Room temperature flexible isocyanate-free polyurethane foams

Preparation of Non-Isocyanate Polyurethanes from Mixed Cyclic-Carbonated Compounds: Soybean Oil and CO2-Based Poly(ether carbonate)

This study presents the synthesis and characterization of non-isocyanate polyurethanes (NIPU) derived from the copolymerization of cyclic-carbonated soybean oil (CSBO) and cyclic carbonate (CC)-terminated poly(ether carbonate) (RCC). Using a double-metal cyanide catalyst, poly(ether carbonate) polyol was first synthesized through the copolymerization of carbon dioxide and propylene oxide. The terminal hydroxyl group was then subjected to a substitution reaction with a five-membered CC group using glycerol-1,2-carbonate and oxalyl chloride, yielding RCC. Attempts to prepare NIPU solely using RCC and diamine were unsuccessful, possibly due to the low CC functionality and the aminolysis of RCC's linear carbonate repeating units. However, when combined with CSBO, solid NIPUs were successfully obtained, exhibiting good thermal stability along with enhanced mechanical properties compared to conventional CSBO-based NIPU formulations. Overall, this study underscores the potential of leveraging renewable resources and carbon capture technologies to develop sustainable NIPUs with tailored properties, thereby expanding their range of applications.

Simultaneous Formation of Polyhydroxyurethanes and Multicomponent Semi-IPN Hydrogels

This study introduces an efficient strategy for synthesizing polyhydroxyurethane-based multicomponent hydrogels with enhanced rheological properties. In a single-step process, 3D materials composed of Polymer 1 (PHU) and Polymer 2 (PVA or gelatin) were produced. Polymer 1, a crosslinked polyhydroxyurethane (PHU), grew within a colloidal solution of Polymer 2, forming an interconnected network. The synthesis of Polymer 1 utilized a Non-Isocyanate Polyurethane (NIPU) methodology based on the aminolysis of bis(cyclic carbonate) (bisCC) monomers derived from 1-thioglycerol and 1,2-dithioglycerol (monomers A and E, respectively). This method, applied for the first time in Semi-Interpenetrating Network (SIPN) formation, demonstrated exceptional orthogonality since the functional groups in Polymer 2 do not interfere with Polymer 1 formation. Optimizing PHU formation involved a 20-trial methodology, identifying influential variables such as polymer concentration, temperature, solvent (an aprotic and a protic solvent), and the organo-catalyst used [a thiourea derivative (TU) and 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU)]. The highest molecular weights were achieved under near-bulk polymerization conditions using TU-protic and DBU-aprotic as catalyst-solvent combinations. Monomer E-based PHU exhibited higher Mw¯ than monomer A-based PHU (34.1 kDa and 16.4 kDa, respectively). Applying the enhanced methodology to prepare 10 multicomponent hydrogels using PVA or gelatin as the polymer scaffold revealed superior rheological properties in PVA-based hydrogels, exhibiting solid-like gel behavior. Incorporating monomer E enhanced mechanical properties and elasticity (with loss tangent values of 0.09 and 0.14). SEM images unveiled distinct microstructures, including a sponge-like pattern in certain PVA-based hydrogels when monomer A was chosen, indicating the formation of highly superporous interpenetrated materials. In summary, this innovative approach presents a versatile methodology for obtaining advanced hydrogel-based systems with potential applications in various biomedical fields.

Antimicrobial Nonisocyanate Polyurethane Foam Derived from Lignin for Wound Healing

