Synthesis,characterization, and pervaporation properties of segmented poly(urethane‐urea)s

Poly(urethane‐urea)s (PUUs) from 2,4‐tolylene diisocyanate (2,4‐TDI), poly(oxytetramethylene)diols (PTMO) or poly(butylene adipate)diol (PBA), and various diamines were synthesized and characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, and density measurements. Transport properties of the dense PUU‐based membranes were investigated in the pervaporation of benzene–cyclohexane mixtures. It was shown that the pervaporation characteristics of the prepared membranes depend on the structure and length of the PUU segments. The PBA‐based PUUs exhibit good pervaporation performance along with a very good durability in separation of the azeotropic benzene–cyclohexane mixture. They are characterized by the flux value of 25.5 (kg μm m⁻² h⁻¹) and the separation factor of 5.8 at 25°C, which is a reasonable compromise between the both transport parameters. The PTMO‐based PUUs display high permeation flux and low selectivity in separation of the benzene‐rich mixtures. At the feed composition of 5% benzene in cyclohexane, their selectivity and flux are in the range of 3.2 to 11.7 and 0.4 to 40.3, respectively, depending on the length of the hard and soft segments. The chemical constitution of the hard segments resulting from the chain extender used does not affect the selectivity of the PUU membranes. It enables, however, the permeability of the membranes to be tailored. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1615–1625, 1999     

Study on synthesis and thermal properties of polyurethane–imide copolymers with multiple hard segments

Different multiple hard segment polyurethane–imide copolymers (MHPUI) were synthesized and characterized. FTIR spectroscopy confirmed the characteristic absorption of the MHPUI copolymer. The difference in the imide group FTIR absorption bands in different MH segment PUI copolymers was found in this study and was explained by the different MH segment types, hard segment contents, and hard segment rigidity with different interactions of the molecular chains. The hard segment interaction in MHPUI with an increase of the structure rigidity of the short hard segments is strengthening. The DSC analysis revealed that the glass‐transition temperature of the soft segment of PUI rose in value from ?42 to ?3.4°C with the introduction of MH and different MH segments. The DSC results suggest that the soft segment is more compatible with the hard segment rigidity increase. The TGA results showed the hard segment structure symmetry has a more important role in the MHPUI thermal stability. Every sample containing symmetrical structure short hard groups (4,4′‐diphenylmethane diisocyanate or 4,4′‐diaminodiphenylmethane) is more thermally stable than that with worse symmetry structure groups (2,4‐toluene diisocyanate or 3,3′‐dichloro‐4,4′‐diamino‐diphenylmethane). The three‐step mechanism of PUI thermal degradation was further verified by the TGA study. The thermally unstable group was confirmed as urethane or a urea–urethane segment. The TGA results showed that MHPUI copolymers with higher separation of the soft–hard phase have higher thermal stability. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2206–2215, 2002     

软段结构对聚氨酯酰亚胺结构与性能的影响

分别以聚乙二醇（PEC）,聚己二酸丁二酯二元醇（PBA）及两者的混合物作软段溶液聚合合成了三种类型的聚氨酯酰亚胺（PUI）,红外光谱证实了聚酰亚胺硬段的存在,TG分析表明聚酯型PUI的热稳定性高于聚醚型PUI,DSC及X射线衍射实验表明聚酯PUI及聚酯含量较高的聚醚－酯混合二元醇作软段的PUI中有微晶区存在,研究PUI的应力一应变行为发现,聚酯型PUI具有更高的弹性模量及断裂强度,聚醚一酯混合型PUI随软段中聚酯含量的增加,断裂强度及弹性模量增加。     

Mechanical,thermal, and electric properties of polyurethaneimide elastomers

Linear polyurethaneimide elastomers (PUI) were obtained from polyether- or polyester-diols, diphenylmethane diisocyanate or bitolylene diisocyanate and pyromellitic acid dianhydride. It was found that these polymers have considerably better mechanical properties than typical linear polyurethanes (PU). The elastic modulus and stress at break increase with contents of the hard polyimide segments. The softening temperatures and thermal stability of the PUI at 500°C were higher than the ones of PU with similar hard segment contents. Electric properties of PUI were close to the ones of conventional PU. It was shown that cellular PUI had considerably lower dielectric constant. T_g's of the soft segments PUI were less than T_g's corresponding to PU. It is connected with greater phase separation of the hard imide segments from the soft polyether– or polyester–urethane matrix.     

