Effect of pyridazine content and crosslinker structure on the properties of polyurethane elastomers

This article studies the development of a series of heterocyclic polyurethanes (PUs) with various pyridazine content and different crosslinker structure in their main chains. All of the isocyanate‐terminated PU prepolymers were prepared from poly(tetramethylene oxide) glycol of molecular weight 1400 (Terathane 1400) and 1,6‐hexamethylene diisocyanate. The properties of the obtained linear and crosslinked pyridazine‐based PU were compared with the properties of common PUs obtained by chain extension with 1,4‐butanediol. All the obtained PUs were characterized through spectral and thermal behavior. The pyridazine‐based PU showed improved thermal stability with 10% weight loss at temperatures above 370–400°C. With the increase of pyridazine content the values of Young's modulus are higher and the strain at break decreases. Increasing pyridazine content leads to increased films surface hydrophilicity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Aqueous-based polyurethane with dual-functional curing agent

Aqueous-based polyurethane (PU) with a carboxyl pendent group was prepared from a conventional PU prepolymer process. Its carboxyl group served as the ionic center for stabilizing the aqueous PU dispersion and as the curing site for post-curing reaction. A curing agent was synthesized from the substitution reaction of phosphorus oxychloride or phenylphosphonic dichloride by aziridine. Each compound consisted of two aziridinyl groups and the phosphorus composition. Its aziridinyl group reacted with a PU carboxyl group and its phosphorus content was introduced to this PU curing system simultaneously. Those compounds served as both curing agent and flame retardant for the PU curing system. The physical and mechanical properties of the resulting PU were improved corresponding to the curing dosage. The thermal properties and the flame inhibition behaviors of those post-cured PUs were evaluated by measurements using thermogravimetric analysis, dynamic mechanical thermal analysis, a limiting oxygen index, and a cone calorimeter.     

Effects of the structures of end groups of pendant polydimethylsiloxane attached to a polyurethane copolymer on the low temperature toughness

End groups with different structures were grafted to polyurethane (PU) using poly(dimethylsiloxane) (PDMS) as a spacer. The low‐temperature toughness of the PUs was tested at ?30°C, and the structure selectivities of the end groups for low‐temperature toughness were compared. The PDMS functioned as a flexible linker that connected the end groups to the PUs. The tensile strength of the PU generally improved despite the grafting of PDMS and end groups. The conventional shape recovery ratio at 45°C remained greater than 90%, regardless of the content and structure of PDMS and the end group. The PU that contained an adamantyl group (cubic) or a naphthyl group (planar rectangle) showed instant recovery, even at ?30°C, but the PU that contained a phenyl (planar square) or phenoxyphenyl (bent squares) group required warming to 0°C for a similar degree of recovery but showed improvement over a linear PU without any end group. The characteristic structure of the end group was responsible for the selective low‐temperature toughness. The low‐temperature toughness results and the thermal and mechanical properties of the PUs are discussed. POLYM. ENG. SCI., 55:1931–1940, 2015. © 2014 Society of Plastics Engineers     

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

In 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.     

Convenient post-curing reactions for aqueous-based polyurethane anionomers

Anionic aqueous-based polyurethane (PU) dispersions were prepared by introducing carboxylic groups into a conventional PU backbone, followed by a water dispersion process. The resulting carboxylic groups containing aqueous-based PUs were amino-terminated anionomers. Two model reactions between an amino and a carboxylic group containing compounds with an epoxide and an aziridinyl compound, respectively were carried out at ambient temperature. Di-functional epoxide and aziridinyl compound were employed as the convenient single post-curing and dual-curing agents for these prepared PU dispersions. Di-aziridinyl compound was stable in aqueous PU dispersions as a latent curing agent when the pH value of the system was 8.0 or above. The curing behaviors of each PU curing system were monitored by measurements of the gel content, average particle size, zeta potential, and fluorescence spectra. The mechanical and thermal properties of these post-cured PUs were evaluated.     

Synthesis and Thermal Characterization of Polyurethane/Clay Nanocomposites Based on Palm Oil Polyol

Polyurethanes (PUs) are very versatile polymeric materials with a wide range of physical and chemical properties. PUs also have desirable properties, such as high abrasion resistance, tear strength, shock absorption, flexibility, and elasticity. Although they have poor thermal stability, it can be improved by using treated clay.

