Urethane Linkages Research Articles

The behavior of semi-rigid polyurethane film based on functionalized rubber by one-shot and two-shot method preparation

Semi-rigid polyurethane (PU) films based on functionalized liquid natural rubber (FLNR) were prepared by one-shot and two-shot methods. FLNR derived from waste crumb rubber acted as the soft segment and the hard segment consisted of 4,4′-methylenebis-(phenylisocyanate) (MDI) and 1,4-butanediol (BDO). The urethane linkage formation was confirmed by FTIR with a –NH-peak at 3317 cm−1 and disappearance of the NCO peak at 2295 cm−1. The semi-rigid PU with low rubber polyol chain favored solubility in non-polar solvent (toluene and chloroform) and low polar solvent (THF). For semi-rigid PU with high rubber polyol chain, it was poorly soluble in any solvent thus it has high stability. Studies on the hydrolytic stability were shown to be highly influenced by the high rubber polyol chain (soft segment contents more than 60%) in semi-rigid PU composition. The thermal stability of semi-rigid PU as determined by thermogravimetric analyses (TGA) showed improved degradation stabilities (more than 270 °C) in the presence of BDO and higher molecular weight of FLNR.

Cytocompatibility and Osteogenesis of Adipose Tissue-Derived Stem Cells on POSS-PEG Coated Collagen.

Nanostructured POSS-PEG nanoparticles (NPs, 42.4 nm ~) synthesized by formation of the urethane linkage between the monoisocyanate group (O═C═N-) of Polyhedral oligosilsesquioxane (POSS) macromers and the diol end groups (-OH) of polyethylene glycol (PEG) homopolymers as catalyzed by dibutyl tin dilaurate are of great interest for biomedical applications. However, NP materials based on nonorganic compounds can be cytotoxic. In this study, the preparation of PEG-POSS NPs followed the coating collagen assembly, which alleviates this problem. They also showed controlled surface properties in such a manner that hydrophobicity and biocompatibility were both reachable to give rise to improved cell viability. It indicates that the PEG-POSS coated collagen was appropriate for the proliferation of adipose tissue-derived stem cells to osteogenesis.

Polyurethane nanofiber strain sensors via in situ polymerization of polypyrrole and application to monitoring joint flexion

Strain sensors made of intrinsically conductive polymers (ICPs) and nanofibers were fabricated and tested for suitability for use in wearable technology. The sensors were fabricated and evaluated based on their surface appearances, and electrical, tensile, and chemical/thermal properties. Polypyrrole (PPy) was in situ polymerized onto polyurethane (PU) nanofiber substrates by exposing pyrrole monomers to ammonium persulfate as oxidant and 2,6-naphthalenedisulfonic acid disodium salt as doping agents in an aqueous bath. The PPy treated PU nanofibers were then coated with polydimethylsiloxane (PDMS). Both pyrrole concentrations and layer numbers were significantly related to change in electrical conductivity. Specimen treated with 0.1 M of PPy and having three layered structure showed the best electrical conductivity. Regarding tensile strength, the in situ polymerization process decreased tensile strength because the oxidant chemically degraded the PU fibers. Adding layers and PDMS treatment generally improved tensile properties while adding layers created fracture parts in the stress–strain curves. The treatment condition of 0.1 M of PPy, two layered, and PDMS treated specimen showed the best tensile properties as a strain sensor. The chemical property evaluation with Fourier transform infrared and x-ray photoelectron spectroscopy tests showed successful PPy polymerization and PDMS treatments. The functional groups and chemical bonds in polyol, urethane linkage, backbone ring structure in PPy, silicon-based functional groups in PDMS, and elemental content changes by treatment at each stage were characterized. The real-time data acquired from the dummy and five human subjects with repetition of motion at three different speeds of 0.16, 0.25 and 0.5 Hz generated similar trends and tendencies. The PU nanofiber sensors based on PPy and PDMS treatments in this study point to the possibility of developing textiles based wearable strain sensors developed using ICPs.

