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Kinetic investigations of trimethylolpropane–diisocyanate reactions
Abstract
Trimethylolpropane (TMP) is frequently used as a trifunctional branching and chain-extending agent in polyurethane production. This article deals with the analysis of the reactivities of the three primary hydroxyl groups of TMP during reactions with two exemplary diisocyanates: aromatic diphenylmethane-4,4′-diisocyanate and aliphatic m-tetramethylxylylene diisocyanate. The method of examination is online attenuated total reflection/Fourier transform infrared spectroscopy. With this method, reactions in progress can be monitored simultaneously. It is shown that the addition of an isocyanate (here phenyl isocyanate) to the alcohol affects the rate of subsequent reactions. The higher the substitution degree is, the smaller the rate constant is of the reaction between the remaining free hydroxyl groups and the diisocyanates. This effect is largely determined by the type of diisocyanate. For reactions with very reactive aromatic diisocyanates, steric hindrance plays a significant role. For aliphatic diisocyanates, the substitution shows only minor effects because of the slowly reacting isocyanate groups. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4090–4097, 2006
... The formation of these chemical species in the reaction mixture requires analytical methods that highlight the structural peculiarities at the molecular level of the products. The kinetics of the reaction between polyols and diisocyanates were investigated in a great number of studies using methods such as Fourier-transformed infrared spectroscopy (FTIR) [24][25][26][27][28][29][30], size exclusion chromatography (SEC) [31,32], differential scanning calorimetry (DSC) [33,34] and chemical titration of NCO functions [35,36]. In addition, such reactions were investigated by combining two or more analysis methods to obtain more accurate information regarding the reaction order for both components and to characterize the final products [37][38][39][40][41][42][43][44][45][46][47]. ...
The reaction of diols with isocyanates, leading to mono-functional and di-functional prepolymers may be investigated using various characterization methods which show the overall conversion of isocyanate monomers. On the other hand, matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) polymer characterization can be employed to identify the monomer units, the end-group functionalities, molecular weight averages, and to determine the copolymer sequence. Herein, we focus on prepolymer synthesis using isophorone diisocyanate (IPDI), a widely used diisocyanate for prepolymers preparation, especially in waterborne polyurethane materials. Thus, the reaction between polyethylene glycol diol and IPDI was in-depth investigated by mass spectrometry to determine the influence of the reaction parameters on the prepolymer's structure. The relative content of the different functional oligomer species at given reaction times was determined in the reaction mixture. More specifically, the offline analysis revealed the influence of reaction parameters such as reaction temperature, the concentration of reactants, and the amount of dibutyltin dilaurate catalyst. The established MALDI MS analysis involved measurements of samples, first, directly collected from the reaction mixture and secondly, following derivatization with methanol. The obtained results revealed the effects of reaction parameters on the functionalization reaction with isocyanates, allowing to achieve a better reaction control.
The kinetics of the urethane forming reactions of hexamethylene diisocianate (HDI), 4,4′-dicyclohexyl-methane-diisocyanate) (HMDI) and isophorone diisocyanate (IPDI) with butan-1-ol were systematically studied by electrospray ionization mass spectrometry (ESI-MS) in the...
Polyurethanes (PUs) are a versatile and major polymer family, mainly produced via polyaddition between polyols and polyisocyanates. A large variety of fossil-based building blocks is commonly used to develop a wide range of macromolecular architectures with specific properties. Due to environmental concerns, legislation, rarefaction of some petrol fractions and price fluctuation, sustainable feedstocks are attracting significant attention, e.g., plastic waste and biobased resources from biomass. Consequently, various sustainable building blocks are available to develop new renewable macromolecular architectures such as aromatics, linear aliphatics and cycloaliphatics. Meanwhile, the relationship between the chemical structures of these building blocks and properties of the final PUs can be determined. For instance, aromatic building blocks are remarkable to endow materials with rigidity, hydrophobicity, fire resistance, chemical and thermal stability, whereas acyclic aliphatics endow them with oxidation and UV light resistance, flexibility and transparency. Cycloaliphatics are very interesting as they combine most of the advantages of linear aliphatic and aromatic compounds. This original and unique review presents a comprehensive overview of the synthesis of sustainable cycloaliphatic PUs using various renewable products such as biobased terpenes, carbohydrates, fatty acids and cholesterol and/or plastic waste. Herein, we summarize the chemical modification of the main sustainable cycloaliphatic feedstocks, synthesis of PUs using these building blocks and their corresponding properties and subsequently present their major applications in hot-topic fields, including building, transportation, packaging and biomedicine.
