Kinetics and mechanism of the isomerization polymerization of 2-methyl-2-oxazoline by benzyl chloride and bromide initiators. Effect of halogen counteranions

Kinetic studies of the isomerization polymerization of 2-methyl-2-oxazoline ( 2 ) initiated with benzyl chloride ( 1a ) or bromide ( 1b ) were carried out by NMR spectroscopy. The polymerization initiated with 1a proceeded exclusively via a covalently bonded alkyl chloride species 5 , whereas the polymerization of the system initiated with 1b proceeded via a oxazolinium bromide 10 as the propagating end. The propagation rate constant k_p with 1a was about 1/40 of that found with 1b at 40°C in CD₃CN. The mechanistic difference is explained by the different nucleophilicities of the counteranions, Cl^— and Br^—. A model compound for the propagation with 1b as initiator was also examined changing the temperature and the solvent.     

4-[Diphenyl(trimethylsilyl)methyl]benzophenone as initiator in the photopolymerization of methyl methacrylate and styrene

The polymerization of methyl methacrylate (MMA) and styrene (St) has been studied using 4-[diphenyl(trimethylsilyl)methyl]benzophenone 1 as photoinitiator. The polymerization follows a free radical mechanism; the polymerization rate increases linearly with the monomer concentration and was found to be proportional to the 0.33 and 1.40 power of the photoinitiator and the monomer (MMA) concentration, respectively. The overall activation energy in the case of MMA photopolymerization was calculated to be 25.0 kJ/mol. From ¹H NMR studies it is concluded that the obtained polymers contain two different trimethylsilyl moieties, one at the head and the other at the tail of the polymer chain, showing primary termination reactions even at low initiator concentrations. The p-benzoyltrityl radical 1^· is incorporated into the polymer chain to a very small extent, acting as a scavenger. This is also concluded by laser flash photolysis (LFP) and ESR spectroscopy measurements. A “living” character of the polymerization was observed only at very low initiator concentrations. The triplet state (³ 1 ^*) of the initiator was quenched by styrene, reducing its efficiency. The rate constant k_q of the quenching process of ³ 1 ^* was measured by LFP (k_q = 3.1 · 10⁹ M⁻¹ · S⁻¹). The triplet state and the photodissociation efficiency of the initiator is unaffected by MMA at various concentrations.     

Polymerization of methacrylic acid esters with the aged system of lanthanum versatate and p-chlorobenzenediazonium tetrafluoroborate

The aged system of lanthanum versatate ( 1 ) and p-chlorobenzenediazonium tetrafluoroborate ( 2 ) was found to initiate effectively the radical polymerization of acrylic monomers including alkyl methacrylates, butyl acrylate and acrylonitrile, although its initiating activity is lower than that of the non-aged system. The polymerization of methyl methacrylate ( 3 ) with the aged 1/2 system was studied kinetically in acetone. The initial polymerization rate (R_p) is expressed by R_p = Kċ[aged 1/2 ]^0.80 ċ [ 3 ]^1.1 at 50°C. The overall activation energy of the polymerization is 59.0 kJ ċ mol⁻¹. The molecular weight of the resulting poly( 3 ) formed in the early stage increases with increasing conversion. The polymerization system involves a persistent radical showing a four-line EPR spectrum with a g-value of 2.004. A three-line spectrum due to the nitroxyl radical was also observed at lower monomer concentrations. The total concentration of persistent radicals was found to correspond well to the instantaneous polymerization rate. The copolymerization of styrene (M₁) and 3 (M₂) with the aged initiator system was examined at 50°C in acetone. r₁ and r₂ are 0.19 and 0.47, respectively. The former is considerably smaller than that (0.52) reported for the conventional radical polymerization.     

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.     

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.     

Die katalyse der 1,4-cis-polymerisation des butadiens mit dem kationischen C12-allylnickel(II)-komplex [Ni(C12H19)]SbF6

The catalytic properties of η³,η²η²-dodeca-2(E),6(E),10(Z)-trien-1-yl-nickel(II) hexafluoroantimonate are investigated in some detail. Under standard conditions the complex catalyses the polymerization of butadiene in toluene at room temperature with an extremely high activity of nearly 15000 mol C₄H₆/(mol Ni · h) and a cis selectivity up to 90%. The activity increases linearly with both the nickel and the butadiene concentration. No change in the selectivity and in the limiting viscosity number [n] has been found in the investigated range of concentration and temperature.     