The objective of the present work is to study the thermal stability of polyurethane, polyurethane/montmorillonite (PU CTAB-mont 3% wt), and polyurethane/montmorillonite containing moca (PU Moca CTAB-mont 3% wt) nanocomposites based on palm oil polyol.

The interest of investigating the synthesis of polyurethane/clay nanocomposites based on palm oil polyol is to explore the use of palm oil polyol to partially replace petrochemical-based polyol.

Polyurethane/clay nanocomposites were prepared by a pre-polymer method and evaluated by Fourier Transform Infrared Spectra (FTIR) to determine micro-domain structures of segmented PU, PU CTAB-mont 3% wt, and PU Moca CTAB-mont 3% wt. The morphology of the nanocomposites was characterized by X-ray diffraction (X-RD), and flame retardant was investigated with thermogravimetric analysis (TGA). The result showed that in comparison with the virgin polyurethane, adding clay and moca demonstrated better thermal stability.     

Reprocessing polyurethane foam using dynamic covalent chemistry in extrusion

Thermoset polyurethanes (PUs) pose recycling challenges due to their crosslinked structure. This study investigates the possibility to directly reprocess PU foams through (dynamic) carbamate exchange using reactive extrusion. By varying compounding temperature and catalyst (dibutyltin dilaurate, DBTDL) concentration, the extrusion process is examined using torque measurements. We clearly show that it is possible to reprocess the PU foam at temperatures well below 200°C and that DBTDL catalyst greatly enhances bond exchange rates during compounding. Reproducible extrusions at 160°C with 0.3 wt% DBTDL result in a material with a gel fraction of 0.90 displaying typical dynamic covalent network behavior, as confirmed by stress relaxation measurements. The measured characteristic relaxation times display an Arrhenius-type temperature dependence with an activation energy of 41 kJ/mol. Successful extrusion of fully crosslinked PU foam at milder temperatures with DBTDL catalyst demonstrates potential for PU foam recycling using reactive extrusion, and generally highlights the feasibility of dynamic crosslink reconfiguration for waste reduction and improved sustainability.     

Preparation of waterborne polyurethanes using an amphiphilic diol for breathable waterproof textile coatings

The application of polyurethanes (PUs) on breathable waterproof fabric coatings requires a balance of water vapor permeability (WVP) and water resistance which can be achieved by tailoring hydrophilic and hydrophobic segments. PU prepolymers were prepared from isophorone diisocyanate, dimethylol butanoic acid, and a mixture of various ratios of amphiphilic PPG2050 (copolymer of ethylene oxide and propylene oxide with –OH end groups) and hydrophobic poly(tetramethylene ether glycol) (PTMEG). After neutralization with triethylamine, the prepolymers were chain-extended with ethylene diamine/1,4-butanediol (1:1 by molar). The WVP values of the fabric coatings prepared using various waterborne PUs were very similar (910–990 g/m² × 24 h). When waterborne PUs prepared using a mixture of PPG2050 and PTMEG were employed for the textile coatings, the resulting PU-coated textiles exhibited excellent waterproof properties (>10,000 mm H₂O). The textile coatings prepared from PPG2050/PTMEG-based waterborne PUs were significantly more waterproof than those prepared from poly(ethylene glycol) (PEG)/poly(propylene glycol) (PPG)/PTMEG-based waterborne PU. This is probably due to a more even distribution of hydrophobic segments in the PUs, even though the WVP values of the PEG/PPG/PTMEG-based PU coatings were considerably smaller than those of the PPG2050/PTMEG-based PU coatings.     

Preparation and characterization of biodegradable polyurethanes composites filled with silver nanoparticles-decorated graphene

