A DSC Study on Cure Kinetics of HTPB-IPDI Urethane Reaction

The kinetics of theurethane-forming cure reaction of hydroxyl terminated polybutadiene (HTPB) with isophorone diisocyanate (IPDI) in presence of ferric tris (acetyl acetonate) (FeAA) catalyst was investigated using differential scanning calorimetry (DSC). The Arrhenius activation parameters, viz., activation energy E and pre-exponential factor A were evaluated using the non-isothermal integral Coats-Redfern equation. The cure reaction was catalysed by ferric acetyl acetonate (FeAA), as revealed from the decrease in reaction temperatures and the increase in rate constants; however, the computed activation energy did not show any correlation to the catalyst concentration. The values of E and A for the uncatalysed reaction at different heating rates showed interdependence through kinetic compensation (KC) effect. Using KC correction, E values were normalised for the value of A for the uncatalysed reaction under identical conditions. The normalised E values decreased exponentially with increase in concentration of FeAA, showing high propensity of the HTPB-IPDI system for catalysis.This revised version was published online in November 2005 with corrections to the Cover Date.     

Cure behavior of diglycidylether of bisphenol A/trimethylolpropane triglycidylether epoxy blends initiated by thermal latent catalyst

Cure behaviors of diglycidylether of bisphenol A (DGEBA)/trimethylolpropane triglycidylether (TMP) epoxy blends initiated by 1 wt % N‐benzylpyrazinium hexafluoroantimonate (BPH) as a cationic latent catalyst were investigated using DSC and rheometer. This system showed more than one type of reaction and BPH could be excellent thermal latent catalyst without any co‐initiator. The cure activation energy (E_a) obtained from Kissinger method using dynamic DSC data was higher in DGEBA/TMP mixtures than in pure DGEBA. Rheological properties of the blend system were investigated under isothermal condition using a rheometer. The gel time was obtained from the analysis of storage modulus (G′), loss modulus (G″) and damping factor (tanδ). The crosslinking activation energy (E_c) was also determined from the Arrhenius equation based on the gel time and curing temperature. As a result, the crosslinking activation energy showed a similar behavior with that obtained from Kissinger method. And the gel time decreased with increasing TMP content, which could be resulted from increasing the activated sites by trifunctional epoxide groups and decreasing the viscosity of DGEBA/TMP epoxy blend in the presence of TMP. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2114–2123, 2000     

Isoconversional method to explore the cure reaction mechanisms and curing kinetics of DGEBA/EMI‐2,4/nano‐SiC system

The curing kinetics of the diglycidyl ether of bisphenol‐A (DGEBA)/2‐ethyl‐4‐methylimidazole (EMI‐2,4)/nano‐sized carborundum (nano‐SiC) system was studied by means of nonisothermal differential scanning calorimetry (DSC). An isoconversional method of kinetic analysis yields a dependence of the effective activation energy E on the extent of conversion that decreases initially, and then increases as the cure reaction proceeds. The variations of E were used to study the cure reaction mechanisms, and the Shrinking Core Model was used to study the resin–particle reaction. The results show that the presence of nano‐SiC particles prevents the occurrence of vitrification, as well as inhibits the cure reaction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 371–379, 2006     

Isothermal cure kinetics of epoxy/phenol‐novolac resin blend system initiated by cationic latent thermal catalyst

The investigation of the cure kinetics of a diglycidyl ether of bisphenol A (DGEBA)/phenol‐novolac blend system with different phenolic contents initiated by a cationic latent thermal catalyst [N‐benzylpyrazinium hexafluoroantimonate (BPH)] was performed by means of the analysis of isothermal experiments using a differential scanning calorimetry (DSC). Latent properties were investigated by measuring the conversion as a function of curing temperature using a dynamic DSC method. The results indicated that the BPH in this system for cure is a significant thermal latent initiator and has good latent thermal properties. The cure reaction of the blend system using BPH as a curing agent was strongly dependent on the cure temperature and proceeded through an autocatalytic kinetic mechanism that was accelerated by the hydroxyl group produced through the reaction between DGEBA and BPH. At a specific conversion region, once vitrification took place, the cure reaction of the epoxy/phenol‐novolac/BPH blend system was controlled by a diffusion‐control cure reaction rather than by an autocatalytic reaction. The kinetic constants k₁ and k₂ and the cure activation energies E₁ and E₂ obtained by the Arrhenius temperature dependence equation of the epoxy/phenol‐novolac/BPH blend system were mainly discussed as increasing the content of the phenol‐novolac resin to the epoxy neat resin. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2945–2956, 2000     

Crystal structure of boron difluoride 3-phenylthiopentane-2,4-dionate. π stacking interactions and luminescence of boron difluoride acetyl acetonates

The crystal structure of boron difluoride 3-phenylthiopentane-2,4-dionate was determined. The relationship between the structure and luminescent properties is traced in the series of boron difluoride acetyl acetonates (acetyl acetonate, phenylacetyl acetonate, and phenylthioacetyl acetonate). The presence of the π stacking interactions in boron difluoride phenylthioacetyl acetonate crystals leads to increased intensity and bathochromic shift of the fluorescence band.     