Difference in propagation rate constants between photo-and thermal-initiated polymerization of styrene – effects of light irradiation

Propagation rate constants (k_p) for photo- and thermal-initiated radical polymerizations of styrene were determined by electron spin resonance (ESR) spectroscopy. The k_p value for the former at 70°C ((420 ± 30) M^?1 · S^?1) was more than twice as large as that for the latter ((190 ± 10) M^?1 · s^?1) although the former value was almost the same as that obtained with the pulsed-laser polymerization method. To evaluate the origin of the difference in the k_p values between photo- and thermal-initiated polymerization the absorption spectrum of a model of the propagating radical was measured and both the influence of the wavelength of the irradiation light on k_p values and the activation energy of the photo-initiated radical polymerization of styrene were determined. k_p decreases for wave-lengths shorter than 370 nm and is in agreement with the k_p value for thermal-initiated polymerization. No wavelength dependence of k_p was obtained for dienes whose propagating radical does not absorb above 300 nm. The difference in k_p values for photo- and thermal-initiated polymerizations is considered to be due to the photoactivation (photoinduced excitation) of the propagating radical of styrene.     

Functionalized monomers, 2. Kinetics of radical polymerization of oxirane- and oxetane-derivatives of styrene and copolymerization of 4-vinylphenyloxirane with styrene

The kinetics of radical polymerization of 4-vinylphenyloxirane ( 1 ), 4-vinylbenzyloxirane ( 2 ), and 2-(4-vinylphenyl)oxetane ( 3 ) initiated by 2,2′-azoisobutyronitrile (AIBN) was studied. In the case of 1 the initial rate of polymerization was found to depend on the initiator and monomer concentrations as (r_p)_total ∝? [AIBN]^0,5 · [M₁]^1,36. The higher order of the polymerization rate with respect to 1 was interpreted as due to a concurrent thermally initiated polymerization; the rate of the latter was found to depend on the monomer concentration squared. The value of the ratio propagation rate constant over square root of termination rate constant k_p/k_t^1/2 = 2,8 · 10^?2 dm^3/2 · mol^?1/2 · s^?1/2 was determined from the measured dependences (r_p)_total = f[AIBN] and (r_p)_total = f([M₁]), corrected for the rate of thermally initiated polymerization of 1 . On the other hand, the kinetics of radical polymerization of 2 and 3 did not deviate from the standard scheme valid for radical polymerization; in both cases the observed reaction order with respect to initiator and monomer was 0,5 and 1, respectively. Radical copolymerization of 4-vinylphenyloxirane (M₁) with styrene (M₂) was characterized by monomer reactivity ratios r₁ = 1,06 and r₂ = 0,78, respectively, corresponding to the Q, e-scheme values Q = 0,9 and e = ?0,36 for monomer 1 .     

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.     

Bestimmung der geschwindigkeitskonstanten und der effektivitäten beim zerfall von 2,2′-azoisobutyronitril in styrol,N-vinyl-2-pyrrolidon und methylmethacrylat

The decomposition rate constants k_d of initiators can be determined by a new method directly in monomers as solvents. If a suitable inhibitor is added to a monomer mixture with the initiator the latter decomposes nearly without monomer conversion. The initiator concentration—after the inhibitor is consumed—can be found by means of the dilatometrically determined polymerization rate after the induction period. The functional connection between polymerization rate and initiator concentration found without inhibitor is used as a calibration curve for that purpose. The dilatometrical measurements were made in the monomers styrene and N-vinyl-2-pyrrolidone using 2,2′-azoisobutyronitrile (AIBN) as initiator and p-quinone as inhibitor. The following decomposition rate constants were found: k_d=1,52 · 10^?5 S^?1 (styrene) and k_d=1,62 · 10^?5 S^?1 (N-vinyl-2-pyrrolidone), which is in agreement with literature values. Initiator efficiencies f were calculated: f=0,46 (styrene), f=0,47 (N-vinyl-2-pyrrolidone). In methyl methacrylate (MMA) 2,2′-diphenyl-1-picrylhydrazyl (DPPH) was used as inhibitor. Under certain conditions the product k_df can be calculated from the consumption rate of DPPH. The value found in MMA (k_df=3,7 · 10^?6 s^?1) is lower than that reported in literature (6,45 · 10^?6 s^?1).     