In this study, polyurethane (PU) was synthesized using 4,4,-diphenylmethane diisocyanate (MDI) as a hard segment, polycaprolactone diol (PCL) as the soft segments and 1,4-butandiol (1,4-BD) as a chain extender. Nanosilver/graphene (Ag/G) was added to the PU matrix to prepare Ag/G/PU nanocomposites. EDS, SEM and XRD are used for assaying the silver content and characterization of Ag/G. TEM, FT-IR, XRD and EDS were used to characterize the structure and morphology of the Ag/G/PUs nanocomposites. The TEM results show that Ag/G belongs to sheet structures and is dispersed in a PU matrix. The SEM showed that the strong interfacial adhesion between the Ag/G and PU is indicated. FT-IR spectra analysis shows that the functional group of PU is free of obvious changes by adding a small amount of Ag/G in the PU matrix. XRD results showed that the main crystalline peak (26°) of Ag/G became more apparent with increasing content of Ag/G, and EDS showed that the content of Ag increased with increasing content of Ag/G in the Ag/G/PUs nanocomposites. The thermal stability and mechanical properties of Ag/G/PUs nanocomposites are improved with increasing content of Ag/G. Contact angle and AFM results showed that the hydrophobicity and surface roughness increased with increasing content of Ag/G. Moreover, the Ag/G/PUs nanocomposites exhibit antibacterial activities toward Staphylococcus aureus as well as Escherichia coli and their antibacterial rates increase with increasing Ag/G. In addition, the electrical conductivity measurements showed that both surface and volume resistance of the Ag/G/PUs nanocomposites decreased as the amount of Ag/G increased.     

Shape memory segmented polyurethanes: dependence of behavior on nanocellulose addition and testing conditions

The response of synthesized shape memory segmented polyurethanes (PUs) was affected by the addition of cellulose nanocrystals, as well as by the various conditions selected to carry out thermomechanical cyclic tests. The PUs were synthesized from an α‐hydro‐ω‐hydroxy‐poly(ethylene oxide), tolylene‐2,4‐diisocyanate and 1,4‐butanediol as chain extender. Nanocomposites were prepared by mixing a suspension of cellulose nanocrystals in N,N‐dimethylformamide with the thermoplastic PU dissolved in the same organic solvent. The thermal properties of the neat PU and resulting composites were examined using differential scanning calorimetry. It was found that cellulose addition increases the PU soft segment melting and crystallization temperatures and the degree of crystallinity of this phase. Shape memory behavior was studied using cyclic thermal tensile tests. Both neat PU and composites exhibit shape memory properties, with fixity and recovery values that depend on heating temperature, imposed deformation, deformation rate and nanofiller addition. Copyright © 2011 Society of Chemical Industry     

Synthesis and characterization of chlorine‐containing flame‐retardant polyurethane nanocomposites via in situ polymerization

We have developed flame‐retardant polyurethanes (FRPUs) and polyurethane (PU) nanocomposites via in situ polymerization. Three series of thermoplastic elastomeric PUs were synthesized to investigate the effect of incorporating 3‐chloro‐1,2‐propanediol (CPD) and nanoclay on mechanical, thermal properties, and also resistance to burning. PU soft segments were based on poly(propylene glycol). Hard segments were based on either CPD or 1,4‐buthane diol (BDO) in combination with methyl phenyl di‐isocyanate named PU or FRPU, respectively. In the third series, CPD was used as chain extender also nanoclay (1% wt) and incorporated and named as flame‐retardant polyurethane nanocomposites (FRPUN). Mechanical properties and LOI of PUs and nanocomposites have been evaluated. Results showed that increasing the hard segment (chlorine content) leads to the increase in flame retardancy and burning time. Addition of nanoclay to CPD‐containing PUs leads to obtain self‐extinguish PUs using lower CPD contents, higher Young's modulus, and strength without any noticeable decrease in elongation at break. Investigation of the TGA results showed that copresence of nanoclay and chlorine structure in the PU backbone can change thermal degradation pattern and improve nanocomposite thermal stability. X‐ray diffraction and transmission electron microscopy studies confirmed that exfoliation and intercalation have been well done. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of novel polyurethanes based on 4,4’-{1,4-phenylenebis[methylylidenenitrilo]}diphenol

A series of novel segmented polyurethanes (PUs) containing imine units in the main chain were prepared by polyaddition reaction of various diisocyanates like 4,4’-diphenyl-methane diisocyanate, tolylene 2,4-diisocyanate, isophorone diisocyanate and hexamethylene diisocyanate with 4,4’-{1,4-phenylenebis[methylylidenenitrilo]} diphenol based diol. The structure of the diol and segmented PUs were determined by Fourier transform infrared, ultraviolet-visible spectrometry and fluoroscence spectroscopy. PUs were soluble is polar aprotic solvents. Thermal properties were done by using differential scanning calorimetry (DSC) and thermogravimetric analysis. DSC data display the PUs having multiple endotherm peaks. MDI based PU show the more thermal stable compared to other PUs.     

