Low-temperature behavior of polyurethane elastomers

A study of the performance at low temperatures of various polyurethane elastomer systems, prepared from polyether and polyester diols with 2,4-toluene diisocyanate and 4,4′-methylenebis(2-chloroaniline), p,p′-diphenylmethane diisocyanate and 1,4-butanediol, and 4,4′-methylenebis(cyclohexylisocyanate) and methylenedianiline, has shown the polytetramethylene ether diols to impart the best low-temperature behavior to the elastomers. The properties studied were the apparent modulus of rigidity with the Clash and Berg torsional apparatus, the hardness with a Shore D Durometer, and the resiliency with the Bashore Resiliometer.     

高性能浇注型聚氨酯弹性体的耐热性能

用不同结构的多元醇和二异氰酸酯合成了一系列浇注型聚氨酯弹性体(PU),研究了PU的物理机械性能、耐热性和动态力学性能.结果表明,当二异氰酸酯选为对苯二异氰酸酯(PPDI)、扩链剂为1,4-丁二醇(BD)时,不同结构的多元醇制备PU的耐热性从优到劣依次为聚己内酯二醇体系,聚己二酸1,4-丁二醇酯体系,聚碳酸酯二醇(PCD)体系,聚四亚甲基醚二醇体系;当多元醇选取PCD、扩链剂为BD时,不同结构的二异氰酸酯制备PU的耐热性从优到劣依次为1,5-萘二异氰酸酯(NDI)体系,对苯二异氰酸酯(PPDI)体系,3,3'-二甲基联苯-4,4'-二异氰酸酯(TODI)体系,4,4'-二苯基甲烷二异氰酸酯(MDI)体系;TODI、NDI制备PU的动态力学性能优于PPDI和MDI制备的PU.     

Thermal stability of polyurethane elastomers before and after UV irradiation

In this work, we investigated the thermal degradation behavior of segmented polyurethane (PUR) elastomers before and after UV irradiation. The thermal degradation of PUR elastomers was studied over the temperature range of 25–600°C in an atmosphere of nitrogen using thermal gravimetric analysis (TGA). Four series of PUR elastomers derived from poly(oxytetramethylene)glycol (PTMO) of 1000 and 2000 molecular weight and poly(caprolactone glycol) (PCL) of 1250 molecular weight, 4,4′‐diphenylmethane diisocyanate (MDI), and 4,4′‐dicyclohexylmethane diisocyanate (H₁₂MDI) and 1,4‐butanediol as an chain extender were synthesized by the prepolymer method. The derivative thermogravimetric (DTG) peaks observed in the experiments indicated that PUR elastomers degraded through two steps. We attributed the first step to degradation of the hard segment. The second degradation step could be ascribed to degradation of the soft segment. We found that the PUR elastomers based on poly(ester polyol) and aromatic diisocyanate exhibit better thermal stability than that of PUR elastomers based on the poly(ether polyol) soft segment in both steps of degradation. The thermal degradation is more prevalent in PUR elastomers based on cycloaliphatic diisocyanate. The higher values of the temperature of initial decomposition (Tⁱ) indicate a higher thermal stability of UV‐exposed elastomers on the beginning of degradation. This may be due to the formation of a crosslinking structure in the presence of UV irradiation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 864–873, 2001     

Thermal degradation of film cast from aqueous polyurethane dispersions

In this paper, water‐dispersible polyurethanes based on isophorone diisocyanate and polytetramethylene glycol were synthesized, and their thermal degradation behavior under nitrogen and air was studied by thermogravimetric (TG) analysis. The influence of NCO/OH ratio and functional group concentration was discussed. The thermal decomposition kinetics under nonisothermal conditions was analyzed using Ozawa method. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2552–2558, 2002     

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.     

Thermal and mechanical properties of thermoplastic polyurethane elastomers from different polymerization methods

Thermoplastic polyurethane elastomers (TPUs) based on 4,4′-methylene-diphenyl diisocyanate, poly(tetramethylene glycol), diamine-terminated aliphatic nylon oligomer, and 1,4-butanediol were synthesized by two different polymerization methods, i.e. one shot and prepolymer methods. The effects of the polymerization method on the thermal and mechanical properties of the TPUs have been studied. A broader distribution of hard segment lengths in TPUs prepared by the one shot method was observed from thermal and tensile property measurements, compared with those prepared by the prepolymer method. TPUs by the one shot method showed a higher T_m of the hard segments and better tensile properties when soft-hard segment interaction was relatively small. However, inferior tensile properties were observed when the soft-hard segment interaction was high; typically when nylon oligomer was used as a soft segment.     

Strategy for kinetic parameter estimation—Thermal degradation of polyurethane elastomers

The kinetics of the thermal degradation of polyurethane (PU) elastomers based on poly(ether polyol) soft segments and an aromatic type of diisocyanate were investigated by thermogravimetric analysis (TGA) under a nitrogen atmosphere employing four heating rates. The corresponding kinetic parameters of the two degradation stages were estimated by minimizing the output error functional and by the Kissinger method. In evaluating the kinetic parameters of the two‐step PU thermal decomposition, a differential thermogravimetry curve was applied as an objective functional in a regression procedure. Parameter estimation was obtained by minimizing the weighted quadratic output error functional with the modified Nelder–Mead simplex search algorithm. The confidence regions in the preexponential factor‐activation energy space were established for both the first and second stages of degradation. The effect of the molecular weight of the soft segment and the content of the hard segment on the activation energy of the degradation process was constructed by response surface methodology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 764–772, 2007     

Thermal decomposition of polyester polyurethane and its elastomers exposed to γ-radiation

The thermal-decomposition parameters of unplasticized and nitrate ester plasticized polyester polyurethane elastomers with unsaturated carbon—carbon bonds in the initial state and after irradiation with doses of 120–380 kGy (γ-quanta ⁶⁰Co) were determined using dynamic thermogravimetry and differential scanning calorimetry. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 133–138, March–April, 2006.     

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.     

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。     

Thermal and mechanical properties of cast polyurethane resin based on soybean oil

The soy polyols were prepared from epoxidation of soybean oil followed by ring opening of oxirane obtained by using methanol as the ring opener. Polyols of hydroxyl (OH) numbers ranging from 128 to 174 mg of KOH/g were obtained by the variation of epoxidation time of soybean oil. A novel cast polyurethane resin has been synthesized by these polyols and 2,4‐toluene diisocyanate. Swelling of networks in toluene showed that the sol fraction varies from 1.13 to 72.06%. The thermal and mechanical properties of cast resins were characterized by differential scanning calorimetry and thermogravimetric analysis. The results showed that the glass transition temperature increases with the increase of OH number and that the thermal stability of the resins was slightly decreased with the increasing OH number. The tensile strength at break increases with the increase of OH number. Polyols with OH number of 174 mg of KOH/g gave glassy polymers, whereas those below this value gave rubbers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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。     

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     

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.     

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.     

Thermal and viscoelastic behavior of polyurethane/polyvinylchloride blends

The potential of melt processing polymer blends to prepare damping materials was investigated. Binary and ternary blends of polyvinylchloride (PVC) with thermoplastic polyurethane elastomers (TPU) were studied. The soft segments of the polyurethanes for the first series were of the ether type and of the ester type for the second series of blends. A series of polymer blends were prepared by mechanical melt mixing and the apparent miscibility was evaluated from the thermal, dielectric, and dynamic mechanical behavior as well as from transmission electron microscopy. Some samples exhibited a single damping peak at low PVC content, indicating miscibility of the blends at the detection scale of the test method. The relationship between the properties and the morphology of the blends was studied.     

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。     

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