Kinetics of polyesterification. II. Foreign acid-catalyzed dibasic acid and glycol systems

Polyesterification of diacid and diol in the presence of the foreign acid p-toluene sulfonic acid as catalyst was carried out under constant reaction temperatures of 140–166°C (rather than at the usual constant oil-bath temperature) and at molar ratios r of diol to diacid of 1.2–3.5. The experimental data obtained do not fit conventional rate equations as they appear in the literature. On the basis of ion pair formation, consideration of proton transfer from acid to alcohol, variation in dielectric constant of the reaction mixture as conversion increases, and inclusion of reverse reaction due to presence of unremoved water, we proposed a reaction mechanism and rate equations. The rate equation fitted our experimental data quite well. In addition the self-catalysis (absence of foreign acid) also showed promise, as confirmed by the experimental data measured under constant reaction temperatures, which appear in Part I.     

Kinetics of polyesterification: Adipic acid with ethylene glycol, 1,4-butanediol,and 1,6-hexanediol

Polyesterifications of adipic acid with ethylene glycol, 1,4-butanediol, and 1,6-hexanediol in the absence and presence of the foreign acid (p-toluene sulfonic acid) as catalyst were carried out under constant reaction temperatures of 140–180°C (rather than at constant oil-bath temperatures) and at ratios of diol to diacid of 0.9867–3.5880. The experimental data fit the rate equations proposed by Chen and Wu: d(RCOOR′)/dt = k_ae^αp(RCOOH)²(R′OH) – k_h(H₂O)(RCOOR′) and d(RCOOR′)/dt = k_ac(AH)e^αp(RCOOH)(RO′H) – k_h(H₂O)(RCOOR′) for self-catalyzed and acid-catalyzed reactions, respectively; the data did not fit the other equations appearing in the literature. Here p is the conversion of acid, and α is the constant related to dielectric constants. The reaction rate constants and activation energies for self-catalyzed and acid-catalyzed reactions are calculated. The activation energy is found to decrease with chain length of the alkyl group of the diol. This result is consistent with that observed by Brauman and Blair using ion cyclotron resonance spectroscopy for the variation of acidity of alcohols with chain length of the alkyl group.     

Kinetic study of polyesterification: Unsaturated polyesters

Synthesis of unsaturated polyesters using adipic acid, ethylene glycol, and fumaric acid in the absence and presence of a foreign acid (phosphoric acid) as catalyst was carried out by a two-stage method under constant reaction temperatures of 160–180°C and at different ratios of diol to diacid. The experimental data fit the Chen–Wu rate equations for self-catalyzed and acid-catalyzed reactions. The reaction rate constants and activation energies for both systems were calculated. The rate constants of fumaric acid–ethylene glycol systems were found to be nearly constant and had negligible variations with increasing chain length of polymer. © 1995 John Wiley & Sons, Inc.     

二元酸溶解度对二元醇与一些芳族二元酸的聚酯化反应动力学的影响

一些芳族二元酸与二元醇的聚酯化反应过程包含非均相和均相两个反应阶段,针对这一反应特性,提出了二元酸在反应混合物中溶解度及反应清晰点的两个计算方程,并据此将Ｃｈｅｎ和Ｗｕ提出的自催化聚酯化反应的动力学模型修改为两个分别适用于非均相和均相反应阶段的速率方程．将这两个速率方程应用于双（对 羧苯基）苯基氧化膦与乙二醇的恒温自催化聚酯化反应,计算值与实验数据相一致,并计算得到了该反应的速率常数和活化能     

Free-radical homopolymerization and copolymerization of ethyl α-hydroxymethylacrylate in tetrahydrofuran

Ethyl α-hydroxymethylacrylate (EHMA) was polymerized in a 3 mol/L tetrahydrofuran solution at 50°C, using 2–2' azobisisobutyronitrile as initiator. The kinetic behavior indicates a higher polymerization rate for EHMA than for methyl methacrylate (MMA). Copolymerization reaction between MMA and EHMA, under the same experimental conditions, was carried out and values of r_MMA = 1.264 and r_EHMA = 1.285 were found for the reactivity ratios. The comparison of triad sequences as determined from Bernouillian statistic to those calculated from the experimental spliting of O-methyl and α-methyl ¹H-NMR signals of the copolymers confirm the obtained results. © 1992 John Wiley & Sons, Inc.     

