In situ FTIR and DSC investigation on cure reaction of liquid aromatic dicyanate ester with different types of epoxy resin

Cure reactions of a liquid aromatic dicyanate ester [1,1′‐bis(4‐cyanatophenyl) ethane, DiCy] associated with a liquid cycloaliphatic epoxy ester (3,4‐epoxycyclohexylmethyl‐3,4‐epoxycyclohexane‐carboxylate, EPC) and with liquid bisphenol A epoxide [2,2‐bis(4‐glycidyloxyphenyl)propane, EPA] were studied through a cross‐reference between in situ FTIR and DSC dynamic scanning. DiCy can act here as a latent catalyst to cure EPC and EPA resins. Reaction mechanisms were found to be different for both curing systems (EPC/DiCy and EPA/DiCy). Two significantly separated exotherms were observed in the DSC thermograms in each system. The reaction mechanism of the EPA/DiCy system was found to follow mainly Bauer pathways. We postulate a new sequence of the mechanism in this system due to the presence of an oxazoline structure during the progression of the curing process. In the curing system of EPC/DiCy, however, another five principle reaction paths, rather than Bauer pathways, are suggested: (1) polycyclotrimerization of DiCy, (2) formation of oxazoline, (3) insertion of EPC into cyanurate, (4) formation of tetrahydro–oxazolo–oxazole, and (5) ring cleavage and reformation of oxazoline to form the insertion structure of cyanurate. The lower temperature peak in the DSC thermogram is primarily contributed by the former three reaction paths, whereas the higher temperature peak can mainly be attributed to the reaction paths 4 and 5. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2934–2944, 2000     

氢化双酚A型环氧树脂的固化动力学

将氢化双酚A与环氧氯丙烷反应合成了氢化双酚A型环氧树脂(HBPA-EP),产物分别用多元胺类或酸酐类固化剂固化,利用差示扫描量热分析(DSC)对固化反应特性进行了研究,得到了相应的固化条件、固化反应活化能和固化反应动力学方程等.结果表明,当分别采用1,3-环己二甲胺、液态聚酰胺、顺式六氢苯酐、甲基六氢苯酐固化HBPA-EP(环氧值为0.45)时,其固化条件分别为100℃、2h,145℃、4h,90℃、2h,120℃、4h,130℃、2h,150℃、4h,140℃、2h和160℃、4h,用这4种固化剂进行固化反应的表观活化能分别为50.62、56.88、74.56 kJ/mol和68.36 kJ/mol,其反应级数分别为0.886、0.901、0.915和0.905.     

Cure kinetics of thermosetting bisphenol E cyanate ester

Resin injection repair is a common method to repair delamination damage in polymer matrix composites (PMCs). To repair high-temperature PMCs, the resin should have a very low viscosity, yet cure into a compatible adhesive with high temperature stability. Normally, thermosetting polymers with high glass transition temperatures (T _g) are made from monomers with high room temperature viscosities. Among the high temperature resins, bisphenol E cyanate ester (BECy, 1,1’-bis(4-cyanatophenyl)ethane), is unique because it has an extremely low viscosity of 0.09–0.12 Pa s at room temperature yet polymerizes as a cross-linked thermoset with a high T _g of 274°C. BECy monomer is cured via a trimerization reaction, without volatile products, to form the high T _g amorphous network. In this study, the cure kinetics of BECy is investigated by differential scanning calorimetry (DSC). Both dynamic and isothermal experiments were carried out to obtain the kinetic parameters. An autocatalytic model was successfully used to model isothermal curing. The activation energy from the autocatalytic model is 60.3 kJ mol⁻¹ and the total reaction order is about 2.4. The empirical DiBenedetto equation was used to evaluate the relationship between T _g and conversion. The activation energy of BECy from the dynamic experiments is 66.7 kJ mol⁻¹ based on Kissinger’s method, while isoconversional analysis shows the activation energy changes as the reaction progresses.     

