The laser flash-initiated polymerization as a tool of evaluating (individual) kinetic constants of free radical polymerization, 1. Outline of method and first results

A method is presented which allows the determination of k_p/k_t-values in free radical polymerization. It is based on measurements of the (average) rate of polymerization under pseudostationary conditions, the polymerization being initiated by laser flashes of short duration. For ρk_t t₀ ? 1 (ρ being the additional polymer radical concentration produced by each laser flash, k_t the bimolecular termination constant between polymer radicals, k_p the rate constant of chain propagation, t₀ the time separating two successive laser flashes) k_p/k_t may be obtained as the slope of a linear plot of the fractional conversion per flash vs. ln t₀. Dividing the intercept by the slope yields ln (pk_t). Thus, if p is accessible, separation of k_p/k_t-data into its individual constituents may be accomplished without making any use of stationary polymerization data. Application of this method to the polymerization of styrene sensitized by benzoin or AIBN at 25°C gives k_p/k_t-values of 1,0 · 10^?6 which are in fair agreement with those obtained by other methods.     

A kinetic study of butyl acrylate free radical polymerization in benzene solution

The free radical polymerization of butyl acrylate has been studied in benzene solutions ranging from 1 to 5 mol·L^–1 at 50°C using 2,2′‐azobisisobutyronitrile as initiator. Under the conditions of our experiments, both the effective rate coefficient for initiation, 2 f k_d , and the coupled parameter, k_p/k_t^1/2, (where k_p and k_t are the constants for propagation and termination reactions, respectively) are dependent on the monomer concentration. The 2 f k_d value shows little increase with monomer concentration. The variation of the k_p/k_t^1/2 parameter has been correlated with the chain length dependence of the termination rate coefficient. This effect is also responsible for the high dependence of the overall polymerization rate, R_p, onthe monomer concentration (1.49).     

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.     

Termination kinetics of styrene free‐radical polymerization studied by time‐resolved pulsed laser experiments

The single pulse (SP)‐pulsed‐laser polymerization (PLP) technique has been applied to measure k_t/k_p, the ratio of termination to propagation rate coefficients, for the free‐radical bulk polymerization of styrene at temperatures from 60 to 100°C and pressures from 1800 to 2 650 bar. k_t/k_p is obtained by fitting monomer concentration vs. time traces that are determined via time‐resolved (μs) near infrared monitoring of monomer conversion induced by single excimer laser pulses of about 20 ns width. Styrene is a difficult candidate for this kind of measurements as conversion per pulse is small for this low k_p and high k_t monomer. Thus between 160 to 300 SP signals were co‐added to yield a concentration vs. time trace of sufficient quality for deducing k_t/k_p with an accuracy of better than ± 20 per cent. With k_p being known from PLP–SEC experiments, chain‐length averaged k_t values are immediately obtained from k_t/k_p. At given pressure and temperature, k_t is independent of the degree of overall monomer conversion, which, within the present study, has been as high as 20%percnt;. The k_t value, however, is found to slightly increase with the amount of free radicals produced by a single pulse in laser‐induced decomposition of the photoinitiator DMPA (2,2‐dimethoxy‐2‐phenyl acetophenone). This remarkable observation is explained by DMPA decomposition resulting in the formation of two free radicals which significantly differ in reactivity. Extrapolation of SP–PLP k_t data from experiments at rather different DMPA levels and laser pulse energies toward low primary free‐radical concentration, yields very satisfactory agreement of the extrapolated k_t values with recent literature data from chemically and photochemically induced styrene polymerizations.     

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.     

Kinetics of free radical solution polymerization of methyl methacrylate over an extended conversion range

The low and intermediate conversion solution polymerization kinetics of methyl methacrylate in toluene and in 2-butanone are investigated. For this purpose, repetitively applied laser pulses are employed to stimulate initiation, and quantitative near infrared spectroscopy is used to determine methyl methacrylate concentrations. The monomer concentration change per pulse is measured; it is shown how this information may be converted into coupled values of the rate coefficient for propagation k_p, the rate coefficient for termination k_t, and the total efficiency of (photo)initiation. In the present case k_p is already known from independent investigations, which enables our pseudostationary state methods to yield k_t directly. The major thrust of this paper, therefore, concerns the effect of solvent on k_t: it is found that at both low and intermediate conversions, k_t increases as the solvent concentration increases; possible causes of this are discussed. The effect of initial solvent fraction on the variation of k_t with conversion is also reported. Although all our experimental measurements are carried out at an elevated pressure (1000 bar) and a single temperature (30°C), there is no reason for suspecting that our findings regarding solution polymerization termination should not be representative for polymerizations of methyl methacrylate (and other methacrylate monomers) in general.     

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.     

