Macroion-pairs and macroions in the kinetics of polymerization of hexamethylene oxide (oxepane)

Cationic polymerization of oxepane (hexamethylene oxide) ( 1 ) in CH₂Cl₂ and C₆H₅NO₂ as solvents was initiated with 1,3-dioxolan-2-ylium hexafluoroantimonate ( 2 ). Dissociation constants (K_D) of the ion-pairs of polyoxepane into ions were measured: K_D (in CH₂Cl₂, T = 25°C) = 2,8·10^?5 mol·l^?1 [ΔH_D = ?3,8 kJ·mol^?1 (?0,9 kcal·mol^?1), ΔS_D = ?98 J·mol^?1·K^?1 (?23,4 cal·mol^?1·K^?1)]; K_D (in C₆H₅NO₂, T = 25°C) = 1,6·10^?3 mol·l^?1 [ΔH_D = ?7,1 kJ·mol^?1 (?1,7 kcal·mol^?1), ΔS_D = ?78 J·mol^?1·K^?1 (?18,7 cal·mol^?1·K^?1)]; these values are close to those of the ion-pairs of polytetrahydrofuran. Rate constants k_p⁺ and k_p^±, determined from the kinetic measurements for degrees of dissociation of macroion-paris ranging from 0,02 to 0,21 (in CH₂Cl₂) and from 0,09 to 0,7 (in C₆H₅NO₂), were found to be identical within an experimental error of kinetic measurements. The activation parameters of propagation were measured and their dependences on the polarity of the polymerization mixtures are discussed.     

Kinetic and electron paramagnetic resonance studies on radical polymerization. Radical copolymerization of p-tert-butoxy-styrene and dibutyl fumarate in benzene

The copolymerization of p-tert-butoxystyrene ( 1 ) (M₁) and dibutyl fumarate ( 2 ) (M₂) initiated with dimethyl 2,2′-azobisisobutyrate ( 3 ) was studied in benzene at 60°C kinetically and by means of electron paramagnetic resonance (EPR) spectroscopy. The monomer reactivity ratios were determined to be r₁ = 0,18 and r₂ = 0,01, indicating that homopropagation of M₂ is almost negligible in the copolymerization. The copolymerization system was revealed to involve EPR-observable propagating polymer radicals under practical copolymerization conditions. The apparent rate constants of propagation (k_p) and termination (k_t) determined by EPR show a rapid increase in the range from 0,9 to 1,0 of feed composition (f₁ = {[M₁]/([M₁] + [M₂])}) of M₁. From the relationship between k_p and f₁ based on Fukuda's penultimate model, the rate constants of propagation of copolymerization were evaluated; k₁₁₁ = 140 L · mol^?1 · s^?1, k₂₁₁ = 4,3 L · mol^?1 · s^?1, k₁₁₂ = 778 L · mol^?1 · s^?1, k₂₁₂ = 24 L · mol^?1 s^?1 and k₁₂₁ = 19 L · mol^?1 · s^?1, suggesting a pronounced penultimate effect.     

Configurational double bond selectivity in the epoxidation of hydroxy-terminated polybutadiene with m-chloroperbenzoic acid

The selectivity of the three different double bonds (CIS, TRANS and VINYL) of hydroxyterminated polybutadiene regarding epoxidation was evaluated, using m-chloroperbenzoic acid in toluene below room temperature (?10°C, ?5°C, 0°C and 5°C). To determine the kinetic constants for the three configuratons (k_1,cis = (2,59–0,6) × 10^?2 L · mol^?1 · min^?1; k_{2, trans} = (5,35–0,82) × 10^?2 L · mol^?1 · min^?1; k_{3, vinyl} = (0,97–0,01) × 10^?2 L · mol^?1 min^?1), ¹H and ¹³C NMR was used along with a system of three parallel equations. The activation energy values were also evaluated (E_{a, cis} = 53,9 kJ · mol^?1; E_{a, trans} = 70,7 kJ · mol^?1 and E_a, vinyl = 261,1 kJ · mol^?1) for the three double bond types.     

