Syntheses and properties of polyurethanes containing side‐chain azobenzene groups

Polymers containing azobenzene groups have the characteristic reaction of photo‐induced cis–trans isomerism. The study of new materials for optical information storage has prompted making use of these photo‐isomerizations. In this study, we report the syntheses and properties of four different polyurethanes (DR‐PUns) containing azobenzene groups in the side‐chains. The structurally similar polyurethanes (DR‐PUns) were synthesized by the polycondensation reaction of Disperse Red 19 (DR 19) and four different diisocyanates in dimethylformamide. By introducing of DR 19 into the polymer, we obtained polymers containing a photochromic group in the side‐chain. The weight‐average molecular weights of the DR‐PUns were in the range 5500–12 900. The T_gs of the DR‐PUns range from 119.5 °C to 157.0 °C, depending on the structure of the diisocyanate. Optical properties and solubilities of the polyurethanes were compared. The diffraction efficiencies of films were measured as a function of the reaction time. Typically, the diffraction efficiencies of the DR‐PU1 film prepared from toluene 2,4‐diisocyanate were observed up to a level of 0.25%. For the DR‐PU1 film, the effect of the intensity of the induced laser beam on the diffraction efficiency is also discussed. © 2003 Society of Chemical Industry     

Renewable resource modified polyol derived aliphatic hyperbranched polyurethane as a biodegradable and UV‐resistant smart material

Renewable resource tailored tough, elastomeric, biodegradable, smart aliphatic hyperbranched polyurethanes were synthesized using castor oil modified polyol containing fatty amide triol, glycerol, diethanolamine and monoglyceride of sunflower oil via an A_x + B_y (x , y ≥ 2) approach. To the best of our knowledge, this is the first report of the synthesis of solely aliphatic hyperbranched polyurethanes by employing renewable resources. The synthesized polyurethanes were characterized by Fourier transform infrared, NMR and XRD techniques. The hyperbranched polyurethanes exhibited good mechanical properties, especially elongation at break (668%), toughness (32.16 MJ m^?3) and impact resistance (19.02 kJ m^?1); also high thermal stability (above 300 °C) and good chemical resistance. Also, the hyperbranched polyurethanes were found to show adequate biodegradability and significant UV light resistance. Moreover, they demonstrated excellent multi‐stimuli‐driven shape recovery ability (up to 97%) under direct sunlight (10⁵ lux), thermal energy (50 °C) and microwave irradiation (450 W). The performance of the hyperbranched polyurethanes was compared with renewable resource based and synthetic linear polyurethane to judge the superiority of the hyperbranched architecture. Therefore, these new aliphatic macromolecules hold significant promise as smart materials for advanced applications. © 2017 Society of Chemical Industry     

Influence of aqueous dispersions in place of organic solvents during the synthesis of shape memory polyurethanes on their structure and properties

In this work, the effect of synthesizing shape memory polyurethanes in aqueous dispersions instead of in organic solvents on the structure and properties of the obtained polymers was investigated. Shape memory polyurethanes based on polycaprolactone diol and isophorone diisocyanate were synthesized by two routes: (1) aqueous dispersion (PU/SM_WATER) and (2) dissolution in THF (PU/SM_THF). The samples were analyzed by infrared spectroscopy (FTIR), X‐ray diffraction (XRD), static light scattering (SLS), atomic force microscopy (AFM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and mechanical tests. The aqueous dispersion method led to the production of polyurethanes with a higher degree of phase separation and a higher degree of crystallinity. The morphology of the obtained polyurethanes demonstrated that PU/SM_WATER displays a structure with better defined phase separated domains. The polyurethanes exhibited similar average molar masses, soft segment glass transitions (T_gs) and mechanical properties. The lower degrees of phase separation and crystallinity of the PU/SM_THF led to lower values for the shape memory properties (shape recovery ratio (R_r)). The observed changes in the structure of the polyurethanes due to the replacement of organic solvent by an aqueous dispersion during their syntheses confirmed the preparation of shape memory polyurethanes with enhanced shape memory properties. POLYM. ENG. SCI., 57:432–440, 2017. © 2016 Society of Plastics Engineers     