A facile synthesis of mixed soft‐segmented poly(urethane‐imide)–polyhedral oligomeric silsesquioxone hybrid nanocomposites and study of their structure–transport properties

The structure–transport properties of mixed soft‐segmented poly(urethane‐imide) (MSPUI) membranes and their microstructures were investigated. Polypropylene glycol, polycaprolactone diol and bis(3‐aminopropyl)‐terminated polydimethylsiloxane were used as the soft segments in the membrane synthesis via a three‐step polymerization reaction. The chemical structures of the MSPUI membranes were characterized using attenuated total reflectance Fourier transform infrared spectroscopy. Morphology and surface properties of the membranes were studied using scanning electron and atomic force microscopy techniques. Surface energy measurements indicated the enrichment of the hydrophobic soft segment in the membranes. The amorphous nature of the polymers was analysed using wide‐angle X‐ray diffraction. The effect of morphology on the permeability and selectivity of the membranes is discussed. Finally, membrane structure–transport property relationships were correlated. © 2013 Society of Chemical Industry     

Synthesis and properties of poly(urethane‐imide) diacid/epoxy composites cured with an aziridine system

A poly(urethane‐imide) diacid (PUI), a diimide‐diacid with a soft structure unit, was directly synthesized from the reaction of trimellitic anhydride and isocyanate terminated polyurethane prepolymer. FT‐IR and NMR were used to characterize its chemical structure. Then PUI was blended with two types of epoxy resins with different chemical structures, diglycidyl ether of bisphenol A (DGEBA) and novolac epoxy (EPN). After curing the blends with polyfunctional aziridine CX‐100, novel polyurethane/epoxy composites were obtained as transparent yellowish films. Thermal, chemical, and morphological properties of the cured composites were investigated using thermal analysis, SEM, TEM, chemical resistance, respectively. All experimental data indicated that epoxy modified PUI composites possessed higher thermal stability than that unmodified PUI, and that modified PUI had much better chemical resistance. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Pervaporation of chlorinated hydrocarbon-acetone mixtures through poly(ethylene-co-vinyl acetate) membranes

Crosslinked and uncrosslinked ethylene-vinyl acetate copolymer membranes were prepared. The permeation characteristics in the pervaporation process were examined using carbon tetrachloride-acetone mixtures. Modified membranes exhibit carbon tetrachloride permselectivity, but unmodified membranes did not display the permselectivity of crosslinked polymer. Furthermore, membranes modified with dicumyl peroxide (DCP) showed a higher flux and selectivity than those of benzoyl peroxide (BP) modified ones. The effects of feed concentration, molecular size, and polarity of the permeating species on pervaporation were analyzed. The influence of crosslinking density of the membranes on pervaporation was also analyzed. The maximum separation and flux were found to be associated with an optimum amount of crosslinking agent in the membrane. A mixture of chloroform and acetone having a composition near the azeotropic region was also separated by the pervaporation technique. © 1996 John Wiley & Sons, Inc.     

Influence of flexible segment length on the phase structure and properties of poly(hexamethylene 2,5-furandicarboxylate)-block-biopolytetrahydrofuran copolymers

Two series of biobased poly(ether-ester)s comprised of poly(hexamethylene 2,5-furandicarboxylate) (PHF) as the rigid segments and biopolytetrahydrofuran (pTHF) with different molecular masses (1000 and 2000 g/mol) as the flexible segments were synthesized employing polycondensation in the molten state. The study mainly focuses on comparing these two series in terms of the length of the flexible segment. The content of pTHF segments in the copolymer chains varied from 25 to 75 wt.%. The molecular structure and composition, phase structure, and thermal and mechanical properties were characterized by nuclear magnetic resonance (¹H NMR) and Fourier-transformed infrared (FTIR) spectroscopies, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and positron annihilation lifetime spectroscopy (PALS). In addition, mechanical performance and thermo-oxidative and thermal stability have been investigated. Moreover, cyclic tensile properties were studied to evaluate the elastic properties. ¹H NMR and FTIR spectroscopies demonstrate that the syntheses were correctly carried out, which made it possible to obtain the desired compositions of the block copolymers with high molecular masses. The decrease in T_m1, T_c1, and X_cPHF values was visible, along with the increase in the flexible segment content. Moreover, the characteristic properties measured by PALS and the values of temperatures designated from TGA (inert and oxidizing atmosphere) did not vary between copolymer series PHF-b-F-pTHF1000 and PHF-b-F-pTHF2000. In turn, along with an increase in flexible segment content and the length of the pTHF, the values of tensile modulus, stress at break, and hardness decrease, while the value of elongation at break increases.     