Vinyl polymerization. 280. Anionic polymerization of acryloyl- and methacryloyl verdazyls

1.5-Diphenyl-3-(p-methacryloyloxymethylphenyl) verdazyl (I), 1.5-diphenyl-3-(p-methacryloyloxyphenyl) verdazyl (II), and 1.5-diphenyl-3-(p-acryloyloxymethylphenyl) verdazyl (III) were synthesized and anionically polymerized with n-butylmagnesium bromide or sodium naphthalene as an initiator to dark green polymers of a molecular weight of about 2300. III was polymerized with a catalytic amount of initiator, while I needed more initiator than the molar equivalent of the monomers suggesting the formation of intermediate metal salts of monomers and subsequent polymerization of the salts. More reactive double bond of III polymerized directly without the formation of the salt between stable free radical and organometallic compounds. Polymeric verdazyls contained up to 68% stable free radical.     

Cationic polymerizations initiated by high energy radiation

Ionizing radiations generate both free radicals and ions upon interaction with matter and under appropriate conditions either free radical or ionic polymerizations are observed. Cationic polymerizations are favored by the presence of halogenated solvents and by low reaction temperatures. Selective inhibitors and copolymerization studies make it possible to determine the relative proportions of the cationic and the free radical contributions to the overall process under a variety of experimental conditions (temperature, reaction medium, radiation dose-rate). Pure, carefully dehydrated hydrocarbon monomers undergo cationic polymerization when irradiated at room temperature. This reaction proceeds at a very high rate and is believed to involve free propagating cations. Propagation rate constants are available for the following monomers: styrene (k_p = 3,5·10⁶ at 15°C), α-methylstyrene (k_p = 4.10⁶ at 0°C), cyclopentadiene (k_p = 6.10⁸ at ?78°C), isobutene (k_p = 1,5·10⁸ at 0°C), and isobutyl vinyl ether (k_p = 3.10⁵ at 30°C). The present views on the mechanism of radiation induced cationic chain initiation and chain propagation are briefly discussed.     

Radical-intiated copolymers of styrene and p-formaylstyrene, 2. Preparation and characterization of emulsifier-free copolymer latices

Monodisperse copolymer latex particles with aldehyde groups at the surface have been prepared by a two-step process, comprising first a soap-free emulsion polymerization of styrene using potassium peroxodisulfate as an initiator and secondly a surface functionalization of the seed particles by copolymerizing p-formylstyrene (system. name: 4-vinylbenzaldehyde) using various addition methods. The final latices were characterized with respect to monomer conversion, copolymer composition, particle size and distribution. Particular attention was paid to the characterization of surface aldehyde groups using two different analytical methods such as X-ray photoelectron spectroscopy (XPS) and radioactive labelling by coupling with (1-³H₁)-2-aminoethanol.     

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.     

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).     

Nitroxide‐Mediated Radical Polymerization with Bisaminooxy Compounds as Initiators – Controlled Biradical Polymerization

Summary: The bisaminooxy compounds Bis‐TEMPO and Bis‐TIPNO derived from 2,2,6,6‐tetramethyl‐piperidine‐1‐oxyl (TEMPO) and 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐oxyl (TIPNO) were applied as “biradical initiators” for the nitroxide‐mediated radical polymerization (NMRP) of styrene and n‐butyl acrylate. It was shown by comparison with analogous alkoxyamines as unimolecular initiators and mixing experiments of mono‐ and biradical species, that in the case of the biradical initiators chain growth occurs at both sides under NMRP conditions. This enables a two‐step synthesis of A‐B‐A‐triblock copolymers. Kinetics and molecular mass development were investigated for the controlled biradical polymerization of styrene at different initiator concentrations, temperatures, and with addition of acetic anhydride as accelerator. For the controlled biradical polymerization of n‐butyl acrylate with Bis‐TIPNO, the effect of added free nitroxide relative to the initiator concentration was studied. The poly(styrene‐block‐n‐butyl acrylate‐block‐styrene) copolymers with higher block length prepared by this method show two glass transition temperatures, which indicates microphase separation of the polymer blocks.

Structure of poly(styrene‐block‐n‐butyl acrylate‐block‐styrene), synthesized by nitroxide‐mediated radical polymerization with Bis‐TIPNO as initiator.     