Medical dressings, as a cover for wounds, can replace damaged skin in the wound healing process to play a temporary barrier role, avoid or control wound infection, and provide a favorable environment for wound healing. Therefore, there is an urgent need for medical antimicrobial dressings for the treatment of chronic wounds. Although traditional polyurethane foam has been widely used in medical dressings, conventional polyurethane foams are primarily prepared using nonbiocompatible isocyanate-based compounds, which are potentially hazardous for both operators and applications in the medical field. Here, we propose nonisocyanate polyurethane foams naturally derived from lignin by enzymatic lignin alkylation, cyclic carbonation modification, and polymerization with diamine and the addition of a blowing agent. Silver nanoparticle solution was added during foaming to confer antimicrobial properties. This lignin-based nonisocyanate polyurethane/silver composite foam (named NIPU foam-silver) using a green synthesis method has good mechanical properties, which can be used to manufacture polyurethane/silver foams, and thermal and antimicrobial properties. Notably, NIPU foam-Ag showed more than 95% bactericidal efficacy against both Escherichia coli and Staphylococcus aureus within 4 h. Evaluation of in vitro wounds in mice showed that this antimicrobial composite foam rapidly promotes wound healing and repairs damaged tissue. This suggests that this biobased biodegradable antimicrobial foam has significant scope for clinical applications in wound management.

Preparation and fire resistance modification on tannin-based non-isocyanate polyurethane (NIPU) rigid foams

Non-isocyanate polyurethane (NIPU) as a new type of polyurethane material has become a hot research topic in the polyurethane industry due to its no utilization of toxic isocyanates during the synthesis process. And the developing on recyclable biomass materials has also much attention in the industrial sector, hence the preparation and application of bio-based NIPU has also become a very meaningful study work. So, in this paper, tannin as a biomass material was used to synthesize tannin based non-isocyanate polyurethanes (TNIPU) resin, and then successfully prepared a self-blowing TNIPU foam at room temperature by using formic acid as initiator and glutaraldehyde as cross-linking agent. The compressive strength of this foam as high as 0.8 MPa, which is an excellent compressive performance. Meanwhile it will return to the state before compression when removing the pressure. This indicating that the foam has good toughness. In addition, formic acid can react with the amino groups in TNIPU to form amide substances, and generated enough heat to initiate the foaming process. Glutaraldehyde, as a crosslinking agent, reacts with the amino group in TNIPU to form a network structure system. By scanning electron microscope (SEM) observation of the cell shapes, it can be seen that the foam cells were uniform in size and shape, and the cell pores showed open and closed cells. The limiting oxygen index (LOI) tested value of this TNIPU foam is 24.45 % without any flame retardant added, but compared to the LOI value of polyurethane foam (17 %-19 %), TNIPU foam reveal a better fire resistance. It has a wider application prospect.

Cascade Exotherms for Rapidly Producing Hybrid Nonisocyanate Polyurethane Foams from Room Temperature Formulations

For decades, self-blown polyurethane foams─found in an impressive range of materials─are produced by the toxic isocyanate chemistry and are difficult to recycle. Producing them in existing production plants by a rapid isocyanate-free self-blowing process from room temperature (RT) formulations is a long-lasting challenge. The recent water-induced self-blowing of nonisocyanate polyurethane (NIPU) formulations composed of a CO2-based tricyclic carbonate, diamine, water, and a catalyst successfully addressed the isocyanate issue, however failed to provide foams at RT. Herein, we elaborate a practical solution to empower the NIPU foam formation in record timeframes from RT formulations. We generate cascade exotherms by the addition of a highly reactive triamine and an epoxide to the formulation of the water-induced self-foaming process. These exotherms, combined to a fast cross-linking imparted by the triamine and epoxide, rapidly raise the temperature to the foaming threshold and deliver hybrid NIPU foams in 5 min with KOH as a catalyst. Careful selection of the monomers enables producing foams with a wide range of properties, as well as with an unprecedented high biobased content up to 90 wt %. Moreover, foams can be upcycled into polymer films by hot pressing, offering them a facile reuse scenario. This robust cheap process opens huge perspectives for greener foams of high biobased contents, expectedly responding to the sustainability demands of the foam sector. It is potentially compatible to the retrofitting of industrial foaming infrastructures, which is of paramount importance to accommodate existing foam production plants and address the huge foam market demands.