On-demand click functionalization of polyurethane films and foams

A novel platform of side-chain functionalized crosslinked polyurethane (PU) films and foams has been used to afford new classes of PU materials. Indeed, alkyne pendant groups located along the polyurethane backbone have been modified via the copper catalyzed Huisgen 1,3-dipolar cycloaddition with various azide components. These cycloaddition reactions were carried out in water or in a mixture of water/acetone under mild conditions (room temperature to 50 °C) in the presence of low amounts of copper catalyst. The resulting functionalized films and foams were all characterized by FT-IR, contact angle measurements and confocal fluorescence microscopy. All these techniques successfully proved that the click chemistry process is valuable in functionalizing PU films and foams in an easy way. The post-functionalization of these alkyne-functionalized PUs afforded the creation of new classes of PU materials with easily adaptable physical properties by choosing the appropriate azide component.     

Thermal and mechanical properties of multiple‐component aliphatic degradable polyurethanes

Macroscopic thermal and mechanical properties of complex aliphatic polycarbonate‐based polyurethane (PU) films containing degradable ester units in PU backbone were studied by a combination of several experimental techniques. Differential scanning calorimetry (DSC) revealed that the synthesized oligomeric diol (DL‐L) contributes (in addition to polycarbonate diol) to the formation of soft‐segment domains, while the hard‐segment domains are formed from 1,6‐diisocyanatohexane (HDI) and butane‐1,4‐diol (BD). Three main phase transitions were detected by DSC and by dynamic mechanical thermal analysis. Thermogravimetric analysis (TGA) of two‐component PUs showed that the PU made from DL‐L and HDI is the least thermostable product, while the PU made from polycarbonate diol and HDI is the most stable one. The differences in the thermal stability of different four‐component PUs are not important. Tensile properties very sensitively reflect the changes in composition and in microstructure of PU samples; the best tensile properties exhibits the degradable sample containing the equimolar ratio of hydroxyl groups of macrodiol, oligomeric diol DL‐L and butane‐1,4‐diol. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41872.     

Synthesis,Thermal and Morphological Properties of Polyurethanes Containing Azomethine Linkage

This paper presents synthesis, photophysical, electrochemical, thermal and morphological properties of Schiff bases containing various side-group substitutions and polyurethanes (PUs) containing azomethine linkage. Morphological properties of PUs containing azomethine bonding were investigated by scanning electron microscopy (SEM). SEM images showed that PU containing azomethine consist of semi-crystalline particles. Thermal transitions in PUs containing azomethine units were studied using DSC. The obtained DSC curves showed that PUs containing azomethine are semi-crystalline materials due to they contain both crystallization and melting peaks. Electrochemical properties also investigated by using cyclic voltammetry (CV). According to the cyclic voltommagrams and CV data, PUs containing azomethine have below 2.0 eV electrochemical band gap.     

Effect of cationic group content on shape memory effect in segmented polyurethane cationomer

To illustrate the importance of cationic groups within hard segments on shape memory effect in segmented polyurethane (PU) cationomers, the shape memory polyurethane (SMPU) cationomers composed of poly(ε‐caprolactone) (PCL), 4,4′‐diphenylmethane diisocyanate (MDI), 1,4‐butanediol (BDO), and N‐methyldiethanolamine (NMDA) or N,N‐bis(2‐hydroxyethyl)isonicotinamide (BIN) were synthesized. The comparison of shape memory effect between NMDA series and BIN series was made. The relations between the structure and shape memory effect of the two series of cationomers with various ionic group contents were investigated. It is observed that the stress at 100% elongation is reduced for these two series of PU cationomers with increasing ionic group content. Especially for NMDA series, the stress reduction is more significant. The fixity ratio and recovery ratio of the NMDA series can be improved simultaneously by the insertion of cationic groups within hard segments, but not for the BIN series. Characterizations with DSC and DMA suggest that the crystallibility of soft segment in SMPU cationomers was enhanced by incorporation of ionic groups into hard segments, leading to a relative high degree of soft segment crystallization; compared with the corresponding nonionomers, incorporation of charged ionic groups within hard segments can enhance the cohesion force among hard segments particularly at high ionic group content. This methodology offers good control of the shape memory characteristic in thin films and is believed to be beneficial to the shape memory textile industries. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 545–556, 2007     

