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The kinetics and mechanism of the atom transfer polymerization of styrene initiated with 1-phenylethyl chloride/CuCl/2,2‘-bipyridine have been investigated in homogeneous media in the presence of dimethylformamide at 130 °C. The results are in agreement with a fisrt-order dependence with respect to CuCl, but an apparent zero-order dependence with respect to the initiator has been observed, contrary to other reports in the literature. This order does not result from side reactions and has been accounted for by assuming a constant value of the [PECl]/[CuCl2] ratio in the range of concentrations investigated. The results do not allow to distinguish between the conventional first-order treatment and that taking into account the persistent radical effect.

The controlled polymerization of indene initiated with cumyl chloride and tin tetrachloride in methylene dichloride solution shows first-order kinetics with respect to SnCl4, which implies the existence of simple equilibria for ionization and dissociation, contrary to the case of TiCl4. Experiments in the presence of a hindered base (2,6-di-tert-butyl-4-methylpyridine) allowed to estimate the propagation rate constant for paired and unpaired ions in the range of 5 × 104−105 L mol-1 s-1 at −40 °C. A fast initial polymerization, which takes place in the absence of base, and is suppressed by the base, is attributed to the larger dissociation constant for the Cum+,SnCl5- ion pairs than for the polyindenyl ones, yielding a transitory excess of free ions. The hindered base suppresses the formation of free ions, may act as a proton trap in the case of zero order transfer, and may also be involved in bimolecular termination.

The cationic polymerization of indene initiated with cumyl chloride and stannic chloride in solution in methylene chloride at −15 °C is controlled up to Mn = 20 000, with a low transfer to monomer ...

Di- and triblock copolymers of styrene and butyl acrylate with controlled molar masses (Mn up to ≈ 105) were sequentially prepared by radical atom transfer polymerization in a homogeneous medium using chlorine end capped polymers as initiators and the copper(I) chloride/bipyridine complex as catalyst, in the presence of dimethylformamide. Random poly(styrene-co-butyl acrylate) was synthesized and the cross-over reactions between Cl end capped polystyrene and poly(butyl acrylate) to the opposite monomers were examined.

Homogeneous atom transfer radical polymerization of styrene initiated with 1-chloro-1-phenylethane/CuCl/2,2‘-bipyridine at 130 °C is easily achieved in the presence of a limited amount of dimethylf...

The polymerization of n-butyl acrylate (BuAc) initiated with a model compound (butyl-2-(N,N-diethyldithiocarbamyl)propionate, RTC) has been investigated. The living character of this polymerization has been assessed and compared with those of styrene and methyl methacrylate. The small variation of M n with yield is explained by the faster propagation than for styrene and methyl methacrylate, which leads to slow initiation and extensive transfer to the initiator. Predominant reversible termination (or deactivation) of the growing chains by the dithiocarbamyl radicals gives, however, polymers of functionality near to unity, which are photoinitiated at the same rate as RTC and reinitiate the polymerization of BuAc with a linear growth of the M n up to 40% yield. This is better than was obtained with methyl methacrylate. Side reactions also take place leading to a decrease of functionality, to the formation of tetraethylthiuram disulphide and of carbon disulphide. Possible mechanisms are proposed for the secondary reactions.

The photolysis of n-butyl-(N,N-diethyl dithiocarbamyl)propionate (RTC), an initiator for 'living' free radical polymerizations, has been investigated in order to elucidate the mechanism of these polymerizations. The photolysis yields tetraethylthiuram disulphide (TED), and its degradation products, butyl acrylate, butyl propionate and head-to-head dimer of butyl acrylate. These compounds result from reactions following the homolytic bond breaking of the carbon sulphur bond of RTC, and correspond to termination reactions in the case of a polymerization. However, a functionalized head-to-tail dimer of butyl acrylate is also formed. Photolysis of RTC in the presence of a small amount of butyl acrylate, which mimics a polymerization process, leads mainly to the formation of functionalized oligomers of butyl acrylate. The change of the concentrations of these compounds with reaction time is an argument in favour of a possible reactivation of the functionalized oligomers.

For isobutyl vinyl ether (IBVE) polymerizations made in the presence of large concentrations of an electron donor such as ethyl acetate (EA), e.g. 0.5 M, evidence for transfer reactions of zero order in monomer concentration has been given earlier. In the present paper, the changes in the transfer processes according to the ester concentration are examined. Polymerizations were made under vacuum at 0°C in toluene. Solvent and monomer were dried over sodium films. Two initiating systems were used. Initiation with trityl tetrachloroaluminate (2.5 x 10 -5 -2 x 10 -4 M) gave very fast reactions, which were stopped at various yields and showed that transfer of first order in [M] is the main transfer reaction (with k trM /k P = 8 x 10 -4 at 0°C). The addition of a small amount of EA (5 x 10 -2 M) lowers the reaction rate considerably but leads only to a small reduction of k trM /k p (to 5.6 x 10 -4 ). Initiation with isobutyl-1-chloroethylether (IBCE) and an excess of aluminium trichloride ([AlCl 3 ]/[IBCE] ∼10) was made in the presence of increasing amounts of EA. This lowers the propagation rate (first order in [M]). For [M] 0 /[I] 0 ratios lower than 300, the linearity of M n with yield is observed ('living' polymerization) but a strong deviation occurs for higher [M] 0 /[I] 0 . The linear increase with reaction time of the concentration [N] of macromolecules resulting from transfer is in agreement with a preponderant transfer of zero order in [M]. Transfer to monomer is considerably reduced. The relative importance of transfer of zero order in [M] increases with [EA], and it involves mainly ethyl acetate. The reduction of direct transfer to monomer in the presence of high concentrations of ethyl acetate is explained by a propagation mechanism involving monomer solvated cationic active species, in equilibrium with inactive species solvated only by ethyl acetate.