Non-isocyanate polyurethanes synthesized from terpenes using thiourea organocatalysis and thiol-ene-chemistry

The depletion of fossil resources as well as environmental concerns contribute to an increasing focus on finding more sustainable approaches for the synthesis of polymeric materials. In this work, a synthesis route towards non-isocyanate polyurethanes (NIPUs) using renewable starting materials is presented. Based on the terpenes limonene and carvone as renewable resources, five-membered cyclic carbonates are synthesized and ring-opened with allylamine, using thiourea compounds as benign and efficient organocatalysts. Thus, five renewable AA monomers are obtained, bearing one or two urethane units. Taking advantage of the terminal double bonds of these AA monomers, step-growth thiol-ene polymerization is performed using different dithiols, to yield NIPUs with molecular weights of above 10 kDa under mild conditions. Variation of the dithiol and amine leads to polymers with different properties, with Mn of up to 31 kDa and Tg's ranging from 1 to 29 °C.

Latest Advancements in the Development of High-Performance Lignin- and Tannin-Based Non-Isocyanate Polyurethane Adhesive for Wood Composites

The depletion of natural resources and increasing environmental apprehension regarding the reduction of harmful isocyanates employed in manufacturing polyurethanes (PUs) have generated significant attention from both industrial and academic sectors. This attention is focused on advancing bio-based non-isocyanate polyurethane (NIPU) resins as viable and sustainable substitutes, possessing satisfactory properties. This review presents a comprehensive analysis of the progress made in developing bio-based NIPU polymers for wood adhesive applications. The main aim of this paper is to conduct a comprehensive analysis of the latest advancements in the production of high-performance bio-based NIPU resins derived from lignin and tannin for wood composites. A comprehensive evaluation was conducted on scholarly publications retrieved from the Scopus database, encompassing the period from January 2010 to April 2023. In NIPU adhesive manufacturing, the exploration of substitute materials for isocyanates is imperative, due to their inherent toxicity, high cost, and limited availability. The process of demethylation and carbonation of lignin and tannin has the potential to produce polyphenolic compounds that possess hydroxyl and carbonyl functional groups. Bio-based NIPUs can be synthesized through the reaction involving diamine molecules. Previous studies have provided evidence indicating that NIPUs derived from lignin and tannin exhibit enhanced mechanical properties, decreased curing temperatures and shortened pressing durations, and are devoid of isocyanates. The characterization of NIPU adhesives based on lignin and tannin was conducted using various analytical techniques, including Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), matrix-assisted laser desorption/ionization with time-of-flight (MALDI-TOF) mass spectrometry, and gel permeation chromatography (GPC). The adhesive performance of tannin-based NIPU resins was shown to be superior to that of lignin-based NIPUs. This paper elucidates the potential of lignin and tannin as alternate sources for polyols in the manufacturing of NIPUs, specifically for their application as wood adhesives.

CO2-Blown Nonisocyanate Polyurethane Foams

Polyurethane (PU) foams are produced from toxic, petrochemical- and phosgene-derived isocyanates. Although nonisocyanate polyurethane (NIPU) has shown promise as a replacement for traditional PU, the synthesis of NIPU foams has not been widely studied due to the difficulties in replicating the foaming process of PU, in situ CO2 production through the hydrolysis of isocyanates. Hereby, we report the synthesis of amine-CO2 adducts and their CO2 adsorption-desorption characteristics under different conditions. The results show that the amine-CO2 adducts can exhibit up to 87% CO2 desorption at 60 °C after aminolysis with cyclic carbonate. The amine-CO2 adduct is used as both a foaming agent and a comonomer to obtain low-density foams (0.203-0.239 g·cm-3) after heating at 50-60 °C for 24-48 h. This marks the successful synthesis of in situ CO2-blown NIPU foams using an amine-CO2 adduct.

Safer Polyurethane Foams with Cyclic Carbonates

Polyurethanes (PUs) are a class of materials usually synthesized from isocyanates, diols, and water. Water is essential for producing carbon dioxide (CO₂ ) which is used for the self-blowing of the foams. Due to safety concerns with the production of isocyanates, alternative chemistries have been evaluated and cyclic carbonate systems have shown great promise. In a recent advancement by Bourguignon, Grignard, and Detrembleur, a cyclic carbonate and diamine system is capable of generating CO₂ for self-blowing through hydrolysis of the carbonate-based monomer. The authors demonstrate that with a simple variation of the diamine monomer a wide range of physical and thermo-mechanical properties were achievable. This work represents a significant step towards safer and more environmentally friendly PUs.

