Linear Segmented Polyurethanes Research Articles

Linear segmented polyurethanes. III. Mathematical model for a two‐steps polymerization

AbstractIn the first article of this sequel (J. Appl. Polym. Sci., 2018, 135, 45747), an experimental and theoretical investigation was developed on the two‐steps synthesis of linear segmented thermoplastic polyurethanes. The reactions were carried out at 60°C, with methylene diphenyl diisocyanate (MDI), two poly(tetramethylene oxide) macrodiols, and 1,4‐butanediol (BD) as chain extender. In our second article (J. Appl. Polym. Sci., 2019, 136, 46946), a mathematical model for the prepolymerization was developed, that involved integrating a differential equation for each generated polymer species. The present article extends such model, and predicts the molecular structure along the finishing stage. In each stage, the new model first solves the molar balances at polymer topologies level (i.e.,: Disregarding the molar mass distribution [MMD] of the reacted macrodiol chains), and then calculates the MMD of the evolving polymer and its main subsets through an algebraic convolution procedure. The model reproduces the prepolymerization predictions of our previous article, but is three orders of magnitude faster. In the finishing stage, up to 156,000 polymer topologies and 4.53 × 108 polymer species were calculated; and the rate constant was readjusted to (k2 = 0.00129 L mol−1 s−1), in order to fit the measured MMDs.

Mechanically robust self-healing and recyclable flame-retarded polyurethane elastomer based on thermoreversible crosslinking network and multiple hydrogen bonds

Self-healing polymers have drawn significant attention because of their great potential for applications in many fields. It is highly desirable to prepare materials capable of self-healing and with excellent mechanical properties. Additionally, the flammability of polymers make them unsafe during use. A novel strategy is proposed to manufacture a multifunctional polyurethane elastomer with high tensile strength (37.11 ± 1.89 MPa) and excellent self-healing efficiency (91.8%), containing a thermo-reversible crosslinking network and multiple hydrogen interactions. The furan-terminated phosphorus-based monomer, tri(2-furyl) phosphoramide (TFP), was successfully synthesized and then conjugated into a maleimide-terminated linear segmented polyurethane (MPU) backbone to prepare self-healing, recyclable, and flame-retarded polyurethane (MPUF). Due to its synergetic dual reversible bonds, the multifunctional polyurethane elastomer possessed ultrahigh strength, and excellent self-healing, shape recovery, and reprocessing properties. The phosphorus containing polyurethane elastomer exhibited improved thermal stability a limiting oxygen index value of 28.5%, and a 12.3% decrease in the peak heat release rate (pHRR) relative to those of unmodified polyurethane. This work demonstrates an effective strategy to prepare multifunctional polyurethane elastomer with both high self-healing efficiency and excellent mechanical properties allowing application for this material in the fields of fire-control coatings and building materials.

Organic–Inorganic Linear Segmented Polyurethanes Simultaneously Having Shape Recovery and Self-Healing Properties

Double-decker silsesquioxane (DDSQ) and hindered urea bonds were simultaneously introduced into the main chains of linear segmented polyurethane (PU) to synthesize organic–inorganic linear segmente...

Tunable ionization degree in cationic polyurethanes and effects on phase separation

A linear non-ionic hard-soft segmented polyurethane (PU0) was prepared by the prepolymer synthesis method. The isocyanate terminated prepolymer, formed by a short and rigid aromatic diisocyanate and a long flexible poly(tetramethylene oxide) (PTMO), was chain extended with a piperazine (PIP) diol derivative. The non-ionic polyurethane was then ionized by a post-modification method, i.e. alkylation of the piperazine nitrogen atoms, thus obtaining cationomers with three different ionization degrees, named PU10, PU50, PU80. The polymers were characterized by means of FT-IR spectroscopy, solution and solid state Nuclear Magnetic Resonance (NMR) spectroscopies, Differential Scanning Calorimetry (DSC) and ThermoGravimetric Analysis (TGA). The chemical structure of the obtained polymers and their cationic content was confirmed by solution state 1H NMR. It was found that the methylation occurs quantitatively up to 50% of the PIP nitrogen atoms and that, even if a large excess of methylating agent is used, in our operating conditions a maximum of 80% of the PIP nitrogen atoms are ionized. All the characterization techniques used suggested that an increasing ionization degree induces a better phase separation between hard and soft domains, with a lower amount of diisocyanate units dispersed in the soft phase. In particular, FT-IR showed that the introduction of ionic sites modifies the hydrogen bond network and induces a better aggregation of the rigid units. In addition, DSC showed that (i) the glass transition temperature values of the polymers decrease and tend to that measured for pure PTMO upon increasing ionization; (ii) a crystalline phase due to PTMO packing in ordered structures appears at the highest ionization degrees, similarly to pure PTMO. 1H Time-Domain NMR and 13C solid state NMR revealed an increase in PTMO mobility with increasing ionic content, in agreement with DSC results.The measurements of proton spin lattice relaxation times in both the laboratory (T1) and rotating (T1ρ) frames allowed limits on the size of the hard domains to be estimated. T1ρ data hint at a phase demixing effect upon increasing the ionization degree.

