Intrinsic self-healing thermoset through covalent and hydrogen bonding interactions

Artificial intelligence models for predicting calcium and magnesium removal by polyfunctional ketone using ensemble machine learners

Calcium (Ca2+) and magnesium (Mg2+) are the major scaling ions of reverse osmosis concentrate in zero-liquid discharge systems, causing performance decline. In this study, we predicted the removal of Ca2+ and Mg2+ from simulated reverse osmosis concentrate by functional polyketones (FPKs). Four amines, including 1,2-diaminopropane (DAP), 1-(2-aminoethyl) piperazine (AEP), 1-(3-aminopropyl) imidazole (API), and butyl amine (BA) used to synthesize FPKs. The effects of various factors such as the amount of adsorbent, feed water concentration, and pH were investigated for process optimization. In this study, ensemble learner artificial intelligence models, decision tree (DT), extreme gradient boost (XGB), and random forest (RF) were used to predict Ca2+ and Mg2+ removal by the FPKs. Datasets were collected experimentally using FPKs to remove Ca2+ and Mg2+ from the simulated reverse osmosis concentrate. The predictions were made by XGB, DT, and RF models for the first chosen amine for Ca2+ and then for Mg2+, subsequently, this process was repeated with each amine. The developed DT, RF, and XGB models demonstrated higher coefficients of determination for predicting Mg2+ removal by AEP and DAP (R2 = 0.841-0.935) than by API and BA (R2 = 0.774-0.801) except in the RF and XGB model results (R2 = 0.801-0.846). Overall, the XGB model displayed good results for both Ca2+ and Mg2+ removal but slight changes were observed in the AEP and BA predictions by DT and RF. Therefore, artificial intelligence models may be a viable alternative for further insight in predicting Ca2+ and Mg2+ removal by FPKs from simulated reverse osmosis concentrate.

Electroactive Thermo-Pneumatic Soft Actuator with Self-Healing Features: A Critical Evaluation

Soft actuators that operate with overpressure have been successfully implemented as soft robotic grippers. Naturally, as these pneumatic devices are prone to cuts, self-healing properties are attractive. Here, we prepared a gripper that operates based on the liquid-gas phase transition of ethanol within its hollow structure. The gripping surface of the device is coated with a self-healing polymer that heals with heat. This gripper also includes a stainless steel wire along the device that heats the entire structure through resistive heating. This design results in a soft robotic gripper that actuates and heals in parallel driven by the same practical stimulus, that is, electricity. Compared to other self-healing soft grippers, this approach has the advantage of being simple and having autonomous self-healing. However, there remain fundamental drawbacks that limit its implementation. The current work critically assesses this overpressure approach and concludes with a broad perspective regarding self-healing soft robotic grippers.

Evaluation of Effective Crosslinking Density for Pseudo-Semi Interpenetrating Polymer Networks Based on Polyether Glycols Mixture by Dynamic Mechanical Analysis

Pseudo-semi interpenetrating polymer networks (pseudo-semi IPNs) are a special example of topological isomerism in macromolecules, which have attracted significant attention in recent years with a high potential in a variety of engineering applications of polymeric materials. In this article, pseudo-semi IPNs were synthetized by sequential polymerization of thermoplastic polymers (TPEs) in the presence of thermosetting elastomer (TSEs) with contents of 10, 20, 30, 40 and 50 wt.% in a vacuum oven at 60 °C for about 72 h. In addition, this article describes a method for researching the elastic modulus, effective crosslinking density and physical crosslinking density of TSEs and pseudo-semi IPNs. The inherent interactions and entanglements of pseudo-semi IPNs were discussed by analyzing the changes in elastic modulus and effective crosslinking density at different temperatures. The results show that after the TPE was added to the TSE matrix as a plastic-reinforced material, the ductility increased from 89.6% to 491%, the effective crosslinking density was increased by 100% at high temperatures and the strength of the material matrix was significantly improved. Two physical events take place in our pseudo-semi IPNs as result of energy dissipation and polymeric chains mobility.

Cross-Linking of Polypropylene with Thiophene and Imidazole

In this work, two novel routes to synthesis cross-linked polypropylene (PP) are introduced by using two different precursors (2-thiophenemethyl amine (TMA) and 1-(3 aminopropyl) imidazole (API)), both cross-linked with 1,1′-(methylenedi-4,1-phenylene) bismaleimide (BM) at two different annealing temperature values (T = 50 °C and T = 150 °C). Both Diels–Alder (DA) and Michael addition reactions were successfully performed with TMA and API, respectively, albeit with different reactivity. Imidazole clearly shows a higher reactivity compared to thiophene. In addition, an increase in annealing temperature leads to a higher degree of cross-linking. The highest degree of cross-linking was obtained by the imidazole product after annealing at 150 °C (IMG1A150) as evident from the highest complex viscosity (|η*|) value of IMG1A150. A difference in rheology and thermal properties between the imidazole and thiophene cross-linked products was also observed. However, both products have superior melt properties and thermal stability compared with the starting material. They show processability at high temperatures. The melt flow behavior and de-cross-linking at higher temperatures can be tuned depending on the choice of imidazole or thiophene. This study shows an advance on the cross-linked PP processing and its product performances for further application on the commercial scale.