Influence of Phosphorus Structures and Their Oxidation States on Flame-Retardant Properties of Polyhydroxyurethanes

This article focuses on the synthesis of polyhydroxyurethane (PHU) materials containing novel phosphorus flame retardants (FR). Four different phosphorus compounds were grafted onto cyclic carbonate: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), diethyl phosphite (DEP), diphenyl phosphite (DPP) and dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO). Thus, three novel phosphorus reactive cyclic carbonates which have never been reported so far were synthetized. Phosphorus FR containing PHU materials were characterized by FTIR to evidence the total conversion of the cyclic carbonate. Moreover, the gel contents up to 80% confirmed the formation of the polymer network. Then, the thermal stability and the flame-retardant properties were investigated by thermogravimetric analyses, cone calorimeter and pyrolysis combustion flow calorimeter. The mode of action of phosphorus compounds, depending on the oxidation state, was especially highlighted. Phosphonate (+III) provided better action in a condensed phase than phosphinate thanks to a more efficient char formation. Among phosphonates, differences were observed in terms of char-formation rate and expansion. DEP provided the best flame-retardant properties, with a reduction of 76% of pHRR with 2 wt% of phosphorus in cone calorimeter analysis. Therefore, this article highlighted the different modes of action of phosphorus flame retardants, depending on the oxidation state of phosphorus, in PHU materials.

Water-Induced Self-Blown Non-Isocyanate Polyurethane Foams

For 80 years, polyisocyanates and polyols were central building blocks for the industrial fabrication of polyurethane (PU) foams. By their partial hydrolysis, isocyanates release CO₂ that expands the PU network. Substituting this toxic isocyanate-based chemistry by a more sustainable variant-that in situ forms CO₂ by hydrolysis of a comonomer-is urgently needed for producing greener cellular materials. Herein, we report a facile, up-scalable process, potentially compatible to existing infrastructures, to rapidly prepare water-induced self-blown non-isocyanate polyurethane (NIPU) foams. We show that formulations composed of poly(cyclic carbonate)s and polyamines furnish rigid or flexible NIPU foams by partial hydrolysis of cyclic carbonates in the presence of a catalyst. By utilizing readily available low cost starting materials, this simple but robust process gives access to greener PU foams, expectedly responding to the sustainability demands of many sectors.

Non-Isocyanate Polyurethane Bio-Foam with Inherent Heat and Fire Resistance

Polyurethanes (PUs) are versatile and widespread, particularly as flexible and rigid foams. To avoid isocyanates and other toxic reagents required for synthesis, such as phosgene, alternative synthetic routes have been utilized to produce non-isocyanate polyurethanes (NIPUs). A thermally and flame-resistant rigid NIPU was produced from environmentally benign and bio-sourced ingredients, requiring no catalyst or solvents. A foamed structure was obtained by the addition of glutaraldehyde and four different carboxylic acids: malic acid, maleic acid, citric acid, and aconitic acid. The resulting morphology, thermal degradation, and flame resistance of each foam were compared. The properties vary with each carboxylic acid used, but in each case, peak thermal degradation and peak heat release are postponed by >100 °C compared to commercial rigid PU foam. Furthermore, in a butane torch test, NIPU foams exhibit an 80% higher remaining mass and a 75% reduction in afterburn time, compared to commercial polyurethane. This bio-based polyurethane eliminates the hazards of traditional PUs, while imparting inherent thermal stability and flame resistance uncharacteristic of conventional foams.

