Studies on aqueous polymerization of acrylonitrile. Cerium(IV)/acetaldehyde redox system

The thermal polymerization of acrylonitrile initiated by the cerium(IV)/acetaldehyde (A) redox system was carried out at 25°C, and the rate of monomer disappearance, –d[M]/dt, was followed by gravimetry and the rate of cerium(IV) disappearance –d[Ce(IV)]/dt by titrimetry. –d[M]/dt was found to be directly proportionsl to [M]^3/2, [A]^1/2, and [Ce(IV)]^1/2. –d[Ce(IV)]/dt was found to be directly proportional to [Ce(IV)] and [A]. A reaction scheme is given together with the kinetic expressions. The activation energy for the overall rate was found to be 67,24kJ.mol^?1 (16,06kcal.mol^?1), and the value of the second order rate constant k_r, was obtained as 2,481.mol^?1s^?1.     

Acrylamide polymerization initiated with the redox system Ce(IV)-cyclohexanone in micellar phase: A kinetic study

The effect of an organized anionic surfactant, i.e. sodium dodecyl sulfate (SDS), on the acrylamide (AM) polymerization initiated with the redox system Ce(IV)-cyclohexanone (CH) in aqueous nitric acid was kinetically studied over a temperature range of 25–45°C. With increasing concentration of SDS, above its critical micelle concentration (CMC) the rate of polymerization, R_p(obs), as well as the rate of Ce(IV) consumption, −R_Ce(obs), were found to increase, while in the presence of cetyltrimethylammonium bromide (CTAB) these rates decreased considerably. R_p(obs) is proportional to [Ce(IV)]^0.5, [CH]^0.5 and [AM]^1.5. −R_Ce(obs) also increases with increasing concentration of Ce(IV), cyclohexanone and acrylamide. The overall activation energy for the process, in the presence and absence of 15 × 10⁻³ M of SDS, was calculated to be 15.1 and 21.4 kcal/mol, respectively. The viscosity average molecular weight of polyacrylamide was found to increase with increasing SDS concentration. A suitable mechanistic scheme for the polymerization process is proposed.     

Mechanism of the polymerization of acrylamide initiated by the glycerol/Ce(IV) redox system

The mechanism of the polymerization of acrylamide in aqueous medium initiated by the glycerol (R)/Ce(IV) redox system was studied. The rate of monomer disappearance was found to be directly proportional to [M]^3/2, and R^1/2 at lower concentrations of Ce(IV). The rate of the disappearance of ceric ions was found to be inversely proportional to [M] and directly proportional to [Ce(IV)] and [R]. Consistent with the findings of earlier investigations, a complex formation between monomer, acrylamide, and ceric ion is indicated. The experimental results show the termination to be mutual. On the basis of these and other kinetic results, an appropriate mechanism is proposed. At higher concentration of Ce(IV), a different mechanism seems to operate. The rates of disappearance of both the monomer and ceric ions are retarded on addition of anions like HSO₄^?, SO₄^{? ?}, or CIO₄^?, but they are accelerated on the addition of Mn(II) ions. Interpretations of the above observations are furnished.     

Über die radikalpolymerisation einiger monomerer in dimethylformamid

The polymerization of acrylonitrile, methyl acrylate, methyl methacrylate, α-chloromethyl acrylate and α-bromo methyl acrylate in dimethylformamide has been investigated using α.α′-azobisisobutyronitrile as initiator. The following relations have been derived at 60°C: for methyl acrylate v = 15.15·10^?4·[I]^0.5·[M], for methyl methacrylate v = 3.46·10^?4·[I]^0.5·[M], for α-chloro methyl acrylate v = 5.25·10^?4·[I]^0.5·[M], and for α-bromo methyl acrylate v = 4.12·10^?4·[I]^0.5·[M]. It has been found that (k_p/k_t^0.5)₆₀ is 14.4·10^?2 for α-chloro methyl acrylate and 12.15·10^?2 for α-bromo methyl acrylate. The relation between the kinetic data obtained and the HAMMETT σ_p constants has been discussed for the substituents in α-position to the double bond which are considered to be the characteristic parameters for the chemical structure of the monomers.     