Cross-Linking of Polypropylene via the Diels-Alder Reaction

In this work, the possibility of preparing cross-linked polypropylene (PP) via Diels−Alder (DA) chemistry is explored. The overall strategy involves reaction of maleated polypropylene (the starting material), furfuryl amine (FFA), and bismaleimide (BM) as the cross-linking agent. The occurrence of reversible cross-linking was studied by checking the presence of relevant peaks in FTIR spectra, i.e., CH out-of-plane bending vibrations of the furan ring’s peak (γCH) at an absorption band of 730−734 cm−1, CH=CH of the BM aromatic ring’s stretching vibrations (υCH=CH) at an absorption band of 1510 cm−1, and the DA adduct (C-O-C, δDAring) at an absorption band of 1186 cm−1. In agreement with the spectroscopic characterization, the presence of a cross-linked network is also confirmed by rheology, namely the higher storage modulus (G′) compared with loss modulus (G″) value (G′ >> G″), as obtained via temperature sweep. Both the maleic anhydride (MA) content as well as the annealing temperature (50 °C and 120 °C) favor the DA reaction, while only partial de-cross-linking (retro DA) is observed at the higher temperature range of 150−200 °C. In addition, the products show higher mechanical robustness and thermal stability compared to the starting material.

Maleimide Self-Reaction in Furan/Maleimide-Based Reversibly Crosslinked Polyketones: Processing Limitation or Potential Advantage?

Polymers crosslinked via furan/maleimide thermo-reversible chemistry have been extensively explored as reprocessable and self-healing thermosets and elastomers. For such applications, it is important that the thermo-reversible features are reproducible after many reprocessing and healing cycles. Therefore, side reactions are undesirable. However, we have noticed irreversible changes in the mechanical properties of such materials when exposing them to temperatures around 150 °C. In this work, we study whether these changes are due to the self-reaction of maleimide moieties that may take place at this rather low temperature. In order to do so, we prepared a furan-grafted polyketone crosslinked with the commonly used aromatic bismaleimide (1,1'-(methylenedi-4,1-phenylene)bismaleimide), and exposed it to isothermal treatments at 150 °C. The changes in the chemistry and thermo-mechanical properties were mainly studied by infrared spectroscopy, ¹H-NMR, and rheology. Our results indicate that maleimide self-reaction does take place in the studied polymer system. This finding comes along with limitations over the reprocessing and self-healing procedures for furan/maleimide-based reversibly crosslinked polymers that present their softening (decrosslinking) point at relatively high temperatures. On the other hand, the side reaction can also be used to tune the properties of such polymer products via in situ thermal treatments.

Thermally Switchable Electrically Conductive Thermoset rGO/PK Self-Healing Composites

Among smart materials, self-healing is one of the most studied properties. A self-healing polymer can repair the cracks that occurred in the structure of the material. Polyketones, which are high-performance thermoplastic polymers, are a suitable material for a self-healing mechanism: a furanic pendant moiety can be introduced into the backbone and used as a diene for a temperature reversible Diels-Alder reaction with bismaleimide. The Diels-Alder adduct is formed at around 50 °C and broken at about 120 °C, giving an intrinsic, stimuli-responsive self-healing material triggered by temperature variations. Also, reduced graphene oxide (rGO) is added to the polymer matrix (1.6-7 wt%), giving a reversible OFF-ON electrically conductive polymer network. Remarkably, the electrical conductivity is activated when reaching temperatures higher than 100 °C, thus suggesting applications as electronic switches based on self-healing soft devices.

pH-Responsive Polyketone/5,10,15,20-Tetrakis-(Sulfonatophenyl)Porphyrin Supramolecular Submicron Colloidal Structures

In this work, we prepared color-changing colloids by using the electrostatic self-assembly approach. The supramolecular structures are composed of a pH-responsive polymeric surfactant and the water-soluble porphyrin 5,10,15,20-tetrakis-(sulfonatophenyl)porphyrin (TPPS). The pH-responsive surfactant polymer was achieved by the chemical modification of an alternating aliphatic polyketone (PK) via the Paal–Knorr reaction with N-(2-hydroxyethyl)ethylenediamine (HEDA). The resulting polymer/dye supramolecular systems form colloids at the submicron level displaying negative zeta potential at neutral and basic pH, and, at acidic pH, flocculation is observed. Remarkably, the colloids showed a gradual color change from green to pinky-red due to the protonation/deprotonation process of TPPS from pH 2 to pH 12, revealing different aggregation behavior.