Synthesis and characterization of polyurethanes containing glucose for selective determination of epinephrine in the presence of a high concentration of ascorbic acid

Polyurethane (PU) films were prepared from glucose, ethylene glycol and diphenylmethane diisocyanate and used to construct a novel polymer electrode for the detection of epinephrine (EP) in the presence of a high concentration of ascorbic acid (AA). The NCO:OH molar ratio was kept constant at 1 and the saccharide content was varied. The PUs were characterized using Fourier transform infrared spectroscopy, differential scanning calorimetry and differential thermal and thermogravimetric analyses, with intrinsic viscosity and adhesive properties also being evaluated. The PUs exhibited high glass transition temperature, good thermal stability and good adhesive properties. The incorporation of saccharides into the PU structure resulted in a higher crosslinking density and a higher content of hard segments. Medium‐ to high‐molecular‐weight polymers were obtained, with inherent viscosities near or higher than 0.98–2.14 dL g^?1. The solubility of the PUs was much better than that of aromatic PUs. The modified polymer electrodes were then used to determine EP in the presence of a high concentration of AA using differential pulse voltammetry. From the amperometric results for the PU electrode, it is concluded that a PU film containing 5 wt% glucose can be used as a membrane for EP detection in the presence of a large concentration of AA, because of its strong adherence to the electrode surface, easy preparation, chemical stability, selectivity and very high statistical confidence (R = 0.9994). © 2012 Society of Chemical Industry     

Biobased chain extended polyurethane and its composites with silk fiber

The biobased chain extended polyurethane (PU) was synthesized by reacting castor oil based polyol with different diisocyanates [toluene‐2,4‐diisocyanate (TDI) and hexamethylene diisocyanate (HMDI)] and chain extender such as glutaric acid. Biocomposites have been fabricated by incorporating the silk fiber into both TDI‐ and HMDI‐based PUs. The effect of incorporation of silk fiber into TDI‐ and HMDI‐based neat PU on the physicomechanical properties such as density, surface hardness, tensile strength, and percentage elongation have been investigated. The dynamic mechanical properties and the thermal stability of neat PUs and the silk fiber incorporated PU composites have been evaluated. The TDI‐based neat PU has showed higher mechanical properties compared to HMDI‐based PU. The incorporation of 10% silk fiber into TDI‐ and HMDI‐based PU resulted in an enhancement of tensile strength by 1.8 and 2.2 folds, respectively. The incorporation of silk fiber into biobased chain extended PU increased the glass transition temperature (T_g) of the resultant biocomposites. The morphology of tensile fractured neat PUs and their biocomposites with silk fiber was studied using scanning electron microscope (SEM). POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Synthesis and characterisation of novel flame retardant polyurethanes containing designed phosphorus units

In this study, 2-carboxyethyl(phenyl)phosphinic acid (CEPPA) and trimethylolpropane (TMP) are used to synthesise a novel flame retardant containing phosphorus units: 5-hydroxy-3-(2-hydroxyethyl)-3-methylpentyl-3-[2-carboxyethylphenylphosphine]propanoate (HMCPP). Then, 4,4′-diphenylmethane diisocyanate (MDI) is taken as a hard segment, with HMCPP and polycaprolactone diol (PCL) as soft segments, and 1,4-butanediol (BD) is used as a chain extender to prepare a novel polyurethane (HMCPP/PUs). The results of ¹H NMR and FT-IR reveal the successful synthesis of the HMCPP flame retardant. The gel permeation chromatography analysis demonstrates that an increase in the HMCPP content is accompanied by a decrease in the molecular weight of PU. The FT-IR analysis reveals the complete NCO group exhaustion of PU and HMCPP/PUs. The thermal analysis shows that the initial decomposition temperature of PU is higher than that of HMCPP/PUs by 19 °C. Both DMA and DSC analyses show that the Tg and the dynamic Tg of PU are higher than those of HMCPP/PU. Stress-strain tests indicate that the HMCPP content is increased, the maximum stress and Young’s modulus of HMCPP/PUs are decreased, and the elongation at break is increased. All of the HMCPP/PUs exhibit excellent flame retardancy, obtaining higher than 27.7 in limiting oxygen indices and a V-0 rating in the UL-94 test.