Nanophase separation in segmented polyurethane elastomers: Effect of specific interactions on structure and properties

Polyurethanes were prepared from 4,4′-methylenebis (phenyl isocyanate) (MDI), 1,4-butanediol (BD) and poly (tetrahydrofurane) polyether polyol (PTHF). The -OH functional group ratio of polyol/total diol was kept constant at 0.4 in all experiments, while the ratio of the isocianate and hydroxyl groups (NCO/OH) changed between 0.940 and 1.150. Melt polymerization was carried out in an internal mixer. The polymers were characterized with a number of methods including GPC, FTIR, WAXS, DSC, DMA and tensile testing. Changing stoichiometry modifies molecular weight as expected, but the relative concentration of end-groups also changes at the same time. The respective end-groups preferentially associate with each other leading to phase separation. -OH end-groups enter into weaker interactions with each other than urethane and amine groups. The extent of phase separation, as well as the size and properties of the dispersed phase depend on composition. Each property of the polymer is affected differently by molecular weight and phase separation. Melt viscosity depends mostly on the length of the molecules, ultimate tensile properties are influenced also by interactions, while stiffness is determined almost exclusively by phase structure.     

Influence of varying hard segments on the properties of chemically crosslinked moisture‐cured polyurethane‐urea

Polyurethane prepolymers are widely used in the reactive hot melt adhesives and moisture‐cured coatings. The chemically crosslinked moisture‐cured formulation based on PEG‐1000 and isophorone diisocyanate was prepared with NCO/OH ratio of 1.6:1.0. Trimethylol propane was used as a crosslinking agent. The excess isocyanate of the prepolymer was chain extended in the ratio of 2:1 (NCO/OH) with different aliphatic diols, and 4:1 with different aromatic diamines. The polymer network maturation during moisture cure was followed by dynamic mechanical thermal analyzer (DMTA) instrument. The thermal and dynamic mechanical properties of the crosslinked polymers were evaluated using thermogravimetric analysis, differential scanning calorimetric analysis and DMTA. Surface properties were evaluated through angle‐resolved X‐ray photoelectron spectroscopy. The present article discusses the physical properties of moisture‐cured polyurethane‐urea (MCPU) containing chemical crosslinks in the hard segment. The complete moisture‐cured polymers showed amorous results toward room temperature modulus, tensile strength, hardness, thermal stability, and transparency. The surface properties showed the enrichment of soft segments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 102–118, 2006     

Control of hard segment size in polyurethane formation

In general, segmented polyurethane elastomers are prepared by reacting an isocyanate-capped polyol prepolymer with a short-chain diol chain extender, yielding an elastomer with hard segments of uniform size. However, the hard segment size will not be uniform if the polyurethane polymer is prepared by forming the hard segment first, followed by soft segment formation. Because the mechanical properties of polyurethane elastomers depend on the relative ratio of the hard to soft segments as well as the effectiveness of the hard segment as a physical crosslinker, the control of the size distribution of the hard segment is a key factor in designing polyurethane elastomers. It was found that reaction conditions can affect the size distribution of hard segments derived from an aliphatic diisocyanate with differential reactivity between the two isocyanate groups. Lower reaction temperatures and simultaneous mixing of all reactants gave the preferred size distribution of hard segments. © 1995 John Wiley & Sons, Inc.     

Thermal and viscoelastic properties of polyurethane-imide/clay hybrid coatings

This paper reports the synthesis and characterization of polyurethane (PU)-imide/clay hybrid coatings based on two types of polyester (PE) polyols (PE-1 and PE-2). PE-1 was prepared from neopentyl glycol (NPG), adipic acid (AA) and isophathalic acid (IPA), whereas PE-2 contains NPG, AA, IPA and TMP (trimethylol propane) with the same hydroxyl value 280 as PE-1. Cetyl trimethyl ammonium bromide (CTAB) modified montmorillonite (K10) was used as the organoclay for the synthesis of the hybrid coatings. The organoclay particles (3 wt%) were well-dispersed into the PE matrix by ultrasonication method. Then the isocyanate terminated PU prepolymers were synthesized by the reaction of polyester polyols with hard segments such as 2,4-toluene diisocyanate (TDI) or isophorone diisocyanate (IPDI) in different NCO/OH ratios e.g., 1.6:1, 2:1 and 3:1, respectively. Finally the thermally stable imide rings were incorporated into the PU backbone by complete reaction of excess NCO content present in the PU prepolymer with pyromellitic dianhydride (PMDA). The thermogravimetric analysis (TGA) shows a higher thermal stability for the PU-imide hybrid coatings with respect to the corresponding PU-imide films. A higher NCO/OH ratio has resulted in higher thermal stability. The activation energies of degradation were calculated by the Broido and Coats-Redfern methods, respectively. The dynamic mechanical thermal analysis (DMTA) results show an enhancement in the glass transition temperature value (T_g) for the clay containing hybrid coatings. The surface analysis by angle resolved X-ray photoelectron spectroscopy (AR-XPS) showed an enrichment of the soft segment towards the surface, and an enhancement in the hard segment composition in the hybrid coatings, resulted in phase mixing.     