Synthesis of ω‐amino‐α‐phenylcarbonate alkanes and their polymerization to [n]‐polyurethanes

Aliphatic [n]‐polyurethanes have recently been synthesized from ω‐isocyanato‐α‐alkanols or, more traditionally, by cationic ring‐opening polymerization of cyclourethanes or by the Bu₂Sn(OMe)₂‐promoted polycondensation of ω‐hydroxy‐α‐O‐phenylurethane alkanes. For the latter procedures, the conditions employed do not seem to be suitable for highly functionalized monomers. In contrast, the polymerization of ω‐amino‐α‐phenylcarbonate alkanes is expected to occur under milder conditions. ω‐Amino‐α‐phenylcarbonate alkanes have been synthesized from 6‐aminohexanol (1) and 3‐aminopropanol (6). The procedure involves the N‐Boc protection of the amino group, followed by activation of the alcohol. Removal of the N‐Boc affords the corresponding ω‐amino‐1‐O‐phenyloxycarbonyloxyalkane hydrochlorides. Other oligomeric comonomers between 1 and 6 have been prepared. The polymerization of these precursors takes place in the absence of metal catalysts to afford the corresponding linear and regioregular [n]‐polyurethanes. The procedure described is useful for the preparation of stable ω‐amino‐α‐phenylcarbonate alkane derivatives, which possess varied chain lengths between the terminal functions. These monomers yield [n]‐polyurethanes having various structures starting from just two aminoalkanols. The polyurethanes were obtained in high yields, with reasonable molecular weight and polydispersity values, and they were characterized spectroscopically and thermally. These studies reveal constitutionally uniform structures that are free of carbonate or urea linkages. Copyright © 2010 Society of Chemical Industry     

Effect of oxygen flow rate on the structural and electrochemical properties of lithium nickel oxides synthesized by the sol–gel method

The structural and electrochemical properties of LiNiO₂ powders were investigated as a function of the oxygen flow rate employed in the preparation of lithium nickel oxide. It was found that oxygen played an important role in the synthesis of highly crystallized LiNiO₂(R3¯m). In the crystallization process of LiNiO₂, a deficiency of oxygen in the calcination reactor induced the formation of impurities and cubic rock-salt structure (Fm3m) in LiNiO₂ powders. For LiNiO₂ prepared at higher oxygen flow rates, the electrode delivered high discharge capacities with relatively good retention rates. But very low electrode capacity was obtained from LiNiO₂ prepared at lower oxygen flow rates.     

Polymers containing sulfur in the side chain

We synthesized new thiodicarboxylic acids, p-tolylmethylthiomethylsuccinic acid and 1-naphthylmethylthiomethylsuccinic acid, and thiodiols, 2-(p-tolylmethylthiomethyl)-1,4-butanediol and 2-(1-naphthylmethylthiomethyl)-1,4-butanediol, by the addition of dimethyl itaconate with p-tolylmethanethiol or 1-naphthylmethanethiol, followed by hydrolysis or reduction, respectively, of the resultant dimethyl esters. These difunctional monomers were used for the synthesis of new linear polyesters and polyurethanes containing sulfur in the side chain. The polyesters were synthesized by melt polycondensation of the obtained acids with 2,2′-oxydiethanol. We found reduced viscosity, molecular weight (by GPC), and softening temperature for the reaction products. Low molecular weights, low softening temperature, and very good solubility in organic solvents are their characteristics. The polyurethanes were prepared by polyaddition diols with hexamethylene diisocyanate and tolylene diisocyanate in benzene. They were characterized by reduced viscosity and some tensile properties. The polyurethane derived from 2-(p-tolylmethylthiomethyl)-1,4-butanediol and hexamethylene diisocyanate (η_red. 1.17 dL/g) behaves like a high elasticity thermoplastic elastomer. Thermal stability of all polymers was determined by thermogravimetric analysis. The structure of the monomers and polymers were confirmed by elemental analysis and FTIR and ¹H-NMR spectroscopy. © 1996 John Wiley & Sons, Inc.     