Cure kinetics of biphenyl epoxy‐phenol novolac resin system using triphenylphosphine as catalyst

The effects of the concentration of triphenylphosphine as a catalyst on the cure reaction of the biphenyl epoxy/phenol novolac resin system were studied. The kinetic study was carried out by means of the analysis of isothermal experiments using a differential scanning calorimeter. All kinetic parameters including the reaction orders, activation energy and kinetic rate constants were evaluated. To describe the cure reaction with the catalyst concentration, the normalized kinetic model was developed. The suggested kinetic model with a diffusion term was successfully able to describe and predict the cure reaction of epoxy resin compositions as functions of the catalyst content and temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 713–720, 1999     

A study of the thermal cure of a phenylethynyl-terminated imide model compound and a phenylethynyl-terminated imide oligomer (PETI-5)

The kinetic mechanism of the thermal cure of a phenylethynyl-terminated imide model compound, 3,4′-bis[(4-phenylethynyl)phthalimido]diphenyl ether (PEPA-3,4′-ODA) and a phenylethynyl-terminated imide oligomer PETI-5 (MW 5000 g/mol) was studied. FTIR was used to follow the cure of the model compound, while thermal analyses (DSC) was used to follow the cure of the PETI-5 oligomer. The changes in IR absorbance of phenylethynyl triple bonds at 2214 cm⁻¹ of PEPA-3,4′-ODA as a function of cure time were detected at 318, 336, 355, and 373°C, respectively. The changes in the glass transition temperature, T_g, of PETI-5 as a function of time were measured at 350, 360, 370, 380, and 390°C, respectively. The DiBenedetto equation was applied to define the relative extent of cure, x, of the PETI-5 oligomer by T_g. For the model compound, the reaction followed first order kinetics, yielding an activation energy of 40.7 kcal/mol as determined by infrared spectroscopy. For PETI-5, the reaction followed 1.5th order, yielding an activation energy of 33.8 kcal/mol for the whole cure reaction, as determined by T_g using the DiBenedetto method. However, the cure process of PETI-5 just below 90% by this method followed first-order kinetics yielding an activation energy of 37.2 kcal/mol. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 461–470, 1998     

Synthesis of poly(glycolic acid‐alt‐12‐aminododecanoic acid): The thermal polymerization kinetics of sodium N‐chloroacetyl‐12‐aminododecanoate

A new regular poly(ester amide) consisting of glycolic acid and 12‐aminododecanoic acid was synthesized by a thermal polycondensation method involving the formation of a metal halide salt. Polymerization could start in liquefied or solid phases, depending on the reaction temperature. The polymerization kinetics were investigated by isothermal and nonisothermal isoconversional methods. The reaction model was selected with both Coats–Redfern and isokinetic relationships. The activation energy was higher when the reaction took place mainly in the solid state. A compensation effect was found between the frequency factor and the activation energy. The thermal properties of the new polymer were studied as well as the isothermal crystallization from the melt state. Melt‐grown spherulites were studied by means of polarizing optical microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1199–1213, 2006     

Fluoropolyethers end‐capped by polar functional groups. II. Effect of catalyst and reagents concentration,solvent nature,and temperature on reaction kinetics of α,ω‐bis(hydroxy)‐terminated fluoropolyethers with cycloalyphatic and aromatic diisocyanates

