Determination of the kinetic parameters for the polymerization of a polyurethane using an improved method of differential scanning calorimetry

The kinetic parameters for the polymerization reactions of two polyurethane systems were determined by using an improved method of differential scanning calorymetry (DSC). The calculated activation energy, reaction order, and Arrhenius prefactor show good correlation with the experimental results. The method used here shows several improvements as respects to other DSC methods: the three kinetic parameters can be calculated directly; it is more accurate than other DSC methods; and it requires only one heating rate, during the calorimetric experiments, to determine the activation energy.     

Comparison of thermal and infrared spectroscopic analyses in the formation of polyurethane,unsaturated polyester,and their blends

Differential scanning calorimetry (DSC) and infrared spectroscopy (IR) are two widely used techniques for the measurement of polymerization kinetics. Reactions of several thermoset polymers: a polyurethane, two unsaturated polyester resins, and polyurethane-polyester blends, were measured by these two methods. Results indicate that the thermal method is easy to use, and can generate both kinetic and thermal information. It is, however, less accurate and cannot detect detailed reaction mechanisms because the measurement relies upon the overall heat generation during reaction. Fourier transform infrared (FTIR) spectroscopy, on the other hand, can provide detailed kinetic information for multicomponent reactions such as styreneunsaturated polyester and polyurethane-polyester blends. Data analysis, however, is more tedious and requires reliable calibration. For an accurate kinetic measurement, both methods should be used because the results from both experiments can calibrate each other.     

聚氨酯柔性固化剂/环氧体系固化动力学及机理

通过不同升温速率下示差扫描量热分析(DSC)研究了自制的聚氨酯柔性固化剂ATPU/环氧树脂E-44体系的固化反应动力学及机理。通过Kissinger和Crane方程求解了表观活化能和反应级数等动力学参数,并运用该参数研究了固化反应速率常数、固化反应速率、固化度等的变化规律及影响因素。通过反应级数的研究证明了固化反应为一复杂反应,不同的固化交联反应同时发生,但主要进行的是伯氨基及仲氨基与环氧基之间的反应,该类反应使得体系得以固化。     

Effects of resin chemistry on redox polymerization of unsaturated polyester resins

Unsaturated polyester resins are the most widely used thermoset resins in the composite industry. In this study, three well‐defined unsaturated polyester resins were used. These resins have similar number‐average molecular weights, and they have different numbers of C?C bonds per molecule. The reaction kinetics of unsaturated polyester resins was studied using a differential scanning calorimeter (DSC) and a Fourier transform infrared (FTIR) spectrometer. The glass transition temperature of the isothermally cured resin was also measured. Trapped radicals were observed in the cured polyester resin from electron spin resonance (ESR) spectroscopy. Considering the diffusion‐limitation effect, a simple kinetic model was developed to simulate the reaction rate and conversion profiles of polyester vinylene and styrene vinyl groups, as well as the total reaction rate and conversion. Experimental results from DSC and FTIR measurements compare favorably with the model prediction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 211–227, 2002; DOI 10.1002/app.10317     

聚氨酯粉末涂料固化行为的研究

运用DSC方法研究了聚氨酯粉末涂料固化时的基本过程及原理.得出的结论表示-OH/-NCO摩尔比(文中简称树脂/固化剂摩尔比)在0.63～0.67时,固化反应有良好的平均速率;催化剂可以明显促进固化反应,但不改变反应的动力学模型.     

Synthesis,characterization and dielectric properties of nickel-based polyoxometalate/polyurethane composites

The aim of this study was to synthesis, characterization and investigation of the influence of the polyoxometalate concentrations (1, 3, 5 and 10 wt%) on chemical, thermal, physical and morphological properties of nickel-based polyoxometalate/polyurethane composite (Ni-POM/PU) materials. Firstly, nickel-based polyoxometalate (Ni-POM) compound has been synthesized and characterized through various spectroscopic techniques. Synthesized Ni-POM compounds have been used for preparation of polyurethane composites as a reinforcement. Three different Ni-POM/PU composites containing Ni-POM were prepared by solution mixing and casting techniques. The chemical structure and morphology of prepared Ni-POM/PU composite samples were confirmed by Fourier transform infrared spectroscopy (FTIR), elemental analysis and SEM techniques. Effects of Ni-POM on thermal stability, glass transition temperature, optical transparency, hydrophilicity and physical properties of polyurethane composites were examined. Thermal stabilities and glass temperatures of the materials have been checked by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). The SEM results confirmed the highly porous structure and the formation of Ni-POM structures in the polymer matrix. Synthesized composites showed high chemical stability, good processability, and low Tg values. The dielectric properties of the prepared Ni-POM/polyurethane composites were also investigated at room temperature. These results displayed that the dielectric constant of the POM/polyurethane composites decreased with the increase of the Ni-POM content in polymeric matrix.     