In this research, the kinetics of the reaction of various polymer polyol crosslinking agents with phenyl isocyanate is reported. Pentaerythritol (PE), Trimethylol propane (TMP), ethoxylated (PEEO) and propoxylated (PEPO) pentaerythritol...
The uncatalyzed reactions of polyols including polypropylene glycol (PPG, Mn = 2000 g/mol), polytetrahydrofuran (PTHF, Mn = 1000 g/mol), poly(-caprolactone)-diol (PCLD, Mn = 2000 g/mol) and polypropylene glycol glycerol triether (PPG_GL, Mn = 1000 g/mol) with 4,4`-diphenylmethane-diisocyanate (MDI) were studied using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The reactions between these polyols and MDI were monitored in time and first-order consecutive reaction kinetics for the formations of polyols end-capped with MDI units were established. The fractional MALDI-TOF MS intensities obtained for the different polymer series at various reaction times were converted into molar fractions versus time data by means of the estimated relative MALDI-TOF MS response factors from which the corresponding rate constants and the relative reactivities of the hydroxyl groups of polyols were determined. It was found that the pseudo first-order rate constants for the polyol-MDI reaction decreased in the order of PCLD > PTHF > PPG PPG_GL. It was also ascertained that the reactivity of the unreacted hydroxyl groups of the diols does not change significantly after the first one has been reacted. On the contrary, in the case of PPG_GL it was found that the reactions of the hydroxyl groups with MDI proceed faster after either of the three hydroxyl groups has been reacted, suggesting positive substitution effect for this system.
The kinetics of methylene diphenyl dicarbamate thermo-decomposition to diphenylmethane diiso-cyanate was investigated in the presence of diisooctyl sebacate. A consecutive reaction model was established by simplifying the thermo-decomposition process and two steps were conformed to be the first-order reaction by integral test model and numerical differential method, respectively. The results show that the activation energies of two steps are 138.82 and 167.78 kJ/mol, while the frequency factors are 1.51 × 1012 and 5.33 × 1014, respectively. Base on the obtained kinetic model, the reaction proceeding can be calculated in given conditions.
Crosslinked polyurethane-ureas based on a mixture of 4,4′-dibenzyl diisocyanate, poly(ethylene adipate) glycol, diethylene glycol (DEG) and trimethylol propane (TMP) were synthesized with various ratios of DEG and TMP. The combination within the network structure of the chemical crosslinks generated by TMP and the cohesive strength of urethane and urea groups, which provide physical crosslinking points, plays a special role in the mechanical and thermal properties. Fourier transform infrared (FTIR) spectroscopy indicated the distribution of hydrogen bonds in these networks. The extent of crosslinking was monitored through dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and atomic force microscopy (AFM) and was found to be significantly influenced by the double function of TMP: plasticizer and crosslinker. The width and intensity of the glass transition region and the evolution of the storage modulus on the rubbery plateau region were analyzed in order to observe the trends in crosslinking and network homogeneity. The improved mechanical properties were generally accredited to the effect of crosslinking resulting from the high hydrogen bonding capability of the urea group in conjunction with the good rubber elasticity of the network. This journal is
The thermal oxidation reaction process and oxidation kinetics of abietic acid were investigated by using self-designed gas–solid reaction equipment. The oxidation product and intermediates of the oxidation reaction of abietic acid were tracked by LC-MS. The results revealed a two-step oxidation reaction of abietic acid: abietic acid forms a peroxide first, followed by cracking to form hydroxyl-containing oxidized abietic acid. Both of the steps followed the pseudo-first order reaction kinetics, in which the kinetic equation of the first step is r1 = cA × 3.51 × 103 × exp(−58.96 × 103/RT), with activation energy of 58.96 kJ mol−1. The kinetic equation of the second step is r2 = cO × 6.09 × 105 × exp(−48.06 × 103/RT) with activation energy of 48.06 kJ mol−1. The kinetic equation of the total reaction is ra = ca × 1.12 × 106 × exp(49.51 × 103/RT) with apparent activation energy of 49.51 kJ mol−1.