Critical transition of epoxy resin from brittleness to toughness by incorporating CO2-sourced cyclic carbonate

A five-membered cyclic carbonate as CO2-sourced monomer was prepared from ethylene glycol diglycidyl ether (EGDE) with CO2 by cycloaddition reaction, abbreviated as 5CC-EGDE, at 130 ℃ under 10 bar CO2 pressure in the presence of quaternary ammonium salt modified amberlyst (D296) for 20 h. The complete conversion and 98.6% selectivity were obtained, respectively. The incorporation of 5CC-EGDE into epoxy resin could reduce the viscosity during preparation process and improve the toughness effectively. It was ascribed to the ring-opening reaction of 5CC-EGDE with curing agent, and hydrogen bonding, formed between urethane groups and other polar groups. Besides, the low crosslinking density and unreacted carbonate groups remaining in epoxy network were beneficial to the movement of molecular chains and dissipation of energy during deformation process. In addition, effects of hydrogen-bonding interactions and crosslinking density on mechanical performances were also investigated by varying EGDE conversion and amount of added curing agent, respectively. The results indicated that mechanical performances of epoxy resin were promoted by combined effects of urethane linkage, hydrogen bonding, low crosslinking density and unreacted carbonate groups.

Effect of organoclay-type and clay-polyurethane interaction chemistry for tuning the morphology, gas barrier and mechanical properties of clay/polyurethane nanocomposites

Abstract Organo-modified montmorillonite (Mt) and bentonite reinforced clay/polyurethane nanocomposite (CPN) films were produced by master-batch based melt-mixing route, followed by compression molding. A novel route for preparation of master-batch by solution mixing was explored by using sonication and high-speed stirring. It was found that master-batch prepared by solvent mixing route resulted in good dispersion of clay-platelets in master-batch and finally in CPN. The concentration of both organoclays was varied from 1 to 5 wt% in final CPN, which were prepared by melt-mixing of master-batch and neat polyurethane (PU) in a twin-screw extruder. The presence of hydroxyl group in the clay-modifier of Mt, attributed to nearly exfoliated structure up to 3 wt% due to improved interaction by hydrogen bonding with ether groups or urethane linkages. Whereas, organo-modified bentonite showed partially intercalated and flocculated morphology, due to the absence of any polar group in the clay-modifier. As a consequence, Mt/PU nanocomposites showed much better mechanical and gas barrier properties in comparison to bentonite/PU nanocomposites. Moreover, a significant reduction in helium gas permeability and improvement in mechanical (tensile and tear) properties were observed for CPN produced with both organoclays in comparison to neat PU. At lower volume fraction of organoclays, a good correlation was obtained between gas permeability values determined experimentally and predicted by two different mathematical models.

In situ synthesis of polyurethane scaffolds with tunable properties by controlled crosslinking of tri-block copolymer and polycaprolactone triol for tissue regeneration

Mimicking the mechanical properties of native tissues is a critical criterion for an ideal tissue engineering scaffold. However, most biodegradable synthetic materials, including polyester-based polyurethanes (PUs), consist of rigid polyester chains and have high crystallinity. They typically lack the elasticity of most human tissues. In this study, a new type of biodegradable PU with excellent elasticity was synthesized based on the controlled crosslinking of poly(ester ether) triblock copolymer diols and polycaprolactone (PCL) triols using urethane linkages. Three-dimensional (3D) porous scaffolds with a defined geometry, tunable microstructures, and adjustable mechanical properties were synthesized in situ using an isocyanate-ended copolymer, a tri-armed PCL, and a chain extender. The mechanical properties of the scaffolds can be easily tuned by changing the ratio of reactants, varying the solution concentration, or using a porogen. Notably, all of these scaffolds, although mostly made of rigid PCL chains, showed remarkable elasticity and cyclical properties. With an optimized molecular design, a maximum recovery rate of 99.8% was achieved. This was because the copolymer provided molecular flexibility while the long chain crosslinking of PCL triol hindered crystallization, thus making the PU behave like an amorphous elastic material. Moreover, the in vitro cell culture of 3T3 fibroblasts and MG63 osteoblast-like cells confirmed the biocompatibility of these PU scaffolds and revealed that scaffolds with different stiffnesses can stimulate the proliferation of different types of cells. All of these attributes make PU scaffolds extremely suitable for the regeneration of tissues that experience dynamic loading.