Preparation of Biobased Nonisocyanate Polyurethane/Epoxy Thermoset Materials Using Depolymerized Native Lignin

Polyurethane polymers are found in a wide range of material applications. However, the toxic nature of isocyanates used in their formulation is a major concern; hence, more environmentally friendly alternatives are of high interest in the search for new sustainable polymer materials. In this work, we present the preparation of isocyanate-free polyurethane/epoxy hybrid thermosets with a high biobased content (85-90 wt %). The isocyanate-free polyurethanes were based on polyhydroxyurethanes (PHUs) prepared from depolymerized native lignin, which we refer to as lignin hydrogenolysis oil (LHO). The LHO was functionalized with epichlorohydrin to yield the epoxidized structure (LHO-GE), which was in turn reacted with CO₂ to form the cyclocarbonated species (LHO-CC). Blends of the LHO-CC and glycerol diglycidyl ether (GDGE) were cured to produce hybrid PHU/epoxy (LHO-CC/GDGE) thermosets. Thermosetting materials with flexural moduli of 4.5 GPa and flexural strengths of 160 MPa were produced by optimizing the mass ratio of the two main components and the triamine hardener. These novel biobased hybrid materials outperformed the corresponding epoxy-only thermosets and comparable hybrid PHU/epoxy materials produced from petrochemicals.

Synthesis and properties of foams from a blend of vegetable oil based polyhydroxyurethane and epoxy resin

This article aims to highlight the synthesis of foams from a blend of hydroxyurethane of castor oil and epoxy resin. An epoxidized castor oil of 4% oxirane oxygen was first converted to cyclic carbonate of castor oil at 120°C, 1 atm CO2 pressure and then it was reacted with three different aliphatic diamines to yield amine terminated Polyhydroxyurethane (PHU). Foams were prepared in a metal mould from the blend of PHU, epoxy resin, epoxy hardener and polymethylhydrogensiloxane blowing agent which releases hydrogen gas upon reaction with amine. FTIR and 1H NMR of cyclic carbonate of castor oil and PHU of castor oil were done to confirm their chemical structures. Optical microscopy and scanning electron microscopy of foams was done to assess their cellular morphology along with DSC and TGA to evaluate their thermal properties. Both flexible and rigid type of foams were synthesised in this study. Resilience of flexible foams was inspected using a ball rebound test and compression-recovery test while thermal insulation property was checked by measuring thermal conductivity, thermal diffusivity and R-values of rigid foams from heat transfer study using a heat transfer apparatus.

Divergent Aminolysis Approach for Constructing Recyclable Self-Blown Nonisocyanate Polyurethane Foams

We report an approach to fabricate self-blown nonisocyanate polyurethane (NIPU) foams by capitalizing on the divergent chemistries of amines with cyclic carbonates─creating the polymer network─and thiolactone─delivering in situ a thiol that generates the blowing agent (CO₂) by reaction with a cyclic carbonate. Multiple linkages (hydroxyurethanes, thioethers, and amides) are created within the polymer network by this domino process. This one-pot methodology furnishes flexible to rigid foams with open-cell morphology at moderate temperature. The foams are easily repurposed into films or structural composites by thermal treatment, showing the first example of recyclable NIPU foams. Remarkably, both the formation and the recycling of the thermoset foams do not necessarily require the use of a catalyst. This facile and robust process is opening new avenues for designing more sustainable PU foams and offers new end-of-life options by facile material repurposing.

Cascade (Dithio)Carbonate Ring Opening Reactions for Self-Blowing Polyhydroxythiourethane Foams

Polyurethane (PU) foams are very common materials that have found many applications over the years. Their use is constantly improving due to their unique physical properties and easy blowing which does not require the addition of a blowing agent. Greener routes have been explored in the recent years to replace isocyanates. One of the most promising routes is leading to Polyhydroxyurethanes (PHU). However, with PHUs, external blowing agent are usually required to obtain a foam. Thus, our work focuses on PHU foam synthesis using in situ reaction to produce NIPU foam. Hence, the aminolysis of thiocyclic carbonate triggers Pearson reaction between released thiols and cyclic carbonates which serves as a chemical blowing agent. This article is protected by copyright. All rights reserved.

Trends in non-isocyanate polyurethane (NIPU) development

The transition towards safer and more sustainable production of polymers has led to a growing body of academic research into non-isocyanate polyurethanes (NIPUs) as potential replacements for conventional, isocyanate-based polyurethane materials. This perspective article focuses on the opportunities and current limitations of NIPUs produced by the reaction between biobased cyclic carbonates with amines, which offers an interesting pathway to renewable NIPUs. While it was initially thought that due to the similarities in the chemical structure, NIPUs could be used to directly replace conventional polyurethanes (PU), this has proven to be more challenging to achieve in practice. As a result, and in spite of the vast amount of academic research into this topic, the market size of NIPUs remains negligible. In this perspective, we will emphasize the main limitations of NIPUs in comparison to conventional PUs and the most significant advances made by others and us to overcome these limitations. Finally, we provide our personal view of where research should be directed to promote the transition from the academic to the industrial sector.