Thermodynamics of copolymerization of 1,3-dioxolane with 1,3-dioxepane and 1,3-dioxane

The equilibrium copolymerization of 1,3-dioxolane with 1,3-dioxepane in CH₂Cl₂ solution and with 1,3-dioxane without solvent is analyzed, and the equilibrium constants of homo- and cross-propagations are estimated and discussed. The corresponding thermodynamic parameters are calculated. The reported thermodynamic parameters of homopolymerization of 1,3-dioxane (ΔH_ss = ?3,1 kJ · mol^?1, ΔS_ss = ?35,5 J · mol^?1 · K^?1), were determined on the basis of the copolymerization data. Predictions of comonomer concentrations and microstructure of copolymers in the equilibrium copolymerization system are presented for any initial composition, on the basis of the determined equilibrium constants.     

Cationic polymerization of 1-azabicyclo[4.2.0]octane, 2. Reactivities of ions and ion-pairs

The cationic ring-opening polymerization of 1-azabicyclo[4.2.0]octane ( 1 ) was studied with initiators providing small and large anions, namely F^?, Br^?, I^?, picryl(Pic^?), CF₃SO₃^?. In nitrobenzene as solvent the macroions and macroion-pairs, independently of the anion size, propagate with the same rate constant k_p⁺ = k_p^± = 7,0 · 10^?3 mol^?1 · l · S^?1 at 35°C ( Δ H_P^≠ = 55 ± 5kj· mol^?1, Δ S_P^≠ = 105 ± 11 j · mol^?1 · K^?1). This result strongly indicates that it is not the large size of anoins which is exclusively responsible for the equality k_P⁺ = k_P^±. The structure of the onium ions, their strong solvation, and the resulting weak interactions with anions are primarily responsible for the observed equalities. In methanol as solvent polymerization proceeds 30 times slowlier than in nitrobenzene and ion-pairs are more reactive by 40% than ions, in agreement with Enikolopyan's findings.     

Acidolytic polymerization of N-methyldodecanelactam

The polymerization rate of 1-methylazacyclotridecan-2-one (N-methyldodecanelactam) ( 1 ) initiated with dodecanoic acid ( 2 ) can be described within the whole range of conversions in terms of the simple relation In ([ 1 ]₀/[ 1 ]) = k[ 2 ]₀t, in spite of the complexity of the overall reaction scheme. The rate constants (k) determined for 240, 260, and 280°C are 0,32, 1,21, and 3,4 kg · mol^?1 h^?1, respectively, and the constants of the Arrhenius equation are A = 6,6 · 10¹³kg · mol^?1 h^?1, E = 140 kJ · mol^?1. The resulting poly(N-methyldodecaneamide) ( 3 ) is a semicrystalline polymer (m.p. 65°C), soluble in polar organic solvents. The following constants of the Mark-Houwink equation were determined for solutions of this polyamide: for 5000 < M?_w < 150 000 g · mol^?1 at 25°C in THF (2-propanol), K = 0,124 (0,161) cm³ · g^?1, a = 0,59 (0,56); for 5 000 < M?_w < 80 000 g · mol^?1 at ?-temperature = 30,5°C in 1,4-dioxane, K = 0,215 cm³ · g^?1, a = 0,50. Analyses of molar masses, both theoretical and experimental (light-scattering, GPC, osmometry, end groups), indicate that at the polymerization temperature of 280°C side reactions already take place, reflected in random cleavage and in branching of chains.     