A reactive phosphorus-containing polyol incorporated into flexible polyurethane foam: Self-extinguishing behavior and mechanism

A novel liquid phosphorus-containing polyol named as PDEO was prepared via reactions between ethylene glycol and phenylphosphonic dichloride. PDEO reacts with the -NCO-terminated prepolymers and forms urethane linkages in the chain extending reaction step, thus, it was used to prepare inherently flame-retardant flexible polyurethane foams (FPUFs). The structure and properties of flame-retardant FPUFs were characterized by scanning electron microscopy (SEM), tensile measurements, limiting oxygen index (LOI), vertical burning tests, cone calorimeter tests and thermogravimetric analysis (TGA). The vertical burning test demonstrated that fire extinguished instantly after the withdrawn of the pilot flame, while the PDEO loading was only 10 php. In addition, the persistent flame retardancy of PDEO in FPUFs was proved by thermal ageing test. The corresponding flame-retardant mechanism of PDEO-containing FPUFs was investigated by pyrolysis gas chromatography mass spectrometry (Py-GC/MS), X-ray photoelectron spectroscopy (XPS), SEM and FTIR, and the results indicated a gaseous phase dominated flame-retardant mechanism of PDEO.

Simultaneous Improvement of Oxidative and Hydrolytic Resistance of Polycarbonate Urethanes Based on Polydimethylsiloxane/Poly(hexamethylene carbonate) Mixed Macrodiols.

The degradation behaviors including oxidation and hydrolysis of silicone modified polycarbonate urethanes were thoroughly investigated. These polyurethanes were based on polyhexamethylene carbonate (PHMC)/polydimethylsiloxane (PDMS) mixed macrodiols with molar ratio of PDMS ranging from 5% to 30%. It was proved that PDMS tended to migrate toward surface and even a small amount of PDMS could form a silicone-like surface. Macrophages-mediated oxidation process indicated that the PDMS surface layer was desirable to protect the fragile soft PHMC from the attack of degradative species. Hydrolysis process was probed in detail after immersing in boiling buffered water using combined analytical tools. Hydrolytically stable PDMS could act as protective shields for the bulk to hinder the chain scission of polycarbonate carbonyls whereas the hydrolysis of urethane linkages was less affected. Although the promoted phase separation at higher PDMS fractions lead to possible physical defects and mechanical compromise after degradation, simultaneously enhanced oxidation and hydrolysis resistance could be achieved for the polyurethanes with proper PDMS incorporation.

Preparation and characterization of maltodextrin-based polyurethane

Maltodextrin (MD) based polyurethane (MDPU) was prepared by the reaction of MD and polyethyleneglicol (PEG) polyurethane prepolymer (PUP). The structure and properties of the MDPU were investigated by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H NMR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscope (SEM), Energy dispersive X-ray spectrometry (EDS), and tensile-testing machine in detail. Chemical structure of MDPU was confirmed by FTIR and 1H NMR. MDPU with 66.7% of PUP (MDPU-0.5) was a thermoset plastic with good elasticity but the others (MDPU-1, MDPU-2, and MDPU-3) were thermoplastics. TGA analysis showed that the MDPUs exhibited three stages of the thermal degradation, mainly including urethane linkage (I, 197–268 °C), MD and PUP components (II, 268–380 °C) and the formed stable structures during thermal degradation (III, 400–505 °C), respectively. The various degrees of miscibility were presented. The mechanical properties of thermoplastic MDPUs exhibited relatively high elongation at break under the given relative humidity.

Impact of supramolecular interactions on swelling and release behavior of UPy functionalized HEMA‐based hydrogels

Supramolecular polymeric hydrogels based on copolymers of 2‐hydroxyethyl methacrylate (HEMA) and HEMA functionalized with ureidopyrimidinone (quadruple H‐bonding motifs and HU comonomer) were prepared at different HU comonomer ratios (PH‐Sn, n = HU mol%). For comparison, HEMA homopolymers (PH‐Cn, n = mol% of a chemical cross‐linker) were synthesized. In contrast to PH‐S0, PH‐Sn copolymers act like cross‐linked hydrogels and absorb large amounts of water while retaining shape. Viscosities of the hydrogels decreased, and elastic and loss moduli increased with increasing HU content. Compression modulus of the swollen PH‐Sn hydrogels increased with HU content and varied between 54 and 240 kPa. Study of metronidazole loading/release behaviors of PH‐S6 hydrogel against PH‐C6 revealed a negligible burst effect for the former and a sustained release that continued for about 120 hours. We conclude that modification of poly(2‐hydroxyethyl methacrylate) with HU through urethane linkages is an effective strategy to developing physical hydrogels with predictable behavior for biomedical applications.