Interpenetrating polymer networks from polyurethanes and methacrylate polymers. I. Effect of molecular weight of polyols and NCO/OH ratio of urethane prepolymers on properties and morphology of IPNs

Two types of reinforced elastomeric interpentrating polymer network (IPN) were prepared by simultaneous polymerization and crosslinking in solution. The first type consisted of polyurethane-poly(methyl methacrylate) (PU/PMMA), and the second, of polyurethane-poly(methyl methacrylate-methacrylic acid) PU/P(MMA–MAA) of constant composition (90/10) and (80/20) by weight, respectively. The members of each type differed in the NCO/OH ratio of the PU prepolymer and the molecular weight (MW) of the polyol in the PU component because we wished to investigate systematically the effect of changing the NCO/OH ratio and MW of the polyol on the mechanical properties and morphology of the resulting IPNs. The mechanical properties, particularly the modulus of both tyes of IPN, increased with increasing NCO/OH ratio and decreased with increasing MW of the polyol in the PU. The morphology of the IPNs was studied by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Improved phase compatibility and decreasing extent of phase separation was observed in both types of IPN with increasing NCO/OH ratio and decreasing MW of the polyol used in the PU. These results may imply that improved interpenetration results from increasing the NCO/OH ratio and decreasing the MW of the polyol in the PU component. The fact that the effect is more pronounced with the type of PU-P(MMA–MAA) IPN can be rationalized as due to the additional hydrogen bonding between the carbonyl in the carboxyl groups and the urethane or urea groups in the PU component.     

Thermal properties of lignin-and molasses-based polyurethane foams

Lignin-and molasses-based polyurethane (PU) foams with various lignin/molasses mixing ratios were prepared. The hydroxyl group in molasses and lignin is used as the reaction site and PU foams with various isocyanate (NCO)/the hydroxyl group (OH) ratios were obtained. Thermal properties of PU foams were investigated by differential scanning calorimetry (DSC), thermogravimetry (TG) and thermal conductivity measurement. Glass transition temperature (T _g) was observed depending on NCO/OH ratio in a temperature range from ca. 80 to 120°C and thermal decomposition temperature (T _d) from ca. 280 to 295°C. Mixing ratio of molasses and lignin polyol scarcely affected the T _g and T _d. Thermal conductivity of PU foams was in a range from 0.030 to 0.040 Wm⁻¹ K⁻¹ depending on mixing ratio of lignin and molasses.     

Shape memory fiber spun with segmented polyurethane ionomer

The effect of cationic groups within hard segments on shape memory polyurethane (SMPU) fibers was studied and the cyclic tensile testing was conducted to assess the shape memory effect. Mechanical properties, hard segment crystallization, and dynamic mechanical properties of SMPU ionomer fibers composed of 1,4‐butanediol (BDO), N‐methyldiethanolamine (NMDA), 4,4′‐methylenebis(phenyl isocyanate) (MDI), and poly(butylene adipate)diol (PBA) were investigated using a universal tensile tester, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The results demonstrate that only 2 wt% NMDA can significantly change the glass transition temperature of the soft segment phase. DSC shows that the ionic group within hard segments can facilitate the crystallization of hard segments in unsteamed SMPU ionomer fibers. But for steamed fiber specimens, this effect is insignificant. Moreover, the ionic groups in hard segments with different hard segment contents (HSC) have different effects. In unsteamed fibers with 64 wt% HSC, 2 wt% NMDA increases the glass transition of soft segments from 63.5 to 70.6°C. However, in fibers with 55 wt% HSC, the glass transition temperature is lowered from 46.7 to 33.5°C. The post‐treatment, high‐pressure steaming is an effective way to remove the internal stress and subsequently improve the dimensional stability of SMPU ionomer fibers. Copyright © 2008 John Wiley & Sons, Ltd.     

