Isocyanate-terminated Prepolymer Research Articles

Supramolecular Organic Nanofiller: A New Reinforcement Strategy for Dynamic Covalent Polymer Networks Toward Upcycling of Carbon Fiber Composites.

Dynamic covalent polymer networks (DCPN) provide an important solution to the challenging recyclability of thermoset elastomers. However, dynamic bonds exhibit relatively weak bond energies, considerably decreasing the mechanical properties of DCPN. Herein, a novel reinforcement strategy for DCPN involving the in situ formation of supramolecular organic nanofillers through asynchronous polymerization is proposed. Owing to the difference in the reactivity of the isocyanate groups and the gradual deblocking of aldimine, asynchronous cross-linking of hexamethylene diisocyanate and isocyanate-terminated prepolymer containing dynamic oxime-urethane bonds with the deblocked tris(2-aminoethyl)amine facilitates the transition from the molecular interpenetration of chains into immiscible polymerization. This results in thermodynamic incompatibility between the hyperbranched clusters and long chains, inducing a spontaneous formation of supramolecular organic nanofillers. Compared to traditional reinforcement strategies, supramolecular organic nanofillers considerably improve the mechanical properties of DCPN. Furthermore, the supramolecular interactions between hyperbranched clusters and dynamic oxime-urethane bonds enable the network with excellent recyclability. The unique reinforcement and recyclability of the prepared DCPN allow their combination with carbon fibers (CF) to form CF composites with outstanding properties for personal-protection applications, achieving CF composite upcycling. This study offers a novel strategy on the reinforcement of DCPN and the upcycling of high-performance CF composites.

Schiff-Base Cross-Linked Hydrogels Based on Properly Synthesized Poly(ether urethane)s as Potential Drug Delivery Vehicles in the Biomedical Field: Design and Characterization.

In situ-forming hydrogels based on the Schiff-base chemistry are promising for drug delivery applications, thanks to their stability under physiological conditions, injectability, self-healing properties, and pH-responsiveness. In this work, two water-soluble poly(ethylene glycol)-based poly(ether urethane)s (PEUs) were engineered. A high-molecular-weight PEU (SHE3350, M̅ n 24 kDa, D 1.7), bearing primary amino groups along each polymeric chain, was synthesized using N-Boc serinol and subjected to an acidic treatment to expose primary amines (ca. 1020 units/gSHE3350). In parallel, a low-molecular-weight PEU (AHE1500, M̅ n 4 kDa, D 1.5) with aldehyde end groups was synthesized by end-capping an isocyanate-terminated prepolymer with 4-hydroxybenzaldehyde, and the aldehyde groups were quantified to be around 1020 units/gAHE1500. Hydrogels were prepared by simply mixing SHE3350 and AHE1500 aqueous solutions and characterized to assess their physico-chemical and rheological properties. Schiff-base bond formation was proved through carbon-13 and proton solid-state NMR spectroscopies. Rheological characterization confirmed the formation of gels with high resistance to applied strain (ca. 1000%). Hydrogels exhibited high absorption ability (ca. 270% increase in wet weight) in physiological-like conditions (i.e., 37 °C and pH 7.4) up to 27 days. In contact with buffer at pH 5, enhanced fluid absorption was observed until dissolution occurred starting from 13 days due to Schiff-base hydrolysis in acidic conditions. Conversely, gels showed a reduced absorption ability at pH 9 due to shrinkage phenomena. Furthermore, they exhibited high permeability and controlled, sustained, and pH-triggered release of a model molecule (i.e., fluorescein isothiocyanate dextran) for up to 17 days. Lastly, the hydrogels showed easy injectability and self-healing ability.

