Initial Activation Energy Research Articles

Synthesis of sorption-active polyfunctional derivatives of polycaproamide and polyglycidyl methacrylate graft copolymers

The kinetic and thermodynamic parameters of polymer-analog conversion of the graft copolymer of polycaproamide and polyglycidyl methacrylate with sulfamic acid (initial rate, duration, and effective activation energy) were determined. It was shown that the values of the initial rates correlate well with the concentration of the sulfamic acid reaction solution. The formation of a new derivative of the PCA—PGMA graft copolymer containing functionally active amino and sulfo acid groups was confirmed by the data from chemical and analytical analysis and IR spectroscopy. A method was developed for obtaining a sorption-active fibrous polyampholyte containing functionally active amino and sulfo acid groups with SECHCl = SECNaOH = 0.895 mmole/g.

Kinetic regularities and mechanism of polymerization of perfluoromethylvinyl ether at high pressures

The kinetics of the thermal polymerization of perfluoromethylvinyl ether (PFMVE) is studied at pressures of 3–13 kbar (300–1300 MPa) and temperatures of 80–260°C. The activation energy (Eact = (76 ± 3) kJ/mol) and activation volume (ΔV0⪼ = −(27 ± 2) cm3/mol) for the overall polymerization rate are determined. The inhibition method is used to estimate the activation energy of thermal initiation (Ein = (79.9 ± 3) kJ/mol). The quantity Ep − (1/2)Et was calculated to be 36.6 ± 3 kJ/mol. The limiting polymerization temperature was evaluated: Tlim = (180 ± 3)°C. A mechanism of PFMVE polymerization is proposed on the assumption that the reaction is bimolecular.

Selective recognition of 2,4-dichlorophenol from aqueous solution by uniformly sized molecularly imprinted microspheres with β-cyclodextrin/attapulgite composites as support

In this study, uniformly sized molecularly imprinted microspheres (MIP) using β-cyclodextrin/attapulgite composites as support were prepared for recognitive adsorption of 2,4-dichlorophenol (2,4-DCP) from aqueous solution. Characterization of MIP were achieved by FT-IR spectra, SEM micrographs, nitrogen adsorption–desorption analysis, EDX measurement and elemental analysis. Equilibrium data, at various temperatures, were described by the Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The thermodynamics parameters (positive values of Δ H° and Δ S°, negative values of Δ G°) indicated that binding system for MIP was endothermic, entropy gained and spontaneous. Kinetic properties were successfully investigated by pseudo-first-order model, pseudo-second-order model, intraparticle diffusion equation, initial adsorption rate, half-adsorption time and activation energy. A diffusion-controlled process as the essential adsorption rate-controlling step was also proposed. MIP could be reused four times without significant loss in adsorption capacity. The selectivity of MIP also demonstrated higher affinity for target 2,4-DCP over competitive phenolic compounds than that of non-imprinted polymers (NIP).

Kinetics and mechanism of thermal polymerization of hexafluoropropylene under high pressures

The basic kinetic parameters of thermal polymerization of hexafluoropropylene, namely, general rate constants, degree of polymerization, and their temperature and pressure dependences in the range of 230–290 °C and 2–12 kbar (200–1200 MPa) were determined. The activation energy (E act = 132±4 kJ mol−1) and activation volume (ΔV 0 ≠ = −27±1 cm3 mol−1) were calculated. The activation energy of thermal initiation of polymerization was estimated. The reaction scheme based on the assumption about a biradical mechanism of polymerization initiation was proposed.

4‐Acetoxystyrene nitroxide‐mediated controlled radical polymerization: Comparison with styrene

AbstractThe nitroxide‐mediated controlled radical polymerization (NM‐CRP) of 4‐acetoxystyrene with an alkoxyamine was analyzed by a combined experimental and modeling approach. At low nitroxide concentrations, thermal initiation was significant, and control of the polydispersity was poor, as was observed previously for styrene. A continuum model based on the method of moments was used to regress the parameters for the reversible nitroxide uncoupling/coupling reactions (activation energy of uncoupling), thermal initiation (activation energy of initiation), and termination (frequency factor of recombination). The model was able to capture the molecular weight averages and the polydispersity index as a function of time and the nitroxide concentration qualitatively and quantitatively. Using this mechanistic framework, we developed kinetic Monte Carlo models that allowed the molecular weight distributions to be predicted explicitly in good agreement with experimental data. A comparison of the NM‐CRP of 4‐acetoxystyrene and styrene is provided to illustrate the effect of the acetoxy substituent. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Modeling and simulation on dynamic recrystallization of 30Cr2Ni4MoV rotor steel using the cellular automaton method