Linear segmented polyurethanes. II. A mathematical model for the prepolymerization stage

Fil: Polo, Mara Lis. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Desarrollo Tecnologico para la Industria Quimica. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnologico para la Industria Quimica; Argentina

Synthesis and characterization of photo-crosslinkable linear segmented polyurethanes based on coumarin

Linear segmented polyurethanes with 10% weight of coumarin groups within the soft segment, the hard segment or equally distributed between both segments were successfully prepared. These polyurethanes, based on polycaprolactones, isophorone diisocyanate, butanediol and a dihydroxylated coumarin monomer, were completely amorphous and homogeneous with a single phase morphology. In non-irradiated polyurethanes Tg value varied linearly with hard segment content that in turn was the main factor influencing the mechanical properties. Photo-dimerization at 354nm produced crosslinked materials with little change on the Tg and outstanding mechanical properties, as high as 54MPa, better than that of any other coumarin-containing polymer described.

Non-isothermal DSC and rheological curing of ferrocene-functionalized, hydroxyl-terminated polybutadiene polyurethane

The curing reaction of a novel linear segmented polyurethane (PU) based on a functional metallo-polyol derivative of hydroxyl-terminated polybutadiene (HTPB), (ferrocenylbutyl)dimethylsilane-grafted HTPB, and isophorone diisocyanate (IPDI) is studied under non-isothermal conditions. This reaction is of particular interest in advanced composite energetic materials for the aeronautic technology. Differential scanning calorimetry (DSC) indicates that the curing mechanism involves multiple reactions, which was further substantiated by a rheological analysis. Rheometry was used to analyse the chemorheological behaviour through the evolution of both complex viscosity (η⁎) and storage modulus (Gʹ) at four different heating rates. The profiles obtained for the viscosity were applied to four- and six-parameter Arrhenius models. The curves of rheological conversion degree were also obtained from the elastic modulus data, and values for the activation energy of this polyaddition reaction were estimated by the application of Kissinger's method.

Kinetic and thermodynamic analysis of the polymerization of polyurethanes by a rheological method

As part of an investigation into the mechanism and chemorheology of linear segmented polyurethane (PU) systems, this paper presents the kinetic and thermodynamic characterization of the reaction between an advanced functional metallo-polyol derivative of hydroxyl-terminated polybutadiene (HTPB), (ferrocenylbutyl)dimethylsilane grafted HTPB, and isophorone diisocyanate (IPDI). The evolution of viscoelastic properties, such as the storage modulus (G′), was recorded in bulk under isothermal conditions at four different temperatures between 50 and 80°C, and a resin curing degree profile was obtained for this elastic modulus. The use of the Kamal-Sourour autocatalytic kinetic model was proposed, describing the overall curing process perfectly. All the kinetic and thermodynamic parameters, including reaction orders, kinetic constants and activation energy, were determined for the polyaddition reaction under study. A relevant autocatalysis effect, promoted by the urethane group, has been found. The isoconversion method was also used to analyze the variation of the global activation energy with conversion. The global activation energy increases slightly as the curing reaction proceeds with a maximum value reached at approximately 30% conversion. In addition, the Eyring parameters were calculated from the obtained kinetic data.