Improved thermal and mechanical properties of water-blown rigid polyurethane foams synthesized with renewable castor oil and toluene diisocyanate-based trifunctional polyols

In this work, glycerol was chemically modified into novel toluene diisocyanate (TDI) based trifunctional polyol (NTP) by a two step process, involving the reaction of TDI with glycerol to form an isocyanate-terminated pre-polymer, followed by the reaction with glycol. A thermal and mechanical property of water-blown rigid polyurethane foam (WB-PUF) was enhanced by the partial substitution (30 & 50 wt%) of castor oil with glycerol or synthesized NTP. The effects of glycerol content and NTP on the WB-PUF properties were investigated using various characterization techniques including ATR-FTIR, TGA, SEM, compression test, and Shore-A hardness test. Notably, the introduction of NTP substitution into the formulation of WB-PUF foams had beneficial impact on the structure of materials enhancing foam density from 77 kg/m3 to 117 kg/m3 and also exhibited superior thermal and mechanical properties compared to those with glycerol and unmodified foams. Shore A hardness and compression strength of those foams ranged from 50 to 69.5 °Sh A and 1.88-3.28 MPa, respectively. These findings suggest potential applications of the modified WB-PUF in areas such as rigid tissue engineering.

Solvent-Free Preparation of Thermally Stable Poly(urethane-imide) Elastomers

Polyurethanes (PUs) are widely used in many applications due to their versatile chemical and physical properties. To meet the increasing demands on PU with respect to intrinsic mechanical and thermal properties, they can be modified with thermally stable aromatic imide structures to form poly(urethane imide) (PUI). However, the preparation of PUI materials has been limited by the need for strong polar solvents, which hinder their industrial scale development. In this work, we prepared imide-containing isocyanate-terminated prepolymers via the reaction of polymeric aromatic or aliphatic isocyanates and pyromellitic dianhydride in completely solvent-free conditions. The subsequent PUI elastomers made from these prepolymers exhibited enhanced char formation and stiffness in comparison to the reference elastomers without imide structures, among which the aromatic PUI elastomer shows improved flame retardancy according to the initial cone calorimetry measurement. This work demonstrates the potential use of imide prepolymers in other PU applications where high thermal stability and flame retardancy are required. The solvent-free synthesis also paves a way for the large-scale production of PUI materials.

Towards Solar-Driven Formation of Robust and Self-Healable Waterborne Polyurethane Containing Disulfide Bonds via in-situ Incorporation of 2D Titanium Carbide MXene

Waterborne polymers are vital for coating industry to reduce carbon emissions. However, formation of robust and self-healable films at ambient temperature remains a challenge owing to high energy cost of film formation process. This work reports a solar-driven film formation of waterborne polyurethanes (WPUs) containing disulfide bonds via in-situ incorporation of 2D titanium carbide (MXene) with ability to convert light to heat. Instead of directly mixed with WPUs, MXene is added to join the reaction with isocyanate-terminated pre-polymer before emulsification process. This approach not only prevents aggregation of MXene in water but stabilizes MXene against thermal degradation which is the key hurdle for mass production of MXene/WPU composites. More importantly, our results show that mechanical performance of WPU films under visible light (100 mW/cm2) is overwhelmingly competitive with that processed in oven. Furthermore, the existence of disulfide bonds in PU chains enables fast self-healing of micro-cracks under natural visible light which could vanish completely within 40 min. The fractured specimens were repaired under natural visible light for 2 h, and the self-healing efficiency of tensile strength and elongation at break reached over 94.00%.

Influence of the Macromolecular architecture on the properties of biobased polyurethane tissue adhesives

Polyurethanes (PU) have recently emerged as promising biomaterials for tissue adhesive applications. Compared to other tissue adhesives, they offer substantial advantages such as the possibility to tailor adhesive strengths and curing times, for instance. All these properties are directly affected by the composition and final architecture. In this work, biobased two-components PU sealants were prepared, based on (i) an isocyanate-terminated prepolymer and (ii) a chain extender. Here, an exhaustive evaluation of the oligoester-diols and chain extenders influence on the sealants properties has been performed. In order to bring controlled variations on the final macromolecular architectures, three different prepolymers were prepared: two are based on poly(3-hydroxybutyrate) diol oligomers and another one on poly(lactic acid) diol oligomers, with a 50/50 isocyanate molar ratio of hexamethylene diisocyanate and biobased dimeryl diisocyanate. To study the chain extenders influence, five different aliphatic and linear bifunctional molecules were assessed, with varying length and functional groups reactivity. Ultimately, PUs obtained after the two-component systems curing were also fully characterized. They exhibited an overall good biocompatibility around 80%, with limited cytotoxicity. A wide range of physico-chemical and mechanical properties were also obtained, evidencing the importance of the macromolecular architecture on the systems final properties.