Poly(urea)urethanes based on amorphous quaternizable hard segments and a crystalline polyol derived from castor oil

A set of poly(urea)urethanes (PUU), with different contents of amorphous hard segment and castor oil-derived crystalline polyol as soft segment, was prepared combining bulk and solution polymerizations. It is shown that both the soft segment crystallinity and hard segment glassy nature control the stiffness of the materials and that phase mixing at intermediate hard segment compositions produces softer materials. Upon yielding, PUU developed large plasticity associated to the nature of soft segments. At longer strains, PUU presented strain-induced crystallization related both to soft segments alignment and crystallization, leading to strong and tough materials, especially with high hard segment content compositions. Despite the hydrophobicity of the soft segments, the PUU with 65 wt% hard segment content was dispersable in water after quaternization with acetic acid. The high amount of urea groups in this quaternized PUU makes one think of these types of polymers as promising water soluble environmentally friendly strong adhesives, coatings, or water soluble polymeric electrolites.     

Preparation of Aqueous Polyurethane Dispersions Using Aromatic Diisocyanate

Aqueous polyurethane dispersions were prepared by the reaction of hydroxyl-terminated poly(ethylene adipate), ethylene glycol, dimethylol propionic acid and aromaic diisocyante, 4,4′-diphenylmethane diisocyanate. The influence of molecular weight of oligoester and molar ratio between isocyanate and hydroxyl groups (NCO/OH) in the prepolymerization step were investigated. Molecular weight, particle size and particle size distribution were measured and compared. It was verified that the molecular weight increases with increasing in NCO/OH molar ratio. The results suggest that the hard segment content plays an important role in particle size and particle size distribution of the dispersions.     

Diaminobisbenzothiazole chain extended polyurethanes as a novel class of thermoplastic polyurethane elastomers with improved thermal stability and electrical insulation properties

This work was devoted to the development of a new class of modified polyurethane as an electrical insulating material. For this purpose, NCO‐terminated urethane prepolymers at different NCO contents were prepared and chain extended by 6,6′‐oxybis(2‐aminobenzothiazole) (ABT) to produce thermoplastic polyurethane elastomers. All of the polymers were characterized by FTIR and ¹HNMR spectroscopies and examined for their thermal, mechanical, and electrical properties. The dynamic mechanical measurements results showed two glass transitions indicating phase separation. A considerable improvement in the thermal and electrical properties in comparison to common polyurethanes was detected for these polymers. The level of enhancement in the measured properties was related to the polyol molecular weight, hard segment content, and consequently the amount of the introduced urea and benzothiazole moieties. These findings indicated the improved high service temperature performance of these materials as electrical insulator for metallic surfaces. Copyright © 2008 John Wiley & Sons, Ltd.     

不饱和聚酯／聚氨酯复合体系的研究

以端羟基不饱和聚酯（ＨＵＰ）与聚氨酯（ＰＵ）浇注型复合网络聚合物（ＣＰＮｓ）为基材，考察了化学动力学及相分离对ＣＰＮ聚合物物理机械性能的影响．数据揭示了不饱和聚酯／聚附聚氨酯（ＨＵＰ／ＰＵ－ｅｓ）ＣＰＮ，当ｒ＝ＮＣＯ／ＯＨ＝０．４时，它的物理力学性能优于不饱和聚酯／聚醚聚氨酯（ＨＵＰ／ＰＵ－ｅｔ）ＣＰＮ或ＨＵＰ／ＰＡＰＩＣＰＮ组成物．最佳ＣＰＮ可通过调整聚氨酯中软段和硬段组分及网络组成而设计与制备．     

Chemical modification of methyl cellulose with HMDI to modulate the thickening properties in castor oil

This work deals with the selective incorporation of reactive isocyanate groups into methyl cellulose in order to be used as reactive thickening agent in castor oil. Resulting gel-like dispersions may have potential applications as green lubricating greases formulated from renewable resources. Two different isocyanate-functionalized methyl cellulose-based polymers were obtained by reaction of methyl cellulose with 1,6-hexamethylene diisocyanate. The functionalization degree, from fully functionalized to a certain number of free hydroxyl groups (58:36:6 ratio between –OMe, –NCO and free –OH groups), was controlled by modifying the reagents molar ratio. These polymers were characterized through nuclear magnetic resonance of protons (¹H-NMR), Fourier transform infrared spectroscopy and thermogravimetric analysis (TGA). Thermal and rheological responses of oleogels prepared by dispersing these polymers in castor oil were studied by means of TGA analysis and small-amplitude oscillatory shear measurements. The evolution of linear viscoelasticity functions with frequency of the oleogel containing isocyanate-functionalized methyl cellulose with lower –NCO content is quite similar to that found for traditional lithium lubricating greases. In relation to long-term stability of these oleogels, the values of viscoelastic functions significantly increase during the first 7 days of ageing and then remain almost constant.     

