Evaluation of the rate constant for primary radical termination in free radical polymerization

Styrene and methyl methacrylate were polymerized with azodiisobutyronitrile (AIBN) at 50, 60, and 70°C. The average degree of polymerization was kept constant while changing the initiator concentration, by using 1-butanethiol as a chain transfer agent. In these polymerizations, a deviation from the simple kinetic rate law was noticed. This deviation was explained in terms of primary radical termination considering the effect of size dependence of the termination rate constant on the kinetics of free radical polymerization and taking into account the fraction of thermal polymerization. The temperature dependence of the characteristic constant, K_tpr/K_pK_i, was estimated to be 5,408 · 10^?5 exp (12915 cal mol^?1/RT) and 7,52 · 10^?3 exp (7791 cal mol^?1/RT) for styrene/AIBN and methyl methacrylate/AIBN, respectively.     

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.     

On the interaction of styrene-maleic anhydride copolymer with styrene

The interaction between alternating styrene/maleic anhydride copolymer as polymeric acceptor and styrene as low molecular weight donor in acetone and/or tetrahydrofuran was investigated by UV spectroscopy and polymerization technique. The equilibrium constant for the complex formation between styrene and the maleic anhydride structural unit of the styrene/maleic anhydride copolymer at 20°C was found to be 0,02 ± 0,001 dm³·mol^?1 in acetone and 0,06 ± 0,003 dm³·mol^?1 in tetrahydrofuran. The results of the thermally initiated polymerization of styrene in acetone in the presence of the alternating styrene/maleic anhydride copolymer indicate that the copolymer or the products of the interaction between the monomeric units of maleic anhydride in the copolymer and styrene do not initiate a radical polymerization of styrene.     

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.     

Variation of the propagation rate coefficient with pressure and temperature in the free-radical bulk polymerization of styrene

The propagation rate coefficient K_p of the free-radical bulk polymerization of styrene is determined between 30 and 90°C up to a maximum pressure of 2800 bar. The data from pulsedlaser polymerizations and product analyses by gel-permeation chromatography (PLP-GPC) are adequately represented by the expression: The conseaquences of deducing activation volumes and activation energies from k_p/(L · mol^?1 · s^?1) or fromk*_p/(kg · mol^-1 ·. S^?1) are outlined.     

N‐tert‐Butyl‐1‐diethylphosphono‐2,2‐dimethylpropyl nitroxide as counter radical in the controlled free radical polymerization of styrene: kinetic aspects

The controlled free radical polymerization of styrene with N‐tert‐butyl‐1‐diethylphosphono‐2,2‐dimethylpropyl nitroxide (DEPN) as counter radical was studied. Polymerizations were performed in bulk, with a DEPN‐capped polystyryl as alkoxyamine initiator, in the presence of an excess of DEPN nitroxyl free radicals. Kinetics of the polymerization were followed at 115°C, 125°C and 130°C. The equilibrium rate constant K = k_d/k_c of exchange between dormant and active species was determined experimentally from the slope of Ln([styrene]₀/[styrene]) versus time. The obtained Arrhenius relation was the following: K (mol·L^–1) = 1.45×10⁷exp (–113.5 kJ·mol^–1/RT), i.e., K = 1.9×10^–8 mol·L^–1 at 125°C. This result is consistent with a much faster polymerization of styrene with DEPN than with Tempo as nitroxyl counter radical (K = 2.1×10^–11 mol·L^–1 at 125°C determined previously by Fukuda).     

Etude cinétique de la dégradation du poly(oxytétraméthylèneoxytéréphtaloyle)

The kinetics of thermal degradation of poly(oxytetramethyleneoxyterephthaloyl) was studied. This polyester undergoes a pyrolysis reaction in the temperature range of processing via a statistical mechanism proceeding by a random scission of the carbon-oxygen bondings. This phenomenon is characterized by an energy of activation of 189,2kJ/mol (45,2kcal·mol^?1) and by a negative entropy of activation [?20,3J·mol^?1·K^?1 (?4,84cal·mol^?1·K^?1)]. Like most of the esters with a hydrogen atom in β position, this polyester undergoes degradation by an intramolecular mechanism involving the formation of a cyclic transition state. The very high value of the degradation constant of this polycondensate is probably a result of the presence, in this chain, of the very flexible tetramethylene segment.     