Polyurethane networks from formiated soy polyols: Synthesis and mechanical characterization

Polyurethanes can be prepared using polyols obtained from vegetable oils in natura, such as castor oil, or from functionalized vegetable oils, such as hydroxylated soybean oil. These polyurethanes have different valuable properties, determined by their chemical composition and cross-linking density. In this study, soy epoxy polyols with different OH contents were prepared through a one-step reaction using the method of in situ performic acid generation. Polyols with OH functionalities from 1.9 to 3.2 were reacted in bulk with different diisocyanates at a NCO/OH molar ratio of 0.8 and 60°C for 24 h. Mechanical properties of the polyurethanes were determined by dynamic mechanical thermal analysis, hardness (Shore A), and swelling measurements. Polymer networks with glass-transition temperatures (T _g ) from −13 to 48°C were obtained. We observed that the higher the OH functionality of the polyols, the higher the T _g and cross-linking density of the polyurethane network. The influence of diisocyanate structure (rigid or flexible chain), curing temperature, and curing reaction time on mechanical properties was also investigated.     

The effect of diisocyanate isomer composition on properties and morphology of polyurethanes based on 4,4′-dicyclohexyl methane diisocyanate and mixed macrodiols (PDMS–PHMO)

Three series of polyurethanes were prepared having 42 wt % hard segments based on 4,4′-dicyclohexyl methane diisocyanate (H₁₂MDI) with trans,trans isomer contents in the 13 to 95 mol % range and 1,4-butanediol chain extender. The soft segments were based on macrodiols poly(hexamethylene oxide) (PHMO, MW 696), α,ω-bishydroxyethoxypropyl polydimethylsiloxane (PDMS, MW 940), and two mixed macrodiol compositions consisting of 80 and 20% (w/w) PDMS. H₁₂MDI with 35, 85, and 95% trans,trans isomer contents were obtained from commercial H₁₂MDI (13% trans, trans) by fractional crystallization, and all polyurethanes were prepared by a one-step bulk polymerization procedure. The polyurethanes based on the commercial diisocyanate-produced materials soluble in DMF with molecular weights in the 53,655–75,300 range and generally yielded clear and transparent materials. The polyurethanes based on H₁₂MDI with trans,trans contents of 35% or higher yielded materials insoluble in N,N-dimethylformamide (DMF) and were generally opaque. Mechanical properties, such as tensile strength and elongation at break, decreased with increasing trans,trans content, while the Young's modulus and Shore hardness increased. The polyurethanes based on mixed macrodiols yielded higher tensile properties than those of materials based on individual macrodiols. The best mechanical properties were observed for a polyurethane consisting of a soft segment based on PDMS–PHMO (80/20) and a hard segment based on commercial H₁₂MDI and BDO. Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize the polyurethane morphology. DSC results confirmed that the polyurethanes based on H₁₂MDI with high trans,trans isomer were very highly phase separated, exhibiting characteristic hard segment melting endotherms as high as 255°C. The other materials were generally phase mixed. FTIR spectroscopy results corroborated DSC results. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 573–582, 1999     

Synthesis and nonlinear optical properties of novel y‐type polyurethanes containing different concentrations of chromophore

A new series of Y‐type polyurethanes containing different concentrations of nonlinear optical (NLO) chromophore with aniline donor and tricyanofurane (TCF) acceptor have been successfully prepared, and characterized by FTIR, UV‐Vis, and ¹H‐NMR spectra. New polyurethanes were synthesized with different chromophore contents by introducing diol N, N‐dihydroxyethylaniline or 4‐[N, N‐(dihydroxyethyl)amino]benzaldehyde. These NLO polyurethanes exhibit good film forming property and high thermal stability up to 281°C. The highest electro‐optic coefficient (r₃₃) of polymers is up to 39 pm V^?1 measured by simple reflection technique at 1310 nm, and the temporal stability of the poling‐induced order at elevated temperature of 80°C was much improved through the introducing of hydrogen bonding interaction in this system. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