Eco-Friendly Ether and Ester-Urethane Prepolymer: Structure, Processing and Properties.

This study concerns bio-based urethane prepolymers. The relationship between the chemical structure and the thermal and processing parameters of bio-based isocyanate-terminated ether and ester-urethane prepolymers was investigated. Bio-based prepolymers were obtained with the use of bio-monomers such as bio-based diisocyanate, bio-based polyether polyol or polyester polyols. In addition to their composition, the bio-based prepolymers were different in the content of iso-cyanate groups content (ca. 6 and 8%). The process of pre-polymerization and the obtained bio-based prepolymers were analyzed by determining the content of unreacted NCO groups, Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, thermogravimetry, and rheological measurements. The research conducted facilitated the evaluation of the properties and processability of urethane prepolymers based on natural components. The results indicate that a significant impact on the processability has the origin the polyol ingredient as well as the NCO content. The thermal stability of all of the prepolymers is similar. A prepolymer based on a poly-ether polyol is characterized by a lower viscosity at a lower temperature than the prepolymer based on a polyester polyol. The viscosity value depends on the NCO content.

Preparation and properties of polyurethane film with photothermal conversion and energy storage capability

Purpose This paper aims to provide a flexible polyurethane (PU) film with visible light trapping ability, photothermal conversion and energy storage performance by covalently bonded a visible light absorbing dye into the polymer through copolymerization. Design/methodology/approach For this target solution copolymerization of diphenyl-methane-diisocyanate (MDI), poly(1,4-butylene adipate) (PBA2000), polyethylene glycol (PEG) of different molecular weight, self-made dye, 1,4-butanediol (BuOH) was carried out in a flame-dried flask under an inert nitrogen (N2) atmosphere. First, an isocyanate-terminated prepolymer of dried PEG, MDI and PBA2000 was prepared in dimethylformamide and stirred for 1 h at 35°C. Then, self-made dye and 1, 4-butanediol (BuOH) were added and heated at 85°C for 3 h to get photothermal conversion polyurethane (PTPU) solution. Allowed the solution to dry at room temperature for seven days and then at 65°C for 12 h to get PTPU films. Findings The flexible PU films with photothermal conversion and energy storage performances were successfully synthesized and the functional films presented both excellent energy storage and mechanical property when the molecular weight of PEG was in the range of 6,000∼10,000. Research limitations/implications The materials that were used in this research paper had a reasonably low cost. Also, the procedures for the synthesis of dye and polymers were extremely easy because there was no need for high pressure or temperature and no dangerous solvents were used. Practical implications The photothermal conversion property and mechanical performance of the synthesized flexible PU films were characterized. The results have proved that these films were soft and elastic, and have certain photothermal conversion and energy storage ability, thus can be used in the surface finishing of special fabric and leather. Originality/value Visible light trapping photothermal conversion PU flexible film with energy storage capability was prepared for the first time.

A Novel Resorbable Composite Material Containing Poly(ester-co-urethane) and Precipitated Calcium Carbonate Spherulites for Bone Augmentation—Development and Preclinical Pilot Trials

Polyurethanes have the potential to impart cell-relevant properties like excellent biocompatibility, high and interconnecting porosity and controlled degradability into biomaterials in a relatively simple way. In this context, a biodegradable composite material made of an isocyanate-terminated co-oligoester prepolymer and precipitated calcium carbonated spherulites (up to 60% w/w) was synthesized and investigated with regard to an application as bone substitute in dental and orthodontic application. After foaming the composite material, a predominantly interconnecting porous structure is obtained, which can be easily machined. The compressive strength of the foamed composites increases with raising calcium carbonate content and decreasing calcium carbonate particle size. When stored in an aqueous medium, there is a decrease in pressure stability of the composite, but this decrease is smaller the higher the proportion of the calcium carbonate component is. In vitro cytocompatibility studies of the foamed composites on MC3T3-E1 pre-osteoblasts revealed an excellent cytocompatibility. The in vitro degradation behaviour of foamed composite is characterised by a continuous loss of mass, which is slower with higher calcium carbonate contents. In a first pre-clinical pilot trial the foamed composite bone substitute material (fcm) was successfully evaluated in a model of vertical augmentation in an established animal model on the calvaria and on the lateral mandible of pigs.

