Activation Energy For Propagation Research Articles

Solution Polymerization of Methyl Methacrylate in an Ionic Liquid Employing Cyclic Multifunctional Initiators

1‐Butyl‐3‐methylimidazolium tetrafluoroborate ([BMIM][BF4]) was used as a solvent during the methyl methacrylate polymerization, in a temperature range of 110 to 130°C, employing two multifunctional cyclic peroxides as initiators, the pinacolone diperoxide and the diethylketone triperoxide, and results were compared with those obtained in N,N‐dimethylformamide (DMF) as a solvent under the same reaction conditions. The polymerization rate was approximately four times faster in [BMIM][BF4] than in DMF, and this behavior is supported by the higher decomposition rate constants calculated for both initiators in pure ionic liquid in comparison with those calculated in DMF. The average molecular weights values were nearly three times lower in DMF than in the ionic liquid, and this is explained by the reduction in the propagation activation energy in the presence of the ionic liquid.

Structural Sensitivity of Carbon Monoxide Hydrogenation by Nano-Structured Iron Catalyst.

A new size dependence kinetic equation for chain growth factor in Fischer-Tropsch synthesis (FTS) was developed using a thermodynamic analysis method. For evaluation of structural sensitivity of FTS reaction, a series of iron oxide nanoparticles were prepared as a catalyst via precipitation by microemulsion method. The experimental results indicated that the difference between activation energies for propagation and termination reactions (Et-Ep) decreased with decreasing the catalyst particle size. Calculated size dependent model parameters were employed for evaluation of surface tension energy (σ) and size-independent activation energy for chain growth probabilities.

Radical Propagation Kinetics of N‐Vinylpyrrolidone in Organic Solvents Studied by Pulsed‐Laser Polymerization–Size‐Exclusion Chromatography (PLP–SEC)

Pulsed‐laser polymerization with subsequent analysis of the polymer molar mass distribution by size‐exclusion chromatography, PLP–SEC, is used to measure the propagation rate coefficient, kp, of N‐vinylpyrrolidone (NVP) in a series of organic solvents, varying the NVP concentration from 5 to 100 wt% and varying the temperature between –5 and +80 °C. In contrast to the 20‐fold increase observed in aqueous solution upon decreasing the NVP concentration from bulk to dilute conditions, the kp values of NVP in butyl acetate, iso‐propyl acetate, N‐ethylpyrrolidone, and N‐ethylformamide stay within 20% of the bulk value and exhibit no significant dependence on monomer concentration. The kp behavior of NVP in methanol and n‐butanol is intermediate between the one in water and in the other organic solvents, with kp increasing by about a factor of 2 upon lowering the monomer concentration from bulk to 5 wt% NVP. The activation energies for propagation in organic solvents agree within experimental uncertainty with the value reported for bulk NVP. The data demonstrate that hydrogen bonding is responsible for the increase in kp upon dilution, with this effect being much stronger in an aqueous environment than in a solution of alcohol. image

Cationic polymerization of isobutylene coinitiated by AlCl3 in the presence of ethyl benzoate

The cationic polymerizations of isobutylene (IB) coinitiated by AlCl3 were carried out in solvent mixture of n-hexane/methylene dichloride (n-hex/CH2Cl2) of 60/40 V/V in the presence of ethyl benzoate (EB) at various temperatures range from −80°C to −30°C. The effects of EB concentration ([EB]) and polymerization temperature on monomer conversion, weight-average molecular weight (Mw) and molecular weight distribution (MWD, Mw/Mn) of polyisobutylene (PIB) products were investigated. The rate of polymerization decreased while Mw of PIB products increased with increasing [EB]. The polymers with high molecular weight could be prepared in the presence of a suitable amount of EB. Significantly, the polymers with high Mw of 80.2 × 104 and 65.4 × 104 could be produced at −80°C and −70°C at [EB] = 0.24 × 10−3 mol/L respectively, which were much higher than that (Mw = 57.9 × 104) of PIB prepared at −100°C in the absence of EB. A simple but effective method for preparing the high molecular weight polyisobutylenes was developed in this work. It has been also found that the activation energy for propagation (Ep) depended on the polymerization temperature range in the presence of EB. An obvious inflection of the linear plots of lnXn versus 1/Tp occurred at the temperature range from −60°C to −50°C at four different concentrations of EB from 0.19 × 10−3 mol/L to 0.33 × 10−3 mol/L, and thus the inflection temperature (Tinf) was in the range of −60°C to −50°C. When [EB] was in the range of 0.24 × 10−3 mol/L to 0.33 × 10−3 mol/L, Ep was determined to be around −12 kJ/mol when the polymerization was carried out at temperatures from −80°C to Tinf and to be around −28 kJ/mol at temperatures from Tinf to −15°C respectively.