The kinetics of the decomposition of dimethylhexane-1,6-dicarbamate to 1,6-hexamethylene diisocyanate was studied. A consecutive reaction model was established and the reaction orders for the two steps were confirmed to be 1 and 1.3 by the integral test method and the numerical differential method, respectively. The activation energies of the two steps were 56.94 ± 5.90 kJ•mol- 1 and 72.07 ± 3.47 kJ•mol- 1 with the frequency factors exp(12.53 ± 1.42) min- 1 and (14.254 ± 0.84) mol- 0.33•L0.33•min- 1, respectively. Based on the kinetic model obtained, the progress of the reaction can be calculated under given conditions.
Methylene diphenyl dicarbamate (MDC) is a key intermediate in the non-phosgene manufacture of methylene diphenyl diisocyanate. The synthesis of MDC by methoxycarbonylation of methylene dianiline (MDA) with dimethyl carbonate in the presence of lead acetate catalyst, which showed high catalytic activity, was studied. Complete conversion of MDA and 98.10% yield of MDC were achieved under optimum conditions. To quantify the influence of both the temperature and reaction time, the kinetic parameters were investigated in the presence of Pb(OAc)2·3H2O. A consecutive reaction model was established by simplifying the methoxycarbonylation process, and the two steps were confirmed to be first-order reactions by the integral test method and the numerical differential method, respectively. The results showed that the activation energies of the two steps are 175.84 and 177.92 kJ/mol, with the frequency factors being 1.91 × 1020 and 1.98 × 1020, respectively. Based on the kinetic model obtained, the progress of the reaction can be calculated under given conditions.
High-performance cross-linked polymeric materials are now prepared from preformed precursors typical by distributions of molecular weights, number and reactivities of functional groups, and specific architectures. This makes theoretical treatment of networks evolution and their final structure difficult. This paper describes kinetically controlled cross-linking of a precursor formed from polyfunctional cores by arm extension by which molecular weight distribution develops and new groups of different reactivity are formed. These precursors are then cross-linked with a polyfunctional cross-linker. If the precursor groups react independently, a random (binomial) distribution of reactive groups results and the gel point conversion and other network parameters are independent of the differences in reactivity the groups with the cross-linker. If the condition of random (binomial) distribution is not met (fixed numbers of groups or substitution effect in the precursor molecules), this independence does not exist. Relations for molecular weight averages prior to gelation and gel fraction and concentration of elastically active network chains in the postgel state are derived. This general treatment applies to precursors obtained by a wide variety of chain extension chemistries and any of the family of cross–linking reactions of A + B type. In the second part, the general form of the theory was adapted to describe polyether precursors prepared by addition of an epoxy ester (glycidyl pivalate) to multifunctional polyols and their curing with a tri-isocyanate. Some of the primary OH groups of the core are chain–extended to form a polyether chain terminated by a secondary OH group. The distributions are altered by additional reactions – transesterification and alcoholysis. The branching theory was modified and the results compared with experiments. Gel point conversions were affected by these additional reactions, but the concentration of elastically active network chains (EANCs) (calculated from equilibrium elastic modulus) did not change much. The fraction of formed bonds wasted in cycles amounted to 12–22%.