Effects of novel polyhedral oligomeric silsesquioxane containing hydroxyl group and epoxy group on the dicyclopentadiene bisphenol dicyanate ester composites

Two types of novel Polyhedral Oligomeric Silsesquioxanes respectively containing hydroxyl group and epoxy group (P-POSS and E-POSS) were achieved and evaluated. The structure had been characterized by IR spectra and NMR spectra. Dicyclopentadiene bisphenol dicyanate ester (DCPDCE) composites were then prepared using P-POSS and E-POSS respectively. Their effect on the curing kinetics, dielectric, mechanical, flame-retardant and thermal properties and water absorption of the resulting composites were investigated. The results suggested that the addition of modified POSS could facilitate the curing reaction of DCPDCE. Besides, the DCPDCE composites containing modified POSS exhibited excellent flame-retardant property over pure DCPDCE resin. Adding only a little amount as small as 1.5 wt% P-POSS or 2.5 wt% E-POSS could change the UL-94V of DCPDCE resin from V-2 to V-0. The composite with P-POSS exhibited better flame-retardant and thermal properties than the composite with E-POSS. However, composite filled with E-POSS presented better dielectric property and lower water absorption.     

DSC study on the effect of isocyanates and catalysts on the HTPB cure reaction

The urethane forming cure reactions of hydroxyl terminated polybutadiene (HTPB) binder with three different isocyanate curatives, viz., toluene diisocyanate (TDI), isophorone diisocyanate (IPDI) and 4,4-methylene bis(cyclohexyl isocyanate) (MCHI), were investigated by differential scanning calorimetry (DSC). The effect of two cure catalysts, viz., dibutyl tin dilaurate (DBTDL) and ferrric tris-acetylacetonate (FeAA) on the cure reactions was also studied. Cure kinetics was evaluated using the multiple heating rate Ozawa method. The reactivities of the three isocyanates and catalytic efficiencies were compared based on the DSC reaction temperatures, activation energies and rate constants. Viscosity build-up in these systems at isothermal temperature was also studied and compared with the results from DSC.     

Silicon‐containing trifunctional and tetrafunctional cyanate esters: Synthesis,cure kinetics,and network properties

The synthesis and physical properties of new silicon‐containing polyfunctional cyanate ester monomers methyl[tris(4‐cyanatophenyl)]silane and tetrakis(4‐cyanatophenyl)silane, as well as polycyanurate networks formed from these monomers are reported. The higher crosslinking functionality compared to di(cyanate ester) monomers enables much higher ultimate glass transition temperatures to be obtained as a result of thermal cyclotrimerization. The ability to reach complete conversion is greatly enhanced by cocure of the new monomers with di(cyanate ester) monomers such as 1,1‐bis(4‐cyanatophenyl)ethane. The presence of silicon in these polycyanurate networks imparts improved resistance to rapid oxidation at elevated temperatures, resulting in char yields as high as 70% under nitrogen and 56% in air in the best‐performing networks. The water uptake in the silicon‐containing networks examined is 4–6 wt % after 96 h of immersion at 85 °C, considerably higher than both carbon‐containing and/or di(cyanate ester) analogs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 767–779     

DSC Analysis of the Induction Period in the Vulcanisation of Rubber Compounds

Vulcanisation of rubber compounds was studied by DSC under isothermal and non-isothermal conditions. The parameters of an Arrhenius-like equation describing the temperature dependence of induction period have been obtained both from isothermal and non-isothermal measurements. A new method for obtaining the kinetic parameters from non-isothermal measurements, based on the dependence of onset temperature of vulcanisation peak on heating rate, is presented. Also, a procedure for the evaluation of temperature difference between the furnace and sample is proposed. It has been shown that the treatment of non-isothermal DSC measurements gives the kinetic parameters free of systematic errors. The new method can also be used for studying other reactions exhibiting the induction period. This revised version was published online in August 2006 with corrections to the Cover Date.     