New T-Shape Polyurethanes: Synthesis,Thermal and Mechanical Properties

A series of new T-shaped polyurethanes were prepared from various diisocyanates and 2,5-dihydroxybenzelidene aniline (azomethine bisphenol). The latter compound was synthesized by the reaction of 2,5-dihydroxy-benzaldehyde with aniline. The structures of azomethine bisphenol and T-shaped polyurethane were confirmed by FT-IR, ¹H-NMR, ¹³C-NMR Spectroscopy and elemental analysis (CHN). The mechanical properties were characterized by tensile strength, tear strength and shore hardness. Thermal properties were also studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Mechanical and thermal studies showed that the synthesized polyurethanes possess good mechanical and thermal properties.     

Synthesis,characterization, and permeation properties of polyether-based polyurethanes

A system of synthesis of polyether-based urethanes was developed which had sufficient flexibility in composition so that transport properties could be optimized. Mixtures of poly(oxyethylene) glycol (PEG) and poly(oxypropylene) glycol (PPG) of a variety of molecular weights were tied together by varying amounts of kinds of “hard segments.” Thus, the water swell, the mechanical properties, and the size of the soft blocks and hard blocks could be varied. With a fixed content of hard segments, the water absorption decreased with decrease in the PEG/PPG ratio, demonstrating the feasibility of producing controlled changes in hydrophilicity of the polymer without significant change in the mechanical strength. Some polyurethanes based on PEG 600 and PPG 425 had a very good high value of P_w/P_s but a somewhat low value of P_w. The polyurethanes prepared by using phenylenediamines as chain extenders had markedly enhanced modulus and an extended rubbery plateau region, as anticipated.     

Preparation and physical properties of polyurethane modified with poly(4,4′-diphenylsulfone terephthalamide)

Three conventional polyurethane (PU) elastomers were blended physically with various ratios of high molecular weight of poly(4,4′-diphenylsulfone terephthalamide) (PSA) to form 12 PU/PSA polyblends in order to modify their physical properties. Also three new polyurethanes were synthesized with a low-molecular-weight PSA prepolymer as a hydrogen donor for chain extending. From dynamic properties, it showed that both the blends and the new polyurethanes (or polyurethane-ureas) exhibited a glass transition temperature (T_g) below 0°C and had a higher modulus E′ than those of the conventional PU. Based on the analysis of X-ray diffraction of the conventional and the new PU, it was shown that the degree of stress-induced crystallization was dependent on the segmental composition of the soft and hard segments and also the degree of its stretching. On the morphological observation, it was revealed that both the blends and the new polyurethanes were in a dispersed phase structure, although new PU exhibited a better compatible state. For tensile properties, it was found that both tensile strength and elongation of the new polyurethanes were better than those of the blends and conventional PU. © 1994 John Wiley & Sons, Inc.     

Flammability and thermal properties of rigid polyurethane foams with additionally introduced cyclic structures

Flammability, smoke evolution, thermal, and thermomechanical properties of low-density rigid polyurethane foams obtained from different aromatic polyols were investigated. The foams were prepared according to a standard formulation ensuring the same foam phosphorus content. Cellular polyurethanes with the best fire resistance were obtained from polyols containing disubstituted naphthalene and biphenyl rings. A linear equation was proposed to describe the influence of various structural units of the polyurethane (the content of cyclic structures C_c, nitrogen content C_N, and crosslinking equivalent M_c) upon its flammability, expressed in terms of its oxygen index (OI) Thermal stability of crosslinked polyurethanes was not found to influence significantly their thermomechanical properties, while crosslink density and the type and quantity of cyclic structures additionally introduced did have a pronounced effect upon these properties.     