Surface morphology of chlorine and castor oil-based polyurethane–urea coatings

The present work deals with surface properties of chlorine containing polyurethane–urea (PU–urea)-coating films. First, isocyanate-terminated pre-polymers were synthesized using castor oil as renewable resource, isophorone diisocyanate, and different weight percentages of 2-chloroethanol and 2,2,2-trichloroethanol. The resultant isocyanate-terminated pre-polymers were cured under atmospheric moisture to obtain chlorine containing PU–urea coatings. The surface properties of the coating films were characterized using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and X-ray diffraction. All characterization techniques suggest that the presence of chlorine species on the surface results in different surface properties when compared to control PU–urea (without the chlorine group)-coating film surface. The viscoelastic, swelling, and contact angle (CA) properties were studied for the prepared coating films. The glass-transition temperatures (Tg) were obtained in the region 29.2–35 °C for the coating films. Tg increased by increasing the chlorine content in polyurethane-coating formulations. The CA for the coating films was found to be in the range of 76°–64° and these properties were found to be decreased with increase in the weight percent content of the chlorine moiety in the final coating formulation. Similarly, the higher chlorine content-coating films have shown more water uptake properties. The overall comparative results indicate that the chlorine containing PU–urea-coating films have different surface-coating properties and these depend upon the chlorine content in the final coating formulation as compared with PU–urea surfaces.

Ladder-Type Poly(3,4-ethylenedioxythiophene)-Poly (ethylene glycol)-Polyurethane Supramolecular Network for Gel Polymer Electrolyte

ABSTRACTA ladder-type poly(3,4-ethylenedioxythiophene)-poly (ethylene glycol)-polyurethane (PEDOT-PEG-PU) supramolecular network was successfully synthesized using graft copolymerization of hydroxymethyl-EDOT with isocyanate-terminated PEG-PU prepolymer. PEDOT functionalized as the frame for a ladder-type supramolecular structure and PEG-PU as the rung. The successful formation of supramolecular network was confirmed by analyzing the Fourier transform infrared spectroscopy (FTIR). A series of PEDOT-PEG-PU gel polymer electrolyte by linking the LiClO4 were prepared as a function of [O/Li+] ratios. The pH effect of their electrical capacitances was investigated using cyclic voltammetry. Ionic conductivities of different PEDOT-PEG-PU/Li+ complexes at a fixed pH were also evaluated through impedance analysis.

Formation of linear and crosslinked polyurethane nanoparticles that self-assemble differently in acetone and in water

For the first time, stable water-borne polyurethane dispersions (PUDs) leading to mechanically strong polyurethane (PU) coatings were prepared without any chain extender. Elimination of this step and using of water-crosslinking gives promising applications of PUDs as biomaterials and production on an industrial scale. The PU system consists of polycarbonate macrodiol (PCD), (2,2-bis(hydroxymethyl)) propionic acid (DMPA), 1,6-diisocyanatohexane (HDI) and N,N-diethylethanamine (TEA). Fourier transform infrared spectroscopy (FTIR), dynamic mechanical thermal analysis (DMTA), static light scattering (SLS), dynamic light scattering (DLS) and atomic force microscopy (AFM) enabled the study of the assembly of the PU chains/nanoparticles into supramolecular structures in acetone and in water. In acetone, the self-assembly of isocyanate-terminated pre-polymer chains occurs in the form of either PU solutions (linear PUs) or PU dispersions (crosslinked PUs). Due to a phase inversion, spherical linear or water-crosslinked PU dispersions are formed after water addition. The isocyanate-to-total hydroxyl ratio is very important; a slight isocyanate (NCO) excess of 1.05 leads to linear rod-like nanoparticles in acetone followed by a core-shell structure after water addition. An isocyanate excess of 1.5 leads to compact sphere or microgel particles initially crosslinked by moisture in acetone, and the final crosslinking and phase inversion occurs after water addition. The chain lengths of the linear PUs and the mesh sizes in PU networks increase with the PCD:DMPA ratio. Thus, the design of PU nanoparticles with desired sizes, shapes and crosslink densities is possible. Unlike the substantially different shapes, sizes and compactness of PUs in acetone, all PUDs in water are spherical nanoparticles with an average diameter from 21 to 72 nm, a zeta potential from −40 to −65 mV and a size-dispersity index from 0.05 to 0.22.