Vinylhydroquinone. III. Copolymerization of vinylhydroquinone and vinyl monomers by tri-n-butylborane

The copolymerization of vinylhydroquinone (VHQ) and vinyl monomers, e.g., methyl methacrylate (MMA), 4-vinyl-pyridine (4VP), acrylamide (AA), and vinyl acetate (VAc), by tri-n-butylborane (TBB) was investigated in cyclohexanone at 30°C under nitrogen. VHQ is assumed to copolymerize with MMA, 4VP, and AA by vinyl polymerization. The following monomer reactivity ratios were obtained (VHQ = M₂): for MMA/VHQ/TBB, r₁ = 0.62, r₂ = 0.17; for 4VP/VHQ/TBB, r₁ = 0.57, r₂ = 0.05; for AA/VHQ/TBB, r₁ = 0.35, r₂ = 0.08. The Q and e values of VHQ were estimated on the basis of these reactivity ratios as Q = 1.4 and e = ?;1.1, which are similar to those of styrene. This suggests that VHQ behaves like styrene rather than as an inhibitor in the TBB-initiated copolymerization. No homopolymerization was observed either under nitrogen or in the presence of oxygen. The reaction mechanism is discussed.     

A kinetic study of the oxidation of L-ascorbic acid by chromium(VI)

The reaction between chromium(VI) and L-ascorbic acid has been studied by spectrophotometry in the presence of aqueous citrate buffers in the pH range 5.69–7.21. The reaction is slowed down by an increase of the ionic strength. At constant ionic strength, manganese(II) ion does not exert any appreciable inhibition effect on the reaction rate. The rate law found is where K_p is the equilibrium constant for protonation of chromate ion and k_r is the rate constant for the redox reaction between the active forms of the oxidant (hydrogenchromate ion) and the reductant (L-hydrogenascorbate ion). The activation parameters associated with rate constant k_r are E_a = 20.4 ± 0.9 kJ mol^?1, ΔH^≠ = 17.9 ± 0.9 kJ mol^?1, and ΔS^≠=?152 ± 3 J K^?1 mol^?1. The reaction thermodynamic magnitudes associated with equilibrium constant K_p are ΔH⁰ = 16.5 ± 1.1 kJ mol^?1 and ΔS⁰ = 167 ± 4 J K^?1 mol^?1. A mechanism in accordance with the experimental data is proposed for the reaction. © 1993 John Wiley & Sons, Inc.     

Some considerations of the kinetics of the acid hydrolysis of poly- and oligosaccharides. Part III. The disaccharides 2-O-(α-D-glucopyranosyluronic acid)-D-xylose, 2-O-(4-O-methyl-α-D-glucopyrano-syluronic acid)-D-xylose,and 2-O-(4-O-methyl-α-D-glucopyranosyl)-D-xylitol

Rate equations have been formulated for the formation and depletion of the hydrolysis product(s) of the title disaccharides. They are based on the assumptions that (1) the rate of acid hydrolysis of the disaccharides is according to first order, and (2) the rate of depletion of the hydrolysis product(s) is constant in the early periods while it approaches first order in the more advanced stages of the reactions. By using experimental rate data from the literature the rate constants of the hydrolysis of the disaccharides and of the depletion of the hydrolysis product(s) have been computed. The validity of the assumptions underlying the rate equations advanced has been confirmed by (a) the agreement between experimental and calculated values and (b) the similar values for the rate constant of the depletion of xylose formed in the hydrolysis of the two biouronic acids. Also discussed are some implications arising from the magnitude of the hydrolysis rate constant of methylaldobiouronic acid and of the depletion rate constant of xylose in relation to complete hydrolysis of polysaccharides.     