Rate coefficients of the free-radical polymerization of 1,3-butadiene

Rate coefficients of termination and transfer in the free-radical polymerization of 1,3-butadiene in chlorobenzene were determined in the temperature range 318 K < T < 333 K. On the basis of an earlier published temperature dependence of the rate coefficient of propagation, for the termination reaction the Arrhenius equation K_t = 1,13 · 10¹⁰ · exp(? 711 K/T) L · mol^?1 · s^?1 was obtained. For the transfer to monomer the experiments yielded the Arrhenius equation K_tr,M = 4,22 · 10⁶ · exp(? 5140 K/T) L · mol^?1 · S^?1 and for the transfer to the solvent K_tr,S = 2,25 · 10⁸ · exp(? 7050 K/T) L · mol^?1 · S^?1.     

Kinetic and ESR studies on radical polymerization. Radical polymerization behavior of N-octadecylmaleimide in benzene

The polymerization of N-octadecylmaleimide ( 1 ) initiated with azodiisobutyronitrile ( 2 ) was investigated kinetically in benzene. The overall activation energy of the polymerization was calculated to be 94,2 kJ·mol^?1. The polymerization rate (R_p) at 50°C is expressed by the equation, R_p = k[ 2 ]^0,6[ 1 ]^1,7. The homogeneous polymerization system involves ESR-detectable propagating polymer radicals. Using R_p and the polymer radical concentration determined by ESR, the rate constants of propagation (k_p) and termination (k_t) were evaluated at 50°C. k_p (33 L · mol^?1 · s^?1 on the average) is substantially independent of the monomer concentration. On the other hand, k_t (0,3 · 10⁴ – 1,0 · 10⁴ L · mol^?1 · s^?1) is fairly dependent on the monomer concentration, which is ascribable to a high dependence of k_t on the chain length of rigid poly( 1 ). This is the predominant factor for the high order with respect to the monomer concentration in the rate equation. In the copolymerization of 1 (M₁) and St (M₂) with 2 in benzene at 50°C, the following copolymerization parameters were obtained: r₁ = 0,11, r₂ = 0,09, Q₁ = 2,1, and e₁ = +1,4.     

Kinetics of the nitrogen dioxide initiated polymerization of acrylic acid

Acrylic acid (AA) was polymerized with NO₂ in tetrahydrofuran (THF) and in 1,4-dioxane. The effects of monomer and initiator concentration and of temperature on polymer conversion, initial rate of polymerization, and molecular weight were studied. The overall activation energy of polymerization was found to be 16,3 kcal mol^?1 (68,23 kJ · mol^?1) and 15,54 kcal · mol^?1 (65,05 kJ · mol^?1) in THF and in 1,4-dioxane, respectively. High molecular weight polymers (M ca. 10⁵) were obtained. The polymerization appears to be initiated by free radicals.     

Study of the mechanism of propagation and transfer reactions in the polymerization of olefins by Ziegler-Natta catalysts, 1. Determination of the number of propagation centers and the rate constant

The number of propagation centers (C_p) and the propagation rate constant (K_p) in the polymerization of ethylene and propene in the presence of heterogeneous TiCl₃ derived Ziegler-Natta catalysts of different composition were determined using the method of quenching the polymerization by radioactive carbon monoxide (¹⁴CO). The values of K_p, (1,2±0,3)·10⁴ l mol^?1 s^?1 at 75°C for ethylene and (90±20) l mol^?1 s^?1 at 70°C for propene polymerization, significantly exceed those ones obtained by use of tritium tagged alcohols as quenching agents. Further, for the polymerization of olefins in the presence of TiCl₃ based catalysts, the influence of catalyst composition, polymerization conditions, and monomer nature on C_p and K_p was studied.     

