Kinetics of Michael addition polymerizations of n,n′‐bismaleimide‐4,4′‐diphenylmethane with barbituric acid

With the addition of sufficient hydroquinone to completely suppress the free radical polymerization, the kinetics of Michael addition polymerizations of N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) and barbituric acid (BTA) with BMI/BTA = 2/1 (mol/mol) in 1‐methyl‐2‐pyrrolidone was investigated independently. A mechanistic model was developed to adequately predict the polymerization kinetics before a critical conversion (ca. 60%), at which point the diffusion‐controlled polymer reactions started to predominate in the latter stage of polymerization. The Michael addition polymerization rate constants and activation energy in the temperature range 383–423 K were determined accordingly. Beyond the critical conversion, a relatively stationary limiting conversion (ca. 69%) independent of the reaction temperature was achieved. A diffusion‐controlled polymerization model taken from the literature satisfactorily predicted the limiting conversion data. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Cure kinetics of epoxy resin and aromatic diamines

The kinetics of curing reaction of a diglycidyl ether of a bisphenol‐A based epoxy (DGEBA) with 4,4′‐diaminostillbene (DAS) and 4,4′‐diaminoazobenzene (DAAB) as curing agents are studied by differential scanning calorimetery (DSC) using the isothermal technique. The experimental data show that the cure reaction is autocatalytic in nature, and all kinetic parameters of the curing reaction are determined using a semiempirical equation. The reaction of DGEBA with DAS is faster than that with DAAB under the same conditions and the activation energies of both systems are higher than those reported for other aromatic diamines. With increasing isothermal temperature and concentration of curing agents the rate constants are increased by the increasing of probability collisions between epoxide and primary amine groups while the activation energies remain constant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1049–1056, 2004     

Kinetic evaluation of tin‐POMS catalyst for urethane reactions

We report the activity for a new tin‐polyhedral oligomeric metal silsesquioxane (POMS) catalyst in 1‐butanol and 2‐butanol model reactions with 4,4′‐methylenebis(cyclohexylisocyanate) (H₁₂MDI) in toluene and N,N‐dimethylformamide (DMF). Kinetic rate constants for varying levels of tin‐POMS ranging between 100 ppm and 1000 ppm tin are reported. We observed urethane reactions in toluene to follow second order reaction kinetics, whereas similar reactions in DMF followed first order reaction kinetics. We determined tin‐POMS is an efficient catalyst system for urethane reactions and found the new catalyst to be easy to handle, soluble, and very effective for catalyzing urethane reactions. By direct comparison of a model reaction between tin‐POMS and dibutyltin dilaurate (DBTDL), tin‐POMS was found to be quite similar to DBTDL for urethane catalytic activity. In addition, we show the efficacy for tin‐POMS to be an excellent polyurethane reaction catalyst through a model reaction of H12MDI with 2000 g/mol poly(ε‐caprolactone) diol. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Primary Hydroxyl Content of Soybean Polyols

Polyurethanes are obtained by reacting polyols with polyisocyanates. The primary hydroxyl content is a very important characteristic of polyols because it affects their reactivity. Typically primary hydroxyls are approximately threefold more reactive than the secondary hydroxyls when reacting with aromatic isocyanates. This paper presents a simple and convenient kinetic method for determining the primary hydroxyl content in soybean polyols, based on the difference in reactivity of primary and secondary hydroxyls with phenyl isocyanate (PI). The reaction kinetics were studied by following the disappearance of the NCO band at 2260 cm⁻¹ with time in the infrared spectra. The reaction of PI with soybean polyols was carried out in a toluene:dimethylformamide (9:1, v/v) mixture. The relative error of the method is in the range of ±5%. The method is characterized by simplicity and good reproducibility, and it can be applied to all soybean polyols irrespective of their structure.     

Synthesis and characterization of novel optically active poly(amide‐imide)s

4,4′‐(Hexafluoroisopropylidene)‐bis‐(phthalic anhydride) (1) was reacted with L ‐leucine (2) in toluene solution at refluxing temperature in the presence of triethylamine and the resulting imide‐acid (4) was obtained in quantitative yield. The compound (4) was converted to the diacid chloride (5) by reaction with thionyl chloride. The polymerization reaction of the imide‐acid chloride (5) with 1,6‐hexamethylenediamine (6a) , benzidine (6b) , 4,4′‐diaminodiphenylmethane (6c) , 1,5‐diaminoanthraquinone (6d) , 4,4′‐sulfonyldianiline (6e) , 3,3′‐diaminobenzophenone (6f) , p‐phenylenediamine (6g) and 2,6‐diaminopyridine (6h) was carried out in chloroform/DMAc solution. The resulting poly(amide‐imide)s were obtained in high yield and are optically active and thermally stable. All of the above compounds were fully characterized by IR, elemental analyses and specific rotation. Some structural characterization and physical properties of those optically active poly(amide‐imide)s are reported. © 1999 Society of Chemical Industry     

