Thermal behavior of cast polyurethane elastomers

Thermal properties like glass transition temperature (T_g), initial decomposition temperature (idt), integral procedural decomposition temperature (ipdt), and temperature at various % weight loss of a number of polyurethane systems are reported in this paper. Glass transition temperature was determined on TMA, and other thermal properties were determined by thermogravimetry. The experiments were designed to understand various factors such as length of chain extender moiety, flexibility of chain extender units by substitution of ether link in the diol chain, nature of bonds (unsaturation) in the extender unit, and nature of diisocyanates.     

Relationship between nanoscale deformation processes and elastic behavior of polyurethane elastomers

The cyclic deformation of two polyurethane elastomers that differed in soft segment content and molecular weight was investigated. The microphase-separated morphology of the polyurethane with higher soft segment content consisted of hard segment domains dispersed in a soft segment matrix. In the polyurethane with lower soft segment content, the hard segment domains appeared to be partially cocontinuous. Following an initial ‘conditioning’ cycle, both polyurethanes exhibited reversible elastomeric behavior. Structural changes that occurred during conditioning were investigated using atomic force microscopy and Fourier transform infrared dichroism. The results provided the basis of a structural model for the deformation behavior. Yielding and reorganization of hard domains resulted in a highly oriented microfibrous morphology. Subsequent unloading and reloading were associated with reversible relaxation and reformation of the microfibrous entities. The elastic behavior of the conditioned polyurethanes was satisfactorily described by classical rubber theory with inextensibility. The structural model proposed here extended previous efforts to describe the deformation processes of polyurethanes during cyclic loading.     

聚氨酯弹性体的新进展

简要分析了近几年来国内外聚氨酯弹性体的投资、生产和消费情况,综述了聚氨酯弹性体生产技术及应用方面的进展情况。     

Characterization of polyurethane network elastomers

Polyester urethane network elastomers with incorporated hard segment oligomers have been prepared by poly(ethylene adipate)glycol (PEA), 2,4-tolylene diisocyanate (TDI), and 1,4-butanediol (BD). These hard segment oligomers were hydroxy-terminated oligomers ([BD-TDI]n-BD; n=1,3), obtained by reacting BD with TDI. Concentrations of allophanate as a cross-linking site were determined by the amine degradation method. Hard segment moieties were obtained by a novel selective hydrolysis of soft segments in the elastomers. Molecular weight distributions of hard segment were measured by means of GPC. Mechanical and thermal properties were measured. Dependence of rubber elasticity on physical cross-linking between normal elastomers and the elastomers with incorporated hard segment oligomers were discussed.     

耐热型聚氨酯弹性体的合成

催化合成了甲苯二异氰酸酯的部分三聚体异氰脲酸酯,然后与聚醚二元醇反应,用二步法手工浇注成异氰脲酸酯改性的聚氨酯弹性体。用红外光谱法证实了产物中异氰脲酸酯的存在。根据用二正丁胺法测得的NCO基团的质量分数可计算出异氰脲酸酯的质量分数,用热重法分析了产物的热稳定性。结果表明,与普通聚氨酸弹性体相比,合成的改型聚氨酯弹性体的热稳定性得到了明显提高。     

Microstructure of as-polymerized thermoplastic polyurethane elastomers

Ten segmented polyether-urethane thermoplastics were studied in the as-polymerized state. Polyethersegment, number-average molecular weight and molecular weight distribution were varied among the set of polymers, as were the molar ratios of diisocyanate to diol chain extender to polyether glycol. Experimental techniques included differential scanning calorimetry, dynamic mechanical analysis, volume-temperature measurements, X-ray diffraction and hot-stage, polarized-light microscopy. At room temperature the materials possessed non-impinging spherulites, about 10 μm in diameter, in a non-birefringent matrix. X-ray diffraction from these same films showed no crystallinity, except in two cases. The spherulites irreversibly disappeared in the temperature range 350–400 K, accompanied by sharp decreases in dynamic modulus and a small thermal transition. Thermal disruption of urethane-dominated domains was observed at considerably higher temperatures, from 400–520 K, depending on molecular structure. Polyether crystallite melting was seen only below 305 K. These observations can be explained by a polymerization-solidification scenario which assumes: (1) de-mixing of isocyanatecapped prepolymers to form spatial gradients based on the urethane weight fraction of the prepolymer chains, and (2) decomposition of the polymerizing melt by nucleation and growth on a molecular scale to form polyurethane-rich spherulites during the reaction.     

