Mechanical behavior during different weathering tests of the polyurethane elastomers films

Segmented poly(ester-urethane)elastomers (PU) based on poly(ethylene diethylene adipate) diols as a soft segment and aromatic diisocyanates in the hard segment were synthesized by a conventional method. The precipitated and compact polyurethane films have been degraded after a limited exposure to natural weathering. The effects on mechanical properties of precipitated and compact polyurethane films were found to be a measure of the degradation due to weathering. The present study attempts to correlate the physical-mechanical properties of the precipitated polyurethane and compact films with time of weathering. In all cases a certain amount of oxidative change had been initiated. This was probably associated with enzyme adsorption on surfaces. We compared natural weathering of PU films carried out in earth, seawater and exposure to sunlight with untreated samples. In common with other weathering tests, the effect was to decrease the ultimate tensile strain, except seawater. It was found that enzymatic degradation in the earth occurred only after, the ageing process was continuous and practically linear with a relatively short initial period of increase in degradation rate.     

Synthesis and characterization of novel h‐HTBN/PEG PU copolymers for tissue engineering: degradation,phase behavior,and mechanical properties

The phase behavior of the as‐prepared polyether polyurethane (PU) elastomers was investigated by dynamic mechanical analysis (DMA), polarized optical microscope (POM), and atomic force microscopy (AFM). This PU copolymers were composed of different compositions of two soft segments, poly(ethylene glycol) (PEG) and hydrolytically modified hydroxyl‐terminated poly(butadiene‐co‐acrylonitrile) (h‐HTBN) oligomers. The microphase separation behavior is confirmed to occur between soft and hard segments as well as soft and soft segments as the h‐HTBN is incorporated into the PU system, depending on soft‐soft and/or soft‐hard microdomain composition, molecular weight (MW) of PEG, and hydrolysis time of HTBN. The driving force for this phase separation is mainly due to the formation of inter‐ and intramolecular hydrogen bonding interaction. The PU‐70, PU‐50 samples with non‐reciprocal composition seem to exhibit larger microphase separation than any other PU ones. The hydrolysis degradation, thermal stability, and mechanical properties of the copolymers were assessed by gravimetry, scanning electron microscope (SEM), thermal gravity analysis (TGA), and tensile test, respectively. The experimental results indicated that the incorporation of h‐HTBN soft segment into PEG as well as low MW of PEG leads to increased thermal and degradable stability based on the intermolecular hydrogen bond interaction. The PU‐70 and PU‐50 copolymers exhibit better mechanical properties such as high flexibility and high ductility because of their larger microphase separation architecture with the hard domains acting as reinforcing fillers and/or physical crosslinking agents dispersed in the soft segment matrix. Copyright © 2009 John Wiley & Sons, Ltd.     

交联密度对脂肪族聚氨酯弹性体结构与性能的影响

采用异佛尔酮二异氰酸酯(IPDI)与聚醚二元醇、三羟甲基丙烷(TMP)和1,4-丁二醇反应制备了具有不同交联密度的脂肪族聚氨酯弹性体.研究结果表明,当聚氨酯弹性体的硬段含量为40 wt%时,随着TMP含量的增加,聚氨酯弹性体的交联密度线性增加.随着聚氨酯弹性体交联密度的提高,聚氨酯中硬段相的玻璃化转变温度由32℃降为2...     

Waterborne polyurethanes and their properties

Anionomer-type waterborne polyurethanes (PUs) were obtained from poly(β-methyl-δ-valerolactone) glycol (PMVL) and isophorone diisocyanate, following a prepolymer mixing process. The soft-hard segment phase separation in response to the variations of composition and structure of PU has been studied from the dynamic mechanical measurements of the emulsion cast films. The structural variation included ionic and hard segment content, molecular weight of NCO-terminated prepolymer, and type and length of the soft segment. It was found that phase separation is more sensitive to the soft segment length, rather than the soft segment content. With only phase separation, the rubbery modulus was significant even with lower hard segment content. Phase separation was much more pronounced with PU from poly(tetramethylene adipate) glycol, rather than from PMVL and poly(caprolactone) © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of poly(dimethylsiloxane‐urethane) elastomers: Effect of hard segments of polyurethane on morphological and mechanical properties