The cellular automaton (CA) method coupling fundamental metallurgical principles was used to simulate the initial microstructure and dynamic recrystallization (DRX) of 30Cr2Ni4MoV rotor steel. For the initial microstructure generation, reasonable transformation rules were established based on the thermodynamic mechanism, the activation energy and the curvature-driven mechanism. For the purposes of obtaining the material constants which were used in the CA model for DRX, including initial grain size, nucleation rate, softening parameter and activation energy, the hot deformation characteristics of 30Cr2Ni4MoV rotor steel were investigated by uniaxial hot compression tests on Gleeble-3500 machine. The effect of a wide range of thermomechanical processing parameters (temperature and strain rate) on the nucleation rate, the percentage of DRX and the final grain size were investigated. By comparison of the flow stress–strain curves and the metallographs, it was shown that the CA model coupling fundamental metallurgical principles can accurately simulate the microstructural evolution and the plastic flow behavior for 30Cr2Ni4MoV rotor steel at various deformation parameters.

An investigation of melt rheology and thermal stability of poly(lactic acid)/ poly(butylene succinate) nanocomposites

AbstractA systematic investigation of the rheological and thermal properties of nanocomposites prepared with poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and organically modified layered silicate was carried out. PLA/PBS/Cloisite 30BX (organically modified MMT) clay nanocomposites were prepared by using simple melt extrusion process. Composition of PLA and PBS polymers were fixed at a ratio of 80 to 20 by wt % for all the nanocomposites. Rheological investigations showed that high clay (> 3 wt %) contents strongly improved the viscoelastic behavior of the nanocomposites. Percolation threshold region was attained between 3 and 5 wt % of clay loadings. With the addition of clay content for these nanocomposites, liquid‐like behavior of PLA/PBS blend gradually changed to solid‐like behavior as shown by dynamic rheology. Steady shear showed that shear viscosity for the nanocomposites decreased with increasing shear rates, exhibiting shear‐thinning non‐Newtonian behavior. At higher clay concentrations, pseudo‐plastic behavior was dominant, whereas pure blend showed almost Newtonian behavior. Thermogravimetric analysis revealed that both initial degradation temperature (at a 2% weight loss) and activation energy of thermal decomposition nanocomposite containing 3 wt % of C30BX were superior to those of other nanocomposites as well as to those of PLA/PBS blend. Nanocomposite having 1 wt % of C30BX did not achieve expected level of thermal stability due to the thermal instability of the surfactant present in the organoclay. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Morphology, mechanical properties, and thermal stability of poly(L‐lactic acid)/poly(butylene succinate‐co‐adipate)/silicon dioxide composites

AbstractPoly(butylene succinate‐co‐adipate) (PBSA) and two types of SiO2 (hydrophilic or hydrophobic) were used to modify poly(L‐lactic acid) (PLLA). The mechanical properties, rheological and thermal behavior, phase morphology, and thermal stability of PLLA/PBSA/SiO2 composites were investigated. The impact strength, flexural strength, and modulus of PLLA/PBSA blends increased after the addition of hydrophobic SiO2 without decreasing the elongation at break, and the elongation at break monotonically decreased with increasing hydrophilic SiO2 content. The melt elasticity and viscosity of the PLLA/PBSA blend increased with the addition of SiO2. The hydrophilic SiO2 was encapsulated by the dispersed PBSA phase in the composites, which led to the formation of a core–shell structure, whereas the hydrophobic SiO2 was more uniformly dispersed and mainly located in the PLLA matrix, which was desirable for the optimum reinforcement of the PLLA/PBSA blend. The thermogravimetric analysis results show that the addition of the two types of SiO2 increased the initial decomposition temperature and activation energy and consequently retarded the thermal degradation of PLLA/PBSA. The retardation of degradation was prominent with the addition of hydrophobic SiO2. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The influence of chain‐ends on the thermal and rheological properties of some 40/60 PES/PEES copolymers