聚十二烷二元酸酯及其共聚酯的合成

通过直接熔融缩聚法合成了一系列聚十二烷二元酸酯，用GPC、^1H—NMR、FTIR对产物进行了表征，并讨论了预聚酯合成时催化剂浓度和种类、预聚反应温度、预聚初始醇酸摩尔比对聚合反应的影响。结果表明，在所选的三个催化剂体系中，氮化亚锡二水合物与对甲苯磺酸复合催化剂的催化效果最好；最佳反应条件：n对甲苯横酯／n二元酸=0．0021～0．0032，反应温度为160～180℃，醇酸摩尔比范围为1．05—1.10。     

Reactive oligomers. I. Preparation and polymerization of ethylene glycol bis(methyl fumarate)

Ethylene glycol bis(methyl fumarate) (EGBMF) was prepared as a new type of divinyl compound and reactive oligomer: a needle crystal, m.p. 104.5°C. Homopolymerization of EGBMF was carried out in dioxane with 0.1 mol/L AIBN at [M] = 1 mol/L and 60°C; the rate of polymerization was estimated to be 4.44 × 10^?6 mol/L s in a good agreement with diethyl fumarate (DEF). The cyclization constant K_c was obtained as 1.64 mol/L, being rather low compared with diallyl oxalate which is 1,9-diene having two ester groups analogous to EGBMF. Gelatin occurred at about 35% conversion. Finally, the copolymerization of EGBMF (M₁) with diallyl phthalate (DAP) (M₂) is tentatively explored with the intention of the improvement of allyl resins in mechanical properties; remarkable rate enhancement was observed for copolymerization. The monomer reactivity ratios were estimated to be r₁ = 0.96 and r₂ = 0.025, the r₁ value being reduced compared with the DEF-DAP copolymerization system. These results are discussed from the standpoint of steric effect on the polymerization of fumarate as an internal olefin.     

Kinetic study of the reaction between a hydroxylated polybutadiene and isocyanates in chlorobenzene,III. Reaction with dimer diacid diisocyanate (DDI)

A kinetic study of the reaction of hydroxylated liquid polybutadiene (M?_n = 2400) R-45M and dimer diacid diisocyanate (DDI) was carried out in chlorobenzene solution. The kinetic data were compared with the data obtained in a previous work using toluene as solvent. This reaction presented an apparent second order rate law, and was faster in chlorobenzene than in toluene. The accelerating effect of chlorobenzene was higher at higher temperatures.     

Homogeneous decomposition of vinyl ethers. The heat of formation of ethanal-2-yl

The thermal unimolecular decomposition of three vinylethers has been studied in a VLPP apparatus. The high-pressure rate constant for the retro-ene reaction of ethylvinylether was fit by log k (sec^?1) = (11.47 + 0.25) - (43.4 ± 1.0)/2.303 RT at <T> = 900 K and that of t - butylvinylether by log k (sec^?1) = (12.00 ± 0.27) - (38.4 ± 1.0)/2.303 RT at <T> = 800 K. No evidence for the competition of the higher energy homolytic bond-fission process could be obtained from the experimental data. The rate constant compatible with the C? O bond scission reaction in the case of benzylvinylether was log k (sec^?1) = (16.63 ± 0.30) - (53.74 ± 1.0)/2.303 RT at <T> = 750 K. Together with ΔH_f,300⁰(benzyl·) = 47.0 kcal/mol, the activation energy for this reaction results in ΔH_f,300⁰(CH₂CHO) = +3.0 ± 2.0 kcal/mol and a corresponding resonance stabilization energy of 3.2 ± 2.0 kcal/mol for 2-ethanalyl radical.     

Kinetics of Formation of Peroxyacetic Acid

The kinetics of the reaction of acetic acid with hydrogen peroxide, leading to peroxyacetic acid, were studied at various molar reactant ratios (AcOH-H₂O₂ from 6 : 1 to 1 : 6) at 20, 40, and 60°C and sulfuric acid (catalyst) concentrations of 0 to 9 wt %. The reaction is reversible, and the equilibrium constant decreases as the temperature rises: K = 2.10 (20°C), 1.46 (40°C), 1.07 (60°C); Δ_r H ⁰ = − 13.7±0.1 kJ mol⁻¹, Δ_r S = −40.5±0.4 J mol⁻¹ K⁻¹. The maximal equilibrium concentration of peroxyacetic acid (2.3 M) is attained at 20°C and a molar AcOH-to-H₂O₂ ratio of 2.5 : 1. The rate constants of both forward and reverse reactions increase with increase in sulfuric acid concentration from 0 to 5 wt %. Further raising the catalyst concentration does not affect the reaction rate. The reaction mechanism is discussed.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 7, 2005, pp. 1187–1193.Original Russian Text Copyright © 2005 by Dul’neva, Moskvin.     