Preparation of surface-modified polystyrene microspheres by an azo-initiator having analogous structure to the head group of phosphatidylcholine

A novel azo-initiator, 2-[(2-ethylphosphatoethyl)dimethylammonio]ethyl 4,4′-azobis-(4-cyanovalerate) (EAP-501), was prepared. EAP-501 [m. p. 97°C (dec.), λ_max 346 nm in H₂O] was found to be amphiphilic, with a Krafft point of 11,5°C and a critical micelle concentration of 47,2 mmol·dm^?3 at 30°C and 48,6 mmol·dm^?3 at 70°C. The rate and activation parameters for the thermal decomposition of EAP-501 at 70°C were estimated to be k_d = 2,35·10^?5 s^?1, ΔH^≠ = 118,4 kJ·mol^?1 and ΔS^≠ = 10,5 J·mol^?1·K^?1. Emulsion polymerization of styrene initiated with EAP-501 gave polymer microspheres in high yield. The resulting polystyrene microspheres were characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The polystyrene microspheres have diameters from 321 to 649 nm by varying the EAP-501 concentration. The ammonium phosphate groups, which are comparable to the polar head group of phospholipids, are concentrated on the surface of the particles. The particles were found to reduce the adsorption of bovine serum albumin (BSA) compared with particles prepared by the emulsion polymerization of styrene initiated with potassium persulfate as an initiator.     

The formation of a coloured complex of partially saponified poly(vinyl acetate) with iodine in the presence of potassium iodide

The red-violet complex which was formed from partially saponified poly(vinyl acetate) and iodine in the presence of potassium iodide was investigated by the Benesi-Hildebrand method. The molar absorption coefficient of the complex at the absorption maximum (488 nm) was found to be 4,74.10⁴1/(mol cm) at 10°C and to decrease with rising temperature. The concentration of units resulting from vinyl acetate (acetoxyethylene units), which can take part in the complex formation with iodine, was below 1% of the total content of acetoxyethylene units in the polymer. The changes of enthalpy (ΔH) and entropy (ΔS) were found to be ?45,01 kJ mol^?1 (?10,75 Kcal/mol) and ?48,40 J mol^?1 K^?1 (?11.56 cal mol^?1 K^?1) at 15°C, respectively.     

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.     

Solvent effect on the propagation rate constant in the radical polymerization of bis(2-ethylhexyl) itaconate

Polymerization of bis(2-ethylhexyl) itaconate ( 1 ) with dimethyl azobis(isobutyrate) ( 2 ) was carried out at 50°C in various solvents. Polar solvents caused a significant decrease in the polymerization rate (R_p) and the molecular weight of resulting poly( 1 ). The propagating poly( 1 ) radical could be observed as a five-line ESR spectrum in the actual polymerization systems used. The stationary concentration of poly( 1 ) radical was determined by ESR to be 4,2–6,4 · 10^?6 mol · L^?1 at 50°C when the concentrations of 1 and 2 were 1,03 and 3,00 · 10^?2 mol · L^?1. Using R_p the monomer concentration and the polymer radical concentration, the propagation rate constant (K_p) was estimated to be 1,4–6,8 L · mol^?1 · s^?1, depending on the solvents used. The k_p value was smaller in more polar solvents. The solvent effect is explained in terms of the solvent affinity for the propagating polymer chain.     