AbstractFour random, differently ended (Cl, NH2, OH, and COO−), polyethersulfone/polyetherethersulfone (PES/PEES) copolymers were studied to investigate the influence of chain ends on thermal and rheological behaviors. The number average molar mass (Mn ≈ 9500 g·mol−1) and the PES/PEES ratio (40/60) of all copolymers investigated were checked by 1H NMR spectra. Thermal degradations were carried out in the scanning mode and initial decomposition temperatures (Ti) and activation energy values of degradation (Ea) were obtained. Glass transition temperature (Tg) was determined by differential scanning calorimetry and complex viscosity (η*) by rheological measurements in isothermal heating conditions (T = 270°C). All parameters determined were largely affected by copolymer chain ends and decreased according to the same order, OH > NH2 > Cl > COO−. The results were discussed and interpreted. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Preparation and characterization of phosphorus‐containing Mannich‐type bases as curing agents for epoxy resin

AbstractTwo novel phosphorus‐containing Mannich‐type bases, [(2‐{[(diethoxy‐phosphoryl)‐phenyl‐methyl]‐amino}‐ ethylamino)‐phenyl‐methyl]‐phosphonic acid diethyl ester (PEDA) and ({2‐[2‐(2‐{[(diethoxy‐phosphoryl)‐phenyl‐methyl]– amino}‐ethylamino)‐ethylamino]‐ethylamino}‐phenyl‐methyl)‐phosphonic acid diethyl ester (PTTA) were prepared and employed as curing agents in an attempt to prepare flame retardant epoxy systems. Through a curing reaction, phosphorus was incorporated in the backbone of the epoxy polymer. The processing characteristic of these systems was studied in terms of gel time at different temperatures. Thermal and flame retardancy properties of the cured epoxy thermosets were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and flammability test. The degradation activation energy was calculated by Kissinger's model. The results showed that the gel time of the phosphorus‐containing epoxy systems was prolonged; the glass transition temperature (Tg) was increased due to the introduction of phosphorus and the initial degradation activation energy of phosphorus‐containing epoxy systems was lower than phosphorus‐free epoxy systems. High char yield (23–27 wt%) and limiting oxygen index (LOI) values of 28–30 were observed for the phosphorus‐containing epoxy thermosets, indicating their improvement in flame retardancy. Copyright © 2008 John Wiley & Sons, Ltd.

PREPARATION AND CHARACTERIZATION OF SOLUBLE SULFONATED POLYBENZIMIDAZOLE FOR PROTON EXCHANGE MEMBRANE MATERIALS

A series of sulfonated polybenzimidazoles (sPBI-SF) were prepared from 2,2-bis(4-carboxyphenyl)hexafluoro- propane (BIS-B-AF), 3,3'-disulfonyl-4,4'-dicarboxyldiphenylsulfone (DSDCDPS) and 3,3'-diaminobenzidine (DAB) at various stoichiometric ratio by solution copolycondensation in poly(phosphoric acid). The chemical structure of the resulting sPBI-SF was confirmed by FTIR and 1 H-NMR. The sPBI-SFs with high molecular-weights (Mn = 39400−65500) were soluble in DMF, DMSO or DMAc. Therefore, they could form some transparent and flexible membranes easily by solution casting. The glass-transition temperatures of the acidic form sPBI-SF were in the range from 222°C to 269°C. The extrapolated onset decomposition temperatures were up to 440°C. The sulfonic groups grafted in the PBI chain had higher initial thermal degradation activation energy and exhibited excellent thermal stability. In addition, these membranes with good mechanical properties presented the swelling degree below 12% and the water uptake about 16%. The proton conductivities of sPBI-SF membranes measured by alternating-current impedance spectroscopy attained to 1.64 × 10 −3 S/cm at 70°C.