Epoxy prepolymers cured with boron trifluoride-amine complexes, 2. Polymerization mechanisms

The kinetics of the polymerization of phenoxymethyloxirane ( 6 ) initiated by the BF₃ complex of 4-chloroaniline ( 7 ) solubilized in oligo(ethylene oxide) of molecular weight 300 (PEO) is characterized by an initial induction period, followed by a propagation step with a rate R_p = k [ 6 ] · [ 7 ]^0,32 · [PEO]^?0,55. The length of the induction period decreases with [ 7 ] and increases with [PEO]. However, R_p increases with [ 7 ] and decreases with [PEO]. The reaction can be explained by the activated monomer mechanism.     

Study of photopolymer, 10. Cationic polymerization of vinyloxyethyl acrylate

Cationic polymerizations of vinyloxyethyl acrylate (VEA) catalyzed by boron trifluorideether complex were carried out in toluene at 10, ?10, and ?30°C. In this system, a critical catalyst concentration (C₀) exists; when the catalyst concentration is below this concentration, the polymerization of VEA cannot be initiated. The rate of polymerization is expressed as –d[M]/dt=k_p(C^*)·[M]^a, where a was found to be 0,44 (at 10°C), 0.51 (at ?10°C), and 0,63 (at ?30°C), respectively. From these results, it is concluded that the rate of polymerization of VEA is proportional to the first power of catalyst concentration and to 0,44–0,63 power of monomer concentration between 10 and ?30°C, respectively. Furthermore, it is recognized that an increasing monomer concentration tends to decrease the degree of polymerization.     

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.     

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.     

Kinetic and electron paramagnetic resonance studies on radical polymerization. Radical-initiated polymerization of methyl N-phenylitaconamate in N,N-dimethylformamide

The polymerization of methyl N-phenylitaconamate(methyl 2-methylenesuccinanilate ( 1 )) with dimethyl 2,2′-azodiisobutyrate ( 2 ) was studied in N,N-dimethylformamide (DMF) kinetically and by means of electron paramagnetic resonance (EPR) spectroscopy. The polymerization rate (R_p) at 55°C is given by the equation: R_p = k[ 2 ]^0,58 · [ 1 ]^1,6. The overall activation energy of the polymerization was calculated to be 54,2 kJ/mol. The number-average molecular weight of poly( 1 ) was in the range between 5000 and 17000. From an EPR study, the polymerization system was found to involve the EPR-detectable propagating polymer radical of 1 at practical polymerization conditions. Using the concentration of polymer radicals, the rate constants of propagation (k_p) and termination (k_t) were determined for 55°C. The rate constant of propagation k_p (between 8,4 and 12 L · mol^?1 · s^?1) tends to somehow increase with increasing monomer concentration. On the other hand, k_t (between 1,9. 10^?5 L · mol^?1 · s^?1) increases with decreasing monomer concentration, which results from a considerable dependence of k_t on the polymer-chain length. Such monomer-concentration-dependent k_p and k_t values are responsible for the high dependence of R_p on the monomer concentration. Thermogravimetric results showed that thermal degradation of poly( 1 ) occurs rapidly at temperatures higher than 200°C and the residue at 500°C amounts to 26% of the initial polymer. For the copolymerization of 1 (M₁) with styrene (M₂) at 55°C in DMF the following copolymerization parameters were found: r₁ = 0,52, r₂ = 0,31, and Q, e values Q₁ = 1,09 and e₁ = +0,55.     