Soy-oil-based segmented polyurethanes

Segmented polyurethanes were prepared from soy polyol, diphenyl methane diisocyanate (MDI), and ethylene glycol or butane diol as chain extenders. Samples were prepared with true hard-segment concentrations (HSC) of about 0, 10, and 40%. Both the soft MDI–polyol and hard MDI/diol segments are glassy at room temperature. These samples were also crosslinked through the polyfunctional polyol soft segment. Partial crystallinity and phase separation were detected in samples with 40% HSC, on the basis of DSC data. Small-angle X-ray scattering shows the existence of phase separation with domain sizes of about 10 nm in the 40% HSC samples, but not in the others. The distribution of domain sizes is considerably broader for the ethylene-glycol extended system compared with that for the butane-diol case. Although the presence of hard segments lowers the crosslink density, samples with higher HSC had higher glass transition temperatures, higher strengths, higher moduli, lower swelling, lower elongation at break, and lower impact strengths. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3178–3190, 2005     

Synthesis and characterization of hyperbranched polyurethane-urea coatings

A series of hyperbranched polyurethane (HBPU)-urea coatings were synthesized by a systematic two-step reaction process. Initially, isocyanate terminated PU prepolymers were prepared from a hyperbranched polyester polyols with isophorone diisocyanate at NCO/OH ratio of 1.6:1 for 5 h at 70-80 °C. The excess NCO content after the synthesis of NCO terminated HBPU prepolymer was completely reacted with atmospheric moisture. The obtained HBPU-urea networks were characterized with Fourier transform-infrared (FT-IR) spectroscopy for the quantitative evolution of the extent of urethane and urea bonds as well as to study the structure-property relationship. In order to find out the changes and types of intermolecular H-bonding interaction in the HBPU-urea films with the variation in polyester structure, the deconvolution of FT-IR spectra were carried out using Origin 6.0 software through Gaussian curve-fitting method. The viscoelastic properties and thermal stability of the synthesized coatings were determined by dynamic mechanical and thermal analyzer and thermogravimetric analyzer, respectively. For HBPU-urea samples glass transition temperature and thermal stability increased with the generation number from the first to the third. Polyester samples showed single step decomposition profile and HBPU-urea samples showed two-steps decomposition with good thermal stability.     

Zum Einfluß von Härte,chemischer Vernetzung und Vorverlängerung auf das Erweichungsverhalten von Polyurethan-Elastomeren mit 1,4-Butandiol als Kettenverlängerer

Zusammenfassung Mit wachsendem Isocyanatgehalt steigt das Modulniveau des kautschukelastischen Zustandes, der Glasübergang wird zunehmend asymmetrisch zu höheren Temperaturen verschmiert. Der letztgenannte Effekt tritt nicht auf im spezifischen Volumen und in der spezifischen Wärme. Aus diesen Befunden wird auf eine zunehmende Durchdringung der Weichsegmente mit harten Bereichen bei wachsendem Isocyanatgehalt und auf eine starke Zerklüftung der Phasengrenzflächen geschlossen.Die Erweichung der Hartsegmentbereiche besteht aus mehreren Einzelprozessen, von denen die beiden mit den höchsten Erweichungstemperaturen dem Aufschmelzen von kristallinen und parakristallinen Hartsegmentaggregaten zugeordnet werden. Eine Deutung der übrigen Umwandlungen war nicht möglich.Neben dem Einfluß des Isocyanatgehaltes werden die Auswirkungen unterschiedlicher Kennzahl (NCOOH) und wachsender Vorverlängerung diskutiert.

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Summary The influence of the isocyanate content on the mechanical and thermal behaviour of polyurethane elastomers is studied by differential scanning calorimetry, thermomechanical analysis, and by dynamic mechanical measurements. It is concluded that the separation between hard and soft segment domains becomes very uncomplete with increasing hardness. This effect causes the very broad glass transition of hard PU-elastomers.The melting behaviour of the hard segment regions is discussed, and the influence of the NCO/OH ratio on the properties of the elastomers is investigated.