Sustained Release of Metoprolol Tartarate from Radiation-Grafted pH-Responsive Hydrogels

pH-responsive hydrogels composed of methacrylic acid (MAA) grafted on poly(ethylene oxide)-poly(vinylpyrrolidone)(PEO-PVP) network were made by electron beam irradiation technique. The grafting was carried out at various concentrations of MAA with different irradiation doses. The gels were characterized by IR, DSC and SEM techniques. The swelling behavior of the gels was studied under different pH conditions. The swelling parameters were evaluated. The mode of water diffusion into the gels was found to be structure-dependent. The pH responsiveness of the gels was evident from the enhanced swelling of the gels with increasing pH of the medium. The suitability of these gels as matrix materials for stimuli-responsive sustained-release drug formulations was studied. The in vitro release profile of an antihypertensive drug, metoprolol tartarate, from these gels was studied at pH 1.2 and 7.4. The extent of drug release is found to be pH-dependent. The data were analyzed to understand the mechanism of drug release from the gels. The gels exhibited diffusion-controlled release behavior. Drug release kinetic analysis indicated “first order” release where the amount of drug released is dependent on the matrix drug load and the value of the diffusion coefficient indicated anomalous diffusion.     

Properties of segmented polyurethanes derived from different diisocyanates

Various segmented polyurethane materials with a polyurethane hard segment (HS) content of 40 wt % were prepared by bulk polymerization of a poly(tetramethylene ether) glycol with M_n of 2000, 1,4‐butanediol, and various diisocyanates. The diisocyanates used were pure 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluene diisocyanate (T100), toluene diisocyanate containing 80% 2,4‐isomer and 20% 2,6‐isomer (T80), isophorone diisocyanate (IPDI), hydrogenated 4,4′‐diphenylmethane diisocyanate (HMDI), and 1,6‐hexane diisocyanate (HDI). The segmented polyurethane materials were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile properties, tear strength, and Shore A hardness. The DSC and DMA data show that the thermal transitions are influenced significantly by the diisocyanate structure. In the segmented polyurethane materials with aliphatic HS, the polyether soft segment (SS) is immiscible with the HS. However, in the segmented polyurethane materials with aromatic HS, the SS is partially miscible with the HS. The diisocyanate structure also influences the mechanical properties significantly and is described as the effect of symmetry and chemical structure of the HS. Various solution polymerized polyurethane resins with solid content of 30 wt % were also prepared and their thickness retention, water resistance, and yellowing resistance were determined for the evaluation of their usage as wet process polyurethane leather. The polyurethane resin with aliphatic HS show poorer thickness retention but better yellowing resistance. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 167–174, 2000     

Isothermal and temperature programmed kinetic studies of thermosets

Differential Scanning Calorimetry (DSC) is a popular method for the characterization of the cure kinetics of thermosetting materials. The experiments may be carried out under isothermal or temperature program modes. Several authors have pointed out the fact that the kinetic rate expressions for non-isothermal experiments must be different from the isothermal ones; however, this fact has been neglected in practice. In this work, we present a kinetic characterization of a thermosetting system using a phenomenological model for the reaction rate expression and DSC data from isothermal and non-isothermal experiments. In general, thermosetting materials exhibit the vitrification phenomenon which stops the reaction before complete conversion is achieved. Vitrification is taken into account in both Isothermal and temperature programmed experiments.     

聚氨酯改性中温快速固化环氧粘合剂的制备与应用

以聚四氢呋喃醚、异佛尔酮二异氰酸酯、2-乙基咪唑为原料,合成了以2-乙基咪唑封端的聚氨酯,并用于改性环氧树脂E-44.利用傅立叶红外分析仪、示差扫描量热仪、拉伸试验机等手段对其与环氧树脂混合物的凝胶时间、固化温度、解封情况、拉伸剪切强度等性能进行了研究.结果表明,咪唑封端的聚氨酯可以在130℃下较好地解封,每10份E-...     