Rheological characterization of thermoplastic polyurethane elastomers

The relationship between the rheological properties and composition of eight thermoplastic polyurethane elastomers (TPUEs) was evaluated using a stress‐controlled rheometer. The composition of the TPUEs was changed by varying the OH/NCO ratio, the chain extender and the molecular weight of the macroglycol used in the synthesis. A high molecular weight macroglycol and a low OH/NCO ratio improved the rheological properties of the TPUEs due to the formation of longer or more abundant soft segments, respectively. The nature of the chain extender influenced the rheological properties to a lesser extent. © 2000 Society of Chemical Industry     

Fluorescently labeled degradable thermoplastic polyurethane elastomers: Visual evaluation for the degradation behavior

Thermoplastic polyurethane elastomers (TPU) were synthesized with isophorone diisocyanate (IPDI) as the rigid segment, poly(lactic‐co‐glycolic acid) (PLGA‐PEG‐PLGA) diol as soft segment, and 1,4‐butanediol (BDO) as the chain extender. During the chain extension process, three kinds of fluorescent monomers 4‐(2‐hydroxyethylamino)?1,8‐naphthoyl‐(2‐hydroxyethyl)imide (HNHI), 1,5‐dihydroxy naphthalene (DHN), and dicoumarin (DIC) were introduced to get the fluorescently labeled degradable TPUs. The structure and degradation properties of the TPUs were characterized in detail. The results showed that there was no significant effect found on average molecular weight, mechanical properties, and glass transition temperature of polyurethane by introducing 0.001% (wt) weight percent of fluorescence monomers. The degradation behavior of fluorescent‐tagged thermoplastic elastomer has been characterized with fluorescence microscopy. Results showed that polyurethane elastomers, in which fluorescence monomers especially HNHI were introduced by chemical reaction, had more homogeneous and stable fluorescence intensity than that with fluorescence monomers introduced by post blending. This work also provides a promising visual characterization approach to monitor degradation behavior of degradable TPUs for tissue engineering applications or drug delivery system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42519.     

Segmented polyurethane elastomers by nonisocyanate route

Novel segmented polyurethane elastomers were successfully synthesized by a nonisocyanate route using dicyclic carbonates as precursors for both soft and hard segments. The hard segment was prepared from the dicyclic carbonate of bisphenol A and m‐xylylenediamine as chain extender. The soft segment was poly(tetramethylene ether) glycol of molecular weight 1000. Three polyurethanes with different morphologies were made with soft segment concentration of 70, 50, and 30%. Method of synthesis consisted in preparation of dicyclic carbonate of bisphenol A from a commercial epoxy resin and carbon dioxide, while dicyclic carbonate of poly(tetramethylene ether) glycol (PTMEG) was made from previously prepared diglycidyl ether of PTMEG and carbon dioxide. Polymers were prepared by reacting dicyclic carbonates with m‐xylylenediamine by one‐pot process. The monomers and polymers were characterized by Fourier transform infrared spectroscopy, differential scanning chromatography, thermogravimetric analysis, ¹H NMR, ¹³C NMR, scanning electron microscopy, and mechanical measurements. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42492.     

Correlations between chemical structure,stress-induced crystallization,and deformation behavior of polyurethane elastomers

The deformation behavior of polyurethane elastomers depends strongly on physical interactions. In this paper the stress-induced crystallization of the polyester or polyether segments in investigated in several polyurethane elastomer systems having different chemical structure for the soft segments. The correlation between the tensile properties (hysteresis loss, extension set, modulus) and the stress-induced crystallization is discussed.     

聚氨酯弹性体耐热性的影响因素

讨论了多异氰酸酯，聚合物多元醇，扩链剂，分子内基团，杂环，离子基团对聚氨酯弹性体耐热性能的影响。指出开发新原料，引入热稳定杂环，严格控制反应条件和原料的纯度及配比，是提高聚氨酯弹性体耐热性的有效途径。     

热熔胶用聚氨酯弹性体的合成

以4,4’-二苯基甲烷二异氰酸酯（MDI）、聚乙二醇（PEG）和I,4-丁二醇（BIDO）为原料合成聚氨酯弹性体,采用流延法制备了热熔胶膜。考察了预聚反应的温度、时间对聚氨酯弹性体性能的影响,并对预聚体中NCO含量、异氰酸酯指数（R）、聚醚多元醇的种类以及相对分子质量等进行了探讨。确定了最佳反应条件：反应温度为（80±5）℃;反应时间为1．5～2．0h。预聚体中NCO质量分数控制在9％～10％,R值取1．02,选用相对分子质量为1500的PEG制备的热熔胶用聚氨酯弹性体性能优异。     

Fireproofing of polyurethane elastomers by reactive organophosphonates

Polyurethane elastomers were prepared with hydroxytelechelic polybutadiene (HTPB) as polyol, modified 4,4′‐diphenylmethane diisocyanate (modified MDI) as liquid polyisocyanate, and phosphonate diols as chain extenders and flame retardant compounds. These phosphonate diols were synthesized by radical thiol–ene addition of allyl or vinyl dialkyl phosphonate to 3‐mercapto‐1,2‐propanediol. For various percentages of phosphorus (0 to 3%, w/w), polyurethane elastomers remain stable up to 250 °C. The percentage of residual char at 600 °C increases with increasing phosphorus content. For the soft segments, no variation in the glass transition temperature (T_g) is observed as the percentage of P increases, whereas the T_g of hard segments increases. Above 0.5% phosphorus content, the limiting oxygen index (LOI) becomes higher than the percentage of oxygen in the air. © 2003 Society of Chemical Industry     