Rheo‐kinetic measurement of thermoplastic polyurethane polymerization in a measurement kneader

The rheo‐kinetics of thermoplastic polyurethane (TPU) formation was investigated in a measurement kneader at high temperatures. The TPU was made of a polyester polyol, methyl‐propane‐diol and a 50/50 mixture of 2,4′‐ and 4,4′‐diphenylmethane diisocyanate (MDI). The reaction proceeded according to a second order reaction for which the kinetic constants were determined by size exclusion chromatography (SEC) analysis. The activation energy was found to be equal to 61.3 kJ/mol, and the pre‐exponential factor was equal to 2.18e6 mol/kg K. For the temperature range under investigation, the flow activation energy was equal to 42.7 kJ/mol, which is comparable to that of a linear polymer. This indicates that the hard segments are completely dissolved at the temperatures investigated. The initial part of the reaction was much faster than anticipated from the kinetic measurements. Diffusion limitations at higher conversions probably cause this decrease in reaction velocity. At longer reaction times, the molecular weight leveled off because of depolymerization. Therefore, additional experiments are necessary to describe the complete polymerization of thermoplastic polyurethane. Polym. Eng. Sci. 44:1648–1655, 2004. © 2004 Society of Plastics Engineers.     

DGEBF/DDS体系固化动力学机理的研究

以4,4′-二氨基二苯砜(DDS)胺类固化剂固化9,9-二[4-(2,3环氧丙氧基)苯基]芴(DGEBF),采用非等温DSC法推导了固化反应参数和固化机理,并用原位红外和移动窗口二维相关红外分析对固化机理和固化模式进行了验证。结果表明:DGEBF/DDS体系固化反应的表观活化能为64.08 kJ/mol,扩散因子为4.05×104s-1,反应级数为1.55;固化工艺为150℃/1.5 h+190℃/2 h+220℃/1.5 h;固化模式为枝状成核的自催化反应;固化机理为伯胺先与环氧基反应生成仲胺,肿胺继续与环氧基反应生成叔胺,2个反应同时进行,以及在高温下的羟基与环氧基的自催化反应,交联的固化网络逐渐形成。     

New segmented polyurethane ureas based on 4,4′-dicyclohexylmethane diisocyanate and on various soft segments

Linear segmented polyurethane ureas were prepared from 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), 4,4′-diamino-3,3′-dicyclohexyl methane (3DCM), and various hydrophilic and hydrophobic soft segments. Kinetic studies of the synthesis of the diisocyanate-terminated prepolymers revealed that the use of too little reactive polyols (that is, polyoxypropylene that bears secondary hydroxyls) could be rather tricky; the noncatalyzed reaction is very slow, but the use of a catalyst soon triggers the formation of side products, and the processing window consequently becomes quite short. Microcalorimetric and dynamic mechanical measurements showed that all the materials were highly phase-segregated elastomers and displayed good mechanical properties up to high temperature (typically 180°C), provided that they had been postcured properly; in this respect, the dramatic effects of isolated (nonchemically linked) hard segments, as well as of too low postcuring temperatures, were demonstrated. Polyurethane ureas compare well with polyureas, and their synthesis can be a good way to cope with the lack of well-adapted commercial diamino-terminated prepolymers. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2331–2342, 1998     

Cure kinetics of neat and graphite-fiber-reinforced epoxy formulations

An investigation was carried out into the cure kinetics of neat and graphite fiber-reinforced epoxy formulation, composed of tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM) resin and diaminodiphenyl sulfone (DDS) curing agent. Two experimental techniques were employed: isothermal differential scanning calorimetry (IDSC) and dynamic differential scanning calorimetry (DDSC). An autocatalytic mechanism with the overall reaction rate order of 2 was found to describe adequately the cure kinetics, of the neat resin and the composite. All kinetic parameters, including reaction rate constants, activation energies and preexponential factors, were calculated and reported. The presence of graphite fibers in the composite had only a very small initial effect on the kinetics of cure.     

Polycondensation kinetics of poly(phenylene ether sulphone)

The synthesis of poly(phenyl ether sulphone) (from the potassium salts of 4,4′-dihydroxydiphenyl sulphone and 4,4′-dichlorodiphenyl sulphone or 4-chloro-4′-hydroxydiphenyl sulphone) was found to have different reaction kinetics according to the route used. By discriminating between rate constants (between monomer/monomer, monomer/polymer, polymer/polymer) a set of multi-parameter kinetic equations is obtained. Experimental and simulated values of the individual rate constants were in good agreement (for both the reaction rate and molecular weight distribution). The polycondensation reaction can be analysed, in terms of the component reactions.     