A series of poly(dimethylsiloxane‐urethane) elastomers based on hexamethylenediisocyanate, toluenediisocyanate, or 4,4′‐methylenediphenyldiisocyanate hard segment and polydimethylsiloxane (PDMS) soft segment were synthesized. In this study, a new type of soft‐segmented PDMS crosslinker was synthesized by hydrosilylation reaction of 2‐allyloxyethanol with polyhydromethylsiloxane, using Karstedt's catalyst. The synthesized soft‐segmented crosslinker was characterized by FT‐IR, ¹H, and ¹³C NMR spectroscopic techniques. The mechanical and thermal properties of elastomers were characterized using tensile testing, thermogravimetric analysis, differential scanning calorimetry (DSC), and dynamical mechanical analysis measurements. The molecular structure of poly(dimethylsiloxane‐urethane) membranes was characterized by ATR‐FTIR spectroscopic techniques. Infrared spectra indicated the formation of urethane/urea aggregates and hydrogen bonding between the hard and soft domains. Better mechanical and thermal properties of the elastomers were observed. The restriction of chain mobility has been shown by the formation of hydrogen bonding in the soft and hard segment domains, resulting in the increase in the glass‐transition temperature of soft segments. DSC analysis indicates the phase separation of the hard and soft domains. The storage modulus (E′) of the elastomers was increasing with increase in the number of urethane connections between the hard and soft segments. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2980–2989, 2006     

Effect of Soft Segment Molecular Weight and 3-Methyl Side Group on Microstructural Separation in Polyurethane Elastomers

Abstract

The object of this study was to assess the effect of the chain length and of the pendant 3-methyl side group in the soft segment of polyurethane (PU) elastomers. In addition, the effect of annealing-quenching on the degree of microstructural segregation between the hard and soft segments was also investigated. The study employed electron spin resonance (ESR), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Samples for ESR measurements were spin-labeled with the nitroxide probe, 4-hydroxy-2,2′,6,6′-piperidine-1-oxyl (TEMPOL), by reaction of an isocyanate group with the hydroxyl group of TEMPOL. The nitroxide label is therefore located at a chain end. The PU's were based on 4,4′-diphenylmethane diisocyanate (MDI), poly(oxytetramethylene) glycols (PTMO), and hydroxyl-terminated random copolymers of tetrahydrofuran and 3-methyl-tetrahydrofuran (THF/Me-THF). Purified 1,4-butanediol (BD) was used as a chain extender. The elastomers made from higher molecular weight (MW) soft segments have better phase segregation than their lower MW counterparts. The 3-methyl side groups on the PTMO backbone have some effect on the arrangements of the two domains. ESR analysis indicated that the increase in the MW of THF/Me-THF decreased the degree of mixing between the hard and soft segments. In PU elastomers made from high MW soft segments, the presence of crystallinity was observed from the DSC measurements. The crystallinity of the soft segments was disrupted by the existence of the 3-methyl side groups.     

Specific essential work of fracture of polyurethane thin films with different molecular structures

A series of polyurethane (PU) thin films with different hard-to-soft segment ratios were synthesized in our laboratory. The molecular and morphological structures of the PU films were characterized with Fourier transform infrared (FTIR), small-angle X-ray scattering (SAXS), wide-angle x-ray diffraction, dynamic mechanical analysis, and differential scanning calorimetry. The PU films showed a single glass transition when the hard-to-soft segment ratio varied from 1:2 to 1:8, suggesting no significant phase separation between the hard and soft segments. FTIR and SAXS results disclosed that the PU films had a network structure with the physical crosslinks formed via the intermolecular hydrogen bonds established between the hard segments. The fracture toughness of the ductile PU films was characterized with the essential work of fracture method under different conditions. It was found that the specific essential work of fracture was a function of the chain length between crosslinks and independent of the test temperature when fracture occurred at a temperature below the glass transition temperature. The physical meaning of this fracture parameter was proposed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1418–1424, 2007     

Novel method for the preparation of poly(urethane–imide)s and their properties

A polymer blend consisting of polyimide (PI) and polyurethane (PU) was prepared by means of a novel approach. PU prepolymer was prepared by the reaction of polyester polyol and 2,4-tolylenediisocyanate (2,4-TDI) and then end-capped with phenol. Poly(amide acid) was prepared from pyromellitic dianhydride (PMDA) and oxydianiline (ODA). A series of oligo(amide acid)s were also prepared by controlling the molar ratio of PMDA and ODA. The PU prepolymer and poly(amide acid) or oligo(amide acid) solution were blended at room temperature in various weight ratios. The cast films were obtained from the blend solution and treated at various temperatures. With the increase of polyurethane component, the films changed from plastic to brittle and then to elastic. The poly(urethane–imide) elastomers showed excellent mechanical properties and moderate thermal stability. The elongation of films with elasticity was more than 300%. The elongation set after the breaking of films was small. From the dynamic mechanical analysis, all the samples showed a glass transition temperature (T_g) at ca. −15°C, corresponding to T_g of the urethane component, suggesting that phase separation occurred between the two polymer components, irrespective of polyimide content. TGA and DSC studies indicated that the thermal degradation of poly(urethane–imide) was in the temperature range 250–270°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3745–3753, 1997     