Bio‐Inspired High‐Performance and Recyclable Cross‐Linked Polymers

Bio-inspired molecular design and synthesis of high-performance and recyclable cross-linked polymers is reported. Reversible cross-links between hard segments are incorporated into linear segmented polyurethane via Diels-Alder reaction between maleimide pendant group and furan cross-linker. The materials form hierarchical structure and exhibit excellent properties with high stiffness, strength and toughness, and can be easily thermally reshaped and re-mended.

Quantitative estimation of the strength of specific interactions in polyurethane elastomers, and their effect on structure and properties

Two sets of segmented polyurethane (PU) elastomers were prepared from crystalline MDI, butanediol and a polyester or a polyether polyol, respectively. The molar mass of both polyols was 1000g/mol. The –OH functional group ratio of polyol/total diol was kept constant at a value of 0.4, while the ratio of the isocyanate and hydroxyl groups (NCO/OH) changed between 0.90 and 1.15 in the polyester, and 0.94 and 1.15 in the polyether polyurethanes, respectively. One step bulk polymerization was carried out in an internal mixer and the samples were compression molded for testing. Advanced molecular modeling was used to estimate the strength of various specific interactions quantitatively in the polymers studied. Fifteen different specific interactions were identified in polyester while thirteen in polyether PU considering only hydrogen bonds. Estimated binding enthalpy changes between 11 and 26kJ/mol. The results proved that hard–soft and not hard–hard segment interactions control phase separation of linear segmented polyurethanes. A new model was developed to quantify the relative importance of specific interactions acting between the two types of segments. The calculations predicted better solubility of the soft phase in hard domains in polyester than in polyether polyurethanes. Besides the mutual solubility of the phases, their size and mechanical properties also depend on these interactions shown by the study of phase structure using a novel combination of various methods in a wide length scale. Properties are determined by different aspects of morphology. Transparency depends on the amount of ordered hard phase, stiffness and hardness on phase composition, while ultimate properties on stoichiometry, which determines molecular weight and the number of physical cross-link points.

Study of the Morphology Exhibited by Linear Segmented Polyurethanes

AbstractFive series of segmented polyurethanes with different hard segment content were prepared by the prepolymer mixing method. The nano‐morphology of the obtained polyurethanes and their microphase separation were investigated by infrared spectroscopy (FTIR), modulated differential scanning calorimetry (MDSC) and small‐angle X‐ray scattering (SAXS). Although highly hydrogen bonded segments were formed, high hard segment contents led to the presence of elevated degree of phase mixture and reduced the chain mobility, decreasing the hard domain precipitation and the soft segment crystallization. The applied techniques were able to show that the hard‐segment content and the hard‐segment interactions were the two controlling factors for determining the structure of segmented polyurethanes.

Nanocomposites made from cellulose nanocrystals and tailored segmented polyurethanes

AbstractThe effect of the addition of microcrystalline cellulose nanofibers into linear segmented polyurethanes (SPU) was investigated. The polymers were synthesized with 4,4‐methylene‐bisphenyldiisocyanate (MDI) and poly(tetramethyleneglycol) (PTMG) with 1,4‐butanediol (BD) as chain extender. The nanocrystals were introduced during the PU polymerization, which resulted in cellulose nanofibrils covalently linked to the polymer. The interactions between the cellulose nanofibrils and the matrix lead to interesting changes in the behavior of the PU, with the hard segment (HS) phase being more affected by these interactions. SPUs with different contents of HS were synthesized to better understand these effects (23 to 45 wt %). Thermal, thermo‐mechanical and mechanical characterization of the nanocomposites were performed. In general, the nanocellulose favored the phase separation between the soft and hard domains generating an upward shift in the melting temperatures of the crystalline phases, an increase in the Young's modulus and a decrease in deformation at break. Comparison of the unfilled polymer responses and that of the nanocomposites showed that by increasing cellulose content, increased dynamic storage and tensile modulus as well as melting temperatures and enthalpy of melting of the soft domains can be achieved. Addition of cellulose during the polymerization essentially erased the potential shape memory behavior originally displayed by some of the SPU. However, a sample prepared by adding the cellulose nanocrystals after the reaction showed that the mechanical properties were still improved, while the shape memory behavior of the polymer was preserved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Relationship between molecular parameters of linear segmented polyurethanes and synthesis conditions

A series of polyurethane samples were prepared, and the relationship between the molecular and rheological characteristics of the polymer, on the one hand, and the synthesis parameters, primarily the functional group ratio ([NCO]/[OH]), on the other hand, was examined.