Effect of side methyl groups of polymer glycol on elongation-induced crystallization behavior of polyurethane elastomers

Effect of side methyl and dimethyl groups of soft segment component on polyurethane elastomers (PUEs) was investigated with and without elongation. The polymer glycols used were poly(oxytetramethylene) glycol (PTMG), PTMG with dimethyl groups (PTG-X) and methyl groups (PTG-L). Phase separation of the PUEs became weaker with an increasing methyl group content. Tensile test revealed that the increasing methyl group concentration made the PUEs be soften and weaken. The PTMG based PUEs obviously exhibited elongation-induced crystallization during elongation process. In contrast, for the PTG-L and PTG-X based PUEs, crystallinity decreased with an increasing side methyl group content, and the PUEs with PTG-L and PTG-X with highest methyl group content did not crystallize. We succeeded the control of the crystallization behavior of elastomers under an elongation by the introduction of side methyl groups.     

Aliphatic polyurethane elastomers with high performance properties

A new diisocyanate, 1,4-eyclohexane diisocyanate (CHDI), has been used in a series of polyether-based polyurethane elastomers. The slightly opaque samples are semicrystalline in nature with high performance properties, including high softening temperature, very good thermal stability, high tensile and tear strengths, excellent solvent resistance, and low hysteresis in compressive fatigue. Polymer properties are in part due to the small, compact, symmetrical structure of the aliphatic CHDI. Comparison of the physical, mechanical, and thermal properties of polyurethanes prepared from the aliphatic diisocyanate 4,4′-dicyclohexylmethane dilsocyanate (H₁₂MDI) reveal the H₁₂MDI polymers to be more flexible and transparent elastomers with lower softening temperatures and tensile moduli and higher hysteretic heat build up. They are generally soluble in organic solvents.     

聚醚-聚硅氧烷嵌段共混聚氨酯弹性体的研究

用共聚混合法制成聚硅氧烷-聚醚型嵌段聚氨酯,结果表明:在聚合物主链引入硅氧烷后,弹性体力学性能略有升高,对三元乙丙橡胶,异戊二烯橡胶的粘合剥离强度得到提高。NCO/OH当量比、硅氧烷和MOCA用量对材料的物理性能有很大的影响。DSC的分析表明,引入的聚硅氧烷链段主要分布于弹性体分子中的软段,使弹性体的相分离更加明显。     

Recycled polyurethane elastomers: a universal adhesive

The practical application of the glycolysis mixture of polyurethane wastes is reported. It was found that in the presence of 4,4′-diphenylmethane diisocyanate (MDI) both the separated upper phase of the glycolysis mixture and the complete two-phase reaction mixture could be used as components of the urethane adhesive mixtures for bonding woods, metals, plastics, glass, ceramics, paper and leather. The adhesive properties were determined by tensile-cutting, cutting- and bending strengths, as well as peel resistance measurements. The method to use the complete glycolysis mixture is also reported. The reaction mechanism of bonding is also discussed.     

Thermoplastic polyurethane elastomers from modified oleic acid

Two novel potentially biodegradable thermoplastic polyurethane elastomers with unique structure and morphology were prepared from modified oleic acid. The hardness and mechanical properties were controlled by adjusting the soft segment concentration (SSC). Epoxidized methyl oleate was converted to methyl‐9‐ or ?10‐hydroxystearate (hydroxystearate) by catalytic hydrogenation. The formed hydroxystearate was transesterified with 1,6‐hexanediol to obtain polyesterpolyol with molar mass 2500. Segmented polyurethanes with 50% and 70% SSC were prepared using the prepolymer method by reacting polyesterpolyol with diphenylmethane diisocyanate and 1,4‐butanediol as chain extender. Thermal and mechanical properties of the polymers indicated good micro‐phase separation. Both soft and hard segments displayed a certain degree of crystallization. Tensile strengths were 18 and 2.4 MPa for samples with 50% and 70% SSC, respectively. Elongations of 130% (50% SSC) and 43% (70% SSC) were somewhat lower than in comparable materials, presumably due to lower molar mass. © 2014 Society of Chemical Industry     

高性能材料-CHDI型聚氨酯弹性体

1，4-环己烷二异氰酸酯(CHDI)分子高度简洁、规整和对称，合成的聚氨酯弹性体相分离度极好，有着优异的机械和物理性能。笔者论述了CHDI的性质和制备方法，讨论了CHDI型聚氨酯弹性体的合成工艺和性能。     

聚氨酯弹性体耐热性的影响因素

耐热性是聚氨酯弹性体的一项重要性能指标。微相分离结构对聚氨酯弹性体的耐热性能有很大的影响。主要介绍了聚氨酯弹性体微相分离结构及其他因素对其耐热性的影响。介绍了聚氨酯弹性体耐热性的改性方法。提高微相分离程度是改善其耐热性的重要方法之一。