Remediation of hydrocarbons polluted water by hydrophobic functionalized cellulose

Remediation of water bodies from petroleum hydrocarbons is of the utmost importance due to health risks related to the high toxicity, mutagenicity and carcinogenicity of the hydrocarbons components that may enter into the food chain. Though several methods were proposed to face up this challenge, they are generally not easily feasible at a contaminated site and quite costly. Here we propose a green, cost-effective technology based on hydrophobized Spanish Broom (SB) cellulose fiber. The natural cellulose fiber was extracted by alkaline digestion of the raw vegetable. The hydrophilic cellulose surface was transformed into a hydrophobic one by the reaction with 4,4′–diphenylmethane diisocyanate (MDI) forming a very stable urethane linkage with the hydroxyl groups of cellulose emerging from the fibers surface. Chemical functionalization was performed with a novel solvent-free technology based on a home-made still reactor were the fiber was kept under vortex stirring and the MDI reactant then spread onto the fiber surface by nebulizing it in form of micrometer-sized droplets.The functionalized fiber, characterized by means of WCA measurements, XPS and ATR-FTIR spectroscopy, shows fast adsorption kinetics adsorption capacity as high as 220 mg/g, among the highest ever reported so far in the literature for cellulosic materials.

FABRICATION AND CHARACTERIZATION OF POLYURETHANE FOAM PREPARED FROM LIQUEFIED OIL PALM MESOCARP FIBRE WITH RENEWABLE MONOMER MADE FROM WASTE COOKING OIL

This study aims performance characteristics of polyurethane foams prepared by the reaction of biopolyol prepared from liquefied oil palm mesocarp fibre and renewable monomer with methylene diphenyl diisocyanate. The effect of prepared oil palm mesocarp biopolyol with incorporation of renewable monomer of PU foam on the thermal stability, mechanical properties and was analyzed by thermo gravimetric analysis, tensile and compressive tests and Fourier transform infrared spectroscopy. The improved thermal properties were achieved at a composition of oil palm mesocarp fibre foams (PMF). Oil PMF foams showed mechanical strength as compared to renewable monomer foams. PU foam prepared from oil palm mesocarp biopolyol with incorporation of renewable monomer improved the foams strength. An infrared spectroscopy study demonstrated the formation of urethane linkage. Keywords: polyurethane foam; oil palm mesocap fibre; biopolyol; renewable monomer

Application of Western red cedar (Thuja plicata) tree bark as a functional filler in pMDI wood adhesives

In this study, Western red cedar (Thuja plicata) tree bark was used as a reactive functional filler (oven-dry particles, <0.1 mm) in polymeric diphenylmethane diisocynate (pMDI) wood adhesives at four different loading levels (5, 10, 15 and 20 wt.%) to improve the bondline formation at the adhesive-substrate interface. Adhesion performance and curing behavior of the bark containing pMDI (B-pMDI) were investigated. B-pMDI adhesive had a higher viscosity than pMDI control and the viscosity value varied according to the bark/pMDI weight ratio. Compared to the pMDI control wood adhesive without bark, B-pMDI showed comparable dry bonding strength and enhanced wet bonding strength for wood substrates. SEM images indicated that B-pMDI formed a thicker and more consistent bondline than the pMDI control due to bark particles effectively bridging the gap between the wood substrates. Based on both Kissinger and isoconversional model-free methods, cure kinetics revealed that oven-dry bark particles chemically reacted with pMDI. Moreover, it was found that a lower activation energy and a higher reaction rate were observed for pMDI curing with moist bark than with oven-dry bark. FTIR characterization suggested the existence of urethane and urea linkages in the cured adhesives.