Kinetic and ESR studies on radical polymerization. ESR and kinetic evidences for the penultimate effect in the radical-initiated copolymerization of N-cyclohexylmaleimide and bis(2-ethylhexyl) itaconate in benzene

The copolymerization of N-cyclohexylmaleimide ( 1 ) (M₁) and bis(2-ethylhexyl) itaconate ( 2 ) (M₂) with dimethyl 2,2′-azoisobutyrate ( 3 ) as an initiator was carried out at 50°C in benzene. Monomer reactivity ratios were estimated as r₁ = 0,34 and r₂ = 0,38. The copolymerization rate (R_p) and the molecular weight of the resulting copolymer increased with increasing concentration of 1 when the total concentration of comonomers was fixed at 1,00 mol. L^?1. R_p was proportional to [ 3 ]^0,5, indicating a usual bimolecular termination in the copolymerization. An electron spin resonance (ESR) spectrum of the propagating polymer radicals was observable in the actual copolymerization system at 50°C. The spectrum of the copolymerization system is inexplicable in terms of any superposition of spectra observed in the corresponding homopolymerization systems, revealing that some penultimate monomeric unit causes a change in the ESR spectrum, that is, the structure of propagating polymer radical. The apparent rate constant of propagation (k_p) and termination (k_t) were estimated by ESR. The k_p values (1,5–50 L · mol^?1 · s^?1) are fairly higher than those estimated on the basis of the terminal model, affording another piece of evidence for the penultimate effect. The k_t value (1,8–5,4·10³ L · mol^?1 · s^?1) shows a behaviour similar to that of the intrinsic viscosity of the resulting copolymer on varying the monomer feed composition, which seems to reflect diffusion-control of termination reactions.     

Modelling and kinetic study on radical polymerization of methyl methacrylate in bulk, 1. Propagation and termination rate coefficients and initiation efficiency

In this work the exact data of the rate coefficients of propagation k_p and termination k_t, and initiator efficiency f as well as their variations with conversion during the whole processes of the polymerization of methyl methacrylate in bulk have been measured using electron paramagnetic resonance (ESR) without any assumptions and approximations. k_p was calculated directly from the synchronously measured data of the concentration of radicals and polymerization rate. k_t was determined under nonsteady-state conditions by using the after-effect technique in the ESR measurement. f for the initiation with dimethyl 2,2′-azoisobutyrate was evaluated from the initiation and termination rates. The ESR spectra show that the polymerization system is in a micro-heterogeneous state and there exist inactive radicals. A model of a diffusion-controlled reaction is proposed.     

Kinetics of the early stages of high‐energy radiation initiated polymerization

We describe our method based on pulse radiolysis with optical detection developed for the examination of the kinetics and mechanism of the first steps of high‐energy radiation initiated polymerization. The absorption spectra of the intermediates were obtained in cyclohexane solution of hexanediol diacrylate (HDDA) of different concentrations. In dilute solution (10 mmol·dm^–3) and short time (10 μs) after the pulse, the spectrum of the monomer radicals was observed. On increasing the monomer concentration, the maximum of the spectrum was shifted to longer wavelength indicating the start of the oligomerization reaction. The increase in the time of observation resulted in a similar shift in dilute solution. From the kinetic curves the rate coefficients of termination for the monomer radicals (2·k_t,m) and average rate coefficients of termination for the oligomer radicals of different chain length (2·k_t) were determined. The average rate coefficient of termination was found to decrease in time (that is with increasing chain‐length).     

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.     

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.     

Propagation and Termination Kinetics of Poly(Ethylene Glycol) Methyl Ether Methacrylate in Aqueous Solution

The propagation rate coefficient, k_p, of poly(ethylene glycol) methyl ether methacrylate (M_n ≈500 g mol^?1) has been measured via pulsed‐laser polymerization (PLP)–size‐exclusion‐chromatography in aqueous solution between 5 wt% monomer and bulk polymerization at temperatures from 22 to 77 °C. k_p increases significantly toward higher water content, as is observed for other water‐soluble monomers. This entropy‐motivated effect enhances the pre‐exponential. The activation energy, E_A(k_p), is more or less identical to the characteristic value of methacrylates. The chain‐length‐dependent rate coefficient, k_t^i,i, for termination of two radicals of chain length i has been investigated at low degrees of monomer conversion via the single‐pulse–PLP–electron paramagnetic resonance technique. k_t^i,i turned out to be adequately represented by the composite model designed by the Russell group. The power‐law exponents for the chain‐length dependence of small and long radicals are close to the numbers reported for other monomers. The rate coefficient for termination of two radicals of chain length unity scales with the fluidity of the reaction mixture. Viscosity measurements prior to polymerization thus enable estimates of termination rate.