Electrically-Conductive Polyketone Nanocomposites Based on Reduced Graphene Oxide

In this work, we investigated the functionalization of polyketone 30 (PK30) with glycyl-glycine (Gly-Gly) via the Paal-Knorr reaction with the aim of homogenously dispersing two types of reduced graphene oxide (rGO, i.e., lrGO and hrGO, the former characterized by a lower degree of reduction in comparison to the latter) by non-covalent interactions. The functional PK30-Gly-Gly polymer was effective in preparing composites with homogeneously distributed rGO characterized by an effective percolation threshold at 5 wt. %. All the composites showed a typical semiconductive behavior and stable electrical response after several heating/cooling cycles from 30 to 115 °C. Composites made by hrGO displayed the same resistive behaviour even if flanked by a considerable improvement on conductivity, in agreement with the more reduced rGO content. Interestingly, no permanent percolative network was shown by the composite with 4 wt. % of lrGO at temperatures higher than 45 °C. This material can be used as an ON-OFF temperature sensor and could find interesting applications as sensing material in soft robotics applications.

Advances in intrinsic self-healing polyurethanes and related composites

Fascinating and challenging, the development of repairable materials with long-lasting, sustainable and high-performance properties is a key-parameter to provide new advanced materials. To date, the concept of self-healing includes capsule-based healing systems, vascular healing systems, and intrinsic healing systems. Polyurethanes have emerged as a promising class of polymeric materials in this context due to their ease of synthesis and their outstanding properties. This review thereby focuses on the current research and developments in intrinsic self-healing polyurethanes and related composites. The chronological development of such advanced materials as well as the different strategies employed to confer living-like healing properties are discussed. Particular attention will be paid on chemical reactions utilized for self-healing purposes. Potential applications, challenges and future prospects in self-healing polyurethane fields are also provided.

Electrically Self-Healing Thermoset MWCNTs Composites Based on Diels-Alder and Hydrogen Bonds

In this work, we prepared electrically conductive self-healing nanocomposites. The material consists of multi-walled carbon nanotubes (MWCNT) that are dispersed into thermally reversible crosslinked polyketones. The reversible nature is based on both covalent (Diels-Alder) and non-covalent (hydrogen bonding) interactions. The design allowed for us to tune the thermomechanical properties of the system by changing the fractions of filler, and diene-dienophile and hydroxyl groups. The nanocomposites show up to 1 × 10⁴ S/m electrical conductivity, reaching temperatures between 120 and 150 °C under 20-50 V. The self-healing effect, induced by electricity was qualitatively demonstrated as microcracks were repaired. As pointed out by electron microscopy, samples that were already healed by electricity showed a better dispersion of MWCNT within the polymer. These features point toward prolonging the service life of polymer nanocomposites, improving the product performance, making it effectively stronger and more reliable.

Data on production and characterization of melamine-furan-formaldehyde particles and reversible reactions thereof

The data present in this article affords insides in the characterization of a newly described bi-functional furan-melamine monomer, which is used for the production of monodisperse, furan-functionalized melamine-formaldehyde particles, as described in https://doi.org/10.1016/j.eurpolymj.2019.04.006 Urdl et al., 2019. In the related research article Urdl et al., 2019 data interpretations can be found. The furan-functionalization of particles is necessary to perform reversible Diels-Alder reactions with maleimide (BMI) crosslinker to form thermoreversible network systems. To understand the reaction conditions of Diels-Alder (DA) reaction with a Fu-Mel monomer and a maleimide crosslinker, model DA reaction were performed and evaluated using dynamic FT-IR measurements. During retro Diels-Alder (rDA) reactions of the monomer system, it was found out that some side reaction occurred at elevated temperatures. The data of evaluating the side reaction is described in one part of this manuscript. Additional high resolution SEM images of Fu-Mel particles are shown and thermoreversible particle networks with BMI2 are shown. The data of different Fu-Mel particle networks with maleimide crosslinker are presented. Therefore, the used maleimide crosslinker with different spacer lengths were synthesized and the resulting networks were analyzed by ATR-FT-IR, SEM and DSC.