Starch-based isocyanate- and non-isocyanate polyurethane hybrids: A review on synthesis, performance and biodegradation

The challenges related to the persistence of plastics in natural ecosystems fostered strong interest in developing biodegradable bioplastics. Among natural biopolymers, starch gained both academic and industrial interest owing to its impressive physicochemical properties. The use of starch in production of polyurethane (PU) composites not only yields PUs with outstanding mechanical properties but also makes the final PU products biodegradable. The hydrophilic nature of starch limits its dispersion in hydrophobic PU polymers, although it is a significant benefit in creating starch-embedded non-isocyanate polyurethane (NIPU) composites. We present a comprehensive overview to highlight important strategies that are used to improve the compatibility of starch with various PU matrices. This review also gives an overview of the recent advances in the synthesis of starch-NIPU hybrids. Moreover, we aim to deliver critical insight into strategies that boost the biodegradation characteristics of PUs along with a discussion on various methods to assess their biodegradation.

Biobased Nonisocyanate Polyurethanes as Recyclable and Intrinsic Self-Healing Coating with Triple Healing Sites

Polymer coatings having high amounts of renewable carbon and self-healing properties are highly sought after in a sustainability perspective. We report here the development of bio-/CO₂-derived nonisocyanate polyurethane (NIPU) coatings which are recyclable and healable via three different types of healing mechanisms. These NIPUs contain furan rings in their main chain which after cross-linking with bismaleimides form organogels having a thermo-reversible sol-gel transition and solvent-borne coatings with improved properties. Judicial selection of the bismaleimide cross-linker structure enabled us to produce recyclable and intrinsic healable coatings mediated by heat (thermo-healing), moisture (moisture-healing), and, more interestingly, dry conditions at room temperature (self-healing). The intrinsic moisture-healing property of NIPU-based coatings is unprecedented and is mainly due to the presence of hydroxyl functionalities in the NIPU structure. The uniqueness of these cross-linked biobased NIPU as recyclable coatings having triple healing sites present in their structure gives these materials potential for sustainable and functional applications.

Recent Developments in Lignin- and Tannin-Based Non-Isocyanate Polyurethane Resins for Wood Adhesives—A Review

This review article aims to summarize the potential of using renewable natural resources, such as lignin and tannin, in the preparation of NIPUs for wood adhesives. Polyurethanes (PUs) are extremely versatile polymeric materials, which have been widely used in numerous applications, e.g., packaging, footwear, construction, the automotive industry, the lighting industry, insulation panels, bedding, furniture, metallurgy, sealants, coatings, foams, and wood adhesives. The isocyanate-based PUs exhibit strong adhesion properties, excellent flexibility, and durability, but they lack renewability. Therefore, this study focused on the development of non-isocyanate polyurethane lignin and tannin resins for wood adhesives. PUs are commercially synthesized using polyols and polyisocyanates. Isocyanates are toxic, costly, and not renewable; thus, a search of suitable alternatives in the synthesis of polyurethane resins is needed. The reaction with diamine compounds could result in NIPUs based on lignin and tannin. The research on bio-based components for PU synthesis confirmed that they have good characteristics as an alternative for the petroleum-based adhesives. The advantages of improved strength, low curing temperatures, shorter pressing times, and isocyanate-free properties were demonstrated by lignin- and tannin-based NIPUs. The elimination of isocyanate, associated with environmental and human health hazards, NIPU synthesis, and its properties and applications, including wood adhesives, are reported comprehensively in this paper. The future perspectives of NIPUs’ production and application were also outlined.