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Herrn Prof. Dr.Otto Bayer zum 70. Geburtstag gewidmet.     

Influence of structure-property relationship on the optical,thermal and mechanical properties of castor oil based transparent polyurethane for catheter applications

Castor oil based transparent polyurethane elastomers were synthesized, which can be used as an advanced catheter material. The effect of NCO: OH ratio on the structural, optical, thermal and physicomechanical properties of polyurethanes (PU) has been studied. The optical properties of the PU was analysed by studying its percentage transmittance and haze. The results showed a high transparency of 90.7% for the PU with a NCO: OH ratio of 0.9:1. Differential scanning calorimetry (DSC) analysis revealed an increase in the glass transition temperature (T_g) of PU with increasing hard segment content whereas thermogravimetric analysis (TGA) shows an increase in the initial decomposition temperature of PU from 262 to 268°C upon increasing the NCO: OH ratio from 0.9 to 1.5. A similar trend of increment in the tensile properties of PU has been observed as a consequence of increasing the molar ratio of NCO: OH. In vitro cytotoxicity analysis of PU was studied using human embryonic kidney (HEK293) cell line that revealed the nontoxic character of PU.     

Effect of polyester zigzag structure on the phase segregation of polyester-based polyurethanes

Polyester-based polyurethanes were synthesized from 4,4′-methylenebis(phenyl isocyanate) (MDI) with butanediol as a chain extender and low molecular weight polyester–diol as a soft segment. Two polyesters were used in the synthesis of polyurethanes. One of the polyesters was synthesized from adipic acid and 1,6-hexanediol, which had an even number of carbon atoms. The other polyester was synthesized from pimelic acid and 1,5-pentanediol, which had an odd number of carbon atoms. The effect of even carbon monomers and odd carbon monomers of polyester soft segments on the phase segregation of soft and hard segments was studied by DSC (differential scanning calorimetry) and FTIR (Fourier transform infrared spectroscopy). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2095–2104, 1999     

High performance UV cured polyurethane dispersion

Imide groups were introduced in the hard segment of UV cured polyurethane dispersion (UV-PUD) by extending the NCO terminated prepolymers with pyromellitic dianhydride (PMDA) where the soft segments were prepared from PTMG, H₁₂MDI, HDI and DMBA. It was found that imide hard segment, as compared with conventional urethane hard segment gave remarkably high mechanical properties as well as thermal stability in terms of decomposition temperature and dynamic mechanical properties at elevated temperatures, and the results were interpreted based on the partial mixing of soft segments and imide hard segments.     

Study of elastomeric polyurethane nanocomposites prepared from grafted organic–montmorillonite

4,4′-Diphenylmethane diisocyanate (MDI) was grafted on to organic–montmorillonite (OMMT) by reaction between hydroxyl groups (−OH) on surface of the montmorillonite and the isocyanate groups (−NCO) of MDI, thus forming grafted organic–montmorillonite (MOMMT). Intercalated nanocomposites based on polyurethane (PU) and MOMMT were prepared by solution intercalation technology. The interface interaction of PU/MOMMT nanocomposites was better than that of PU/MMT composites. The tensile strength, elongation at break, and tear strength of the PU/MOMMT nanocomposites increased for MOMMT content up to 5% w/w, and then decreased with further increase in MOMMT content. At the same filler content, the tensile strength and tear strength of PU/MOMMT nanocomposites were higher than those of PU/OMMT nanocomposites, whereas the elongations at break of PU/MOMMT nanocomposites were smaller than those of PU/OMMT nanocomposites. The initial temperatures of weight loss of PU/MOMMT nanocomposites were lower than for PU/MMT composites in the first step of thermal degradation, whereas in the second step initial temperatures of weight loss were higher for PU/MOMMT nanocomposites.     

The role of domain structure in the development of thermomechanical and fatigue properties of microcellular polyurethanes

The effect of the isocyanate index, which is the molar ratio NCO:OH, on the development of structural mechanical and fatigue characteristics of microcellular polyurethanes has been studied. The correlation between fatigue and mechanical characteristics of microcellular polyurethanes at an elevated temperature (100°C) has been established. Fatigue lifetime has been found to be proportional to the concentration of heat-resistant ordered domains of hard blocks, which was estimated by the DSC method.