A kinetic study on non-catalytic reactions in hydroprocessing Boscan crude oil

Non-catalytic hydrothermal cracking reactions are known to associate with catalytic hydrocracking reactions. In a recent study on hydroprocessing of Boscan crude over a specific catalyst system containing three distinct catalysts, it was found that hydrodesulfurization (HDS) and hydrodemetallation (HDM) reactions continued even when the catalyst is severely deactivated. Since the reactor was packed with considerable amount of inert material besides the three catalysts, it will be advantage to determine if the inert materials can also facilitate hydroprocessing reactions. A series of kinetic experiments for the inert particles was undertaken under different space velocity and temperature conditions.The extent of catalytic and non-catalytic hydroprocessing reactions was assessed. Through statistical analysis, the initial reaction rate constant, reaction order and activation energy for various hydroprocessing reactions were then determined. The absolute average deviations (AAD) of the kinetics values obtained for inert materials are less than 10%.

N-hydroxyphthalimide-initiated radical polymerization of vinyl monomers

The initiating ability of N-hydroxyphthalimide in polymerization of methyl methacrylate and acrylonitrile was examined. For the polymerization of methyl methacrylate, the initial polymerization rates and activation energies were determined, and the dependences of the polymerization rates on the initiator and monomer concentrations were evaluated. An initiation mechanism was suggested.

Efficient regioselective acylation of 1-β-d-arabinofuranosylcytosine catalyzed by lipase in ionic liquid containing systems

Seven ionic liquids (ILs) were tested for use in the regioselective acylation of 1-β-D-arabinofuranosylcytosine (ara-C) by vinyl propionate, catalyzed by immobilized Candida antarctica lipase B. The results demonstrated that the nature of both the cations and the anions of ILs had a significant effect on the initial rate and the substrate conversion, but little effect on the regioselectivity of the reaction. The lipase displayed enhanced activity toward ara-C when the alkyl chain of CnMIm·BF4 increased in length (n = 4–8) and no acylation reaction occurred in C4MIm·Cl or C4MIm·Br. To further enhance the initial rate and substrate conversion, co-solvent mixtures of ILs and organic solvents were investigated. Among various IL-containing systems examined, 10% (v/v) C4MIm·PF6–tetrahydrofuran gave the highest initial rate and substrate conversion. In this reaction medium, the optimal water activity, vinyl propionate/ara-C molar ratio, temperature and shaking rate were 0.07, 15 ∶ 1 (mol/mol), 60 °C and 250 rpm, respectively. Under these conditions, the initial rate, substrate conversion and the regioselectivity were 94.0 mM h−1, 98.5% and 99%, respectively. An additional comparative study demonstrated that the enzymatic acylation proceeded with very similar initial rate, substrate conversion, regioselectivity and activation energy whether the reaction medium was 10% (v/v) C4MIm·PF6–tetrahydrofuran or 28% (v/v) hexane–pyridine (the best organic solvent mixture for the reaction). However, the lipase exhibited a much higher stability in the IL-containing system, which may also have environmental advantages. The product of the lipase-catalysed reaction was characterized by NMR, FT-IR spectroscopy and was shown to be the 5′-O-monoester of ara-C.

Chitosan/carboxymethyl cashew gum polyelectrolyte complex: synthesis and thermal stability

Chitosan/carboxymethyl cashew gum polyelectrolyte complexes were synthesized using different proportions of chitosan (CH) and carboxymethyl cashew gum (CMCG). The optimum CH:CMCG ratio was 25:75, which produced highest product yield. Polyelectrolyte (PEC) samples were characterized by thermogravimetric analysis and FT-IR spectroscopy. Parameters such as initial and maximal degradation temperatures and activation energy ( E a) were determined. Activation energies follows the order CMCG > CH > PECs samples. Infrared analysis from residual products after heating at 280 °C in different times indicated that cleavage of the glycosidic bond and formation of unsaturated products occurred.

Characterization and thermal behavior of polymer-modified asphalt

A styrene-butadiene-styrene modified asphalt cement was characterized by infrared, differential scanning calorimetry, thermogravimetric analysis and empirical tests such as ring and ball softening point, penetration and elastic recovery. After aging in the rolling thin-film oven, the polymer-modified asphalt presented structural changes relating to oxidation of the material. The infrared spectra showed an increase in hydroxyl groups and the formation of carbonyl compounds and sulphoxides. The percentage of crystallized fraction calculated from differential scanning calorimetry was 0.41%. Thermogravimetric analyses in inert and oxidative atmospheres revealed distinct events during thermal decomposition; the initial activation energies were similar, but changed as the process evolved.