Cure kinetics and modeling of an epoxy resin cross‐linked in the presence of two different diamine hardeners

An epoxy resin diglycidyl ether of bisphenol A (DGEBA) is cross‐linked with the help of two aromatic diamine 4,4′‐diaminodiphenylsulfone (DDS) + 4,4′‐methylenebis 3‐chloro 2,6‐diethylaniline (MCDEA) of nearly equal flexibility but different reactivities. The ratio of the two amines is varied while keeping the stoichiometry of the epoxy/amino hydrogen groups constant. The experimental cure kinetics are studied at four different isothermal temperatures. Their modeling is carried out by a phenomenological Kamal‐Sourour kinetic model. The procedure is two‐fold: 1) linear combinations of the values of rate constants from the two neat thermosets (based on only one amine) and 2) values calculated directly from isothermal cures of reactive amine mixtures. A good correlation was observed between the experimental data and the model predictions (both procedures). These amine formulations provide “mixed” epoxy thermosets and will be used later to control thermoset/thermoplastic blend morphologies for which reaction kinetics need to be predicted. POLYM. ENG. SCI. 45:1581–1589, 2005. © 2005 Society of Plastics Engineers     

Addition polyimides. I. Kinetics of cure reaction and thermal decomposition of bismaleimides

The thermal polymerization of four structurally different bismaleimide resins, prepared by reacting maleic anhydride with four aromatic diamines, viz., 4,4′-diaminodiphenyl methane, 4,4′-diamino diphenyl ether, 4,4′-diamino diphenyl sulfone, and 3,3′-diamino diphenyl sulfone, was followed by differential scanning calorimetry (DSC). The enthalpy change and the kinetic constants for the polymerization reactions were evaluated from the DSC curves. Thermal stability of the cured polymers was studied by thermogravimetry (TG). The kinetic parameters, viz., activation energy E and preexponential factor A, for the thermal decomposition of the cured bismaleimides were calculated from the TG curves using three nonmechanistic integral equations. The kinetic constants (E and A) follow a trend similar to the thermal stability of the polymers.     

Synthesis and characterization of novel pyridine‐based polyureas with enhanced solubility and high thermal stability

The main aim of this study was the preparation of modified polyureas with improved thermal stability and solubility. Accordingly, a series of aromatic/aliphatic pyridine‐based polyureas was synthesized from the reaction of a novel diamine (DA) with different diisocyanates, including 4,4′‐diphenylmethane diisocyanate, toluene diisocyanate, 1,5‐naphthalene diisocyanate, and isophorone diisocyanate, by a solution polymerization route. The DA monomer was prepared via a two‐step reaction. The nucleophilic substitution reaction of oxydianiline with 6‐chloronicotinoylchloride led to the preparation of a diamide dichloro compound, and the subsequent reaction of this compound with 4‐aminophenol resulted in the preparation of the DA. After polymerization, the structural characterization and physical properties of the polymers were examined. The resulting polymers were soluble in common polar aprotic solvents, and they showed improved thermal stabilities in comparison with common polyureas. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Kinetics of the nonstationary photopolymerization of diacrylates

The kinetics of non‐stationary photopolymerization (post‐polymeryzation) of some diacrylates at the wide range of initial conversions was investigated. All kinetic curves has two regions: quick and short, slow and long. Experimental results were compared with the kinetic model of the photoinitial three‐dimensional photopolymerization. It was determined that kinetic model allows us to describe the process of the post‐polymerization in the whole range of conversions. The rate constants of the linear break of the primary and secondary chains in the interphase layer were estimated. The increasing rate constants in the interphase are the similar for investigated diacrylates and do not depend on the glicol chain. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1892–1895, 2002     

Effect of chain extender structure on the properties and morphology of polyurethanes based on H12MDI and mixed macrodiols (PDMS–PHMO)