Synthesis and thermal studies of block copolymers from NR and MDI‐based polyurethanes

Five series of block copolymers based on natural rubber and polyurethane were prepared from hydroxyl terminated liquid natural rubber (HTNR) and polyurethane (PU) formed by the reaction of diphenyl methane—4,4′—diisocyanate (MDI) with a chain extender diol, viz., ethylene glycol (EG)/propylene glycol (PG)/1,4‐butane diol (1,4‐BDO)/1,3‐butane diol (1,3‐BDO)/bisphenol A (BPA), by solution polymerization. Structural characterization of the block copolymers was done by infrared (IR) analysis. Thermal studies and kinetic analysis on thermal degradation of the block copolymers were undertaken with the view of characterizing them. Energy of activation and entropy change for the degradation were determined and a probable mechanism for the solid state degradation was suggested which corresponds to a three dimensional diffusion mechanism. DSC analysis has been used for the study of microphase separation in the block copolymers. Thermal transition of the hard segment significantly varies with the extender diol which highlights the effect of extender diol structure on the chain stiffening mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheokinetic of polyurethane crosslinking time-temperature-transformation diagram for rotational molding

In this work, the rheokinetic of polyurethane crosslinking was studied by different methods: differential scanning calorimetric (DSC), rheometry, and infrared spectrometry. The conversion ratio and the glass transition temperature were followed by time of reaction. The results of the isothermal and nonisothermal test were compared. The evolution of viscosity was measured at different frequencies. The intersection of these curves is considered as gel point. A simplified mechanism has been proposed for crosslinking reactions. Based on this mechanism, a kinetic model describing the evolution of reactive system was developed. This model then was compared with the results of experiments performed by infrared spectrometry. The time-temperature-transformation diagram was established showing the evolution of physical state change of the reactive system. This diagram may be used to evaluate the zone of rotomoldability of the reactive polyurethane. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Relationship on structure and properties of polyurethane modified Diels–Alder addition polymer

A series of linear and crosslinked polyurethane modified materials were prepared by Diels–Alder cycloaddition reaction. Based on raw materials, some novel equations were designed and effects of equation parameters on the mechanical properties of modified material were explored. It was demonstrated that tensile strength of modified materials and elongation at break were changed from 3.68 to 18.71 MPa, 200 to 866%, respectively. In addition, the optimal reaction temperature of retro-Diels–Alder (r-DA) reaction was determined by differential scanning calorimeter (DSC). Gel permeation chromatography (GPC) and tensile experiments were used to characterize the properties of repolymerized material after degradation. The results indicated the optimal temperature of r-DA for linear and crosslinked polyurethane modified materials is 127 and 150 °C. Moreover, after decomposed, the product was slowly repolymerized at 60 °C, and can more effectively restore material strength under the action of the solvent to achieve self-healing effect. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47355.     

油酸存在下的聚氨酯(脲)固化动力学

采用差示扫描量热法(DSC)研究了油酸存在下聚氨酯(脲)固化过程反应动力学参数.利用Kissinger法求得不同油酸含量固化反应的表观活化能Ea,Crane方程计算该体系的固化反应级数n.结果表明,加入油酸后固化体系的活化能减小,油酸为聚氨酯(脲)固化反应的催化剂;油酸质量分数为0.9%时,固化反应的E.为27.91 ...     

Kinetic Parameters of PBX Based on Cis‐1,3,4,6‐tetranitroocta‐hydroimidazo‐[4,5‐d] imidazole Obtained by Isoconversional Methods using Different Thermal Analysis Techniques

The thermal decomposition kinetics of the interesting polycyclic nitramine cis‐1,3,4,6‐tetranitrooctahydroimidazo‐[4,5‐d]imidazole (BCHMX) and its polymer bonded explosive (PBX) based on polyurethane matrix, have been investigated using different thermal analysis techniques and methods. The used polyurethane matrix is based on hydroxyl‐terminated polybutadiene (HTPB) cured by hexamethylene diisocyanate (HMDI). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used nonisothermally, whereas the vacuum stability test (VST) was used isothermally. Kinetic parameters were determined by using isoconversional (model‐free) methods. Furthermore, the Advanced Kinetics and Technology Solution (AKTS) software was used to determine the kinetic parameters of the studied samples in order to provide a comparison. It was found that the decomposition temperature of BCHMX/HTPB is lower than that of pure BCHMX. All the applied techniques as well as computational results showed that BCHMX/HTPB has a lower activation energy than pure BCHMX. The different methods used, Kissinger, Ozawa, Flynn, and Wall (OFW) and Kissinger‐Akahira‐Sunose (KAS) methods presented activation energies in the same range of the AKTS software results. Also the results proved that VST technique could be a useful tool to present results suitable for calculation of the kinetic parameters of explosives.     