A comparative kinetic study of the dibutyltin dilaurate (DBTDL) and 1,4‐diazabicyclo[2,2,2]octane (DABCO) catalyzed reactions of α,ω‐bis(hydroxy)‐terminated fluoropolyethers (FPEs)—Z‐DOLs and Z‐DOL TXs—of various molecular weights and purity, with 4,4′‐dicyclohexylmethane diisocyanate (H₁₂MDI), isophorone diisocyanate (IPDI) and 2,4‐toluene diisocyanate (TDI) was carried out in different solvents. An analytical method was used to follow the kinetics of the reactions at four different temperatures. The rate of NCO disappearance measured by two independent methods—IR spectroscopy and chemical titration were found to be very close. Straight proportionality between rate constants k_cat and catalyst concentration was found. But in some cases for the DBTDL catalyzed reactions effect of catalyst saturation along with appearance of the limiting DBTDL concentration C_lim below which the rate of reaction was close to zero were observed. Reactivity of Z‐DOLs in the tin‐catalyzed urethane reactions was found to decrease with their storage time at RT due to the slow hydrolysis of the end  COOR groups impurities, which give the corresponding acids that act as a strong inhibitor of the DBTDL activity. These acid admixtures have no influence on the DABCO catalyzed reactions. For the DBTDL and DABCO catalyzed reactions of Z‐DOLs with IPDI the dependence of effective rate constants k_eff (where k_eff = k_cat · 0.01/[DBTDL] and catalyst concentration is taken in mol % based on IPDI) on total reagents concentration were found to be described by curves with a maximum. Critical reagents concentration, after which the relationship k_eff = f (C) changes from proportional to inverse proportional, seems do not substantially depend on the solvent nature. Hydrogenated analog poly(ethylene glycol) MW 400 (PEG‐400) differs greatly from Z‐DOLs: only steady decrease of k_eff was observed with increase of reagents concentration C from 5 up to 95 wt %. Activation energies for all the studied reactions are within the range of 10.8–16.7 kcal/mol. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2579–2602, 2000     

A study of the kinetics of the microwave cure of a phenylethynyl‐terminated imide model compound and imide oligomer (PETI‐5)

The kinetic mechanism of the microwave cure of a simple phenylethynyl‐terminated imide model compound, 3,4′‐bis[(4‐phenylethynyl)phthalimido]diphenyl ether (PEPA‐3,4′‐ODA) and a phenylethynyl‐terminated imide oligomer (PETI‐5, M_n 5000 g/mol) was studied. Dielectric properties of the model compound and PETI‐5 were measured in the microwave range from 0.4 GHz to 3 GHz. FTIR was used to follow the cure of the model compound (PEPA‐3,4′‐ODA), while thermal analysis (DSC) was used to follow the cure of the PETI‐5 oligomer. The changes in room temperature IR absorbance of phenylethynyl triple bonds at 2214 cm⁻¹ of PEPA‐3,4′‐ODA as a function of cure time were measured after cure temperatures of 300, 310, 320, and 330 °C. The changes in the glass‐transition temperature, T_g, of PETI‐5 as a function of cure time were measured after cure at 350, 360, 370, and 380 °C, respectively. The T_g 's were determined to calculated the relative extent of cure, x, of the PETI‐5 oligomer according to the DiBenedetto equation. For the model compound, the reaction followed first order kinetics, yielding an activation energy of 27.6 kcal/mol as determined by infrared spectroscopy. For PETI‐5, the reaction followed 1.5th order, yielding an activation energy of 17.1 kcal/mol for the whole cure reaction, as determined by T_g using the DiBenedetto method. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2526–2535, 2000     

Curing reaction of biphenyl epoxy resin with different phenolic functional hardeners

The investigation of cure kinetics and relationships between glass transition temperature and conversion of biphenyl epoxy resin (4,4′-diglycidyloxy-3,3′,5,5′-tetramethyl biphenyl) with different phenolic hardeners was performed by differential scanning calorimeter using an isothermal approach over the temperature range 120–150°C. All kinetic parameters of the curing reaction including the reaction order, activation energy, and rate constant were calculated and reported. The results indicate that the curing reaction of formulations using xylok and dicyclopentadiene type phenolic resins (DCPDP) as hardeners proceeds through a first-order kinetic mechanism, whereas the curing reaction of formulations using phenol novolac as a hardener goes through an autocatalytic kinetic mechanism. The differences of curing reaction with the change of hardener in biphenyl epoxy resin systems were explained with the relationships between T_g and reaction conversion using the DiBenedetto equation. A detailed cure mechanism in biphenyl-type epoxy resin with the different hardeners has been suggested. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 773–783, 1998     

Effect of the substituted benzene group on thermal and mechanical properties of epoxy resins initiated by cationic latent catalysts

Epoxy resins (DGEBA) were cured by cationic latent thermal catalysts, that is, N‐benzylpyrazinium hexafluoroantimonate (BPH) and N‐benzylquinoxalinium hexafluoroantimonate (BQH) to investigate the effect of substituted benzene group on cure kinetics and mechanical properties of epoxy system. Differential scanning calorimetry (DSC) was undertaken for activation energy of the system. It was also characterized in terms of flexural, fracture toughness, and Izod impact strengths for the mechanical tests. As a result, the cure reaction of both epoxy systems resulted in an autocatalytic kinetic mechanism accelerated by hydroxyl groups. Also, the conversion and cure activation energy of the DGEBA/BQH system were higher than those of DGEBA/BPH system. The mechanical properties of the DGEBA/BQH system were also superior to those of the DGEBA/BPH system, as well as the morphology. This was probably due to the consequence of the effect of the substituted benzene group of the BQH catalyst, resulting in increasing the crosslinking density and structural stability in the epoxy system studied. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2419–2429, 2004     