对苯二异氰酸酯基聚氨酯弹性体交联度对其形态与摩擦性能的影响

聚氨酯弹性体的摩擦性能在诸如船舶、汽车、生物医用等领域具有十分重要的意义,而通过化学修饰策略实现该类材料摩擦性能的精细设计,仍具有十分迫切的研究需求和广泛的应用前景。 本工作以对苯二异氰酸酯(PPDI)与聚四氢呋喃醚二醇(PTMG)为原料,通过调节1,4-丁二醇与三羟甲基丙烷两种扩链交联剂的混合比例,采用预聚体法合成了具备不同交联度的PPDI基聚氨酯弹性体。 其中,傅里叶变换衰减全反射光谱(FTIR-ATR)、广角X射线衍射(WAXD)、差示扫描量热仪(DSC)等表征结果表明,聚氨酯弹性体中硬段和软段的结晶度随交联度的提升均呈下降趋势。 同时,力学测试表明,材料的弹性模量随之降低,而PPDI基聚氨酯弹性体摩擦系数则明显增大。 此外,滞后回环曲线表明,交联度的改变影响了PPDI基聚氨酯弹性体的阻尼特性,而聚氨酯弹性体阻尼的差异在其摩擦性能对速率的依赖关系中则有所体现。 本工作由此提出,利用不同交联度下PPDI基聚氨酯中软硬段结晶度的变化,在对材料弹性模量和损耗模量进行可控调节的同时,能够实现对其摩擦性能的改变,为PPDI基聚氨酯弹性体的摩擦性能调控提供了一种简单有效的途径。     

1,5-萘二异氰酸酯与1,4-丁二醇基为基质的多嵌段聚氨酯弹性体的合成与性能

利用 1 ,5_萘二异氰酸酯 (NDI)和 1 ,4_丁二醇 (BDO)为均匀硬质分子单体 ,与不同软质分子单体 (聚醚、聚酯、聚硅氧烷 )缩合制备多嵌段聚氨酯弹性体 ,详细研究了硬嵌段相 (NDI)弹性体的结构与性能间的关系 ,发现随着硬嵌段相长度的增加 ,或者氨基甲酸酯中胺基与聚醚、聚酯、聚硅氧烷中软段氧原子间氢键的减弱 ,都导致微相分离程度的增加 ,造成聚合物熔点和熔化热的升高。硬嵌段相熔化的多峰行为是由于形成了NDI/BDO半微晶区 ,在退火时转变为更加有序的结晶微区 ,当温度高于 1 80℃时 ,由于氢键的断裂 ,NDI/BDO硬嵌段发生分解反应 ,该过程源于不很有序的硬嵌段半结晶微区。当温度高于 2 5 0℃时 ,发生快速的分解。在动态力学行为方面 ,NDI基聚醚弹性体比其它硅氧烷基的弹性体展示了更高的硬嵌段区的稳定性 ,同时 ,在使用温度范围内 ,也显示出最高的储能模量值 ,表明刚性对温度的依赖性 ,以及NDI/BDO硬嵌段中活性填料的显著影响     

New type of thermoplastic multiblock elastomers––poly(ester-block-amide)s––based on oligoamide 12 and oligoester prepared from dimerized fatty acid

Multiblock poly(ester-block-amide)s (PEA) elastomers comprising hard blocks of oligoamide and oligoester soft segments were prepared and their structure-property relations were analysed. The polycondensation reaction of oligoesters (prepared from 1,4-butanediol and dimerized fatty acid) with oligolaurolactam (PA12) gave copolymer series with variable blocks content (the soft segments content was varied from 24 to 60 wt.%). PEAs are the phase system composed of crystallised sequences of oligoamide (hard segment phase) as well as oligoesters (soft segment phase). Mixing between the hard and soft phases was studied by thermal and mechanical measurements (DSC, DMTA). These results have indicated on a multiphase structure of investigated materials. The relationship between the observed thermal and tensile properties and the soft/hard segments content indicated on an increase of the phase separation with soft segments content.     