Free radical polymerization in the presence of non-solvents, 1. Styrene

During styrene (STY) polymerization, initiated by radicals formed by thermal or photochemical decomposition of 2,2′-azoisobutyronitrile (AIBN) the overall polymerization rate constant K defined by relation K = R^p/([AIBN]^0,5 [STY] η) and the ratio k_p/(2k_t0) increase with decreasing styrene concentration by hexane or benzene (R_p is the polymerization rate and η_MIX the viscosity of the reaction system). In the thermally initiated polymerization K = k_p (2f k_d/(2k_t0))^0,5 and in the photochemically initiated polymerization K = k_p (2,303 ? I₀? d/(2k_t0))^0,5 where k_d, k_p, and k_t0 are respectively, the rate constants of AIBN decomposition, of propagation, and of termination (for a system of the viscosity 1 mPa·s) reactions, ? is the quantum yield of radicals entering into reaction with the monomer, I₀ the intensity of the incident light, ? the molar absorption coefficient of AIBN, and d the path length of the light. The increase of K and of k_p/(2k_t0) with decreasing monomer concentration is more marked for the system styrene/hexane than for styrene/benzene and this increase is greater at 30°C than at 60°C. For Θ-systems formed by binary mixtures like styrene/hexane, styrene/decane and styrene/C₁ – C₄ alcohols the values of k_p and k_t0 at 30°C range between 57 and 91 dm³·mol^?1·s^?1 and (0,9 to 2,2)·10⁷ dm³·mPa·mol^?1, i.e. they are in principle identical with the tabulated values of these rate constants for styrene bulk polymerization.     

Kinetics of the anionic polymerization of ϵ-caprolactone with K+ · (dibenzo-18-crown-6 ether) counterion. Propagation via macroions and macroion pairs

Following our earlier work on the polymerization of lactones involving crowned cations, kinetics of the anionic polymerization of ?-caprolactone (?CL) with K⁺ · (dibenzo-18-crown-6 ether) (K⁺DB18C6) counterion was studied calorimetrically in THF solution in the temperature range from 0 to 20°C. Dissociation constants of CH₃(CH₂)₅O^?K⁺DB18C6, modelling the active centers, were determined conductometrically: K_D (20°C) = 7,7 · 10^?5 mol · dm^?3, ΔH = 9,3 ± 0,2 kJ · mol^?1, ΔS = ?47 ± 2J · mol^?1 · K^?1. From kinetic measurements and from measurements of the dissociation constant of CH₃(CH₂)₅O^? K⁺DB18C6, rate constants of propagation via macroions and via macroion pairs were determined. Activation parameters for propagation via these species are equal to: ΔH = 39,2 ± 0,2 kJ · mol^?1, ΔS = ?63 ± 1 J · mol^?1 · K^?1, ΔH = 13,7 ± 0,1 kJ · mol^?1, ΔS = ?185 ± 2 J · mol^?1 · K^?1. At 20°C, k = 3,50 · 10² dm³ · mol^?1 · s^?1 and k = 5,2 dm³ · mol^?1 · s^?1. Due to the large difference of ΔH^≠ for propagation via macroions and macroion pairs (vide supra), the isokinetic point (k = k) would appear at ?65°C.     

Anionic polymerization of one-ended “living” strontium-polystyrene in tetrahydropyran in the presence of tetraglyme and in benzene

The anionic polymerization of the strontium salt of one-ended living polystyrene (SrS₂) was investigated at 20°C in tetrahydropyran (THP) in the presence of two different concentrations of added tetraglyme. Similarly to BaS₂ in tetrahydrofuran (THF) and to SrS₂ in THF and in pure THP, the observed pseudo-first-order rate constant of propagation, k_obs, was nearly independent of the total concentration of salt, their values being 7,5.10^?3 s^?1 and 9 · 10^?3 s^?1, respectively, i. e. about 100 to 120 times higher than in pure THP. This indicates that the propagation occurs mainly via an increased but constant amount of free S^? anions resulting from the two already known equilibria SrS₂ ? (SrS)⁺ + S^?(K₁) and 2 SrS₂ ? (SrS)⁺ + (SrS₃)^? (K₂) and the equilibrium of glymation (SrS⁺) + G ? G, (SrS)⁺ (K_i). A small not exactly determinable contribution of glymated ion-pairs and/or triple ions, whose rate constants would then probably be of the order of 18 l · mol^?1 · s^?1 and 80 l · mol^?1 · s^?1, respectively, could not be excluded. The glymation constant K_i was found to be about 3 · 10⁶ 1 · mol^?1, i.e., approximately 17 times greater than for the Na⁺ cation. Finally, a kinetic experiment with SrS₂ at 20°C in pure benzene (contaminated, however, with some remaining THP from the preparation of SrS₂) indicated that propagation by ion-pairs is possible with a bimolecular apparent rate constant K_app = 1,1 · 10^?1 l · mol^?1 · s^?1.     