Synthesis of non-isocyanate polyurethanes with high-performance and self-healing properties

Due to the utilization of the potentially hazardous monomer, isocyanate compound, polyurethanes (PUs) with good properties are restricted in several fields, such as bio-engineering. Non-isocyanate polyurethanes (NIPUs) with high overall performance and self-healing properties were synthesized by dicarbamate, bio-based isosorbide (IS) and polycarbonate diols (PCDLs) through a solvent-free and ecologically friendly melt polycondensation route. Previously, few bio-based monomers have been introduced into polycondensation reactions of PUs. Chemical structures of NIPUs were analyzed by Fourier transform-infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC). With changing the IS content and the molecular weight of PCDL, the obtained NIPUs had linear structures and high molecular weights ranging from 3.3 × 10⁴ to 5.9 × 10⁴ g/mol. Results of tensile testing, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) suggested NIPUs had well thermal and mechanical properties, with T_d,5% above 286.2°C and tensile strength between 8.0 and 16.7 MPa due to the crystallization and the hydrogen bonding interactions. Furthermore, the NIPUs exhibited self-healing ability and recyclability, having great potential for industrialization.     

Structure‐property relationship in polyurethane elastomers containing starch as a crosslinker

Polyurethane elastomers were synthesized using polypropylene glycol (PPG 2000) as the polyol and starch as the multifunctional crosslinker in varying concentrations. Thermal and mechanical properties were measured by DSC, DMA and tensile tests. The morphology was examined by SEM. The swelling behavior of the polyurethanes in various solvents was investigated and the solubility parameter was determined. All these properties were compared with those of polyurethanes containing 1,1,1 ‐trimethylol propane (TMP) as the crosslinker. Starch‐based polyurethanes exhibited better mechanical properties. The effect of varying the starch:TMP ratio on the mechanical strength was also studied. With increasing starch content, the tensile strength and elongation increased. The starch‐based PUs exhibited two glass transitions, whereas TMP‐based PUs exhibited one T_g. No significant difference in the T_gs of the two PUs was observed. The activation energy of St‐PU calculated from DMA was 69 kcal/mol. Soil degradation tests indicated greater biodegradability in polyurethanes containing starch than in those containing TMP.     

Preparation of Novel Sensors Based on Polyimide Membrane for Sensitive and Selective Determination of Dopamine

Polyimides as dopamine selective membrane were prepared from 4,4′-diaminodicyclohexylmethane and different dianhydrides. The chemical structure and thermal properties of these polyimides were examined. For the voltammetric sensor applications, polyimides exhibited suitable glass transition temperature (T_g), high thermal stability, and good adhesive properties. Moreover, polyimides were coated onto Pt electrode surface for the preparation of dopamine selective electrodes. Electrochemically dopamine responses of polyimide-coated electrodes were examined by differential pulse voltammetry. The sensor characteristics such as sensitivity, linearity, selectivity, response time, and stability of the prepared sensors have been determined. Prepared polyimide-coated electrodes can be used for selective and sensitive dopamine detection.     

Synthesis and characterization of biodegradable polyurethanes with unsaturated carbon bonds based on poly(propylene fumarate)

The segmented polyurethanes synthesized from biodegradable polyesters are very promising and widely applicable because of their excellent physiochemical properties. Poly(propylene fumarate) (PPF), a kind of linear aliphatic unsaturated and biodegradable polyesters, has been well recognized in biomedical applications. Herein novel polyurethanes (PPFUs) were synthesized based on the PPF‐diol, diisocyanates such as 1,6‐diisocyanatohexane, l ‐lysine diisocyanate, and dicyclohexylmethane diisocyanate, and chain extenders such as 1,4‐butylene glycol and l ‐lysine methyl ester hydrochloride (Lys‐OMe·2HCl). By varying the types of diisocyanates, and chain extenders, and the proportion of hard segments, the PPFUs with tailored properties such as mechanical strength and degradation rate were easily obtained. The synthesized PPFUs had an amorphous structure and slight phase separation with strong hydrogen bonding between the soft segments and the hard segments. The elongation of PPFU elastomers reached over 400% with a slow deformation‐recovery ability. The PPFUs were more sensitive to alkaline (5 M, NaOH) hydrolysis than acid (2 M, HCl) and oxidative (30 vol.%, H₂O₂) erosion. The tensile strength, deformation‐recovery ability, and glass transition temperature of the PPFUs were improved with the increase of hard segment proportion, while the degradation rate was opposite because of the faster degradation of the soft segments. In vitro culture of smooth muscle cells in the extractant of the PPFUs or on the PPFUs film surface revealed low cytotoxicity and good cytocompatibility in terms of cell viability, adhesion, and proliferation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42065.     