Synthesis and Characterization of Polyurea Resin for Dielectric Coating Applications

ABSTRACTIn this article, polyurea coatings were synthesized by reaction between toluene diisocyanate, and polyether difunctional and trifunctional amines PO-1 and PO-2 by incorporating urea linkage. The isocyanate-terminated prepolymers formed were further reacted with short-chain amines as chain extender as well as curing agents. These resins were synthesized by varying the molar ratio of amines and isocyanate and keeping the molar ratio of other monomers constant. The presence of functional groups were determined using Fourier transform infrared spectroscopy. The thermal stability of polymers was determined using the thermogravimetric analysis and differential scanning calorimetry. The polymers were further tested for mechanical and electrical properties. It was observed that on increasing the hard segments in the polymer the electrical properties increase whereas elongation decrease. As isocyanate content increases, crosslinking increases resulting in improvement in dielectric properties. The maximum dielectric strength observed was 45 kV mm−1 and dissipation factor was 0.068.

Thermosetting solid–solid phase change materials composed of poly(ethylene glycol)-based two components: Flexible application for thermal energy storage

The thermosetting solid–solid phase change materials (SSPCMs) composed of poly(ethylene glycol)-based two components, isocyanate-terminated prepolymer and tetrahydroxy prepolymer, were synthesized via solvent-free bulk polymerization, endowing the thermosetting PCMs with flexible application capability. The chemical structures, crystalline properties, phase change properties, thermal energy storage mechanism, thermal reliability and stability of the synthesized PCMs were respectively characterized by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, polarizing optical microscopy, accelerated thermal cycling testing and thermogravimetric analysis. The intrinsic crystalline structure in SSPCMs is not influenced by the crosslinking reaction between two components. However, compared with the poly(ethylene glycol) (PEG), the lamellae and spherulite size in SSPCMs decrease to some entente and dramatically, respectively. The SSPCMs have proper phase change temperature of about 45°C and high phase change enthalpy of about 100J/g much less than the PEG, resulted from the small spherulite and lamellae size working together. The SSPCM-based thermal energy storage relies on the phase change from the crystalline state to the amorphous state and vice versa. The SSPCMs have good thermal reliability and stability with the degradation temperature higher than 300°C.

A mathematical model of rheological behavior of novel bio-based isocyanate-terminated polyurethane prepolymers

In this paper, the results of rheological study on isocyanate-terminated polyurethane prepolymers, containing modified soybean oil residues incorporated into the chemical structure are described. Isocyanate-terminated prepolymers were synthesized from 4,4′-diphenylmethane diisocyanate and the mixture of hydroxylated soybean oil and commercial polyether. The measurements were performed by using rotary rheometer R/S-CPS+ (Brookfield, USA), while the rheological parameters were calculated by using Rheo3000 program. Based on rheological measurements, the viscosity curves and flow curves for prepolymers in the temperature range from 50 to 70°C were plotted. Prepolymer samples were tested with controlled shear rate (CSR). It was found that a viscosity of bio-based isocyanate-terminated prepolymers decreases with increasing content of hydroxylated soybean oil in the polyol mixture. The rheological data for bio-based polyurethane prepolymers were also mathematically modeled. It was found that the synthesized prepolymers are non-Newtonian fluids that can be described by Ostwald-de Waele and Herschel Bulkley functions as optimal individual models. The conducted investigations showed that the dynamic viscosity and rheological behavior of bioprepolymers samples could depend on the amount of hydroxylated soybean oil used in the polyol mixture.

New Polyurethane Elastomers with Enhanced Thermal Stability

A series of polyurethane elastomers with enhanced thermal stability was prepared and their physical and thermal properties were studied. For this purpose in the first step, an excess amount of methylene diphenyl diisocyanate was reacted with poly(tetramethylene ether) glycol to produce isocyanate-terminated polyurethane pre-polymer. In the second step, a new imide-based diol chain extender was synthesized via reaction of benzophenonetetracarboxylic dianhydride with 5-amino-1-naphthol. Finally, reaction of the pre-polymer with chain extender resulted in preparation of polyurethane elastomers. Presence of imide unit in the polymer backbone improved their properties and enhanced thermal stability of polyurethane.