Prediction of compressive strength of fly ash concrete by new apparent activation energy function

A new prediction model using apparent activation energy is proposed to estimate the variation of compressive strength of fly ash concrete with aging. After analyzing the experimental result with the model, fly ash replacement content and water–binder ratio influence on apparent activation energy was investigated. According to the analysis, the model provides a good estimation of compressive strength development of fly ash concrete with aging. As the fly ash replacement content increases, limiting relative compressive strength and initial apparent activation energy increase. Concrete with water–binder ratio smaller than 0.40 gives nearly constant limiting relative compressive strength and initial apparent activation energy when analyzed with various water–binder ratios. However, concrete with water–binder ratio larger than 0.40 increases limiting relative compressive strength and initial apparent activation energy.

Propene hydrogenation over truncated octahedral Pt nanoparticles supported on alumina

Colloidal Pt nanoparticles synthesized by a 1:5 concentration ratio of K 2PtCl 4 to polyacrylate were loaded on nanoporous alumina using the impregnation method at room temperature. The deposited Pt particles, present on the external surfaces of the support, were characterized by transmission electron microscopy, which indicated predominantly truncated octahedral (TO) shapes with a mean diameter of 10 nm. Their catalytic performance in the hydrogenation of propene at 30–80 °C was studied as a test reaction. The initial rate, reaction order, rate constant, activation energy, and turnover frequency were determined. The activation energy was found to be 8.4±0.2 kcal/mol, which is slightly lower than results reported for other platinum systems (10–14 kcal/mol). The TO platinum nanoparticles have atom-high surface steps, ledges, and kinks, and these atomic-scale fine structures are expected to decrease the activation energy. The reactivity of the surface atoms in this nanoparticle is so high that above 50 °C side reactions leading to complete surface poisoning take place within a few minutes. The effect of the polymer concentration of the polyacrylate-capped TO Pt/Al 2O 3 on the hydrogenation catalytic activity was also investigated.

Radical polymerization behavior of ethyl ortho‐(4‐phenyl‐1,3‐dioxolan‐2‐yl)phenyl fumarate

AbstractThe polymerization of ethyl ortho‐(4‐phenyl‐1,3‐dioxolan‐2‐yl)phenyl fumarate (EPDPF) with dimethyl 2,2′‐azobisisobutyrate (MAIB) was kinetically investigated in benzene. The polymerization rate (Rp) at 60 °C was presented by Rp = k[MAIB]1.1[EPDPF]0.8. The number‐average molecular weight of poly(EPDPF) was in the range of 2500–3500. Analysis of 1H and 13C NMR spectra of the resulting polymers suggested that the radical polymerization of EPDPF proceeds in a complicated manner involving vinyl addition, intramolecular hydrogen abstraction, and ring opening of the cyclic acetal. The polymerization system involved electron spin resonance (ESR)‐observable poly(EPDPF) radicals under the practical polymerization conditions. ESR‐determined apparent rate constants (2.0–8.5 L/mol s) of propagation increased with increasing initiator concentration and decreasing monomer concentration. The apparent rate constants (0.68–6.6 × l06 L/mol s) of termination decreased with the monomer concentration and slightly increased with the initiator concentration. The activation energies of initiation (Ei), propagation (Ep), and termination (Et) were calculated as Ei = 158, Ep = 41, and Et = 30 kJ/mol, respectively. Radical copolymerization of EPDPF with styrene was also examined at 70 °C in benzene. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2945–2955, 2002

The dispersion polymerization of unsaturated monomers initiated by the macromonomeric initiator

The dispersion polymerizations of styrene (St) and methyl methacrylate (MMA) initiated by poly(oxyethylene) macroinimer (PEO-MIM) in ethanol/water were investigated at 50, 60 and 80 °C. The polymerisation rate vs. conversion dependence was described by with a maxim at the beginning of polymerisation. Polymerization was faster with MMA than with St. The limiting conversion was inversely proportional to temperature and was much more pronounced with St. The rate of polymerization increased with temperature. The overall initial activation energy increased with conversion and reached value ca. 25 kJ.mol -1 for MMA and 50 kJ.mol -1 for styrene at ca. 60% conversion. The particle size was observed to decrease with increasing the macroinimer concentration. The polymer dispersions were unstable and a large amount of coagulum appeared during the polymerisation especially in the styrene-containing reaction system.