Properties of crosslinked polyurethanes synthesized from 4,4′‐diphenylmethane diisocyanate and polyester polyol

Polyurethanes were synthesized using the high functional 4,4′‐diphenylmethane diisocyanate (MDI), polyester polyol, and 1,4‐butane diol. The synthesized polyurethanes were analyzed using differential scanning calorimeter (DSC), dynamic mechanical thermal analysis (DMTA), Fourier transform infrared (FTIR) spectrometer, and swelling measurement using N,N′‐dimethylformamide. From the result of thermal analysis by DSC and DMTA, single T_gs were observed in the polyurethane samples at all the formulated compositions. From this result, it is suggested that the polyurethanes synthesized in this study have crosslinked structure rather than the phase‐separated segmented structure because of the high functionality (f = 2.9) of the MDI. By annealing the polyurethane samples using DSC, the T_gs were increased by 4.7∼16.0°C at the various annealing temperatures. From the results of FTIR and swelling measurement of polyurethanes, it is suggested that the increase of T_g of the polyurethanes by annealing is not due to increase of the hydrogen bond strength but mainly due to the increase of the crosslink density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 624–630, 2000     

Polyurethanes derived from caprolactone polyesters and diamines

Thermoplastic, light-stable polyurethanes have been prepared by the interfacial poly-condensation of secondary diamines with the bischloroformates of polyester diols derived from ε-caprolactones. A straight-line relationship was obtained from a logarithmic plot of inherent viscosity versus M _n. The effect of some structural variations on the properties of the polyurethanes is discussed. These variations included the molecular weight of the polyester diol, the initiator used in preparing the polyester diol, the introduction of a methyl substitutent on the caprolactone ring, and the structure of the diamine. Polyurethanes prepared from polyester diols of M _n from 2000–4000 are opaque, stiff materials which undergo a melting transition at 40–50°C. characteristic of the polyester component. Polyurethanes which are flexible and translucent at room temperature are obtained either by using a low molecular weight polyester diol or a copolyester diol containing > 25% methyl ε-caprolactone. The polyurethanes described are soluble in several common solvents and can be cold-drawn to produce material of high tensile strength. Thermal studies using DTA and TGA Show an exothermic reaction starting above 300°C. Rapid weight loss beginning at 300–330°C. and leveling off near 500°C. accounted for 85–90% of the total sample and is attributed to decomposition of the polyester Chains.     

Tailoring new bisphenol a ethoxylated shape memory polyurethanes

Shape memory polyurethanes (SMPUs) have generated great attention because of their unique properties. These properties are result of a particular molecular structure consisting of flexible molecular chains with low glass transition temperatures alternating with hard urethane segments. In this field, bisphenol A (BA) has been used for a long time as chain extender due to the good properties of the obtained SPMU materials. Nevertheless, the high toxicity of this compound has caused a high decrease on its use. For this reason, it has been selected a lower toxicity compound, bisphenol A ethoxylate (BAE). In this work, it is described a new SMPUs based on BAE and the influence of the hard segment on the thermo-mechanical properties and shape memory capacity. For that, both the proportion of the components and the diisocyanate employed (2,4-toluene diisocyanate (TDI), 4,4′-methylene bis(phenylisocyanate) (MDI) or a TDI/MDI mixture) have been modified. Then, depending on the molecular architecture achieved, the polyurethanes present different properties, which were studied by different techniques, such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic-mechanical thermal analysis (DMTA). It has been observed that glass transition temperature (T_g) increases as the hard phase content in the PU samples increases. In addition, T_g-MDI > T_g-MDI-TDI > T_g-TDI, so it is possible to control the T_g of the material, that is, shape memory transition temperature varying the diisocyanate. Finally, the shape memory capacity of the PUs was evaluated by thermo-mechanical analysis (TMA). All the synthesized PUs have shown good shape memory effect with fixation ratios up to 80% and recovery ratios close to 100%.