Characterization of polyurethane foams from soybean oil

Modified soy‐based vegetable oil polyols were successfully incorporated as a replacement for conventional polyols to produce flexible slabstock polyurethane foams. The oil was characterized for its hydroxyl value and fatty acid composition. The modified oils had higher hydroxyl values and lower unsaturated acids than regular unmodified oils. Three different modified polyols were used to investigate the reactivity with isocyanates. The effects on the foaming reaction of two different isocyanates, namely TDI and MDI, were investigated. The reactions were also carried out with a mixture of polyols containing synthetic polyols and vegetable oil‐based polyols to delineate the effect of each component. FTIR technique was used to identify the sequence of chemical reactions during the foaming process. The effect of water levels and isocyanate content on the kinetics of the foaming reaction was investigated. Information regarding the formation of hard and soft segments with the varying compositions was obtained. As the water content increased, the amount of the hard segment and urea formation increased in both soy oil polyols and synthetic polyols. Increased synthetic polyols in the mixture increased the rate of reaction and phase mixing due to the availability of primary hydroxyl groups. Scanning electron microscopy (SEM) and small‐angle X‐ray scattering (SAXS) were used to probe the morphology. As the water content increased, the cell size increased. At lower water content a more uniform cell structure was evident and at higher water levels hard domain size increased. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3097–3107, 2002     

改性壳聚糖渗透蒸发膜用于酯化反应过程强化

壳聚糖(chitosan, CS)作为渗透蒸发膜材料来源广泛、亲水性好,但结构致密、渗透性较低。为改善CS膜的分离性能,将CS与聚醚-聚酰胺嵌段共聚物Pebax 1657共混,涂覆在NaOH水解处理的聚丙烯腈(polyacrylonitrile,PAN)超滤膜表面制备复合膜,用于渗透蒸发醇水分离过程,并进一步用渗透蒸发方法对乳酸-乙醇酯化反应进行强化。Pebax的聚酰胺与聚醚链段分别发挥调节膜结构与促进水跨膜传递的作用,有效地提高了膜分离性能。CS与Pebax质量比为2:1时,渗透蒸发醇水分离性能及对酯化反应强化的性能达到最优:渗透通量703 g·m^-2·h^-1、分离因子308,较未改性CS膜分别提高61%、65%;反应8 h后的乳酸乙酯产率由58%提高至73%。     

Structure–property relationships of thermoplastic polyurethane elastomers based on polycarbonate diols

The phase-separation behavior and morphology of polycarbonate-based polyurethanes were investigated as a function of the soft-segment molecular weight and chemical structure and the 4,4′-diphenylmethane diisocyanate/1,4-butanediol based hard-segment contents. Polarized optical microscopy and atomic force microscopy images showed that the surface morphologies changed as the soft-segment molecular weight and hard-segment content varied and also when the sample preparation conditions were modified. An increase in the soft- and hard-segment lengths led to increased phase separation with respect to the lower molecular weight soft segment, and this showed an interlocked and connected morphology of intermixed soft and hard domains. The surface morphology of phase-separated polyurethanes with hard segments composed of more than four to five 4,4′-diphenylmethane diisocyanate units contained globular hard-segment domains formed by spherulites, in which the size and connectivity between the branched lamellae changed with the hard-segment size. Interlamellar areas related to the soft segment were seen in the spherulites. Variations in the hard-segment spherulites were observed for polyurethanes based on soft segments of different molecular weights. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Elasticity and inelasticity of thermoplastic polyurethane elastomers: Sensitivity to chemical and physical structure

Cyclic tensile responses of fourteen polyurethane elastomers were studied, with respect to their chemical composition and physical structure. Hard segment, soft segment and chain extender were varied, while keeping the hard segment fraction at ca 40% and soft segment molar mass at 2000 g/mol. Hard segments were generated from 4,4′-methylene bis(phenyl di-isocyanate) (MDI), or 4,4′-dibenzyl di-isocyanate (DBDI). Physical structure was characterized by X-ray scattering (SAXS and WAXS), revealing significant variations in degree of phase separation and degree of crystallinity, especially in the DBDI-based polymers. Large differences were found in the mechanical responses during first loading to a given strain. Tensile modulus and work input increased significantly with degree of hard phase crystallinity, but were independent of degree of phase separation. First cycle hysteresis was found to increase with reduced phase separation and with replacement of MDI by DBDI. In second and subsequent load cycles, however, in which the Mullins effect was observed, a remarkable degree of uniformity of response was discovered. A unique linear relation was obtained between second cycle hysteresis and second cycle work input, for all strain levels, and for all materials except for two (with highest phase separation) which showed slightly lower second cycle hysteresis. The results can be explained in terms of pull-out of segments from the hard phase on the first cycle, to form a new series-coupled soft phase, whose constitutive response then appears almost independent of chemical and physical structure.     