Kinetics of the polymerization of isoprene with isopropoxyneodymium dichloride/triethylaluminium binary lanthanide catalyst system

The kinetics of the polymerization of isoprene with the heterogeneous rare earth catalyst system isopropoxyneodymium dichloride/triethylaluminium (Nd(OPrⁱ)Cl₂-AlEt₃) was examined in a specially designed dilatometer. The rate of polymerization is expressed as R_p ≈ ?d[M]/dt = k[Nd]^1.40 [M]. The main kinetical parameters such as the concentration of active propagating chain, the efficiency of lanthanide catalyst used (ELCU), the absolute rate constant of propagation as well as the average life time of growing chains, were determined at 30°C, 40°C, 45°C and 50°C.     

Vinyl polymerization 270. Polymerization of methyl methacrylate initiated by azibenzil

The polymerization of methyl methacrylate initiated by azibenzil (AB) was studied kinetically. The initial rate of polymerization (R_p) was found to be expressed by the equation R_p = k[AB]^0.47[MMA]^0.97. The polymerization proceeded through a radical mechanism. The overall activation energy for the polymerization was estimated as 16.1 kcal/mole. Furthermore, the rate of decomposition of AB was measured in benzene and the following rate equation was obtained: k_d[sec^?1] = 5.75·10¹⁰ exp(-21.9 kcal/RT). From these results the initiation mechanism was discussed.     

Application of spin trapping technique to radical polymerization, 20. Vinyl polymerization initiated by triphenylboron

Triphenylboron was found to serve as an effective radical initiator for vinyl monomers without any participation of oxygen. The polymerization of methyl methacrylate (MMA) initiated by triphenylboron was studied kinetically in acetonitrile. The over-all activation energy of the polymerization was calculated to be 60,3 kJ/mol. The polymerization rate (R_p) can be expressed as follows: R_p = k (Triphenylboron)^0,9[MMA]^1,8. Spin trapping studies revealed formation of phenyl radicals by decomposition of triphenylboron in the absence of oxygen. Decomposition of triphenylboron in toluene yielded o-, m-, and p-methylbiphenyls, the isomer ratio of which was close to that observed in the decomposition of benzoyl peroxide in toluene. Furthermore, an ethanol solution of triphenylboron was found to give a very stable boron centered radical. From these findings, the initiation mechanism for the polymerization is proposed and discussed.     

Styrene polymerization induced by anilino radicals

The polymerization of styrene (St) initiated by 1,4-dimethyl-1,4-diphenyl-2-tetrazene ( 1c ) is studied kinetically in benzene. The polymerization proceeds through a radical mechanism. The rate equation is as follows: R_p = k [ 1c ]^0,5[St]^1,0. The overall activation energy for the polymerization of St is found to be 105,9 kJ · mol^?1. The efficiency of the initiator is also calculated to be 0,67. On the basis of the results, the initiating ability of N-methylanilino radicals is discussed.     

Vinyl polymerization initiated with the lanthanum versatate/p-chlorobenzenediazonium tetrafluoroborate system

The system of lanthanum versatate ( 1 ) and p-chlorobenzenediazonium tetrafluoroborate ( 2 ) was found to induce effectively polymerizations of electron-accepting monomers such as methyl methacrylate ( 3 ) and di-2-ethylhexyl itaconate (DEHI). The polymerization rate (R_p) was expressed by R_p = k[ 1 / 2 ]^0,44 [ 3 ]^0,65 at 50°C fixing the mole ratio of 1 and 2 at unity. The overall activation energy of the polymerization was calculated to be 37, 1 kJ · mol^?1. The spin trapping result revealed that the initiator system produces p-chloropheneyl radicals. The polymerization system of DEHI was observed to involve ESR-observable propagating polymer radicals, indicating that the polymerization initiated with the 1/2 system proceeds through radical mechanism. During the polymerization, the ESR spectrum was changed in shape, suggesting that the propagating polymer radicals interact with some species formed by the initiation reaction. Interacting polymer radicals were also observed in the polymerizations of diethyl itaconate and N-dodecylmaleimide with the 1/2 system. The polymerization systems of MMA, styrene and butyl acrylate were also found to involve ESR-observable radicals, although it is vague whether they are propagating polymer radicals or not.     