The polymerization of n-butyl acrylate has been initiated, in toluene solution at 30°C, by photolysis of n-butyl-2-(N,N-diethyl dithiocarbamyl) propionate, which is a model of terminal groups end-capped by dithiocarbamate. The ratio of initiation to propagation rates is low, but the polymers have approximately the theoretical DPn . Initiation with a functionalized polybutyl acrylate shows that reactivation of the end-groups takes place at the same rate as with an equivalent concentration of initiator. The reaction scheme assumes reversible termination by reactivation of the dithiocarbamyl end-groups and non reversible terminations such as combination of the growing chains and degradative chain transfer (with formation of tetraethylthiuram disulfide). It has been shown that the functionalizing reversible termination is predominant.

The kinetics of the polymerization of indene in dichloromethane solution, initiated with cumyl methyl ether and cumyl chloride, in the presence of titanium derivatives (TiCl 4 and TiCl 3 OBu), at variable temperatures (0 to -62 °C), have been investigated by adiabatic calorimetry under vacuum. At -40 °C, with cumyl methyl ether as an initiator, an internal first-order plot with respect to the monomer is observed after 60% yield, and initiation is completed before the end of the polymerization. The polymerization is apparently living or living, which means only that the molecular weight increases linearly with polymer yield. With the CumCl/TiCl 4 initiating system, complete initiation is obtained only in the presence of dimethyl sulfoxide (DMSO). Addition of DMSO increases the initiation rate, decreases the apparent propagation rate constant, and allows the observation of a first-order plot and an apparently living process. The use of a common ion salt (tetra-n-butylammonium pentachlorotitanate) has a similar effect. With the CumCl/TiCl 3 OBu initiating system, an apparently living polymer is obtained without additive. These data, and the negative apparent activation energies observed, imply that several types of chain ends are present in variable concentrations in the solution (covalent inactive species, ions pairs, and free ions), involving a reversible termination. These results, as well as the occurrence of transfer reactions, may be explained, as in conventional carbocationic polymerization, by a propagation involving ionic active centers.

The available data concerning the polymerization of three classes of monomers deemed to yield living polymers, vinyl ethers, styrenic monomers and isobutylene, are discussed from the point of view of transfer and termination reaction. In the case of vinylethers, linearity of [Mbar]n with a yield up to 30,000 has been obtained, but when higher [Mbar]n are planned, there is evidence for the occurrence of transfer reactions. In the case of isobutylene, indene, and p-Me-styrene, the linearity (up to [Mbar]n ∼ 105) of [Mbar]n with the amount of monomer polymerized which has been observed (but only at low temperature) is compatible with values of transfer constants to monomer measured in “conventional” systems. In these living systems, irreversible terminations are often not very important but may become significant toward the end of monomer consumption. The main termination process is reversible termination which may lead to narrow molecular weight distributions. The linearity of [Mbar]n with yield is...

The polymerization of indene in CH 2 Cl 2 solution initiated with cumyl chloride and TiCl 4 has been investigated as a possibly «living» system. At ∼40°C, initiation is quantitative only in the presence of DMSO) ab an electron-donating compound. Linear growth of the M n with the amount of monomer converted can be observed for monomer to initiator ratios lower than 200, although transfer does take place (k trM /k p,-40°C = 6×10 -4 ). At +5°C, linear growth is observed only up to M n ≃ 15000, initiation is quantitative without DMSO, and this compound does not reduce transfer (k trM /k p,+5°C = 1.4×10 -3 in both cases)

Polymerization of indene using cumyl methyl ether as initiator and TiCl 4 as coinitiator in CH 2 Cl 2 solution was apparently living polymerization. At -40 and -75°C, there is a linear relationship between the M n and the amount of monomer polymerized, with a number of macromolecules near to that of the initiator. However, it was shown that at -40°C significant transdfer reactions occur, the same tranfer constant being found for polymerizations which were and were not apparently living. At -75°C, transfer could no longer be detected. With Ti(OBu)Cl 3 as coinitiator, the transfer constant was near zero at -40°C

The cationic polymerization of isobutyl vinyl ether initiated with the title system apparently has some features of a living polymerization (linear increase of number average molecular weight Mn with conversion). However, evidence is given for the occurrence of a transfer reaction resulting in the increase of the number of macromolecules, and this even for relatively low molecular weights.