Microstructure and properties of polyurethanes derived from castor oil

The goal of this work was the synthesis of novel segmented polyurethanes with a high percentage of components derived from renewable sources. The soft segment was a polyol derived from castor oil and the hard segment structure was varied by means of different chain extenders, petrochemical-based 1,4-butanediol (BD) and corn sugar-based 1,3-propanediol (PD). The synthesis was carried out in bulk and without catalyst via a two-step polymerization varying hard segment ratio. Physico-chemical, mechanical and morphological characterization was performed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), atomic force microscopy (AFM), mechanical testing and termogravimetric analysis (TGA). Properties have been discussed from the viewpoint of hard/soft microdomain phase separation and also the hard segment nature and formed structure. An increase in hard segment content was accompanied by an increase in hard domain order, crystallinity, and stiffness. The hard segment structures, in addition to the elastic nature of soft segment, provide enough physical crosslink sites to impart properties ranging from elastomeric to rigid behaviour with the increase of hard segment content. Polyurethanes synthesized from bio-based chain extender showed a slightly lower crystallinity in the hard segment structure than that synthesized from BD as the chain extender. This lower crystallinity avoids strength concentrations at the soft/crystalline hard segment interface, thus improving the mechanical properties at high hard segment content. The slightly higher thermal stability observed for BD based polyurethanes is related with their more packed structures and crystallinity observed in the hard segment structure.     

Enhanced mechanical and shape memory properties of polyurethane block copolymers chain-extended by ethylene diamine

Effect on shape memory and mechanical properties of polyurethane (PU) copolymers by changing the chain extender from 1,4-butanediol (BD) to ethylenediamine (ED) was investigated. PU copolymers composed of the different ratio of hard and soft segment were prepared and characterized by IR, DSC, XRD, and UTM. Glass transition temperature of PU increased to room temperature range by adopting ED as a chain extender. The XRD peak pattern changed with hard segment content. ED type PU achieved the high mechanical properties at lower hard segment content than BD type PU. Especially, strain at break of ED type significantly improved compared to BD type. Shape recovery rates were similar for both types of PU, but ED type showed better shape retention rate than BD type. The reason for the differences between two types of PU is discussed in this paper.     

Robust self-healing waterborne polyurethane coatings via dynamic covalent Diels-Alder bonds for corrosion protection

For waterborne polyurethanes (PUs), balancing robust mechanical performances and excellent self-healing ability is a great challenge. Here, we show that this goal can be achieved by a rational tuning of the PU chemistry. In particular, we synthesized an anionic self-healing waterborne PU using acetone process, in which 2,2-bis(hydroxymethyl)propionic acid (DMPA) serves as inner emulsifier, thermally dynamic Diels-Alder bonds act as healing motifs and hexamethylene diisocyanate trimer is the crosslinker. The mechanical performance can be tuned by increasing DMPA concentration due to the gradually increased hard segment contents and ionic interactions. The tensile stress and elongation at break of films containing 5.6 wt% of DMPA are 24.9 MPa and 911.9%, respectively. Moreover, dynamic reversible Diels-Alder bonds located in main chains and cross-linking points ensure excellent self-repairing capability. Upon mechanical damage, the tensile stress can be restored to 95% of its initial value. Electrochemical impedance spectroscopy also points out an outstanding barrier ability and excellent corrosion protection performance of the coatings, which can be recovered even after serious damages.     

Structure analysis of polyether-based thermoplastic polyurethane elastomers by FTIR, 1H NMR and 13C NMR

One kind of unknown structure sequence and composition ratio of thermoplastic polyurethane elastomers were characterized by nuclear magnetic resonance spectroscopy, Fourier transformed infrared spectroscopy, and gel permeation chromatography (GPC). The results showed that the polyurethane (PU) was obtained from poly(tetramethylene glycol) (PTMG) as soft segment, 1,4-butanediol (BDO) as chain extender, and 4,4′-methylenediphenyl diisocyanate (MDI) as hard segment. Furthermore, the composition ratio of MDI:PTMG:BDO was 2.07:1.22:1.00. At last, the molecular weight of PU was determined by GPC, and the number average molecular weight (M_n) and weight average molecular weight (M_w) are 63,300 and 133,800?g?mol^?1, respectively.     

Aqueous dispersion of polyurethane ionomers from hexamethylene diisocyanate and trimellitic anhydride

Polyurethane (PU) ionomers were prepared from trimellitic anhydride (TMA), poly(tetramethylene adipate) glycol (PTAd), and hexamethylene diisocyanate (HDI) in acetone. Upon neutralizing the carboxylic groups with a tertiary amine (TEA), and adding water to PU ionomer solution, followed by removing the acetone, stable aqueous PU dispersions were obtained.Effects of interionic molecular weight and nonionic hydrophilic segment, viz. monofunctional ethylene-propylene oxide ether on particle, size, emulsion viscosity, mechanical, and viscoelastic properties of the emulsion cast films were examined.     