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.     

4-(α,α-dimethylbenzyl)phenyl methacrylate, 2. Polymerization in N,N-dimethylformamide

The polymerization rate of 4-(α,α-dimethylbenzyl)phenyl methacrylate in DMF at 70°C is of the order 1,6 in [monomer] and first order in [AIBN], which deviates from classical kinetics. This could be reconciled by a reaction scheme in which dimeric monomer associates and a spontaneous termination are postulated. The scheme is supported by the dependence of the kinetic chain length, v, on the 1,6-th power in [monomer] and zeroth power in [AIBN]. The degree of polymerization is smaller than v, which indicates some chain transfer. A remarkable feature is the constancy of the dispersion degree, M?_w/M?_n, of the polymers of about 1,4 up to high degrees of conversion. The overall activation energy of the polymerization, E_a, is 60,1 kJ · mol^?1, and the preexponential factor ln A ≈ 15,5 (A in (mol · dm^?3)^?1,5 · s^?1). The polymer chains seem to have a rod-like character in THF as deduced from the Mark-Houwink exponent of 1,46. In toluene the polymer tends to form associates.     

Vinylpolymerisation mit reduzierenden Übergangsmetallverbindungen, 3. Polymerisation in gegenwart von initiatorsystemen aus vanadium(II)- und vanadium (III)-chlorid sowie organischen halogenverbindungen

The polymerization of methyl methacrylate initiated by the redox system vanadium(III) chloride/carbon tetrachloride was studied. The rate of polymerization can be described by the equation R_p = k · [VCl₃]^0,5·[CCl₄]^0,5·[MMA]^1,0. The overall activation energies were estimated to be 74,5 kJ·mol^?1 for VCl₃/CCl₄ and 59,5 kJ·mol^?1 for VCl₂/CCl₄. Vanadium (II) chloride acts as a retarder in the polymerization of styrene initiated by 2,2′-azoisobutyronitrile (AIBN). The polymerization of acrylonitrile and methyl methacrylate is inhibited by vanadium (II) chloride. The polymerization of acrylonitrile initiated by AIBN is retarded by vanadium (III) chloride.     

Polymerization of acrylonitrile initiated by the redox system manganese (III) acetate/ethylene glycol

The kinetics of polymerization of acrylonitrile initiated by the redox system manganese (III) acetate/ethylene glycol was studied in aqueous sulfuric acid medium in the temperature range from 30 to 40°C. The effect of varying the concentrations of monomer (M), acetic acid, and sulfuric acid and the addition of some electrolytes on the rate of polymerization (R_p) was investigated. Based on the experimental observations of the dependence of (R_p) on various parameters, a suitable kinetic scheme could be proposed. The plot of R_p²[M]² vs. [M] was found to be linear, a striking general phenomenon observed for all the substrates we have studied in this laboratory.     

Application of spin trapping technique to radical polymerization, 17.N-hydroxysuccinimide as a radical initiator

N-hydroxysuccinimide (NHS) and N-hydroxyphthalimide were found to initiate effectively vinyl polymerizations of acrylate monomers. The polymerization of methyl methacrylate (MMA) with NHS was investigated in detail. The polymerization rate (R_p) was found to depend highly on the solvents. The over-all activation energy of the polymerization in ethyl acetate was calculated to be 76,2 kJ/mol (18,2 kcal/mol). In the low monomer concentration, R_p can be expressed as R_p = k [NHS]^1/2 [MMA]^3/2. The copolymerization of MMA with styrene, initiated by NHS, could be shown to proceed via radical mechanism. In order to elucidate the initiation mechanism, spin trapping technique was applied to this polymerization system. In the reaction of MMA with NHS in acetone, the 2-carbomethoxypropyl radical was trapped by 2-methyl-2-nitrosopropane, a spin trapping reagent, to give the corresponding aminyl oxide radical 2 . From the results, the initiation mechanism of this polymerization is proposed and discussed.     

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.