Monte Carlo Study of Binary Copolymerizations. 2. The Determination of Reactivity Ratios,Applications

This paper discusses an improved and efficient version of the MEMØRY-7 computer program described in a previous paper. The program, called MEMØRY-7/1, implements a Monte Carlo algorithm to compute reactivity ratios in binary irreversible copolymerizations. For the copolymerization of acrylic acid and methyl acrylate, the computed r₁, r₂ values (r₁ = 1.374, r₂ = 1.038) compare quite well with experimentally determined ones (r₁ = 1.4, r₂ = 1.0; Eldridge and Treloar).     

The effect of zeolite on the curing of epoxy resin by polyaniline: a kinetic study

Polyaniline sulfate‐zeolite composite was prepared by emulsion polymerization. Epoxy resin was cured using polyaniline‐sulfate salt and various amounts of polyaniline sulfate‐zeolite composite. The kinetics of the cure reaction for an epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) with polyaniline‐sulfate and polyaniline sulfate‐zeolite composite have been studied using differential scanning calorimetry (DSC) under isothermal and dynamic conditions. Isothermal kinetics analysis was performed using the phenomenological model of Kamal. Dynamic kinetic analysis was performed using Kissinger's method. Copyright © 2002 John Wiley & Sons, Ltd.     

Kinetics of thermoset cure and polymerization in the glass transition region

A theoretical approach to thermoset cure kinetics based on Arrhenius kinetics and mobility was developed by considering the activation of the reacting group and chain mobility as elementary steps for reaction. This extended kinetic equation was successfully applied to the curing of an epoxy by an amine, the trimerization of a cyanate, and to the polymerization of methyl methacrylate. Full agreement between theory and experimental data was obtained in all cases. The activation energies for chain mobility were exceptionally low (0.3–1 kJ/mol for bisphenol-A-based epoxy and cyanate) which indicates that the structural units must undergo only small-angle rotational oscillations to allow a reaction. A theoretical time–temperature–transformation (TTT) diagram is also presented. © 1993 John Wiley & Sons, Inc.     

Computer simulation of thermal analysis in heat-flux DSC applied to metal solidification

A general mathematical treatment for heat-flux differential scanning calorimetry is given. It combines equations derived for heat transfer in the calorimeter cell with an approach to the solidification of metal or alloy carried out in this type of instrument. The differences are discussed between temperature evolution, kinetics of latent heat and undercooling evolution within the sample, and temperature evolution, recorded signal and measured undercooling at the monitoring station.

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Zusammenfassung Es wird ein allgemeine mathematische Behandlung von Wärmefluß-DSC gegeben. Es verbindet Gleichungen für den Wärmetransport in der Kalorimeterzelle mit einer Annäherung der Verfestigung von Metall oder Legierung, die in diesem Gerätetyp durchgeführt werden. Es werden die Unterschiede zwischen: Temperaturevolution, Kinetik latenter Wärme und Unterkühlungsevolution innerhalb der Probe und zwischen: Temperaturevolution, aufgezeichnetes Signal und gemessene Unterkühlung an der Monitorstation diskutiert.

     

Differential scanning calorimetric study on the curing behavior of epoxy resin/diethylenetriamine/organic montmorillonite nanocomposite

The curing mechanisms and kinetics of diglycidyl ether of bisphenol A with diethylenetriamine as the curing agent and different amounts of organic montmorillonite were examined with isothermal and dynamic scanning calorimetry. The modified Avrami equation was used to calculate the activation energy and reaction orders in the isothermal experiment. A single peak was observed in each dynamic scan. The curing mechanism and kinetics of the curing reaction were also analyzed by two kinds of methods—Kissinger and Flynn–Wall–Ozawa. The results obtained from those methods under dynamic measurement agreed with those obtained from the modified Avrami equation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 378–386, 2003     

Low dielectric thermoset. IV. Synthesis and properties of a dipentene‐containing cyanate ester and its copolymerization with bisphenol A dicyanate ester