Pervaporation of water–ethanol mixtures through plasma graft polymerization of polar monomer onto crosslinked polyurethane membrane

To improve the pervaporation performance, the plasma post-graft polymerization of 2,3-epoxypropylmethacrylate (EPMA) onto the crosslinking polyurethane (CPU) membrane, EPMA-g-CPU, was synthesized in this study. The crosslinking between soft–soft hydroxyl-terminated polybutadiene (HTPB) segments were prepared by the introduction of benzoyl peroxide to the HTPB-based PU membrane. The effect of plasma treatment time and plasma supply power on the grafting yield was discussed. The optimum plasma treatment conditions were 10 W supply power and 120 s treatment time. The surface properties of the EPMA-g-CPU membrane were characterized by Fourier transform infrared spectroscopy, electron spectroscopy for chemical analysis, and a contact angle meter. A separation factor of 97 and a 240 g m⁻² h⁻¹ permeation rate through the EPMA-g-CPU membrane with a 4.81 mg/cm² grafting yield for a 90 wt % feed ethanol concentration were obtained. Compared with ungrafted CPU membrane, the EPMA-g-CPU membrane effectively improved the pervaporation performances. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1789–1797, 1998     

Dielectric and viscoelastic properties of some meta-tetramethyl xylene diisocyanate-based polyurethanes as a function of sample composition

A series of linear segmented polyurethanes were synthesized, based on soft segments of polycaprolactone having an average number molecular weight of 2100, or hydroxy–terminated polybutadiene having an approximate molecular weight of 2800. Hara segments were made of meta–tetramethyl xylene diisocyanate and diethyl toluene diamine. The dynamic Young's modulus and loss tangent, relative permittivity, and dielectric loss, were found to be significantly affected by soft segment polarity and hard segment content. These results are discussed in terms of polymer morphology, such as degree of phase separation and soft segment phase state.     

Thermoplastic polyurethane elastomers based on polycarbonate diols with different soft segment molecular weight and chemical structure: Mechanical and thermal properties

A series of thermoplastic polyurethane elastomers based on polycarbonate diol, 4,4′‐diphenylmethane diisocyanate and 1,4‐butanediol was synthesized in bulk by two‐step polymerization varying polycarbonate diol soft segment molecular weight and chemical structure, and also hard segment content, and their effects on the thermal and mechanical properties were investigated. Dynamic mechanical analysis termogravimetric analysis, differential scanning calorimetry, Fourier transform infrared‐attenuated total reflection spectroscopy and mechanical tests were employed to characterize the polyurethanes. Thermal and mechanical properties are discussed from the viewpoint of microphase domain separation of hard and soft segments. On one hand, an increase in soft segment length, and on the other hand an increase in the hard segment content, i.e., hard segment molecular weight, was accompanied by an increase in the microphase separation degree, hard domain order and crystallinity, and stiffness. In phase separated systems more developed reinforcing hard domain structure is observed. These hard segment structures, in addition to the elastic nature of soft segment, provide enough physical crosslink sites to have elastomeric behavior. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

粒料法合成不同相对分子质量和软段的聚氨酯分散体研究

以异佛尔酮二异氰酸酯(IPDI)为硬段、二羟甲基丙酸(DMPA)为亲水单体,采用粒料法合成了不同Mη(黏均相对分子质量)和不同软段的PU(聚氨酯)离聚物粒料,并制备了固含量约为40%的PUD(PU分散体)。结果表明:PU的Mη随R值[R=n(-NCO)/n(-OH)]增加呈先升后降态势;PU的Mη越高,PUD的平均粒径越小,粒径分布越窄,黏度越大;PUD粒子呈大小不一的球形结构,并且PU的Mη越高,PUD胶膜的拉伸强度越大;聚酯型PUD胶膜的拉伸强度大于聚醚型PUD,并且前者的软段和硬段之间相容性较好,而后者的软段和硬段之间因出现相分离现象而相容性较差;PUD胶膜的吸水率均不超过5.93%,说明其耐水性能优异。     