Synthesis and Characterization of Pyridine-Based Polyurethanes

A series of novel linear segmented polyurethanes (PUs) containing a pyridine unit in the main chain have been synthesized by polycondensation reaction of various diisocyanates, 4,4′-diphenyl-methane diisocyanate (MDI), toluene 2,4-diisocyanate (TDI), isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI), with 4,4′-{pyridine-2,6-diylbis[nitrilomethylylidene]}diphenol-based diol. The structure of the diol and segmented PUs were established by NMR, Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis) and fluorescence spectroscopic methods. The thermal behavior of the synthesized PUs was further characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). All PUs were soluble in polar aprotic solvents.

Synthesis and characterization of semi‐interpenetrating polymer networks based on polyurethane and N‐isopropylacrylamide for wound dressing

Thermosensitive semi-interpenetrating polymer networks (semi-IPNs) composed of crosslinked poly(N-isopropylacrylamide) (PNiPAAm) and linear segmented polyurethane urea (SPUU) were synthesized via thermal initiated free radical polymerization. Synthesized semi-IPNs of various compositions were characterized by Fourier transform infrared spectroscopy, water equilibrium swelling at different temperatures, drug lading, drug release, cell adhesion, and detachment. The semi-IPN films of all the compositions were transparent in dry state and negative thermosensitivity in their swelling ratio, that is, lower swelling levels with increasing temperature. The drug release study revealed that the rate of drug release is fast in case of pure SPUU compared to PNiPAAm and semi-IPN film. Drug release depended mainly on solubility of the drugs and physical networks between SPUU and PNiPAAm. Finally NIH3T3 cells were seeded on the semi-IPN films and found that cells were securely attached and proliferated to confluence. Upon cooling, cells were detached from the semi-IPN films. Therefore, the semi-IPN films may be good candidate materials for wound dressing applications.

Synthesis and thermal crosslinking of oxazolidine‐functionalized polyurethanes

AbstractA new oxazolidine derivative was obtained from phenol, 2‐amino‐2‐methylpropane‐1,3‐diol and paraformaldehyde. The reaction of this novel oxazolidine diol with phenylisocyanate lead to a urethane model compound which can be polymerized thermally by oxazolidine ring opening to give a Mannich bridge structure. Linear segmented polyurethanes were prepared by reaction of different ratios of oxazolidine diol and commercial polyethylenglycol (Mw ∼ 400) with 4,4′‐methylenbis (cyclohexylisocyanate) (HMDI, 90% isomers mixture). The polyurethanes were thermally characterized and crosslinked by oxazolidine ring opening to obtain materials which showed improved thermal stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4965–4973, 2007

Fluorinated segmented polyurethane anionomers for water–oil repellent surface treatments of cellulosic substrates

AbstractThree model structures of linear segmented anionomeric polyurethanes based on perfluoropolyether dimethylol‐terminated oligomers, isophorone diisocyanate, and dimethylol propionic acid were synthesized and obtained in the form of aqueous dispersions. The structures differed from each other in the chemical nature of the chain extender (diol or diamine) and in the content of carboxylic acid. Dispersions and polymer films were characterized by dynamic light scattering, dynamic mechanical analysis, differential scanning calorimetry, and contact angle measurements. Diluted aqueous dispersions were also evaluated as protective sizing agents in paper treatment, both as bulk modifiers and as surface treatments. Paper sheets characterized by high water and oil repellence were obtained. The results showed that performance is mainly related to the ionic group content of the polymer and to its molecular architecture. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1364–1372, 2005