PEG对生物可降解聚氨酯性能影响的研究

以不同相对分子质量的聚乙二醇(PEG)为引发剂,通过开环聚合引发丙交酯和己内酯单体合成聚己内酯–丙交酯–聚乙二醇(PCLA–PEG)的共聚物;用六亚甲基二异氰酸酯(HDI)对合成的共聚物进行封端,并进行扩链反应制备一系列PEG含量不同的生物可降解聚氨酯。通过红外以及DSC研究了PEG含量对聚氨酯材料结构的影响,发现采用相对分子质量较高的PEG制备的材料,其软硬段相分离程度较高;另外对样品的力学性能、亲水性及降解性进行了测试,发现PEG含量增加,样品的力学性能下降,亲水性能提高,降解速度加快。     

A nonisothermal differential scanning calorimetry study of the curing kinetics of an unsaturated polyester system

Nonisothermal differential scanning calorimetry (DSC) measurements were used to estimate the kinetic parameters for the curing reaction of a commercial unsaturated polyester resin. The reaction rate expression was derived from a mechanistic kinetic model based on the concept of free radical polymerization, accounting also for the diffusion controlled reaction. The total heat of reaction was evaluated in experiments run at very low scan speeds and using high amount of initiator. The kinetic parameters were found to show no dependency on the heating rate nor on the initiator concentration. Dynamic DSC measurements provide reliable kinetic data over a broad range of temperatures that is mostly significant for process simulations.     

Comparative Properties of Hydrophilic and Hydrophobic Fumed Silica Filled Two-Component Polyurethane Adhesives

Two fumed silicas, one hydrophilic and another hydrophobic, were added to a two-component polyurethane (PU) adhesive and their properties compared. The filled polyurethanes were characterized by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and water and diiodomethane contact angle measurements. The adhesive strength was evaluated from single lap-shear tests of solvent wiped stainless steel/polyurethane adhesive joints. The fumed silicas were well-dispersed in the polyurethane matrix as bundles of nanometric spherical silica particles. However, some micron size agglomerates of fumed silica appeared in the filled polyurethane. The addition of fumed silica favoured the degree of phase separation between the hard and the soft segments in the polyurethane. The polyurethanes were not fully cured under the conditions used in this study and the addition of fumed silica inhibited the curing reaction; the extent of the curing reaction was not affected by the hydrophilic or hydrophobic nature of the fumed silica. The filled polyurethanes were further cured during DSC experiments and this was noticed by the appearance of the melting of the hard segments and the displacement of the second glass transition to a higher temperature. On the other hand, the addition of fumed silica increased the wettability and the surface energy of the polyurethane; this increase was mainly due to an increase in the polar component of the surface energy. The increase in surface energy is somewhat more marked in the case of the hydrophilic silica filled polyurethane, indicating that the polarity of the fumed silica affected the surface properties of the polyurethane. Finally, the addition of the hydrophilic fumed silica increased the adhesion of the filled polyurethane adhesive to stainless steel which was in agreement with the higher surface energy of the hydrophilic fumed silica filled polyurethane.     

Synthesis and properties of polybenzoxazine modified polyurethanes as a new type of electrical insulators with improved thermal stability

A new class of electrical insulating materials with improved thermal stability was prepared from combination of polybenzoxazine with epoxy terminated polyurethane prepolymer (EPU). EPU was prepared by the reaction of glycidol with NCO‐terminated urethane prepolymer. The prepolymer was prepared from polycaprolactone polyol (molecular weight 1000), and hexamethylene diisocyanate. Bisphenol‐A and aniline were used for preparation of benzoxazine monomer. Mode of reactions and optimum curing condition were determined by DSC and FTIR analysis. Upon these analysis as well as DMTA findings, formation of interpenetrating polymer networks was suggested for blends consisted different weight ratios of two components. Viscoelastic behavior, mechanical, thermal, and electrical properties of the prepared samples was studied and their relation to the chemical structure and composition of blends were elucidated. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

环氧粉末涂料的固化动力学和固化工艺的研究

采用非等温示差扫描量热法(DSC)研究了E-12/双氰胺(固化剂)和E-12/双氰胺/2-甲基咪唑(促进剂)体系的固化反应动力学。采用Kissinger法和Crane公式对DSC数据进行处理,获得了固化反应动力学参数,应用热重分析(TGA)研究了固化产物的热稳定性。结果表明:双氰胺、2-甲基咪唑的最佳用量分别为环氧树脂质量的4%和0.4%,最佳固化条件为160℃/15min。E-12/双氰胺体系和E-12/双氰胺/2-甲基咪唑体系的表观活化能分别为105.12kJ/mol和70.62kJ/mol,固化反应级数n=0.92。起始分解温度约为410℃,促进剂2-甲基咪唑的加入对体系热稳定性没有影响。