A 2,6‐dimethylphenol‐dipentene dicyanate ester ( DPCY ) was synthesized from the reaction of 2,6‐dimethylphenol‐dipentene adduct and cyanogen bromide. The proposed structure was confirmed by Fourier transform infrared (FTIR), elemental analysis, mass, and nuclear magnetic resonance (NMR) spectra. DPCY was then cured by itself or cured with bisphenol A dicyanate ester ( BADCY ). Thermal properties of cured epoxy resins were studied using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric analysis (DEA), and thermogravimetric analysis (TGA). These data are compared with those of BADCY . The cured DPCY exhibits a lower dielectric constant (2.61 at 1 MHz), dissipation factor (29.3 mU at 1 MHz), thermal stability (5% degradation temperature and char yield are 429 °C and 17.64%, respectively), glass transition temperature (246 °C by TMA and 258 °C by DMA), coefficient of thermal expansion (33.6 ppm before Tg and 134.1 ppm after Tg), and moisture absorption (0.95% at 48 h) than those of BADCY , but higher moduli (5.12 GPa at 150 °C and 4.60 GPa at 150 °C) than those of the bisphenol A system. The properties of cured cocyanate esters lie between cured BADCY and DPCY , except for moduli. Moduli of some cocyanate esters are even higher than those of cured BADCY and DPCY . A positive deviation from the Fox equation was observed for cocyanate esters. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3986–3995, 2004     

Kinetics of the crosslinking reaction of a bisnadimide model compound in thermal and microwave cure processes

The kinetic studies of the crosslinking reaction of a nadic end-capped imide model compound, N,N′-(oxydi-3,4′-phenylene) bis(5-norbornene-2,3-dicarboximide), a bisnadimide, in thermal and microwave processes were investigated. The conversion of the endo isomer to exo isomer proceeds at a much lower temperature than the crosslinking reaction. The crosslinking reaction was monitored by the combined decrease in the infrared absorptions of the endo and exo isomers at 840 and 780 cm⁻¹, respectively. The decrease in the concentration of starting materials follows first-order kinetics in the thermal and microwave processes. At the same temperatures (230 or 280°C), the crosslinking reaction proceeds at about 10 times faster in the microwave process than in the thermal process. Solid-state ¹³C-NMR showed no significant loss in C=C double bond resonance in the cured products by comparison with the starting material. This study provides direct evidence that the microwave process may be an efficient method to cure nadic end-capped polyimides. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2653–2665, 1998     

Calculation of smoothing factors for the comparison of DSC results

Complex mixtures of long chain organic compounds often show overlapping glass transition temperatures (T _gs) when analyzed by differential scanning calorimetry (DSC) or modulated DSC (MDSC). In such cases, subjective and inconsistent smoothing of data acquired under different conditions can lead to the misinterpretation of results. A quantitative method for the selection of smoothing factors for the analysis and comparison of (M)DSC results is presented. The method is most useful for the analysis of the derivative of the heat capacity, dC _p/dt or dC _p/dT, plots which best highlight overlapping T _gs. Four equations are shown to relate the heating rate and the smoothing factor. The equations allow a comparison of data acquired i) at different heating rates and plotted vs. temperature, ii) at a single heating rate and plotted vs. both time and temperature, i.e., dC _p/dt vs. dC _p/dT, iii) at different heating rates and plotted vs. both time and temperature, and iv) at different heating rates, and shown exclusively in the time domain. Examples of the use of the equations are provided for the analysis of bitumen, a complex mixture of natural origin.     

Transformation of dynamic DSC results into isothermal data for the curing kinetics study of the resol resins

Kinetics of thermosetting polymers curing is difficult to study by isothermal methods based on the differential scanning calorimetry (DSC) technique. The difficulty is due to the low sensitivity of the equipment for total reaction heat measurements during high temperature process. The aim of this paper is to display the equivalence between a dynamic model, the Ozawa method, and an isothermal isoconversional fit, which allows predicting the isothermal behavior of the resol resins cure through dynamic runs by DSC. In this work, lignin–phenol–formaldehyde and commercial phenol–formaldehyde resol resins were employed. In addition, the isothermal kinetic parameters for both resins were performed by means of transformation of the data obtained from the dynamic Ozawa method.     