正电子湮没谱研究聚烯烃聚氨酯的自由体积、微观结构和溶剂的扩散行为

用正电子湮没技术(PAS)结合示差扫描量热法(DSC)研究了聚烯烃聚氨酯的自由体积特征和微相分离结构的关系.结果表明,硬段含量增加,自由体积孔洞平均半径和自由体积分数减小;丁腈聚氨酯相分离程度小,相应自由体积孔洞平均半径和自由体积分数小,而丁羟聚氨酯的情况正好相反.石英弹簧法对苯和乙醇蒸气的溶解和扩散行为的研究表明,聚烯烃聚氨酯的自由体积孔洞平均半径和自由体积分数与苯和乙醇溶剂蒸气的无限稀释扩散系数呈正相关,但它们的无限稀释扩散系数和自由体积分数关系无法用Fujita的自由体积模型描述,可能归因于它们对聚烯烃聚氨酯复杂的溶胀行为.     

Segmented polyurethanes derived from novel siloxane–carbonate soft segments for biomedical applications

A novel macrodiol based on mixed silicone and carbonate chemistries was synthesized and used as a soft segment precursor in the synthesis of two series of segmented polyurethane (PU) copolymers varying in hard segment content and soft segment molecular weight. The hard segments in these copolymers were derived from 4,4‐methylene diphenyl diisocyanate and 1,4‐butane diol. The phase transitions, microphase separation behavior, and mechanical properties of the copolymers were investigated using a variety of experimental methods. When compared with segmented PU copolymers having predominately poly(dimethyl siloxane) soft segments, these siloxane–carbonate soft segment copolymers exhibit enhanced intersegment mixing, and consequently relatively low mechanical modulus. With relatively low modulus and siloxane units in the soft phase, the siloxane–carbonate PUs have potential for use in cardiac and orthopedic biomedical applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Preparation of high‐temperature polyurethane by alloying with reactive polyamide

A series of novel poly(urethane amide) films were prepared by the reaction of a polyurethane (PU) prepolymer and a soluble polyamide (PA) containing aliphatic hydroxyl groups in the backbone. The PU prepolymer was prepared by the reaction of polyester polyol and 2,4‐tolylenediisocyanate and then was end‐capped with phenol. Soluble PA was prepared by the reaction of 1‐(m‐aminophenyl)‐2‐(p‐aminophenyl)ethanol and terephthaloyl chloride. The PU prepolymer and PA were blended, and the clear, transparent solutions were cast on glass substrates; this was followed by thermal treatments at various temperatures to produce reactions between the isocyanate group of the PU prepolymer and the hydroxyl group of PA. The opaque poly(urethane amide) films showed various properties, from those of plastics to those of elastomers, depending on the ratio of the PU and PA components. Dynamic mechanical analysis showed two glass‐transition temperatures (T_g's), a lower T_g due to the PU component and a higher T_g due to the PA component, suggesting that the two polymer components were phase‐separated. The rubbery plateau region of the storage modulus for the elastic films was maintained up to about 250 °C, which is considerably higher than for conventional PUs. Tensile measurements of the elastic films of 90/10 PU/PA showed that the elongation was as high as 347%. This indicated that the alloying of PU with PA containing aliphatic hydroxyl groups in the backbone improved the high‐temperature properties of PU and, therefore, enhanced the use temperature of PU. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3497–3503, 2002     

Effect of the crosslink density on the morphology and properties of reaction‐injection‐molding poly(urethane urea) elastomers

The effect of the crosslink density on the morphology and properties of reaction‐injection‐molding poly(urethane urea) (PUU) elastomers was investigated. Fourier transform infrared spectroscopy data showed that the linear and crosslinked PUU had entirely different hard‐domain sizes and hard‐segment ordering. A study of the morphology indicated that an increase in the crosslink density increased microphase mixing. Differential scanning calorimetry studies indicated that the hard‐segment initial glass‐transition temperature was independent of the crosslink density. The glass‐transition temperature of the soft segment was highest when the network was perfect. The tensile‐strength behavior showed that the mechanical properties of PUU reached a maximum when the network was perfect. The increase in the resilience of the crosslinked PUU elastomer was higher than that of the linear PUU elastomer with an increase in temperature, and the reduction of the hardness of the former was also higher than that of the latter. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1126–1131, 2004