Polyurethane-elastomer-actuator

Polyurethane elastomers were investigated as electrically active materials for actuators. Components in hard segment and soft segment in the elastomers were varied. The elastomers with excellent electrostrictive properties were limited to those which had soft segments of polyesters and polylactones. It turned out, that the elastomers, whose soft segments are polyethers are electrically inert under the experimental conditions. The chemical structure of the hard segment seems not to influence to the electrostrictive property. The charging and discharging process was investigated. The charging process was found to proceed simultaneously with the contracting process caused by the electric field, suggesting that the orientation of the soft segment in the elastomer plays critical rolls in the electrostrictive action. In the elastomer, which has a soft polyether segment and was inactive to the electric field, could be actuated very efficiently when the elastomer was swollen with dimethyl sulfoxide. We conclude that the polyurethane elastomer, whose soft segment has chemical bonds with a relatively large dipole moment, can be actuated by the electric field application, and that even the elastomer, whose soft segment is inactive, could be actuated in the presence of a solvent with a large dipole moment. Thus, the concept found with the gel, could be applied to an elastomer, the soft segment of which plays partly the roll of the solvent in the gel.     

Gas permeability of model polyurethane networks and hybrid organic-inorganic materials: Relations with morphology

Various polyurethane (PU) and hybrid organic-inorganic networks based on isocyanate chemistry were synthesized using a two-stage method. All the networks were amorphous. For PU membranes the morphology and the permeability coefficients of different gases (H₂, N₂, O₂) were a function of the polarity and the chain length of the soft segment and a function of the composition of the networks. The membranes based on the same soft segment chain length and on the same molar composition were structurally nanoheterogeneous systems for the less polar soft segments (α, ω-hydroxy-terminated hydrogenated polybutadiene and a fatty acid oligoester). They were homogeneous for a polycaprolactone type soft segment. The gas diffusion was appreciably hindered in the case of better miscibility between the soft chains and the hard crosslinks. Decreasing the soft segment length decreased the gas permeability coefficient of the network. As the chemical compositions were changed by increasing the soft segment content, an increase in permeability coefficients was observed. The morphology and transport properties of PU networks and hybrid organic-inorganic networks with low inorganic content were compared for the same soft segment content. The similarities observed between the two types of networks led us to conclude that the organic or inorganic nature of the crosslinking agent has no influence on the gas transport properties of these networks. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2579–2587, 1997     

Different approaches for creating nanocellular TPU foams by supercritical CO<Subscript>2</Subscript> foaming

In this study, three different approaches were applied to obtain thermoplastic polyurethane (TPU) nanocellular foams. The TPU was synthesized with a 4, 4′-methylenebis (phenyl isocyanate) and 1, 4-butanediol (MDI/BD) hard segment system using a pre-polymer method. The three approaches included increasing the hard segment content, adding a graphene nucleation agent, and replacing the soft segments. Although the synthesized TPUs had a different hardness, it was possible to obtain nanocellular structures with all of the methods. The cell structure is not a function of hardness only. Crystallinity affects the cell structure as well. The addition of graphene and replacement of the soft segments were more effective at yielding nanocellular foams. Our best results showed that after adding 0.1 wt% of graphene, the average cell size of the TPU foam decreased to 715 nm, and the cell density was improved to 4.94 × 10¹¹ cells/cm³. The relative density of the foam could be as low as 0.77. This study first reported elastomer-based nanocellular structures with such low relative density.     

软段结构对聚氨酯弹性体性能的影响

分别以聚四氢呋喃二醇(PTMG)、聚己内酯二醇(PCL)、高顺式端羟基聚丁二烯(HTPB)和自由基聚合制得的端羟基聚丁二烯(FHTPB)为软段,采用溶液聚合两步法制得了四种聚氨酯弹性体(PUE)。通过拉伸试验、动态力学性能分析(DMA)、差示扫描量热(DSC)和热重分析等手段,考察了软段结构对它们室温及低温下力学性能、热性能等的影响。结果表明,四种PUE低温(-30℃)下的拉伸强度和断裂伸长率均大于室温下的对应值。这不仅与低温下软段诱导结晶所产生的自增强效应有关,也与软、硬两段的微相分离程度增大有关。相较于其他三种PUE,HTPB-PUE软段不仅玻璃化温度(T _g)最低,而且极性也最弱,因而微相分离程度高,具有优异的柔性,-30℃下其断裂伸长率仍达660%以上。PCL-PUE和PTMG-PUE因软段易结晶,且软段与硬段的微相分离程度低,则刚性强。低温循环拉伸试验表明,-30℃下HTPB-PUE和FHTPB-PUE有较强的弹性恢复能力,而PCL-PUE和PTMG-PUE则相对较差。DSC和DMA结果显示HTPB-PUE的T _g远低于其他三种PUE,其T _g(DSC)低至-103℃。此外,四种PUE的初始分解温度十分相近,均在270℃左右。