Kinetic studies on the thermal polymerization of N‐chloroacetyl‐11‐aminoundecanoate potassium salt

A potassium salt of N‐chloroacetyl‐11‐aminoundecanoate was thermally polymerized to obtain the corresponding poly(glycolic acid‐alt‐11‐aminoundecanoic acid). A kinetic study was then performed that was based on isothermal and nonisothermal polymerizations performed in a differential scanning calorimeter. The complete kinetic triplet was determined (the activation energy, pre‐exponential factor, and integral function of the degree of conversion). A kinetic analysis was performed with an integral isoconversional procedure (free model), and the kinetic model was determined both with the Coats–Redfern method (the obtained isoconversional value being accepted as the effective activation energy) and through the compensation effect. The polymerization followed a three‐dimensional growth‐of‐nuclei (Avrami) kinetic mechanism. Isothermal polymerization was simulated with nonisothermal data. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1166–1176, 2005     

Studies on Polymerization of Vinyl Compounds Initiated by Metal Chelate III. Accelerating Effect of Aniline on the Polymerization of Methyl Methacrylate Initiated by Nickel Chelate of β-Diketone

Aniline markedly accelerated polymerization of methyl methacrylate initiated by metal chelates of β-diketones. The kinetic studies of the polymerizaion of methyl methacrylate initiated by Ni (II) acetyl acetonate in the presence of aniline yielded R_p=[I]^0.55 [A]^0.66 [M]^1.87. The polymerization was of free radical in character. The accelerating effect of aniline was attributed to its reduction activation of the chelate. The activation energy for the overall polymerization was 21.3Kcal/mole, which yielded 33.4Kcal/mole for the activation energy for the initiation.     

Catalysis of N‐Methylaniline‐Blocked Polyisocyanate‐Hydroxyl‐Terminated Polybutadiene Cure Reaction

Catalysis of cure reaction between N‐methylaniline‐blocked polyisocyanate and hydroxyl‐terminated polybutadiene was investigated using a variety of tertiary amine and organotin catalysts. The catalytic activity of amine and organotin compounds was determined from the cure‐time results. It was found that the activity of the catalyst depends upon the steric constrain around the catalytic center. The organotin compounds showed higher catalytic activity than the amine catalysts. FTIR results obtained under isothermal condition revealed that DABCO selectively catalyze the urethane formation reaction, whereas DBTDL catalyze both the allophanate formation and urethane formation reactions during curing process. The synergistic effect of amine and organotin mixed catalysts on the cure reaction was also investigated.     

Arrhenius parameters determination in non-isothermal conditions for the uncatalyzed gasification of carbon by carbon dioxide

Non-isothermal thermogravimetric data were used to evaluate the Arrhenius parameters (activation energy, E, and pre-exponential factor, A) for the uncatalyzed gasification by carbon dioxide of two carbons, select as steam activated carbon (BPL) and SP-1 spectroscopically pure graphite. The paper reports on the application of the model-free isoconversional method (KAS/Vyazovkin linear method) for evaluating the activation energy of the gasification process. Activation energies have been calculated by this method were in good agreement with literature data for similar carbons. On the other hand, by means of the kinetic compensation relation between E and ln A, which was established by the model-dependent Coats–Redfern method, the value of the pre-exponential factor was estimated from the known value of the model-independent activation energy.     

Evaluation of the thermal oxidative stability of polyimides via TGA techniques

Thermogravimetric analysis (TGA) has been used for many years to evaluate polymer thermal stability. The objective of this study is to determine if weight-loss curves from TGA and isothermal TGA (IGA) can be used to determine degradation activation energies and thus rank the thermal stability (TS) and thermooxidative stability (TOS) for selected polyimides. Two high-temperature stable addition-cured polyimides and two aromatic condensation polyimides, all four containing fluorinated connecting linkages in the dianhydride monomers, were compared. Three TGA kinetic methods (Coats/Redfern, Ingraham/Marier, Horowitz/Metzger) were used to determine the activation energy for decomposition in air. The results were then used to rank polyimide stability compared to more traditional rankings based on long-term isothermal air aging weight-loss (IWL) studies and thermal decomposition temperatures (T_d) from TGA data. Use of TGA coupled to a Fourier transform infrared (TGA–FTIR) spectrophotometer allowed for the simultaneous identification and relative quantification of evolved decomposition products (CO₂, CO, ArNCO, and CHF₃) of the four polyimides degraded in air or nitrogen. Isothermal TGA–FTIR (IGA–FTIR) was also done in air to determine the relative rate of product evolution at a constant temperature. Activation energies using TGA and IGA data were determined and then compared with IWL values for the degradation of the polyimide to examine for correlations of real-life thermal oxidative aging to accelerated aging techniques. The Coats/Redfern method and T_d were found to best reproduce stability rankings of those from long-term, high-temperature IWL studies. Together, they may provide a time-saving technique to evaluate polyimide thermal oxidative stability. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3943–3956, 1999     