Non-Furanic Humins-Based Non-Isocyanate Polyurethane (NIPU) Thermoset Wood Adhesives

Predominantly non-furanic commercial humins were used to prepare humin-based non-isocyanate polyurethane (NIPU) resins for wood panel adhesives. Pure humin-based NIPU resins and tannin–humin NIPU resins were prepared, the latter to upgrade the humins’ performance. Species in the raw humins and species formed in the NIPU resins were identified by Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI ToF) spectrometry and Fourier Transform Infrared (FTIR). Humins, fulvic acid and derivatives, humic acid and its fragments, some lignans present and furanic oligomers present formed NIPU linkages. Thermomechanical analysis (TMA) showed that as with other biomaterials-based NIPU resins, all these resins also showed two temperature peaks of curing, the first around 130 °C and the second around 220 °C. A decrease in the Modulus of Elasticity (MOE) between the two indicated that the first curing period corresponded to linear growth of the oligomers forming a physical entanglement network. This then disentangled, and the second corresponded to the formation of a chemical cross-linked network. This second peak was more evident for the tannin–humin NIPU resins. All the laboratory particleboard made and tested either bonded with pure humins or with tannin–humin NIPU adhesives satisfied well the internal bond strength requirements of the relevant standard for interior grade panels. The tannin–humin adhesives performed clearly better than the pure humins one.

Chemo- and Regioselective Additions of Nucleophiles to Cyclic Carbonates for the Preparation of Self-Blowing Non-Isocyanate Polyurethane Foams

Polyurethane (PU) foams are indisputably daily essential materials found in many applications, notably for comfort (for example, matrasses) or energy saving (for example, thermal insulation). Today, greener routes for their production are intensively searched for to avoid the use of toxic isocyanates. An easily scalable process for the simple construction of self-blown isocyanate-free PU foams by exploiting the organocatalyzed chemo- and regioselective additions of amines and thiols to easily accessible cyclic carbonates is described. These reactions are first validated on model compounds and rationalized by DFT calculations. Various foams are then prepared and characterized in terms of morphology and mechanical properties, and the scope of the process is illustrated by modulating the composition of the reactive formulation. With impressive diversity and accessibility of the main components of the formulations, this new robust and solvent-free process could open avenues for construction of more sustainable PU foams, and offers the first realistic alternative to the traditional isocyanate route.

Production and Characterization of Non-Isocyanate Polyurethane/SiO2 Films Through a Sol-Gel Process for Thermal Insulation Applications

The reaction of cyclic carbonates with amines is the most attractive among the synthesis methods for isocyanate-free polyurethane. Non-isocyanate polyurethane films with SiO₂ NPs fabricated by a sol-gel process are reported, where cyclic carbonates (CC) were produced under mild conditions by CO₂ insertion in an epoxide complex in the presence of LiCl. A reaction of CC and polyamines was carried out in a low concentration polymer matrix of PVA. The materials were characterized by ¹H-NMR, FTIR, UV-Vis, SEM, TGA, DTG, and a KD₂ pro technique. polymer FTIR results are consistent with the literature, even with the use of a non-conventional methodology, where the found chemical interactions values were 3330, 2930 and 1637 cm^-1. There are differences in the polymers' morphologies due to the presence and absence of SiO₂ NPs according to SEM, where the spherical morphology and homogenous particle size distribution of NPs around 100 nm. According to TGA results, all polymers showed their last stage decomposition after 300 °C and polymers with higher concentration of NPs showed even better stability. Due to the obtained results, the polymers have the potential to be used for thermal insulation without negative effect on the environment.

Hybrid Poly(hydroxy urethane)s: Folded-Sheet Morphology and Thermoreversible Adhesion

Hybrid poly(hydroxy urethane)s (PHUs) are synthesized by copolymerizing aromatic/alicyclic cyclic carbonates with a polyether amine via addition polymerization. They result into polymers with an average molecular weight of 10 kDa and exhibit solubility in common organic solvents. The hybrid PHUs display T g up to 18 °C. PHUs are enriched with multiple H-bonded interactions and they are assessed using temperature-dependent 1H NMR and Fourier-transform infrared studies. PHUs possess folded-sheet morphology with nanogap between folds and nanowidth between chains. The secondary interactions bestow thermoreversible property to PHUs, and they display good adhesion to both polar (Al-Al) and nonpolar (HDPE-HDPE) substrates. Hybrid PHUs show improved optical transparency compared to homo PHUs. The PHUs are thermally stable up to 250 °C.