Nonconventional Emulsion Polymerization of Methyl Methacrylate. Effect of Cu(II)/Histidine Complex Catalyst and Different Peroxo-Salts

The characteristics of nonconventional (soap-free) aqueous emulsion polymerization reactions of methyl methacrylate were evaluated by the catalytic effect of in situ developed different transition metal (II) chelate complex with amino acids initiated by different peroxo salts like potassium monopersulfate (KMPS, KHSO5), potassium persulfate (KPS, K2S2O8), ammonium persulfate (APS, (NH4)2S2O8). From the comparative data, the CuSO4/histidine chelate complex was selected as a novel catalyst for a detailed kinetic and spectrometric study of polymerization. Both kinetic and thermodynamic aspects of the polymerization dictate which initiator and particle morphology are obtained. The complex catalyzed polymerization proceeded smoothly until high conversion and yielded stable emulsions. The apparent activation energies (Ea) for the complex catalyzed emulsion polymerization were computed for different initiators to be 34, 38, and 46 kJ mol-1, each a very low value. Use of these values and activation energies of propagation and termination for MMA gave an unexpectedly low activation energies (Ed, 26, 34, and 51 kJ mol-1 for KMPS, KPS, and APS respectively) to the decomposition of different persulfate initiators in the complex catalyzed system. The emulsion polymer latex was characterized through the determination of average molecular weights of the purified polymers by gel permeation chromtography (GPC) and viscosity methods and the morphology by scanning electron microscopy (SEM). The coordination complex catalytic system shows excellent industrial performance characteristics in preparing micro- to nano-scale latex particles.

Kinetic study of olefin polymerization with a supported metallocene catalyst. IV. Comparison of bridged and unbridged catalyst in gas phase

AbstractA kinetic study of ethylene/1‐hexene (E/1‐H) copolymerization is conducted with a supported bridged metallocene catalyst in a gas phase reactor. The investigation into the kinetics of ethylene/1‐hexene copolymerization includes the effects of operational parameters such as the reaction temperature, pressure, and comonomer concentration. On‐line perturbation techniques are implemented to determine key kinetic parameters such as the activation energies for propagation and catalyst deactivation. A comparison of the kinetic parameters and behavior is made between the bridged and a previously studied unbridged catalyst. Finally, a two‐site model is proposed to explain the observed kinetic behavior with changing reaction temperature and comonomer concentration. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1451–1459, 2001

Kinetic study of olefin polymerization with a supported metallocene catalyst. II. Ethylene/1‐hexene copolymerization in gas phase

AbstractA kinetic study of ethylene/1‐hexene copolymerization is conducted with a supported metallocene catalyst in a gas‐phase reactor. The investigation into the kinetics of ethylene/1‐hexene copolymerization includes the effects of operational parameters such as the reaction temperature, pressure, and comonomer concentration. The large variations in gas‐phase composition using only an initial charge of 1‐hexene are illustrated by experiment. To remedy this, the ability to control the comonomer composition of 1‐hexene online for the entire duration of the reaction is demonstrated. Online perturbation techniques are implemented to determine key kinetic parameters such as the activation energies for propagation and catalyst deactivation. From pressure perturbation results, a reaction rate order close to 1 is obtained for ethylene in the presence of 1‐hexene. Finally, all the parameters obtained from the study are compared to those determined from ethylene–propylene (E–P) copolymerization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1096–1119, 2001

A kinetic study on polymerization of methyl methacrylate with di-t-butyl perfumarate

Di-t-butyl perfumarate (DBPF) was found to induce the radical polymerizations of various vinyl monomers at 60°C in benzene, although the initiation activity was considerably lower than those of dimethyl 2,2'-azobisisobutyrate and benzoyl peroxide. The polymerizations with DBPF showed a tendency of dead-end polymerization. The polymerization of methyl methacrylate (MMA) with DBPF was kinetically studied in chlorobenzene. The initial polymerization rate (R p ) was given by R p = k [DBPF] 0.5 [MMA] 1.1 . The overall activation energy of the polymerization was 47 kJ/mol, a very low value. Use of this value and activation energies of propagation and termination for MMA gave an unexpectedly low activation energy (65 kJ/mol) to the decomposition of DBPF, a t-butyl perester, in the polymerization system. An ESR study on the polymerization of di-2-ethylhexyl itaconate with DBPF revealed that the observed dead-end tendency comes from the consumption of DBPF. These results suggest that the initiator efficiency of DBPF is considerably low in the present polymerization systems. Some solvent effect was observed on the polymerization of MMA with DBPF.