Electrically-Responsive Reversible Polyketone/MWCNT Network through Diels-Alder Chemistry

This study examines the preparation of electrically conductive polymer networks based on furan-functionalised polyketone (PK-Fu) doped with multi-walled carbon nanotubes (MWCNTs) and reversibly crosslinked with bis-maleimide (B-Ma) via Diels-Alder (DA) cycloaddition. Notably, the incorporation of 5 wt.% of MWCNTs results in an increased modulus of the material, and makes it thermally and electrically conductive. Analysis by X-ray photoelectron spectroscopy indicates that MWCNTs, due to their diene/dienophile character, covalently interact with the matrix via DA reaction, leading to effective interfacial adhesion between the components. Raman spectroscopy points to a more effective graphitic ordering of MWCNTs after reaction with PK-Fu and B-Ma. After crosslinking the obtained composite via the DA reaction, the softening point (tan(δ) in dynamic mechanical analysis measurements) increases up to 155 °C, as compared to the value of 130 °C for the PK-Fu crosslinked with B-Ma and that of 140 °C for the PK-Fu/B-Ma/MWCNT nanocomposite before resistive heating (responsible for crosslinking). After grinding the composite, compression moulding (150 °C/40 bar) activates the retro-DA process that disrupts the network, allowing it to be reshaped as a thermoplastic. A subsequent process of annealing via resistive heating demonstrates the possibility of reconnecting the decoupled DA linkages, thus providing the PK networks with the same thermal, mechanical, and electrical properties as the crosslinked pristine systems.

Effect of the Polyketone Aromatic Pendent Groups on the Electrical Conductivity of the Derived MWCNTs-Based Nanocomposites

Electrically conductive plastics with a stable electric response within a wide temperature range are promising substitutes of conventional inorganic conductive materials. This study examines the preparation of thermoplastic polyketones (PK30) functionalized by the Paal⁻Knorr process with phenyl (PEA), thiophene (TMA), and pyrene (PMA) pendent groups with the aim of optimizing the non-covalent functionalization of multiwalled carbon nanotubes (MWCNTs) through π⁻π interactions. Among all the aromatic functionalities grafted to the PK30 backbone, the extended aromatic nuclei of PMA were found to be particularly effective in preparing well exfoliated and undamaged MWCNTs dispersions with a well-defined conductive percolative network above the 2 wt % of loading and in freshly prepared nanocomposites as well. The efficient and superior π⁻π interactions between PK30PMA and MWCNTs consistently supported the formation of nanocomposites with a highly stable electrical response after thermal solicitations such as temperature annealing at the softening point, IR radiation exposure, as well as several heating/cooling cycles from room temperature to 75 °C.

Totally Organic Redox-Active pH-Sensitive Nanoparticles Stabilized by Amphiphilic Aromatic Polyketones

Amphiphilic aromatic polymers have been synthesized by grafting aliphatic polyketones with 4-(aminomethyl)benzoic acid at different molar ratios via the Paal-Knorr reaction. The resulting polymers, showing diketone conversion degree of 16%, 37%, 53%, and 69%, have been complexed with the redox-active 2,3,5-triphenyl-2H-tetrazolium chloride, a precursor molecule with which aromatic-aromatic interactions are held. Upon addition of ascorbic acid to the complexes, in situ reduction of the tetrazolium salt produced 1,3,5-triphenylformazan nanoparticles stabilized by the amphiphilic polymers. The stabilized nanoparticles display highly negative zeta potential [-(35-70) mV] and hydrodynamic diameters in the submicron range (100-400 nm). Nonaromatic polyelectrolytes or hydrophilic aromatic copolymers showing low linear aromatic density and high linear charge density such as acrylate/maleate and sulfonate/maleate-containing polymers were unable to stabilize formazan nanoparticles synthesized by the same method. The copolymers studied here bear uncharged nonaromatic comonomers (unreacted diketone units) as well as charged aromatic comonomers, which furnish amphiphilia. Thus, the linear aromatic density and the maximum linear charge density have the same value for each copolymer, and the hydrophilic/hydrophobic balance varies with the diketone conversion degree. The amphiphilia of the copolymers allows the stabilization of the nanoparticles, even with the copolymers showing a low linear aromatic density. The method of nanoparticle synthesis constitutes a simple, cheap, and green method for the production of switchable totally organic, redox-active, pH-sensitive nanoparticles that can be reversibly turned into macroprecipitates upon pH changing.

Functional polyketones for the removal of calcium and magnesium from water (part I): synthesis and chemical characterization

The aim of the present study was to design and synthesize a new class of compounds for the softening of hard water, i.e. for the removal of the divalent cations Ca2+ and Mg2+. To that end, a class of alternating aliphatic polyketones (copolymers of ethylene and propylene with carbon monoxide, PK30) was functionalized with a variety of amines employing the Paal-Knorr reaction, a relatively straightforward reaction-route to synthesize functional polyketones. The amino groups included aliphatic and aromatic structures with a molecular weight ranging from 74.1 to 129.2 g/mol. Elemental analysis was used to establish the degree of functionalization, whereas 1H-NMR spectroscopy was used to identify the molecular structure of the prepared polymers. Model compounds were used as reference for guiding structure determination and for studying the (relative) reaction kinetics.