Water transport properties of thermoplastic polyurethane films

AbstractTwo linear segmented polyurethanes, based on poly(oxyethylene) (POE) as a soft segment and 4,4′‐diphenylmethane diisocyanate and 1,4‐butanediol as hard segments and differing in their soft segment length, have been studied from a water vapor transport point of view. For both polyurethanes, the water sorption is governed by a Fickian process, and the thermoplastic polyurethane with the longer POE segments displays the higher water diffusion rate. The water sorption isotherms are Brunauer Emmet Teller (BET) type III for both thermoplastic polyurethanes, and the water uptakes are directly related to the polymer POE content. The Flory–Huggins theory cannot correctly describe the sorption isotherms. More sophisticated approaches (Koningsveld–Kleinjtens or Guggenheim‐Anderson‐de Boer (GAB) models) are needed to fit the experimental water uptakes. The positive deviation from Henry's law and the decrease in the apparent diffusion coefficient observed at a high activity have been particularly studied. In this activity range, an isotherm analysis based on the cluster integral of Zimm and Lundberg suggests some clustering phenomenon, which seems consistent with the diffusion coefficient variation. In agreement with the sorption results, the water permeability coefficients are small at low activities, and they increase greatly with the relative pressure of water. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 473–492, 2004

Liquid crystalline properties of unsegmented and segmented polyurethanes synthesised from high aspect ratio mesogenic diols

AbstractA series of novel tetrad high aspect ratio mesogenic diol monomers 4‐{[4‐(n‐hydroxyalkoxy)‐phenylimino]‐methyl}‐benzoic acid 4‐{[4‐(n‐hydroxyalkoxy)‐phenylimino]‐methyl}‐phenyl ester were prepared with varying alkoxy spacer length (n=2,4,6,8,10) by reacting 4‐formylbenzoic acid 4‐formylphenyl ester and 4‐(n‐hydroxyalkoxy) anilines. Two series of thermotropic main chain liquid crystalline unsegmented polyurethanes (PUs) were obtained by the polyaddition of the mesogenic diols with hexamethylene diisocyanate (HMDI) and methylene bis(cyclohexylisocyanate) (H12MDI) in dimethylformamide respectively. The effect of the incorporation of a third component namely polyol on the liquid crystalline properties of the polyurethanes was also studied. Linear segmented PUs were synthesised by a two‐step block copolymerisation method. The PUs synthesised were based on six spacer mesogenic diol chain extender, soft segments poly(tetramethylene oxide)glycol (PTMG) (Mn= 650,1000,2000) and polycaprolactone diol (PCL) (Mn=530,1250,2000) of varying molecular weights and different diisocyanates including HMDI, H12MDI and methylene bis(phenylene isocyanate) (MDI). Structural elucidation was carried out by elemental analysis, fourier transform infra red (FT‐IR), nuclear magnetic resonance (1H NMR and 13C NMR) spectroscopy. Inherent viscosity of the unsegmented polymers measured in methanesulphonic acid at 26°C was in the range of 0.13 ‐ 0.65 dL/g while the molecular weights and molecular weight distribution of the segmented polyruethanes was determined using gel permeation chromatography (GPC). Mesomorphic properties were studied by differential scanning calorimetry (DSC) and hot stage polarising optical microscopy and the thermal stability was determined by thermogravimetric(TG)analysis. The monomeric diols and the polyurethanes exhibited nematic texture and good mesophase stability. It was observed that the partial replacement of the mesogenic diol by the polyol of varying molecular weights influenced the phase transitions and the occurrence of mesophase textures. The phase transition temperatures of the investigated polyurethanes showed dependence on the chain length of the soft segment and on the content of the mesogen moiety. A higher content of mesogenic moiety was needed to obtain liquid crystalline property when the soft segment length was increased as observed in the case of PTMG. Grained and threaded textures were observed depending on the molecular weight of the soft segment, the mesogen content and the diisocyanate. The stress‐strain analyses showed that the polymers bused on high molecular weight PTMG soft segment have elastomeric property while the PCL based PUs displayed no elastomeric property.

Selection of elastomeric materials for compliant-layered total hip arthroplasty.

A selection procedure has been developed to identify suitable commercial materials for use in compliant-layer artificial hip joints. Mechanical requirements, notably hardness and strength, as well as biocompatibility, constituted the specification for the compliant layer. Applying these constraints, candidate materials were identified in a broad range of polymeric material classes. Detailed sourcing and literature searching helped to identify materials appropriate to the application, with suitable mechanical and physical properties, as well as a history of successful clinical use. Some likely materials were identified but were prohibited from further consideration by limited commercial availability. Physical and mechanical characterization together with literature data were used to determine the relative ranking of the candidate materials and through a weighted materials property selection procedure the materials of choice were identified. The linear segmented aromatic polyurethanes, Tecothane 1085 and Estane 5714F1, emerged as the preferred materials.