Stereocontrol in the free radical polymerization of N-vinylcarbazole

The free radical polymerization of N-vinylcarbazole (VK) was investigated in hexane, nonane, toluene, HMPT, DMF, DMAC, and DMSO. Isotactic propagation was found to be energetically favoured by between 1500 and 4600 J · mol^?1 for all the solvents investigated, although the entropy difference between syndiotactic and isotactic propagation strongly favoured syndiotactic propagation by between 11 and 20 J · mol^?1K^?1. Variation in the steric microstructure between an isotactic mole fraction of 0,25 and 0,47 was obtained by varying the polymerization temperature and solvent. The activation enthalpy differences between isotactic and syndiotactic propagation (ΔH≠_s/i ? ΔH≠_i/s), for the free radical polymerization of methyl methacrylate (MMA) and VK were compared and the steric configurations involved in the propagation process considered. It was concluded that electronic interaction between radical and monomer appeared to determine the energetic preference of the growing chain for isotactic or syndiotactic propagation in free radical propagation. This energetic preference was correlated with the e-factor in the Q ? e scale. Data for the free radical polymerization of VK, MMA, and vinyl trifluoroacetate showed that solvent polarity has a weak influence on the energetic preference of the growing chain for isotactic or syndiotactic propagation. This energetic preference was correlated with the π* solvent polarity scale.     

Effect of SnCl4 on the radical-initiated polymerization of diethyl itaconate: Kinetical and ESR studies

The effect of SnCl₄ on the polymerization of diethyl itaconate ( 1 ) with dimethyl 2,2′-azoisobutyrate ( 2 ) in benzene was investigated kinetically and ESR spectroscopically. The polymerization rate (R_p) at 50°C shows a flat maximum on varying the SnCl₄ concentration. The molecular weight of the resulting polymer decreases with increasing SnCl₄ concentration. The overall activation energy of the polymerization is lowered from 52 to 33 kJ · mol^?1 by the presence of SnCl₄, (0,342 mol · L^?1). An NMR study revealed that 1 and SnCl₄ form 1:1 and 2:1 complexes with a large stability constant in benzene. The propagating polymer radicals in the absence and presence of SnCl₄ are ESR-observable as a five-line spectrum under the actual polymerization conditions. The complexed polymer radicals show further three-line splitting due to two methylene hydrogens of the ethyl ester group. The polymer radical concentration increases with the SnCl₄ concentration. The rate constant (k_p) of propagation was determined using R_p and the polymer radical concentration. k_p (6,3–2,9 L · mol^?1 · s^?1 at 50°C) decreases with increasing SnCl₄ concentration. The presence of SnCl₄ (0,342 mol · L^?1) reduces the activation energy of propagation from 29 to 21 kJ · mol^?1. The rate constant (k_t) of termination was estimated from the decay curve of the polymer radicals, k_t (3,1–1,1 · 10⁵ L · mol^?1 s^?1) also decreases with the SnCl₄ concentration. The activation energies of termination in the absence and presence of SnCl₄ (0,342 mol · L^?1) are 30 and 24 kJ · mol^?1, respectively. Suppression of propagation and termination by SnCl₄ seems to be explicable in terms of an entropy factor.     

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.     

Kinetics of the polymerization of styrene with butoxytitanium trichloride and trialkylaluminium

The kinetics of polymerization of styrene in heptane was investigated using butoxytitanium trichloride and triethylaluminium/triisobutylaluminium as cocatalysts. A steady state polymerization after an initial period of declining rates lasting for 20 – 60 min was observed. Both the catalysts systems polymerize styrene at a slow rate ( ≈ 10^?6 mol · dm^?3 · s^?1). The steady state rates show a maximum at an [A1] : [Ti] ratio of 1,5 and exhibit a first-order rate law with reference to both the monomer and the catalyst. Addition of triethylamine, an electron donor, greatly influences the rates of polymerization when triethylaluminium is used, whereas in the case of triisobutylaluminium, the rates are not greatly influenced by the presence or absence of triethylamine. The effect of the electron donor on the rates of polymerization can be explained by the competitive complexation of the alkylaluminium and the electron donor at the active site. The overall activation energy of polymerization (44 – 46 kJ · mol^?1) is in accord with a coordinated anionic mechanism. An alkylated alkoxytitanium halide species as the chemical entity affecting polymerization is suggested.     