The initiation of polymerization of unsaturated tertiary amines with carboxylic acids

The polymerization rate (R_p) of N-methyl-N-phenyl-2-aminoethyl methacrylate (MPAEMA) initiated with 2,2' -azodiisobutyronitrile (AIBN) at 50°C increased considerably after the addition of CCI₃COOH, and distinctly after the addition of CH₃COOH. R_p in a benzene solution of 2 mol. dm^?3 MPAEMA and 5 · 10^?2 mol. dm^?3 CCl₃COOH (without AIBN) was 13% · h^?1. [η] of the obtained polymer corresponded to 64 cm³ · g^?1. The polymerization order of MPAEMA initiated with CCl₃COOH is 0,93 with respect to monomer and 0,51 with respect to CCl₃COOH. The overall activation energy of polymerization of MPAEMA calculated from the temperature dependence of R_p between 20 and 50°C is 43 ± 1,2 kJ · mol^?1. In a benzene solution of 2 mol.dm^?3 MPAEMA, 5 · 10^?2 mol · dm^?3CCl₃COOH and 5 · 10^?3 mol · dm^?3 1,4-benzoquinone at 50°C the polymerization does not proceed for 6 h. In a benzene solution of 2 mol · dm^?3 4-dimethylaminostyrene (4-DMAS) and 2 mol · dm^?3 CH₃COOH (without AIBN), 40% of monomer polymerized within one hour. [η] of the polymer was 4 cm³ · g^?1. The overall activation energy of polymerization of 4-DMAS in the presence of CH₃COOH is ca · 54 kJ · mol^?1. The addition of 5 · 10^?3 1,4-benzoquinone slows down the polymerization rate only slightly. The effect of acids on the elementary polymerization reactions is characterized.     

Free-radical propagation rate coefficients for cyclohexyl methacrylate,glycidyl methacrylate and 2-hydroxyethyl methacrylate homopolymerizations

Propagation rate coefficients (k_p) for the homopolymerization of cyclohexyl methacrylate (CHMA), glycidyl methacrylate (GMA) and 2-hydroxyethyl methacrylate (HEMA) were determined by the pulsed laser polymerization (PLP)/size-exclusion chromatography (SEC) technique. Temperature was varied between −10 and 90°C and pressure up to 2500 bar. k_p values for CHMA and GMA agree within the experimental accuracy of ± 20 per cent. They are by about a factor of 2.5 below k_p of HEMA. The activation energies and activation volumes of k_p of methacrylates studied so far, including linear and branched alkyl methacrylates, are close to each other: E_A(k_p) = (22 ± 2) kJ · mol⁻¹ and ΔV^≠(k_p) = −(16 ± 2) cm³ · mol⁻¹, respectively, indicating a pronounced family-type behavior.     

Capacity flow method for determination of propagation and termination rate constants in radical polymerization

The possibility of determination of the propagation and termination rate constants k_p and k_t, resp., as well as their ratios k_p/k_t and k_p/k in homogeneous radical polymerization is shown using the capacity flow method. A theoretical analysis is carried out and relatively simple equations are introduced. The essential point is that the life time of the growing polymer chain is obtained graphically from the residence time of the reactants in the reactor vessel, which is a given quantity. As an experimental example the polymerization of methyl methacrylate initiated by benzoyl peroxide in benzene is investigated in a flow reactor with perfect mixing at 80°C. It is characteristic that the process can be followed by means usually applied for studying slow reactions. The degree of conversion is measured turbidimetrically and gravimetrically, whereas the initiation rate is analysed iodometrically. Thus, through a numerical linear approximation by the method of least squares k_p/k_t = (2,28±0,45)·10^?5, k_p/k = (1,50±0,22). 10^?1 are found from the experimental data, and hence k^p = (9,95±0,83)·10² l mol^?1 s^?1 and k_t = (4,36±0,49)·10⁷ l mol^?1 s^?1 are obtained.     