Properties of Compatible Soy Protein Isolate/Polycaprolactone Composite with Special Interface Structure

It is important to improve the compatibility and ultimately the properties of biobased polymer materials as alternative materials for non‐degradable polymer materials. In this study, polyurethane prepolymer (PUP) was synthesized from PCL diols, and the PUP with special structure was used as a compatibilizer to improve the compatibility between hydrophilic soy protein isolate (SPI) and hydrophobic PCL composites. The structure and properties of the soy protein isolate‐polycaprolactone (SPI‐PCL) composites were investigated. The results showed that the mechanical properties such as the tensile strength, impact strength, and bending strength of the modified composites were increased as compared to un‐modified composites, respectively. Also, the SEM results showed that the interfacial adhesion between the hydrophobic PCL and hydrophilic SPI was also enhanced because of the existence of compatible PU interfacial layer in the composites. Clearly, the strong urethane linkage interaction between the PU interfacial layer and the SPI particles, and the PCL–PCL crystallinity interactions between the PU interfacial layer and PCL matrix were responsible for the improved compatibility in the SPI–PCL composites. Therefore, the addition of the PUP with the special structure improved the compatibility and the properties of the SPI–PCL composites significantly. POLYM. COMPOS., 40:E383–E391, 2019. © 2017 Society of Plastics Engineers

Controllable degradation of polyurethane elastomer via selective cleavage of C[sbnd]O and C[sbnd]N bonds

The degradation and recovery of waste polyurethane materials have confronted enormous challenge. Controllable degradation of polyurethane elastomer is developed via selective cleavage of CO of urethane linkages and CN bonds. It was founded that the selective cleavage of carbon-heteroatom bonds could be efficiently performed in 70% ZnCl2 aqueous solution. The transition metal Zn2+ coordinated with N and O atoms due to their unshared electron pairs. The CO of urethane linkages and CN bonds were readily cleaved using ZnCl2 as catalysts at 140 °C for 2 h. However, the CC bonds and COC of ether linkages as framework structure remain intact in the degradation process. Eventually, the high-value-added chemicals including 2,4-diaminotoluene, polytetramethylene ether glycol (PTMEG) and 3,3′-dichloro-4,4′-diaminodiphenylmethane (MOCA) were retrieved via selective cleavage of CO of urethane bonds and CN bonds.

Organic/inorganic hybrid nanocolloids of water dispersible polyurethanes with antibacterial activity

We report an in-situ synthetic strategy to prepare water dispersible polyurethane (WDPU) from an organic/inorganic hybrid nanocolloids in which the organic component is dinitrobenzene-modified hydroxyl-terminated polybutadiene (HTPB-DNB)-based polyurethane and the inorganic part is TiO2 (core)–SiO2 (shell) nanoparticles. The shape, size, and polydispersity of the hybrid nanocolloids are determined using microscopic and light scattering studies and are found to be slightly dependent on the loading of core–shell nanofillers. FT-IR and solid-state NMR studies prove the presence of the interaction between the carbonyl functionality of the urethane linkage and the SiO2 present in the shell part of the particles, and this interaction is found to be the driving force for the formation of stable nanocolloids. The films, obtained from the nanocolloids of WDPU upon curing, display better thermal and mechanical properties, and also, these properties increase with increasing loading of nanofillers. Higher tensile strength and Young modulus are obtained in WDPU nanocolloids films compared to pristine WDPU films. The antibacterial activity of WDPU nanocolloids was studied on Staphylococcus aureus (Gram-stain-positive bacterium) and Escherichia coli (Gram-stain-negative bacterium) displayed significantly higher zone of inhibition in both the cases, indicating the potential use of these nanocolloids in antibacterial coating.

Generalization and Modelling of Rigid Polyisocyanurate Foam Reaction Kinetics, Structural Units Effect, and Cell Configuration Mechanism

PIR/PUR ratio was derived from differential manipulation of generalized polyisocyanurate kinetic model. The structural unit effects on polymerization of isocyanurate, urethane and urea linkages were evaluated based on Mayo-Lewise tercopolymerization scheme. The cell microstructural configuration model was further developed from profiled FOAMAT reactivity parameters with integrated analysis of cell interface physics. The interstitial border area was defined by interface free energy theory, the shear viscosity was evaluated by foam motion, gas fraction, and partial pressure, and the cell inflation was re-examined by gas-liquid surface tension variability. The cell anisotropic degree, assumed as an aspect ratio of infinitesimal volume elements in cell uniformity, was characterized by equilibrated work increase of surface energy approximated by 2D stretching deformation from sphere cell to spheroid cell. The relationship between pressure and surface tension of elongated cells was also derived from modelling at the same condition of cell deformation.