Polyurethane prepolymer prepared from nonequivalent amounts of toluene diisocyanate (TDI) over trifunctional trimethylolpropane (TMP) was followed by gel permeation chromatography (GPC). Steric hindrance of TMP was considered as the main factor affecting the molar mass distribution, especially in the higher molecular weight region. An optimum reaction condition was the initial NCO/OH ratio of 3 and the reaction temperature of 50 °C. Then polyurethane prepolymer could be purified through the thin film evaporator with excellent properties. A combination of mass spectrometry (MS) and 1H nuclear magnetic resonance (NMR) spectroscopy was employed to identify and confirm the individual compounds presented from GPC analysis.
A C-NMR study of the reaction between ethylene glycol or 1,2-propylene glycol with diphenylmethane-4,4′-diisocyanate is reported. Assignation of -CH2-, -NHCOO-, and -CH3 groups was made and their concentration dependence on reaction time established. On the basis of these data, the rate constants for different reactions were calculated. It was found that the primary groups of 1,2-propylene glycol are more reactive than the secondary -OH group, and that ethylene glycol is more reactive than 1,2-propylene glycol. Side reactions at low temperature and without catalyst do not take place.
The rates of reaction of glycerol and two polyether macrodiols, differing in molecular weight by a factor of 6, with a commercial grade of liquid polymeric 4,4′-diphenylmethane diisocyanate (MDI) were determined using data from reaction calorimetric studies. Rate constants were determined for the reactions of each of the macrodiols and glycerol with the isocyanate. The reactivities of the primary hydroxyl groups in glycerol were similar to those of the macrodiols. The more sterically hindered secondary hydroxyl group in glycerol was found to have a reactivity one third that of the primary hydroxyl groups.
The mechanisms of tri-dimensional polyesterifications in bulk at 180°C of ternary mixtures of o-phthalic anhydride (P) + azelaic acid (Z) + trimethylolpropane (T), as well as the distributions of acid branches on the potential crosslinking T units, have been studied by liquid 13C n.m.r. before (sol) and after (gel) gelation. The critical time for gelation is found to decrease when Z increases, and in all cases the actual critical conversions are larger than those calculated by the classical statistical Flory-Stockmayer relation. Transesterification reactions actually occur during polyesterification. Before as well as after gelation, the distributions of P and Z in diesters and triesters of T follow two slightly different Bernouillian statistics because of the better reactivity of Z than P.
Polyesterifications in bulk of trimethylolpropane (T) with azelaic acid (Z) and o-phthalic anhydride (P) and copolyesterification of a (Z + P + T) ternary mixture have been studied by 13C nuclear magnetic resonance (n.m.r.) before and after gelation. It has been found that Z is more able than P to give covalent gels. 13C n.m.r. allows quantitative determinations of the conversions of acid functions of Z and P and alcohol functions of T as well as the distributions of monoester and diester of P and those of free, mono-, di- and triesterified T. In all cases, the actual critical conversions are larger than the theoretical ones calculated due to the Flory-Stockmeyer statistics because (i) 3–5% of free T and P are trapped and (ii) the two acid functions of P or Z and the three alcohol functions of T do not have the same reactivities. For the ternary system, four types of T triesters have been identified and quantitatively determined, and finally, reticulation should only occur if more than one-third of T are triesterified. In the copolyesterification in bulk of the (0.5Z + 0.5P + 0.8T) mixture, the distributions of Z and P on the mono-, di- and triesterified T follow Bernoullian statistics.
The uncatalyzed and catalyzed polymerization of polypropylene glycols (MW 400-2000) with toluene diisocyanate has been studied in toluene solution at three different temperatures. Discontinuity was observed in the second-order plots of uncatalyzed reactions in contrast to the catalyzed reactions which showed straight-line plots. The rate constants (k1, k2) and the activation parameters (Ea1 Ea2, δS 1, δS 2) for the isocyanate groups in the 4- and 2-positions were calculated. In the uncatalyzed and diethylcyclohexylamine-catalyzed reactions, the rate constants were found to decrease with increasing molecular weight of the polyols, whereas in the dibutyltin-dilaurate-catalyzed reactions the rate constants and the activation parameters were found to be independent of the molecular weight of the polyols.
