Designing New Sustainable Polyurethane Adhesives: Influence of the Nature and Content of Diels-Alder Adducts on Their Thermoreversible Behavior

With a view to the development of new sustainable and functional adhesives, two Diels-Alder (DA) adducts are incorporated as a third component into the curing process of solvent-based and solvent-free polyurethanes in this study. The influence of the nature and content of the DA molecules on the retro-DA (rDA) reaction and its reversibility and cyclability is investigated. It is demonstrated that the bonding/debonding properties of the adhesives are mainly controlled by the concentration of the DA adducts, with a minimum thermoreversible bond (TB) content required that depends on the system and the total ratio between all the diols in the formulation. For the solvent-based system, rDA/DA reversibility can be repeated up to ~20 times without deterioration, in contrast to the solvent-free system where a gradual loss in the DA network reconstruction efficiency is observed. Despite this limitation, the solvent-free system presents clear advantages from an environmental point of view. The changes observed in the physical properties of these new thermoreversible adhesives are of great relevance for recycling strategies and, in particular, their potential for separating multilayered film packaging materials in order to recycle the individual polymer films involved.

An Overview of Self-Healable Polymers and Recent Advances in the Field

The search for materials with better performance, longer service life, lower environmental impact, and lower overall cost is at the forefront of polymer science and material engineering. This has led to the development of self-healing polymers with a range of healing mechanisms including capsular-based, vascular, and intrinsic self-healing polymers. The development of self-healable systems has been inspired by the healing of biological systems such as skin wound healing and broken bone reconstruction. The goal of using self-healing polymers in various applications is to extend the service life of polymers without the need for replacement or human intervention especially in restricted access areas such as underwater/underground piping where inspection, intervention, and maintenance are very difficult. Through an industrial and scholarly lens, this paper provides (a) an overview of self-healing polymers, (b) classification of different self-healing polymers and polymer-based composites, (c) mechanical, thermal, and electrical analysis characterization, (d) applications in coating, composites, and electronics, (e) modeling and simulation, and (f) recent development in the past 20 years . This review highlights the importance of healable polymers for an economically and environmentally sustainable future, the most recent advances in the field, and current limitations in fabrication, manufacturing, and performance. This article is protected by copyright. All rights reserved.

Blocking and Deblocking of Diisocyanate to Synthesize Polyurethanes

Diisocyanates, particularly toluene diisocyanate (TDI), are useful for the preparation of various polyurethanes with specific applications as leather-like materials, adhesives and insoles, etc. Blocking agents can be used for the operational simplicity and to reduce the hazards of TDI. In this paper, we reported the use of 3-(4-bromo-phenyl)-1H-pyrazole to block toluene diisocyanate (TDI). FTIR, NMR, thermogravimetric analysis, contact angle analysis and differential scanning calorimetry (DSC) were used for the characterization. The effectiveness of the blocking was confirmed by spectroscopic techniques. The DSC thermogram showed that blocked adducts deblock at 240 °C, causing the regeneration of TDI, and causing the diisocyanates to react with polyols of different molecular weights, forming polyurethanes. The characterization of the polyurethanes was performed by infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry and a contact angle study.

Thermally Remendable Polyurethane Network Cross-Linked via Reversible Diels-Alder Reaction

We prepared a series of thermally remendable and recyclable polyurethanes crosslinked via reversible furan-maleimide Diels-Alder reaction based on TDI end-caped branched Voranol 3138 terminated with difurfurylamine and 4,4'-bis(maleimido)diphenylmethane (BMI). We showed that Young modulus strongly depends on BMI content (from 8 to 250 MPa) that allows us to obtain materials of different elasticity as simple as varying BMI content. The ability of DA and retro-DA reactions between furan and maleimide to reversibly bind material components was investigated by NMR spectroscopy, differential scanning calorimetry, and recycle testing. All polymers obtained demonstrated high strengths and could be recovering without significant loss in mechanical properties for at least five reprocessing cycles.

Renewable Responsive Systems Based on Original Click and Polyurethane Cross-Linked Architectures with Advanced Properties

A new chemical architecture from oleic acid, consisting of a diol structure containing pendant furan rings, denoted the furan oligomer (FO) was synthesized and fully characterized. The FO was integrated into a linear rapeseed-based polyurethane (PU) backbone and cross-linked through a Diels-Alder (DA) reaction by using pendant furan rings and a short polypropylene oxide-based bismaleimide. This is the first time that a thermoreversible PU network based on vegetable oil has been reported. The effects of varying proportions of FO in linear and cross-linked systems, by DA, were studied. These materials were analyzed by classic characterization techniques. The stability and recyclability of the cross-linked materials were shown by successive reprocessing cycles and reanalyzing the mechanical properties. Self-healing properties were macroscopically exhibited and investigated by tensile tests on healed materials. The resulting cross-linked materials present a large range of properties, such as tunable mechanical and thermoresponsive behavior, good thermal recyclability, and self-healing abilities.

Facile Preparation of Highly Stretchable and Recovery Peptide-Polyurethane/Ureas

In this work, a new class of highly stretchable peptide-polyurethane/ureas (PUUs) were synthesized containing short β-sheet forming peptide blocks of poly(γ-benzyl-l-glutamate)-b-poly(propylene glycol)-b-poly(γ-benzyl-l-glutamate) (PBLG-b-PPG-b-PBLG), isophorone diisocyanate as the hard segment, and polytetramethylene ether glycol as the soft phase. PBLG-b-PPG-b-PBLG with short peptide segment length (<10 residues) was synthesized by amine-initiated ring opening polymerization of γ-benzyl-l-glutamate-N-carboxyanhydrides (BLG-NCA), which shows mixed α-helix and β-sheet conformation, where the percent of β-sheet structure was above 48%. Morphological studies indicate that the obtained PUUs show β-sheet crystal and nanofibrous structure. Mechanical tests reveal the PUUs display medium tensile strength (0.25⁻4.6 MPa), high stretchability (>1600%), human-tissue-compatible Young's modulus (226⁻513 KPa). Furthermore, the shape recovery ratio could reach above 85% during successive cycles at high strain (500%). In this study, we report a facile synthetic method to obtain highly stretchable and recovery peptide-polyurethane/urea materials, which will have various potential applications such as wearable and implantable electronics, and biomedical devices.

Polyurethane with an ionic liquid crosslinker: a new class of super shape memory-like polymers

Polyurethane (PU) with an ionic liquid crosslinker (with a unique double network having a combination of covalent as well as ionic crosslinking) showed excellent shape-recovery as well as excellent shape-fixity properties compared to linear PU and non-ionic crosslinked PU. The non-ionic crosslinker resulted in hard and soft phases intermixing, whereas the ionic interaction in ionic liquid crosslinked PU kept the phase separation intact.