Radical Polymerization and Copolymerization of 12‐[(N‐Methacryloyl)carbamoyloxy]octadecanoic Acid

Radical polymerization of 12‐[(N‐methacryloyl)carbamoyloxy] octadecanoic acid ( 1 ) was kinetically and ESR spectroscopically investigated in acetone, using dimethyl 2,2′‐azobisisobutyrate ( 2 ) as initiator. The polymerization rate (R_p) is given by R_p = k [2]^0.7[1]^1.4 at 50°C. Propagating poly( 1 ) radical was observed as a 13‐lines spectrum by ESR under the actual polymerization conditions. The ESR‐determined k_p values (1.8–7.9 L/mol·s) are much lower than those of usual methacrylate monomers. The rate constant (k_t) of termination was determined to be k_t = 1.0–2.7·10⁴ L/mol·s from decay curve of the propagating radical. The Arrhenius plots of k_p and k_t gave the activation energies of propagation (63 kJ/mol) and termination (24 kJ/mol). A significant solvent effect was observed on the radical polymerization of 1 . The copolymerizations of 1 with styrene(St) and acrylonitrile were examined at 50°C. Copolymerization parameters obtained for the 1  (M₁)/St (M₂) system are as follows; r₁ = 0.73, r₂ = 0.57, Q₁ = 0.83, and e₁ = 0.13.     

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.     

Spectroscopic measurements on spontaneously polymerizing styrene, 2. The estimation of the reactivity of the two Diels-Alder-isomers towards polymer radicals

Spectroscopic measurements at 335 nm on polymerizing styrene have been carried out with spontaneously polymerizing as well as dibenzoyl peroxide (BPO)-initiated bulk systems. The evidence for the formation of two Diels-Alder-intermediates, 1a and 1b , out of which only 1a seems to be capable to produce initiating radicals by reaction with the monomer, can also be derived from the development of the absorption, characteristic for the intermediates, during the BPO-initiated polymerization. From the dependence of the overall rate constants of consumption of 1a , k_2,a[M] , and 1b , k_2,b[M] , on the rate of polymerization the reactivity of 1a and 1b towards polymer radicals can be estimated. Whereas 1b , the less reactive intermediate, seems to be mainly consumed by polymer radicals through copolymerization, chain transfer being unimportant, (the rate constant of consumption of 1b by polymer radicals, k_3,b, relative to the constant of chain propagation k_p ranges from 2,1 at 60°C to 3,2 at 80°C) the corresponding ratio for 1a , k_3,a/k_p, which goes from 113 at 80°C to 143 at 60°C, is supposed to represent primarily the constant of chain transfer of 1a in styrene polymerization. Under the condition of spontaneous polymerization the reaction with polymer radicals contributes 16% (for 1a ) and 5–8,5%, depending on temperature (for 1b ), to the overall rate of consumption of the intermediates. The stationary concentration of 1a , the isomer which accordingly is solely responsible for initiation as well as chain transfer in spontaneous styrene polymerization, is calculated to range from 5,2·10^?6 mol l^?1 at 60°C to 8,5·10^?6 mol l^?1 at 80°C.     

Thermally induced radical promoted cationic polymerization using a novel N-allyloxypyridinium salt

A system consisting of a novel N-allyloxypyridinium salt and a radical initiator is highly appropriate for the thermal initiation of cationic polymerizations. Radicals formed upon the thermolysis (at 70°C) of initiators as 2,2′-azoisobutyronitrile or benzoyl peroxide add to the double bond of the pyridinium salt N-[2-(ethoxcarbonyl)allyloxy]-α-picolinium hexafluoroantimonate (1) . Subsequently, the pyridinium salt is fragmented yielding pyridinium-type radical cations, species able to initiate cationic polymerizations. In the case of the radical initiator phenylazotriphenylmethane (triphenylmethaneazobenzene), the polymerization is extremely rapid, since additionally the triphenylmethyl cation formed by electron transfer initiates the polymerization. The initiation capability of the system described was demonstrated for a number of monomers, such as cyclohexene oxide, butyl vinyl ether and the bifunctional 3,4-epoxycyclohexylmethyl 3′,4′-cyclohexanecarboxylate. With the latter, an insoluble polymer network was readily obtained.