Preparation and Performance Test of Solvent-Free Heavy-Duty Polyurethane Coating

Isocyanate-terminated prepolymer was prepared by reaction of polyether polyols with toluene diisocynate and was modified by adding CaO, hydroxyl silicone oil and hexamethylene diisocyanate, then solvent-free heavy-duty PU coating was got. The curing process of coating was studied by infrared spectrum. Physical, chemical and electrochemical properties of the coating were tested. The results showed that the coating could finish curing in 20 h at room temperature and its adhesion on the substrate of rusted carbon steel was 11.22 MPa. There was no rust change when the salt fog resistance reached 2200 h, the open-circuit potential electrode of coating showed the anticorrosion mechanism of it was given priority to shielding, linear polarization resistance of it exceeded 220 kΩcm2. All the above showed that solvent-free heavy-duty polyurethane coating had excellent anti-corrosion performance.

Synthesis and characterization of aqueous (polyurethane/aromatic polyamide sulfone) copolymer dispersions from castor oil

Abstract Aqueous dispersions of castor oil-based polyurethane (PUCO)/aromatic polyamide sulfone (APAS) block copolymers (PUCO-co-APAS) were successfully synthesized via a copolymerization reaction. PUCO was prepared by an emulsion polymerization process in four steps, namely isocyanate-terminated prepolymer preparation step (PUCONCO), neutralization step, chain extension step and dispersion step, using castor oil (CO), toluene diisocyanate (TDI), dimethylol propionic acid (DMPA) and ethylene diamine (EDA) as a chain extender. APAS was prepared by a polycondensation reaction between bis(4-aminophenyl)sulfone (in molar excess) and terephthaloyl chloride to produce amino-terminated APAS. Three PUCO-co-APAS were prepared via a copolymerization reaction between the amino-terminated APAS and isocyanate-terminated PUCONCO prepolymer. APAS, PUCO and PUCO-co-APAS copolymers were characterized using FTIR, 1H NMR, particle size distribution (PSD), zeta potential (ZP), thermal analysis (DSC and TGA) and GPC. The effect of the copolymerization process on the thermal, chemical, physical and mechanical properties of PUCO films was studied. The obtained results revealed that the mean particle size of PUCO decreased from 80 nm to 46–49 nm after the copolymerization process. Additionally, narrower size distribution was obtained by the copolymerization process. However, the molecular weight increased with increasing the amount of APAS in the copolymer chains. The copolymerized samples showed better thermal stability than PUCO as a result of the stronger hydrogen bonds and the rigid aromatic groups introduced by APAS in the copolymeric chains.

Preparation of Solvent-Free Moisture Curable Heavy Anti Corrosion PU Coating

Isocyanate-terminated prepolymer was synthesized by reaction of polyether polyols with toluene diisocynate and was modified by CaO and hydroxyl silicone oil, then solvent-free moisture curable heavy anti corrosion PU coating was prepared. The structure of cured coating was characterized by FTIR spectra and SEM. The mechanical properties, water tolerance, water contact angle of cured coating were analysed. The results showed that the solvent-free moisture curable heavy anti corrosion PU coating had the best combination property with 5% polyether polyols N210, 4% CaO and 4% hydroxyl silicone oil.

Chain Extender of Waterborne Polyurethanes Used for Warp Sizing

The effects of chain extender used in the extension of isocyanate-terminated pre-polymer during the preparation of waterborne-polyurethane (WPU) sizes were determined based on properties such as adhesion to fibers, film properties, desizability, and aerobic biodegradability. The extenders used included ethylene glycol (EG), butanediol (BD), hexanediol (HD), and ethylenediamine (EDA). The resulting effects and properties were strongly depended on the extenders. Diols were superior to EDA in increasing the molecular weights of extended WPUs, enhancing the adhesion to polyester fibers, and improving the film properties and aerobic biodegradability. EDA was unsuitable for the extension. For the diols, BD was the most preferred. Comparisons on the properties of the resulting WPUs versus PVA and starch were made.