     

Effect of alkyl groups on the rate constants of propagation and termination in the radical polymerization of dialkyl itaconates

Polymerization of dialkyl itaconates with dimethyl azoisobutyrate ( 5 ) was studied in benzene at 50°C by means of electron spin resonance (ESR). The monomers used are dimethyl ( 1 ), diethyl ( 2 ), dibutyl ( 3 ) and di-2-ethylhexyl ( 4 ) itaconates. All the polymerization systems involve ESR-observable propagating polymer radicals under the actual polymerization conditions. The polymerization rate (R_p) and degree of polymerization of the resulting polymer increase in going from shorter to longer alkyl groups. The ESR-determined rate constants of propagation (k_p) and termination (k_t) decrease as the alkyl chain becomes longer. k_p of 1 is 3,3 times higher than that of 4 , while k_t of 1 is 590 times higher than that of 4 . Thus, the steric effect due to the alkyl group suppresses much more termination than propagation, leading to the fact that R_p increases as the alkyl group becomes larger.     

Dependence of termination kinetics in methyl acrylate–dodecyl acrylate free‐radical copolymerization on comonomer composition,pressure, temperature and conversion

The termination kinetics of the free‐radical bulk copolymerization of dodecyl acrylate (DA) and methyl acrylate (MA) has been investigated at various monomer mole fractions between 15 and 50 °C and up to 2000 bar. The ratio of termination to propagation rate coefficients, (k_t/k_p)_copo, is measured via the single pulse‐pulsed laser polymerization (SP‐PLP) technique. Chain‐length averaged k_t,copo are deduced from (k_t/k_p)_copo in conjunction with k_p,copo data that are estimated via a simplified version of the implicit penultimate unit effect (IPUE) model. At low and moderate degrees of monomer conversion extended ranges of almost constant k_t are observed where termination is controlled by segmental diffusion with important contributions of steric effects. These plateau k_t values are significantly – by almost two orders of magnitude – different for MA and DA. The increase with MA content of k_t,copo is adequately described by a penultimate unit model which uses the geometric mean approximation for estimating rate coefficients of cross‐termination between radicals of different free‐radical terminus. The model applies within the entire pressure and temperature range of the present study. At high degrees of monomer conversion, at and above 50%, homo‐k_t and k_t,copo are almost insensitive toward the composition of the monomer mixture. The termination rate under these conditions is essentially controlled by reaction diffusion.

Relative monomer conversion, c_M(t)/c_M,0, vs. time, t, plot of a methyl acrylate (MA) – dodecyl acrylate (DA) copolymerization (f_MA,0 = 0.5) induced by a single laser pulse at 30 °C and 10 bar. The difference between measured and fitted (to Equation (4)) data is illustrated by the plot of residuals (res) in the lower part of the figure.     

Evaluation of the kinetic parameters for styrene polymerization and their chain length dependence by kinetic simulation and pulsed laser photolysis

Pulsed laser photolysis (PLP) has been employed to determine propagation rate constants k_p for styrene polymerization in benzene over a wider temperature range (20?80°C) than previously converd. It is proposed that a small chain length dependence of k_p (overall) may, in part, be a consequence of a marked chain length dependence of k_p for the first few propagation steps [i.e. k_p(1) > k_p(2) < k_p(3) ≥ k_p(≥4)]. The propagation rate constant for styrene polymerization is given by the expression: In k_p = 16,0₉ ? 289₅₀/(RT) (overall) or In k_p = 16,4₇ ? 300₈₄/(RT) (chain length ≥ 4). Kinetic simulation has been applied both as an aid in data analysis and to demonstrate the reliability of the PLP technique for evaluation of propagation rate constants (k_p) in radical polymerization. This has been achieved by examining the sensitivity of the molecular weight distribution of polymers formed in PLP experiments to the values of the kinetic parameters associated with polymerization and their chain length dependence. The termination rate constants (k_t = k_c + k_d) and the ratio of combination to disproportionation (k_c: k_d) markedly affect the molecular weight distribution of polymer formed in PLP experiments. The prospects for evaluating the values of k_t, its chain length dependence and k_c : k_d by direct analysis of the molecular weight distribution are discussed in the light of these results.     

Termination processes in free radical polymerization, 5,,. The numerical solution of a kinetic scheme with chain length dependent termination

In order to assess the general consequences of an eventual chain length dependence of the bimolecular termination rate constant k_t in free radical polymerization, an iterative procedure for solving the kinetic scheme was developed for this case. The iteration process is based on the equation for the propagation probability of a radical chain of length x, α_x, which constitutes a cyclic definition of the α-values, with F(x,y) giving the functional dependence of k_t = k F(x, y) on the lengths x and y of the two radicals involved in the termination process. As, in addition, α_x links the stationary concentrations of radicals of adjacent length, [R_x?1] and [R_x], solving for the set of α_x allows to build up the complete chain length distribution of polymer radicals from which all relevant kinetic quantities may be calculated. The following types of functional dependence have been used in practice The case of F₂, which is the slightly less realistic one, allows to separate the variables x and y in the equation for α_x, thus leading to an immediate comfortable solution. Irrespective of the type of F(x, y) chosen (the differences being quantitative in nature rather than qualitative) it can be shown that nearly all the familiar relationships known from “classical” polymerization kinetics with chain length independent termination (b = 0) break down. The new relationships, however, can be cast into comparatively simple power laws. The general consequences of the concept of chain length dependent termination are discussed in some detail.     