Synthesis and Characterization of Plug-and-Play Polyurethane Urea Elastomers as Biodegradable Matrixes for Tissue Engineering Applications.

The highly tunable mechanical properties and resilience of polyurethanes make them promising candidates for tissue engineering applications. Biodegradability is conferred by incorporation of hydrolytically or enzymatically cleavable moieties into the polyurethane structure. A common choice for the biodegradable soft segment is a poly(ether ester) triblock copolymer synthesized by ring opening polymerization of the polyester from a polyether macroinitiator. Herein, we describe a new "plug-and-play" approach for triblock synthesis based on urethane block coupling that enables finer control of block lengths and ease of segmental tuning. The inclusion of urethane linkages in the soft segment was also hypothesized to promote hydrogen bonding between the segments with an associated increase in modulus, tensile strength, and ultimate elongation. Hard segment content of the biodegradable polyurethane urea was varied to demonstrate the tunable tensile properties and degradation rate. As expected, increasing hard segment content led to large increases in initial secant modulus and tensile strength. A corollary decrease in ultimate elongation, elastic recovery, and degradation rate was also observed with increasing hard segment content. Finally, cytocompatibility and hydrolytic degradation of electrospun polyurethane meshes were evaluated to establish the potential use of these biodegradable matrixes as tissue engineering scaffolds. All of the polyurethane formulations displayed comparable cytocompatibilty to tissue culture plastic controls and hydrolytic chain scission of the polyester soft segment. Overall, this synthetic approach provides a platform to produce biodegradable polyurethane ureas with enhanced control over segmental chemistry, mechanical properties, and degradation rate.

Environment‐friendly chemical recycling of aliphatic polyurethanes by hydrolysis in a CO2‐water system

ABSTRACTIn order to develop a chemical recycling system of polyurethanes (PUs), environment‐friendly hydrolysis of two types of aliphatic PUs was studied under pressured CO2 in water, in which the carbonic acid generated from CO2 acted as an acid catalyst. Two PUs, namely H‐PU or I‐PU, were synthesized starting from 1,4‐butanediol and 1,6‐hexamethylene diisocyanate or isophorone diisocyanate, respectively. The hydrolysis of PUs depended on the experimental conditions, such as the temperature and CO2 pressure. As a result, 98% of H‐PU and 91% of I‐PU were successfully hydrolyzed under the typical conditions of 190 °C for 24 h at 8.0 MPa CO2. The reaction mixtures afforded 1,4‐butanediol and diamines without the formation of any byproducts. Both of these raw materials generated from the originated PUs by selective hydrolytic cleavage of the urethane linkages, and they were easily isolated in high yields simply by evaporation of the water‐soluble components within the reaction mixture. By comparing the results of the two aliphatic PUs with those of an aromatic PU (M‐PU), the hydrolyzability was found to decrease in the order H‐PU, I‐PU, and M‐PU. The difference can be ascribed to the hydrophilicity of the aliphatic or aromatic groups connected to the urethane moieties at the terminals of PUs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45897.

Formation of new, cytocompatible hydrogels based on photochemically crosslinkable levan methacrylates

Levan is a high molecular weight fructose-based biotechnologically available polysaccharide with a range of interesting properties qualifying this molecule for applications in biomedicine. In this study, new levan derivatives containing methacrylate groups attached either via ester or urethane linkages to the fructan backbone could be synthesized and structurally characterized by conventional analytical techniques. The photochemical crosslinking of these substances applying different photoinitiator systems and reaction conditions resulted in hydrogels of diverse properties which were investigated with regard to mechanical behaviour, hydrolytic degradability, and cytocompatibility. It was found that crosslinkable levan derivatives represent a new class of promising biopolymer-based macromers broadening the spectrum of available biomaterials to facilitate the adaption to the requirements of specific applications.