The effect of chain extender structure on properties and morphology of α,ω‐bis(6‐hydroxyethoxypropyl) polydimethylsiloxane (PDMS) and poly(hexamethylene oxide) (PHMO) mixed macrodiol‐based aliphatic polyurethane elastomers was investigated using tensile testing, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). All polyurethanes were based on 50 wt % of hard segment derived from 4,4′‐methylenecyclohexyl diisocyanate (H₁₂MDI) and a chain extender mixture. 1,4‐Butanediol was the primary chain extender, while one of 1,3‐bis(4‐hydroxybutyl)tetramethyldisiloxane (BHTD), 1,3‐bis(3‐hydroxypropyl)tetramethyldisiloxane (BPTD), hydroquinonebis(2‐hydroxyethyl)ether (HQHE), 1,3‐bis(3‐hydroxypropyl)tetramethyldisilylethylene (HTDE), or 2,2,3,3,4,4‐hexafluoro‐1,5‐pentanediol (HFPD) each was used as a secondary chain extender. Two series of polyurethanes containing 80 : 20 (Series A) and 60 : 40 (Series B) molar ratios of primary and secondary chain extenders were prepared using one‐step bulk polymerization. All polyurethanes were clear and transparent and had number‐average molecular weights between 56,000 and 122,100. Incorporation of the secondary chain extender resulted in polyurethanes with low flexural modulus and high elongation. Good ultimate tensile strength was achieved in most cases. DSC and DMTA analyses showed that the incorporation of a secondary chain extender disrupted the hard segment order in all cases. The highest disruption was observed with HFPD, while the silicon‐based chain extenders gave less disruption, particularly in Series A. Further, the silicon chain extenders improved the compatibility of the PDMS soft segment phase with the hard segment, whereas with HFPD and HQHE, this was not observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2979–2989, 1999     

Synthesis and characteristics of thermoplastic elastomer based on polyamide‐6

A new class of polyether amide thermoplastic elastomers (TPAE) was synthesized via a three‐step polymerization route. In the first step a binary carboxyl terminated polyamide‐6 (PA6) with relatively low number‐average molecular weight was prepared via a caprolactam hydrolytic ring‐opening process. 4,4′‐Diphenylmethane diisocyanate (MDI) was reacted with the PA6 to produce PA6–MDI hard segments in the second step. Chain extension of the hard segments with poly(tetramethylene glycol) was the last step to furnish a series of new TPAEs. Structural characterization, physical properties and the effects of reaction conditions on the properties of the copolymer were investigated by infrared spectroscopy, ¹H nuclear magnetic resonance spectroscopy and other analytical techniques. Possible side reactions and phase separation are reported. Copyright © 2011 Society of Chemical Industry     

Kinetics and thermal characterization of epoxy‐amine systems

The curing behavior of epoxy resins was analyzed based on a simple kinetic model. We simulated the curing kinetics and found that it fits the experimental data well for both diglycidylether of bisphenol A–4,4′‐methylene dianiline and diglycidylether of bisphenol A–carboxyl‐terminated butadiene acrylonitrile–4,4′‐methylene dianiline systems. The kinetic results showed the curing of epoxy resins involves different reactive process and reaction stages, and the value of activation energy is dependent on the degree of conversion. By analyzing the effect of vitrification, at low curing temperature, we found the curing reaction at the later stage was practically diffusion‐controlled for unmodified resin, and the rubber component did not markedly decrease T_g at the early stage of reaction as would be expected. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2401–2408, 1999     

Curing kinetics and thermal property characterization of an o‐cresol formaldehyde epoxy resin and 4,4′‐diaminodiphenyl ether system

The kinetics of the curing reaction for a system of o‐cresol formaldehyde epoxy resin (o‐CFER) with 4,4′‐diaminodiphenyl ether (DDE) as a curing agent were investigated with differential scanning calorimetry (DSC). An analysis of the DSC data indicated that an autocatalytic behavior appeared in the first stages of the cure for the system, and this could be well described by the model proposed by Kamal, which includes two rate constants and two reaction orders (m and n). The overall reaction order (m + n) was 2.7–3.1, and the activation energies were 66.79 and 49.29 kJ mol^?1, respectively. In the later stages, a crosslinked network was formed, and the reaction was mainly controlled by diffusion. For a more precise consideration of the diffusion effect, a diffusion factor was added to Kamal's equation. In this way, the curing kinetics were predicted well over the entire range of conversions, covering both the previtrification and postvitrification stages. The glass‐transition temperatures of the o‐CFER/DDE samples were determined via torsional braid analysis. The results showed that the glass‐transition temperatures increased with the curing temperature and conversion up to a constant value of approximately 370 K. The thermal degradation kinetics of the system were investigated with thermogravimetric analysis, which revealed two decomposition steps. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 182–188, 2004     

Cure kinetics of epoxy formulations of the type used in advanced composites

An analysis of the cure kinetics of three different formulations composed of tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM) epoxy resin and diaminodiphenyl sulfone (DDS) was performed. A series of isothermal tests was run, and the experimentally obtained results were checked against the proposed kinetic model. An autocatalyzed mechanism with the overall reaction order of 2 was found to adequately describe the cure kinetics. An increase in reaction rate was observed at higher temperature and higher DDS concentration. For a given formulation, the extent of reaction corresponding to the maximum reaction rate was independent of temperature. A secondary exotherm was detected, particularly in formulations with low DDS concentration, at approximately 40% conversion. At that point, the rate of primary amine–epoxide reaction decreases, and other reactions dominate the curing process. Such a mechanism is likely to cause a formation of an inhomogeneous thermoset morphology.