, including the very recent past, with a particular focus on their structure–property relationship. Considering all the SMPs, the most commonly used SMPs like polyurethane, epoxy, polycaprolactam, polylactic acid, and polyvinyl alcohol along with carbon-based (i.e., CNTs, carbon black, graphene oxide, graphene nanoplatelets, graphene quantum dots, nano-diamonds), metal oxide-based (i.e., Fe3O4, TiO2), cellulose-based (i.e., cellulose nanocrystals, nano-cellulose gel), and other nanomaterials like nano-clay, TiN, AuNRs, organic nanoparticles, silica, sepiolite, silsesquioxane, and hydroxyapatite nanofillers are discussed. The future development of SMPNCs may enhance their performance under thermal, electric, light (UV/NIR), magnetic, and solvent (pH/water) stimuli, which may open the door to more advanced applications in the field of aerospace, robotics, sensing and actuation, and biomedical.

Shape memory polymer nanocomposite: a review on structure–property relationship

Materials imparting flame retardancy play a pivotal role in the development of advanced materials due to their ability to reduce the annihilating effect of fire on man and environment. Realizing the commercial significance of epoxy resins, an attempt has been made to enhance their flame retardancy even under demanding conditions. Among the various flame-retardant materials, phosphorus-containing compounds are gaining interest both in academic and industrial areas due to their simple mechanism of action which involves char formation, a barrier between the substrate and the fire which protects the substrate from being burnt. In the present research work, unconventional starting material—diethanolamine—was used to synthesize phosphorus-based flame-retardant precursors. Intermediates formed in first step were reacted with epichlorohydrin to form epoxy resins. Structure of the compounds was confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, hydroxyl, and epoxy values. Resins were cured with commercial polyamide, and properties were compared with commercial epoxy resin. Coating films were characterized by various physical, mechanical, and thermal properties like impact resistance, pencil hardness, gloss, solvent resistance, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The TGA and DSC results showed that the char yield value has increased from 3.36 to 8.53%, and the glass transition temperature (Tg) has increased from 72.86 to 82.05°C while the initial degradation temperature decreased. Coatings showed excellent flame retardancy with maximum Limiting Oxygen Index value of 35 and a self-extinguishing behavior as confirmed by the UL-94 test.

Siddhesh Mestry

Papers

Developments in pressure-sensitive adhesives: a review

Phosphorus- and silicon-containing amino curing agent for epoxy resin

Cardanol derived P and Si based precursors to develop flame retardant PU coating

Shape memory polymer nanocomposite: a review on structure–property relationship

Synthesis of epoxy resins using phosphorus-based precursors for flame-retardant coating