Reversible Kinetics and Thermodynamics of the Homopolymerization of l-Lactide with 2-Ethylhexanoic Acid Tin(II) Salt

The reversible kinetics of l-lactide bulk polymerization with tin(II) ethylhexanoate was determined over a wide range of temperatures, 130−220 °C, and monomer to initiator molar ratios, 1000−80 000. Both polymerization and depolymerization are accurately described by a reversible model with a propagation term that is first order in monomer and catalyst. The activation energy of propagation is 70.9 ± 1.5 kJ mol-1. The enthalpy, entropy, and ceiling temperature of polymerization are −23.3 ± 1.5 kJ mol-1, −22.0 ± 3.2 J mol-1 K-1, and 786 ± 87 °C, respectively. Crystallization increases the propagation rate and decreases the apparent monomer equilibrium in proportion to the degree of crystallinity. Natural hydroxyl impurities stoichiometrically control the polymer molecular weight but do not significantly affect the propagation rate.

Radical Polymerization Behavior of N-Acryloyl-2,2-dimethyl-5(R)-phenyl-1,3-oxazolidine

The radical polymerization of N-acryloyl-2,2-dimethyl-5(R)-phenyl-1,3-oxazolidine (ADPO) was investigated kinetically and by means of ESR spectroscopy. The polymerization of ADPO was carried out in benzene with dimethyl 2,2'-azobis(isobutyrate) (MAIB) as an initiator in the temperature range of 50-70°C. From the Arrhenius plot of the initial polymerization rate (R p ), the overall activation energy of the polymerization was calculated to be 82 kJ mol -l . R p at 60 °C was expressed by R p = k[MAIB] 0.5 [ADPO] I .°. Thus the polymerization of ADPO was found to show the usual kinetic behavior. An ESR spectrum was observed in the actual polymerization, which was ascribed to the propagating poly(ADPO) radical. Using the spectrum, the concentration of the propagating polymer radical was determined and the rate constants of propagation (k p ) and termination (k t ) of ADPO were estimated at 50, 60, and 70 °C. From the Arrhenius plots of k p and k t , the activation energies of propagation and termination were estimated. Furthermore the copolymerization of ADPO (M1) with styrene (M 2 ) was also examined at 60 °C, and the following copolymerization parameters were obtained using a curve-fitting method ; r 1 = 0.22, r 2 = 0.76 (SD = 0.01), Q 1 = 0.45, e 1 = +0.53. The rate constants of cross-propagations of copolymerization were also estimated.

Kinetic and EPR studies on radical polymerization. Radical polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate

The polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate (1) with dimethyl 2,2′-azobisisobutyrate (2) was studied, in benzene, kinetically and spectroscopically with the electron paramagnetic resonance (EPR) method. The polymerization rate (R p) at 50°C is given by the equation:R p=k[2]0.48 [1]2.4. The overall activation energy of polymerization was calculated to be 34 kJ·mol−1. From an EPR study, the polymerization system was found to involve EPR-observable propagating polymer radicals of 1 under the actual polymerization conditions. Using the polymer radical concentration, the rate constants of propagation (k p) and termination (k t) were determined. With increasing monomer concentration,k p(1.5∼4.3 L·mol−1·s−1 at 50°C) increases andk t (1.0·104∼4.2·104 L·mol−1·s−1 at 50°C) decreases, which seems responsible for the high dependence ofR p on the monomer concentration. The activation energies of propagation and termination were calculated to be 11 kJ·mol−1 and 84 kJ·mol−1, respectively. For the copolymerization of 1(M 1) and styrene (M 2) at 50°C in benzene the following copolymerization parameters were found:r 1=0.2,r 2=0.53, Q1=0.57, ande 1=+0.7.