The polymerisation kinetics of lower dialkyl itaconates

The free radical polymerisation kinetics of diethyl- (DEI), dipropyl- (DnPI), dibutyl- (DnBI), and dihexyl itaconate (DHI) in the bulk were studied in the temperature range from 50 to 70°C. The concentration of the initiator, 2,2′-azoisobutyronitrile (AIBN), was varied between 0.02 and 0.085 mol/dm³. The rate of polymerisation (R_p), degree of polymerisation (DP), overall polymerization rate constant (K), the ratio of the propagation and termination rate constants (k_p/k_t^1/2), as well as the chain transfer constant to monomer (C_M) were determined. The values of R_p, K, and k_p/k_t^1/2 of the investigated monomers all increase with increasing size of the alkyl group in the ester substituent, whereas C_M decreases when going from the dimethyl to the dihexyl ester. The values of C_M are larger than the corresponding values for the alkyl esters of methacrylic acid.     

On the kinetics of polymerization and copolymerization of poly(oxyethylene) macromonomers and styrene

The homogeneous and the dispersion polymerzation and copolymerization of methacryloyl-terminated poly(oxyethylene) (MMA-PEG) and of p-vinylbenzyl-terminated poly(oxyethylene) (St-PEG) macromonomers and styrene, initiated by a radical initiator, was investigated using conventional gravimetric and NMR methods at 60°C. The batch polymerizations in N,N-di-methylformamide and in ethanol/water were conducted to either low or high conversion. The fractional conversion rates of the solution polymerization and copolymerization indicate that the homopolymerizations of macromonomers involve steady-state conditions, whereas copolymerizations proceed under non-stationary conditions. The ratios of the rate constants for propagation and termination (k_p/k) for polymerization and copolymerization of MMA-PEG and St-PEG are by one order of magnitude higher than that for styrene. The increase in k_p/k is more pronounced in dispersion polymerization, which is ascribed to the decrease of both k_p and k_t. The rates of dispersion polymerization are proportional to the particle concentration. The number of particles increses up to 50% conversion. The particle growth is suggested to proceed via association of partcles and by propagation within polymer particles. The decrese of the number of radicals per particles as conversion proceeds is ascribed to the decrese of the growing radical activity and to the transfer of monomeric radicals to the continuous phase. The molecular weights correlate inversely with the particle size.     

ESR determination of rate constants for the radical polymerization of methyl phenethyl itaconate

Phenethyl 2-(methoxycarbonylmethyl)acrylate (methyl penethyl itaconate) ( 1 ) was prepared and its polymerization with dimethyl 2,2′-azoisobutyrate ( 2 ) was investigated kinetically in benzene. The polymerization rate (R_p) was found to be expressed by R_p = k·[ 2 ]^0,5·[ 1 ]^1,8 (at 50°C). Further, a higher dependence of R_p (2nd order) on the concentration of 1 was observed at 61°C. The overall activation energy of the polymerization was calculated to be a low value of 50,3 kJ/mol. The initiator efficiency (f) of 2 was determined to be 0,48 to 0,22 at 50°Cand 0,50 to 0,28 at 61°C. f decreases with increasing monomer concentration due to the high viscosity of 1 . The poly( 1 ) radical is stable enough to be observable by ESR at high temperatures (50–60°C). Rate constants of propagation (k_p) and termination (k_t) were estimated using the poly( 1 ) radical concentration determined by ESR. k_p [6,0 to 121/(mol·s) at 50°Cand 7,1 to 15 1/(mol·s) at 61°C] shows a trend to increase with the concentration of 1 . On the other hand, k_t [2,9·10⁴ to 17·10⁴1/(mol·s) at 50°Cand 6,9·10⁴ to 45·10⁴1/(mol. s) at 61°C] decreases with increasing MPI concentration. This behavior is responsible for the high order with respect to monomer concentration. Copolymerization of 1 (M₁) with styrene (M₂) at 50°Cgave the following results: r₁ = 0,36, r₂ = 0,40, Q₁ = 0,82 and e₁ = + 0,59. Using the above results, the rate constants of the cross-propagations were estimated to be k₁₂ = 22 1/(mol·s) and k₂₁ = 308 1/(mol·s) at 50°C.