Penultimate model description of the propagation kinetics for the free radical copolymerization of styrene and methyl methacrylate

Recently experimental data on the free radical copolymerization of styrene and methyl methacrylate in bulk were shown to obey penultimate model kinetics. These data were now reevaluated with respect to copolymerization parameters by means of a simultaneous fit of the penultimate model both to the copolymer composition and to the overall propagation rate coefficient, and in dependence on the monomer feed composition. Different simultaneous fit procedures were used and compared. The following parameters are finally suggested: r₁₁ = 0,498; r₂₁ = 0,589; r₂₂ = 0,463; r₁₂ = 0,547; s₁ = 0,478 and s₂ = 0,256.     

The reaction of O(3P) with H2O2

The rate constant for the reaction of O(³P) with H₂O₂ was measured as a function of temperature and the [H₂O₂]₀/[O]₀ ratio. The numerical solution of the appropriate rate equations was used to arrive at a mechanism which adequately describes our results and the rather divergent data in the literature. A recommended expression for the temperature dependence of the absolute rate constant is presented from consideration of the available experimental data.     

Thermal hydrocracking of indan. Effects of the hydrogen pressure on thekinetics and Arrhenius parameters

The kinetics of the thermal hydrocracking of indan were investigatedin a high-pressure flow reactor at temperatures from 470 to 530°C, total pressures of up to 300 atm, and molar ratios from 3 to 40. The effect of the hydrogen pressure was reflected especially in a change of the experimental rate equations for the formation of toluene from r_T=k [indan]^0.5 [hydrogen] to r_T=k′ [indan] ^0.75[hydrogen]^0.75 with hydrogen partial pressureincreasing from 73 to 230 atm. The rate equation of n-propylbenzene remained constant at r_Pr=k″ [indan] [hydrogen]^1.5. Simultaneously the Arrheniusparameters of toluene changed significantly, while those of n-propylbenzene remained unchanged. The observed effect of the hydrogen pressure is explained as a change inthe rates of the intermediate reactions; it provides an excellent agreementbetween the theoretical and experimental data. It was found that the steady-state concentration of the hydrogen atoms, which act as chain carriers in the thermal hydrocracking, was much smaller than the thermodynamic equilibrium concentrations     

Emulsion copolymerization of styrene and methyl methacrylate

Chain transfer constants to monomer have been measured by an emulsion copolymerization technique at 44°C. The monomer transfer constant (ratio of transfer to propagation rate constants) is 1.9 × 10^?5 for styrene polymerization and 0.4 × 10^?5 for the methyl methacrylate reaction. Cross-transfer reactions are important in this system; the sum of the cross-transfer constants is 5.8 × 10^?5. Reactivity ratios measured in emulsion were r₁ (styrene) = 0.44, r₂ = 0.46. Those in bulk polymerizations were r₁ = 0.45, r₂ = 0.48. These sets of values are not significantly different. Monomer feed compcsition in the polymerizing particles is the same as in the monomer droplets in emulsion copolymerization, despite the higher water solubility of methyl methacrylate. The equilibrium monomer concentration in the particles in interval-2 emulsion polymerization was constant and independent of monomer feed composition for feeds containing 0.25–1.0 mole fraction styrene. Radical concentration is estimated to go through a minimum with increasing methyl methacrylate content in the feed. Rates of copolymerization can be calculated a priori when the concentrations of monomers in the polymer particles are known.     