Aqueous polymerization of vinyl monomers in the presence of surfactants, 2. Methacrylamide

The kinetics of the polymerization of methacrylamide initiated by potassium peroxodisulfate in water and 2,2′-azoisobutyronitrile (AIBN) in a water/ethanol mixture (mass ratio 9/1) were studied in the presence of the emulsifier sodium dodecylphenoxybenzenedisulfonate. The emulsifier was found to affect the relative molecular mass of polymethacrylamide, but it showed no effect on the polymerization rate. The transfer constant to the emulsifier determined amounts to 1,8 · 10^?2. The polymerization rate is proportional to the square root of the potassium peroxodisulfate concentration and to the first power of the methacrylamide concentration. During initiation by AIBN, the exponent of the concentration of AIBN in an equation expressing the dependence of the polymerization rate on AIBN concentration amounts to 0,82; the exponent of methacrylamide concentration is equal to 1. The activation energy for the polymerization initiated by K₂S₂O₈ is 67 kJ · mol^?1, whereas for the polymerization initiated by AIBN it is 44,0 kJ · mol^?1.     

Anionic polymerization of 2-Oxo-1,3,2λ5-dioxaphosphorinane. Thermodynamics

Thermodynamics of the polymerization of 2-oxo-1,3,2λ⁵-dioxaphosphorinane in bulk initiated by sodium metal is described. Enthalpy (ΔH_p = 6,28 ± 0,84 kJ · mol^?1) and entropy (ΔS = 19,25 ± 2,51 J · mol^?1 · K^?1) of polymerization were evaluated from the temperature dependence of the equilibrium nomomer concentration determined directly by ³¹P{¹H} NMR. The results are compared with those obtained previously for the polymerization of other 2-alkoxy-2-oxo-1,3,2λ⁵-dioxaphosphorinanes.     

Kinetic and ESR studies of the radical-initiated polymerization of N-(2,6-dimethylphenyl)itaconimide

The polymerization of N-(2,6-dimethylphenyl)itaconimide (1) with azoisobutyronitrile (2) was studied in tetrahydrofuran (THF) kinetically and spectroscopically with the electron spin resonance (ESR) method. The polymerization rate (R_p) at 50°C is given by the equation: R_p = K [2] ^0,5 · [1] ^2,1. The overall activation energy of the polymerization was calculated to be 91 kJ/mol. The number-average molecular weight of poly (1) was in the range of 3500–6500. From an ESR study, the polymerization system was found to involve ESR-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 at 50°C. k_p (24–27 L · mol^?1 · s^?1) is almost independent of monomer concentration. On the other hand, k_t (3,8 · 10⁴–2,0 · 10⁵ L · mol^?1 · s^?1) increases with decreasing monomer concentration, which seems mainly responsible for the high dependence of R_p on monomer concentration. Thermogravimetric results showed that thermal degradation of poly (1) occurs rapidly at temperatures higher than 360°C and the residue at 500°C was 12% of the initial polymer. For the copolymerization of 1 (M₁) with styrene (M₂) at 50°C in THF the following copolymerization parameters were found; r₁ = 0,29, r₂ = 0,08, Q₁ = 2,6, and e₁ = +1,1.     

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.     

Free-radical polymerization of methyl methacrylate initiated by N,N-dimethylaniline

N,N-Dimethylaniline (DMA) does initiate the free-radical polymerization of methyl methacrylate (MMA), methyl acrylate, and methyl vinyl ketone. The overall rates of polymerization of MMA were obtained at 40, 50, and 60°C. From the results of a detailed kinetic investigation, the activation enthalpy and activation entropy of polymerization were calculated as 63,2 kJ mol^?1 and ?153 J mol^?1 K^?1 at 60°C. Rate equation was also obtained as R_p = k[DMA]^1/2[MMA]^3/2 and the polymerization was inhibited by benzoquinone. Though styrene alone was not polymerized by DMA, the copolymerization of MMA with styrene by DMA (reactivity ratios: r_MMA=0,45 and r_St=0,50) followed a typical free-radical mechanism. An electron-transfer complex between DMA and MMA is proposed as the initiation species.