Inclusion polymerization of 1‐chlorobutadiene in a deoxycholic acid canal

AbstractInclusion polymerization of 1‐chlorobutadiene was studied using 3α,12α‐dihydroxy‐5β‐cholan‐24‐oic acid (deoxycholic acid, DCA) as host molecules. It was found that the poly(1‐chlorobutadiene) had almost 100% of head to tail, trans‐1,4‐structure on the basis of 13C‐NMR and IR spectroscopies. This was the first example of preparing the highly regulated poly(1‐chlorobutadiene) by using the inclusion polymerization technique. The polymers obtained were optically active and the maximum value of specific rotation was [α]D‐41.9°. Both the rate constants and the value of activation energy of the elementary reactions of inclusion polymerization of 1‐chlorobutadiene were determined by graphical evaluation. The activation energy of propagation and termination was 11.7 and 11.1 kcal/mol, respectively.

Free radical copolymerization of sulfur dioxide with 1‐alkynes

AbstractFree radical copolymerization of SO2 with 1‐alkynes (AY) was studied by evaluation of the copolymerization rate under controlled conditions of copolymerization temperature and monomer concentration product ([AY][SO2]). The poly(alkyne sulfone)s always contained equimolar units of SO2 and alkyne, regardless of the copolymerization conditions. Using 1‐hexyne (HY) and 1‐octyne (OY) as comonomers of SO2, the values of ceiling temperature (Tc) were determined: when [HY][SO2] = [OY][SO2] = 0.25 mol2/L2, the values of Tc were 90.5 and 84.5°C, respectively. Tc increases with increasing monomer concentration product. The activation energies for propagation (Ep) and depropagation (Ed) of the SO2‐alkynes copolymerization system were investigated, using the SO2OY copolymerization system, and estimated to be 12.2 and 26.7 kcal/mol, respectively. The value of Ed is high compared with that of the copolymerization of SO2 and 1‐butene (20.3 kcal/mol), demonstrating that the free radical endings (∼ OYSO2 and ∼ SO2OY) are difficult to depropagate, compared with those formed from the copolymerizaton of SO2 and 1‐butene. ΔS and ΔHp, calculated from experiments, were found to be −37.7 cal/mol K and −14.3 kcal/mol, respectively

Metallocene–methylaluminoxane catalyst for olefin polymerization. II. Bis‐η5‐(neomenthyl cyclopentadienyl)zirconium dichloride

AbstractBis(neomenthyl cyclopentadienyl)zirconium dichloride/methyl aluminoxane (η5‐(NMCp)2ZrCl2/MAO) catalyst has been investigated for ethylene polymerization. About 51% of the Zr forms active sites more or less instantaneously according to quenching with tritiated methanol. There is an initial drop of rate of polymerization, Rp, of about 30% which remains constant thereafter. The catalytic activity increases monotonically with temperature; it is proportional to [MAO]1.75 at a constant [Zr] = 1.5 μM and proportional to [Zr]−1.2 at a constant [MAO] = 64.5 mM. At very large [MAO]/[Zr], the catalyst has extremely high activity; κp = 5 × 103 (Ms)−1 at 50°C. There is also facile chain transfer to aluminum, κ = 0.14 s−1 at 50°C. Both κp and κ are about 30 times greater than the corresponding rate constants for MgCl2 supported TiCl3 catalysts. The TiCl3/MgCl2 and (NMCp)2/MAO catalysts have nearly the same activation energy for propagation (ca. 7 kcal/mol−1). The higher activity of the latter is due to its larger preexponential factor in κp. The dependence of catalytic activity on the [MAO]/[Zr] ratio may be explained by rapid association‐dissociation equilibria of MAO involving acid‐base and/or electron deficient bridge complexation.

Evaluation of the activation energies of elementary propagation steps in the catalytic polymerization of olefins

The possible relation between the activation energies of adsorption and insertion reactions and the heat of olefin adsorption for the two-step mechanism of propagation have been evaluated on the basis of calculated preexponential factors for the propagation rate constants and the experimental activation energies of propagation.

Absolute Rate Constants for Hydrocarbon Autoxidation. XXI. Activation Energies for Propagation and the Correlation of Propagation Rate Constants with Carbon–Hydrogen Bond Strengths

The rate constants, kp, for the abstraction of a hydrogen atom from a wide variety of organic substrates at 30° have been correlated with the strengths of the C—H bond that are broken, D[R—H] (in units of kcal/mol). Two empirical relations have been derived, one for tertiary peroxy radicals,[Formula: see text]and one for secondary peroxy radicals,[Formula: see text]These equations hold extremely well for hydrocarbons and reasonably well for substrates containing heteroatoms. The activation energies and pre-exponential factors for the oxidation of some hydrocarbons by t-butylperoxy radicals have been measured and the empirical relation[Formula: see text]derived. If D[t-ROO—H] is taken as 88 kcal/mol, this yields the Polanyi equation,[Formula: see text]where ΔH is the heat of the hydrogen abstraction reaction. These empirical equations permit the calculation of the rate constants for chain propagation in the autoxidation of many organic substrates at 30° and also at other temperatures.