NCOCH2(CF2)6CH2OCN cyanate ester resin. A detailed study

The NCOCH₂(CF₂)₆CH₂OCN fluoromethylene cyanate ester monomer and resin are synthesized and characterized. The monomer is prepared by a large‐scale bench‐top synthesis, characterized by differential scanning calorimetry, infrared, ¹H‐, ¹³C‐, ¹⁵N‐, and ¹⁹F‐NMR spectroscopies and analyzed for catalytically active impurities. Conversion of the monomer to prepolymer and cured resin is characterized by IR and NMR spectroscopies and kinetically analyzed. Resin properties characterization includes thermal, tensile, dynamic mechanical, dielectric, refractive index, thermodielectric and thermogravimetric stabilities, and water absorption. Relevant property comparisons with the commercial AroCy F cyanate ester resin (6F bisphenol A dycyanate) and a Jeffamine‐bisphenol diglycidyl ether epoxy are made. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 135–150, 1999     

Flash DSC crystallization study of blown film grade bimodal high density polyethylene (HDPE) resins. Part 2. Non‐isothermal kinetics

Non‐isothermal ultra‐fast cooling crystallization tests were conducted on three blown film grade bimodal high density polyethylene (HDPE) resins using a fast differential scanning calorimeter, the Flash DSC. Non‐isothermal tests were performed at cooling rates between 50 and 4000°K/s, and the data were analyzed using the modified Avrami model by Jeziorny (Polymer, 1978 , 19, 1142). Non‐isothermal data were used to propose a new method named crystallization–time–temperature–superposition, and the two activation energies were obtained for each of the resins. This is very useful for obtaining theoretical crystallization kinetics data at different cooling rates, allowing its use in ultra‐fast cooling polymer processes such as blown film. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1822–1827     

A study of thermal crystallization in glassy Se80Te20 and Se80In20 using DSC technique

Different methods have been used by various workers to determine the activation energy of thermal crystallization (E_c) in chalcogenide glasses using non-isothermal DSC data. In the present work, the crystallization kinetics of two important binary alloys Se₈₀Te₂₀ and Se₈₀In₂₀ is studied using non-isothermal DSC data. DSC scans of these alloys have been taken at five different heating rates. The values of activation energy of crystallization (E_c) have been determined by four different methods, i.e., Kissinger's method, Matusita-Sakka method, Augis-Bennett's method and Ozawa's method, have been used to calculate E_c. The results obtained have been compared with each other to see the effect of using different methods in the determination of E_c.     

Effect of organoclay on the curing reactions in bismaleimide/diallyl bisphenol a resin

4,4′‐Bismaleimidodiphenyl methane (BMPM)/2,2′‐diallyl bisphenol A (DBA)/organoclay nanocomposites were synthesized. The effects of organoclays on the curing reactions in the BMPM/DBA system at low temperatures (ene reaction) and high temperatures (Diels–Alder reaction, homopolymerization of BMPM, and alternative copolymerization) were investigated with differential scanning calorimetry and Fourier transform infrared techniques. The results showed that these reactions were affected to different extents in the presence of organoclays. The ene reaction was accelerated to different degrees depending on the acidity of the modifier and the accessibility of the organoclays used. The exfoliation degree of organoclays in the prepolymers showed great effects on the curing behavior of BMPM/DBA. When an organoclay was less intercalated, the curing behavior of the system was different from that of neat BMPM/DBA. On the other hand, when the organoclay was better exfoliated in prepolymers, the curing behavior of the system was similar to that of the neat BMPM/DBA system. However, even in this case, the reactions at high temperatures occurred in different ways in the presence of an organoclay. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 994–1006, 2005