Thermal stability and toughening of epoxy resin with polysulfone resin

The cure behavior, thermal stability, and mechanical properties of diglycidylether of bisphenol A (DGEBA)/polysulfone (PSF) blends initiated by 1 wt % N‐benzylpyrazinium hexafluoroantimonate as a cationic latent catalyst were investigated. The DGEBA/PSF content was varied within 100/0–100/40 wt %. Latent properties were studied through the measurement of the conversion as a function of the curing temperature, and the cure activation energy (E_a) was studied by the Kissinger method with a dynamic differential scanning calorimetry analysis. The thermal stabilities, largely based on the integral procedural decomposition temperature (IPDT) and decomposed activation energy (E_t), were investigated by the measurement of thermogravimetric analysis. For the mechanical properties of the casting specimens, the critical stress intensity factor (K_IC) test was performed, and their fractured surfaces were examined with scanning electron microscopy. E_a, IPDT, E_t, and K_IC increased with PSF increasing in the neat epoxy resin up to 30 wt %. However, there was a marginal decrease in the blend system in both the thermal and mechanical properties due to the phase separation between DGEBA and PSF. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 121–128, 2001     

Research on the Blocking Reaction Kinetics and Mechanism of Aqueous Polyurethane Micelles Blocked by 2,4,6-Trichlorophenol

The blocked terminal-isocyanate (NCO) aqueous polyurethane micelles were prepared by using the 2,6-hexamethylene diisocyanate (HDI), polyethylene glycol (PEG), dimethylol propionic acid (DMPA), and 2,4,6-trichlorophenol (TCP) as blocking agent. This paper was focused on the kinetics research of the TCP blocking terminal-NCO of pre-polymer, which occurred during the preparation process of TCP blocked aqueous polyurethane micelles. The kinetics parameters were obtained in the absence and presence of dibutyl tin dilaurate (DBTDL) as catalyst, respectively. Furthermore, the mechanism for TCP blocking terminal-NCO of pre-polymer was explored. The results showed that the blocking reaction was second order reaction, and the reaction activation energy was 43.890 KJ/mol without catalyst. In the presence of DBTDL, the blocking reaction activation energy was reduced to 34.412 KJ/mol, and the reaction rate was improved significantly. In addition, TCP blocking terminal-NCO of pre-polymer could be ascribed to the nucleophilic addition between nucleophilic phenolic hydroxyl of TCP and the carbon atom of -NCO group.     

Phosphorus Schiff base ligand and its complexes: Experimental and theoretical investigations

A phosphorus-containing Schiff base was prepared from bis{3-[2-(4-amino-1,5-dimethyl-2-phenylpyrazol-3-ylideneamino)ethyl]indol-1-ylmethyl}phosphinic acid and paraformaldehyde as a novel antibacterial compound. The reaction of the Schiff base ligand with VO(IV), Ni(II), Co(II), Cu(II), Zn(II), Cd(II), Hg(II), Pd(II) and Pt(IV) led to binuclear species of metal complexes, depending on the ratio of metal ion and ligand. The ligand and its complexes were investigated using elemental analysis, Fourier transform infrared, ¹H NMR, ¹³C NMR, UV–visible and mass spectra, thermogravimetric analysis, conductivity measurements and thermal analysis. The results showed that the Schiff base behaves as a tetradentate ligand; moreover, on the basis of conductance results, of all the prepared complexes are non-electrolytes, excepting the Pt(IV) complex. The metal complexes were found to be formed with a metal-to-ligand ratio of 2:1, except for the Pt(IV) complex with a ratio of 1:1. The activation thermodynamic parameters (ΔE*, ΔH*, ΔS*, ΔG* and K) and the activation energy of thermal decomposition were determined from thermogravimetric analysis using the Coats–Redfern method. The biological activities of the metal complexes were screened against the growth of bacteria and fungi in vitro to assess the antimicrobial potential and study the toxicity of the compounds. The prepared compounds have noteworthy antimicrobial properties.