Free‐ionic polymerization of isobutyl vinyl ether by radiation

AbstractRadiation‐induced free‐ionic polymerization of isobutyl vinyl ether in bulk system has been studied by dilatometry and electrical conductivity measurement. Some refinements in kinetic treatment of estimate the propagation rate constant kp from the rate of polymerization and steady‐state conductivity were attempted. Polymerization of superdried monomer which gave a half‐power dose‐rate dependence of Rp was carried out at 0, 25, and 50°C. The kp value obtained at 25°C and an activation energy for propagation were estimated as 1.2 ± 0.4 × 105 I./mole‐sec and 9.6 ± 2.8 kcal/mole, respectively. In isobutyl vinyl ether, a propagation reaction in free‐ionic mechanism was found to be characterized with a high frequency factor and presumably higher activation energy, compared with ion‐pair mechanism. Discussions were also made as to several contrasting behaviors between the polymerization of alkyl vinyl ethers and other vinyl monomers as styrene both in free‐ion and ion‐pair mechanisms.

Anionic polymerization of o‐ and p‐methoxystyrene

AbstractThe butyllithium‐initiated polymerization of o‐ and p‐methoxystyrene was studied in toluene at 20°C by dilatometry. Initiation of o‐methoxystyrene was found to be instantaneous as evidenced by the absence of any induction period. The propagation rate proceeds by an internal first order with respect to the monomer concentration while the order with respect to the living chain ends varies from 0.67 to 0.51 over a concentration range from 4.5 × 10−4 to 1.8 × 10−2 mole/1. The rate may thus be expressed by the equation, where [M] and [PLi] denote concentration of monomer and poly‐o‐methoxystyryllithium, respectively, and n varies from 0.67 to 0.51. It is assumed that the propagation proceeds exclusively via the monomeric form of the ion‐pairs in analogy with the polymerization of styrene. The variable order results from the relatively high value of the dissociation equilibrium constant of dimeric into the monomeric ion‐pairs K that was evaluated graphically to be 10−3 instead of 10−6 for styrene. The propagation rate constant kp was found to be equal to about 50 l./mole‐min; the propagation activation energy is equal to 12 kcal/mole. No appreciable termination was found in the polymerization of o‐methoxystyrene. On the contrary, no quantitative data could be obtained for the polymerization of p‐methyoxystyrene due to a slow initiation and a relatively fast termination reaction with formation of a precipitate of highly branched or crosslinked polymer. It is assumed that this precipitate results from a secondary ring metallation reaction.

Kinetics of polymerization of benzyl acrylate in bulk

AbstractThe kinetics of polymerization of benzyl acrylate has been studied at 55, 60, and 65°C with azobisisobutyronitrile as initiator. The overall rate of polymerization, degree of polymerization, chain transfer due to monomer, and the ratio of propagation and termination constant were calculated. The overall activation energy, the difference between the activation energy of propagation and termination, and the frequency factor are also reported.

Homogeneous anionic polymerization. IV. Kinetics of butadiene and isoprene polymerization with butyllithium

AbstractThe kinetics of polymerization of butadiene and isoprene with butyllithium initiator have been studied both in n‐hexane and tetrahydrofuran solution. The overall polymerization rates were much faster in the THF solutions than in n‐hexane, and the latter also exhibited relatively slow initiation rates compared to propagation. By use of a preinitiation technique, where necessary, it was possible to study the propagation kinetics without any interference by initiation. The propagation reaction was found to be first‐order with respect to monomer in both solvents, but much faster in THF. Furthermore, it was first‐order with respect to growing chain concentration in the THF system, but only half‐order in the n‐hexane system. This was taken to indicate the existence, in n‐hexane solution, of an association equilibrium between active single chains and inactive chain pairs. The activation energy for propagation was found to be 6–7 kg. cal. in THF and about 22 kg. cal. in n‐hexane for both monomers, but the latter value obviously includes the heat of dissociation of the associated chain pairs. The Arrhenius expression for the propagation rate in THF contains a very low frequency factor (∼︁104) and leads to a propagation rate constant at least two orders of magnitude less than the corresponding value for free radical propagation.