Non-isocyanate urethane linkage formation using l-lysine residues as amine sources

Bio-based polyurethane materials are broadly applied in medicine as drug delivery systems. Nevertheless, their synthesis comprises the use of petroleum-based toxic amines, isocyanates and polyols, and their biocompatibility or functionalization is limited. Therefore, the use of lysine residues as amine sources to create non-isocyanate urethane (NIU) linkages was investigated. Therefore, a five-membered biscyclic carbonate (BCC) was firstly synthetized and reacted with a protected lysine, a tripeptide and a heptapeptide to confirm the urethane linkage formation with lysine moiety and to optimize reaction conditions. Afterwards, the reactions between BCC and a model protein, elastin-like protein (ELP), and β-Lactoglobulin (BLG) obtained from whey protein, respectively, were performed. The synthesized protein materials were structural, thermally and morphologically characterized to confirm the urethane linkage formation. The results demonstrate that using both simple and more complex source of amines (lysine), urethane linkages were effectively achieved. This pioneering approach opens the possibility of using proteins to develop non-isocyanate polyurethanes (NIPUs) with tailored properties.

Polymers Based on Cyclic Carbonates as Trait d'Union Between Polymer Chemistry and Sustainable CO2 Utilization

Given the large amount of anthropogenic CO₂ emissions, it is advantageous to use CO₂ as feedstock for the fabrication of everyday products, such as fuels and materials. An attractive way to use CO₂ in the synthesis of polymers is by the formation of five-membered cyclic organic carbonate monomers (5CCs). The sustainability of this synthetic approach is increased by using scaffolds prepared from renewable resources. Indeed, recent years have seen the rise of various types of carbonate syntheses and applications. 5CC monomers are often polymerized with diamines to yield polyhydroxyurethanes (PHU). Foams are developed from this type of polymers; moreover, the additional hydroxyl groups in PHU, absent in classical polyurethanes, lead to coatings with excellent adhesive properties. Furthermore, carbonate groups in polymers offer the possibility of post-functionalization, such as curing reactions under mild conditions. Finally, the polarity of carbonate groups is remarkably high, so polymers with carbonates side-chains can be used as polymer electrolytes in batteries or as conductive membranes. The target of this Review is to highlight the multiple opportunities offered by polymers prepared from and/or containing 5CCs. Firstly, the preparation of several classes of 5CCs is discussed with special focus on the sustainability of the synthetic routes. Thereafter, specific classes of polymers are discussed for which the use and/or presence of carbonate moieties is crucial to impart the targeted properties (foams, adhesives, polymers for energy applications, and other functional materials).

En route to CO2-containing renewable materials: catalytic synthesis of polycarbonates and non-isocyanate polyhydroxyurethanes derived from cyclic carbonates

The strategies and challenges in the preparation of fully renewable materials prepared from CO₂ and biomass enabled by catalysis are presented.

Advances in the use of CO2 as a renewable feedstock for the synthesis of polymers

Carbon dioxide offers an accessible, cheap and renewable carbon feedstock for synthesis. Current interest in the area of carbon dioxide valorisation aims at new, emerging technologies that are able to provide new opportunities to turn a waste into value. Polymers are among the most widely produced chemicals in the world greatly affecting the quality of life. However, there are growing concerns about the lack of reuse of the majority of the consumer plastics and their after-life disposal resulting in an increasing demand for sustainable alternatives. New monomers and polymers that can address these issues are therefore warranted, and merging polymer synthesis with the recycling of carbon dioxide offers a tangible route to transition towards a circular economy. Here, an overview of the most relevant and recent approaches to CO2-based monomers and polymers are highlighted with particular emphasis on the transformation routes used and their involved manifolds.

Renewable polyols for advanced polyurethane foams from diverse biomass resources

This review highlights recent advances in the synthesis of renewable polyols, used for making polyurethane foams, from biomass.