Die durch Triäthylamin katalysierte Reaktion von Oligomethylenglykolen und von Oligoäthylenglykolen mit Phenylisocyanat in Dioxan bei 25°C wurde untersucht. Die Reaktionsgeschwindigkeit innerhalb der homologen bzw. polymerhomologen Reihe ist unter den angewandten Bedingungen unabhängig von der Kettenlänge und der chemischen Struktur der Kette.The reaction of oligomethylene glycols (I) and oligooxyethylene glycols (II) with phenyl isocyanate in dioxane at 25°C. catalyzed by triethylamine was investigated. Under the applied conditions the reaction rate within the homologous and polymerhomologous series is independent of the chain length and the chemical constitution of the chain.
A general kinetic reaction network has been suggested for the gradual chian growth polyaddition process for the synthesis of linear chain polyurethane. Based on the results from the kinetic investigation of the reactions of model aromatic/aliphatic isocyanates and alcohols and hydroxyethers, some methods were set forth to provide rate-constant values for the reactions included in this network. Model equations were derived from the collision theory, giving dependencies of reaction rate constant values on the molecular weights of the reacting substances. It was found that it was the structure of the reactants that had the most significant effect on the rate of carbamate-yielding reactions; the effects derived from temperature, catalyst, and size of reacting molecules follow. © 1995 John Wiley & Sons, Inc.
The reaction rates for the uncatalyzed as well as the dibutyltin dilaurate-catalyzed reactions between polyether polyols and tolylene diisocyanate (80/20 mixture of 2,4 and 2,6 isomers) are reported. Titration and infrared absorption methods were used for the determination of the residual isocyanate content, to follow the progress of the reactions. At equivalent reactant concentrations, the rate constants were found to be essentially independent of the chain length and the functionality of the polyether polyols studied. The reaction rates of polyether polyols containing terminal primary hydroxyl groups (e.g., Pluronic polyols) were greater than those of polyols with secondary hydroxyl groups and were greatly accelerated in the presence of the tin catalyst.
A study has been conducted of the kinetics of the reaction of ether alcohols, primary and secondary methoxypropanols, with phenyl isocyanate in the presence of metal catalysts. The proximity of the methoxy and methyl groups to the hydroxyls had a significant effect on the reaction rates as did the type and concentration of metal catalysts (lead naphthenate or dibutyltin dilaurate). The reaction rates in toluene solution were found to be faster than in Cellosolve acetate solution. The study of the reaction of poly(oxy-propylene)glycols with isocyanate showed the existence of two rate constants due to the reactions of the primary and secondary alcohol groups present in the glycols. The mechanism of the metal-catalyzed reaction between alcohols and isocyanates was investigated by means of IR and NMR spectra. No direct evidence of alcohol-catalyst complex formation could be obtained by IR spectroscopy. NMR spectra indicated the existence of a 1:1 complex in the system dibutyltin dilaurate-1-methoxy-2-propanol.
Kinetic and statistical aspects of the polymerization of toluene diisocyanate (TDI 80:20) with a commercial polyether polyol based on sorbitol have been analysed. The polymerization kinetics were measured under isothermal and adiabatic conditions, using different amounts of triethylamine (TEA) as catalyst. The kinetics were described by two independent second-order equations giving the reaction of ortho- and para-NCO groups. The activation energy for the reaction of o-NCO was significantly higher than that corresponding to p-NCO. Both activation energies decrease on increasing the catalyst concentration. For uncatalysed systems, o-NCO reacts 100 times slower than p-NCO at 25°C, while both reactivities become equivalent at temperatures close to 125°C. A general gelation condition was found using a recursive procedure. Systems polymerized with a high excess of TDI show evidence of isocyanurate ring formation, while OH-terminated prepolymers may be used to decrease the gel conversion and the time to gel at room temperature.