Determination of absolute rate constants for radical polymerization and copolymerization of ethyl α-cyanoacrylate in the presence of effective inhibitors against anionic polymerization

The absolute rate constants of propagation k_p and of termination k_t of ethyl α-cyanoacrylate (ECNA) were determined in bulk at 30°C by means of the rotating sector method under conditions to suppress anionic polymerization; k_p = 1 622 1 · mol^?1 · s^?1 and k_t = 4,11 · 10⁸ 1 · mol^?1 · s^?1 for the polymerization in the presence of acetic acid, and k_p = 1610 1 · mol^?1 · s^?1 and k_t = 4,04 · 10⁸ l · mol^?1 · s^?1 for the polymerization in the presence of 1,3-propanesultone. The magnitude of k/k_t determined was 6,39 · 10^?3 l · mol^?1 · s^?1. The absolute rate constants for cross-propagation in ECNA copolymerizations were also evaluated. Quantitative comparison of the rate constants with those of common monomers and polymer radicals shows that the strong electron-withdrawing power of the ethoxycarbonyl and cyano groups enable the poly(ECNA) radical to add to monomers as fast as the other polymer radicals. The relatively high reactivity of ECNA, regardless of the type of attacking polymer radical, is interpreted by a transition state greatly stabilized by both the ethoxycarbonyl and the cyano groups.     

Solvent effects on free-radical polymerization, 2. IR and NMR spectroscopic analysis of monomer mixtures of methyl methacrylate and N-vinyl-2-pyrrolidone in bulk and in model solvents

Binary systems of methyl methacrylate (MMA)/N-vinyl-2-pyrrolidone (NVP) and MMA/N-methyl-2-pyrrolidone (NMP) with NMP as saturated model of NVP and of NVP/methyl isobutyrate (MiB) with MiB as saturated model of MMA were investigated by means of IR and NMR spectroscopy. Investigations were carried out at room temperature or at 60°C in CHCl₃ (IR) or CDCl₃ and C₆H₁₂/C₆D₁₂ (NMR). It can be concluded from IR and NMR spectra that the polarity of MMA increases in the presence of NVP and the polarity of NVP decreases in the presence of MMA. Equilibrium constants K of complex formation were determined to: K = 0,169 ± 0,037 L · mol^?1 for MMA/NVP at 30°C, 0,112 ± 0,024 L · mol^?1 for NVP/MiB at 60°C and 0,125 ± 0,030 L · mol^?1 for MMA/NMP at 60°C.     

Thermisch und UV-photochemisch initiierte hochdruckpolymerisation des ethylens, 1. Molmassen-mittelwerte

Ethylene is polymerized with thermal and with UV-photochemical initiation at temperatures between 130°C and 255°C up to pressures of 2500 bar. The conversions are between two and five percent. The degrees of polymerization as obtained from viscosity experiments are dependent on reaction temperature and pressure, but are insensitive to the kind of initiation, thermal or photochemical. These observations are explained by an equation which relates the degree of polymerization to kinetic parameters of the system which have partly been determined by independent experiments. From this equation, the activation energy and the activation volume of the transfer constant with the monomer, c_m, are determined to be E_a(c_m) = 43,9 ± 4 kJ · mol⁻¹ and ΔV^≠ (c_m)=20,1 ± 3 cm³ · mol⁻¹, respectively.