Synthesis and characterization of new optically active poly(amide‐imide)s containing epiclon and L‐methionine moieties in the main chain

Epiclon [3a,4,5,7a‐tetrahydro‐7‐methyl‐5‐(tetrahydro‐2,5‐dioxo‐3‐furanyl)‐1,3‐isobenzofurandione] (1) was reacted with L ‐methionine (2) in acetic acid and the resulting imide‐acid 3 was obtained in high yield. The diacid chloride 4 was prepared from diacid derivative 3 by reaction with thionyl chloride. Thermostable poly(amide‐imide)s containing epiclon structure were synthesized by reacting of diacid chloride 4 with various aromatic diamines. Polymerization reaction was performed by two conventional methods: low temperature solution polycondensation and short period reflux conditions. In order to compare conventional solution polycondensation reaction methods with microwave‐assisted polycondensation, the reactions were also carried out under microwave conditions with a small amount of o‐cresol that acts as a primary microwave absorber. The reaction mixture was irradiated for 6 min with 100% radiation power. Several new optically active poly(amide‐imide)s with inherent viscosity ranging from 0.15 to 0.36 dl/g were obtained with high yield. All of the above polymers were fully characterized by ¹H‐NMR, FT‐IR, elemental analyses and specific rotation techniques. Some structural characterizations and physical properties of these new optically active poly(amide‐imide)s are reported. Copyright © 2005 John Wiley & Sons, Ltd.     

Correction for instrument time constant and baseline in determination of reaction kinetics

Rates of reactions can be expressed as dn/dt = kf(n), where n is moles of reaction, k is a rate constant, and f(n) is a function of the properties of the sample. Instrumental measurement of rates requires c(dn/dt) = ckf(n), where c is the proportionality constant between the measured variable and the rate of reaction. When the product of instrument time constant, τ, and k is ? 1, the reaction is much slower than the time response of the instrument and measured rates are unaffected by instrument response. When τ k < 1, = 1, or >1, the reaction rate and instrument response rate are sufficiently comparable that measured rates are significantly affected by instrument response and correction for instrument response must be done to obtain accurate reaction kinetics. This paper describes a method for simultaneous determination of τ, k, c, and instrument baseline by fitting equations describing the combined instrument response and rate law to rates observed as a function of time. When τ cannot be neglected, correction for instrument response has previously been done by truncating early data or by use of the Tian equation. Both methods can lead to significant errors that increase as τk increases. Inclusion of instrument baseline as a fitting parameter significantly reduced variability in k and c compared with use of measured instrument baselines. The method was tested with data on the heat rate from acid‐catalyzed hydrolysis of sucrose collected with three types of calorimeters. In addition, to demonstrate the generality of this method of data analysis, equations including τ, k, c, and instrument baseline are derived for the relation between the reaction rate and the observed rate for first order, second order (first in each reactant), nth order in one reactant, autocatalytic, Michaelis–Menten kinetics, and the Ng equation. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 53–61, 2011     

Inverse emulsion polymerization of acrylamide. II. Synthesis and characterization of copolymers with methacrylic acid

Inverse emulsion copolymerization studies of acrylamide (Am) with methacrylic acid (MAA) are reported. Aqueous monomer solutions were emulsified in toluene with a blend of two surfactants (sorbitan sesquioleate and C18-terminated acrylamide oligomers). Polymerization kinetics in presence of an oil-soluble initiator (AIBN) were determined at 40°C as a function of methacrylic acid content and aqueous-phase pH. Polymerization rates were found to be faster at basic pH than at acidic pH, which appeared to be related to the actual concentration of methacrylic acid in the aqueous phase. Monomer reactivity ratios have been derived as r_A-M = 0.58 ± 0.02 and r_M-A = 4.0 ± 0.10 at pH 4, r_A-M = 0.56 ± 0.005 and r_M-A = 0.15 ± 0.03 at pH 10. These differences were found to have an effect on the molecular characteristics of the copolymers. Initial emulsions and final inverse latexes displayed the same broad size distribution; under basic pH the particle size is relatively insensitive to the ionic comonomer concentration. Poor latex stability is characteristic of copolymer latexes prepared under acidic conditions. Based on these experimental results, some aspects of the polymerization mechanism are discussed.