The kinetics of the photo-initiated polymerization of n.butyl acrylate by p -xylylene bis-( N , N -diethyldithiocarbamate) have been investigated in order to check the living character of this polymerization initiated with an “iniferter”. The reaction shows some features of a living system viz. growth of the molecular weight during the reaction under chosen conditions (high [M]/[I] ratios) and preparation of block copolymers. This confirms the existence of a reversible termination reaction between the growing chains and the dithiocarbamyl radicals. However, evidence has been found for the intervention of side reactions (formation of tetraethylthiuram disulphide, and decrease of the functionality of the polymers during the polymerization), indicating that the polymerization is not strictly living.

Elimination diet (ED) in children with food allergy (FA) could be responsible of inadequate caloric and essential fatty acids (EFA) intake. We investigated the plasmatic profile of EFA in children with FA on ED. Methods. Prospective multicenter study including children with FA (6-36 m) on ED for at least 30 days compared to healthy children. EFA were measured by capillary gas-chromatography at the enrolment (T0) and after 6 m (T1) of elimination diet established after specific dietary counseling. Results. We enrolled 86 children with FA, and 66 healthy controls. The length of ED diet was 10.8 m (95%CI 8-14 m). Table reports EFA profiles in study groups (*p

lind procedure. The most common food allergen was cow’s ilk proteins (82.2%). Data of each patient were collected rom 4 days before FC and during the 7 days following the rocedure. The results of the forms were interpreted by 3 hysicians unaware to the patient’s history. The protocol has specificity and sensitivity of 100% and 83.3%, respectively. he positive and negative predictive values were 100% and 7.3%, respectively. Conclusions. Our data showed that the new protocol to erform FC including an accurate registration of gastroinestinal symptoms and a objective evaluation of intestinal nflammation and permeability has a high specificity and senitivity. This protocol could be helpful for the diagnosis and he follow up of children with FA.

The mechanisms of transfer reactions in the polymerisation of α-methylstyrene initiated with AlEt2Cl from — 70°C to — 30°C have been investigated using cationic grafting on a poly(isobutylene-co-chloromethylstyrene). Besides the bimolecular transfer to the monomer, evidence has been found for the occurrence of a kinetically unimolecular transfer reaction, which may be attributed to transfer to the counter ion but might also result from transfer to the solvent. Transfer is not important at — 70°C and — 50°C. From the variation with conversion of the molar concentration of homopolymer chains (formed by transfer), transfer constants could be estimated (for transfer to monomer ktrM/kp = 10-5 at −70°C and 10-4 at −50°C; for unimolecular transfer ktrkp = 5 × 10-5 mol litre−1 at −70°C and 4 × 10-4mol litre−1 at −50°C). At both temperatures, initiation is not instantaneous but takes place throughout the polymerisation. At — 30°C, initiation seems to be rapid and quantitative, all the chloromethyl groups are modified and transfer becomes preponderant.

Resume L'amorcage de la polymerisation anionique de la vinyl-4 pyridine dans le THF par des composes organo metalliques (Na et K) fait intervenir des reactions secondaires analogues a celles deja observees dans le cas de la polymerisation de la vinyl-2 pyridine et les polymeres vivants obtenus ont des spectres d'absorption electronique semblables. Les constantes de dissociation des especes ioniques sont voisines pour la vinyl-2 et la vinyl-4 pyridine lorsque la chaine des polymeres (copolymeres sequenes styrolene, vinyl-4 pyridine) ne renferme qu'un seul motif vinyl pyridine (K n ≈ 10 −9 ). Par contre, lorsque le DP de la sequence polyvinyl-4 pyridine augmente, la conductivite croit et atteint des valeurs comparables a celles du polystyrene vivant (K D ≈ 10 −7 ). Ce phenomene pourrait etre du a une solvatation du contre-ion par les chaines de polyvinyl-4 pyridine jouant le role d'un agent complexant polydentate.

The kinetics of the alternating copolymerization of styrene and methyl methacrylate (MMA), in the presence of ethylaluminium sesquichloride or diethylaluminium chloride, in carbon tetrachloride solution, have been investigated in order to compare the results with those previously obtained in toluene. Cryometric measurement established that in CCl 4 the binary association of the MMA with the complexing agent involves a dimeric molecule of the organochloroaluminium compound. When the concentration of one of the monomers is increased, the polymerization rate goes through a maximum for a nearly equimolar feed of the monomers, and the usual deviations from the equimolar composition at extreme feed ratio have been observed. The kinetic schemes proposed in the literature only partially account for the experimental data and the maximum value for the polymerization rate could be only qualitatively explained.

The influence of monomer concentration on copolymer composition and on its evolution during reaction has been investigated for the alternating copolymerization of styrene with methyl methacrylate (MMA), in the presence of ethylaluminium sesquichloride and diethylaluminium chloride, in toluene solution at 20°. The results are in agreement with the hypothesis of a statistical copolymerization involving the uncomplexed monomers and complexed MMA. Using this scheme, the reactivity ratios have been calculated in the particular case in which the concentration of styrene varies, those of the other reagents being kept constant. The copolymer compositions derived from these ratios are in good agreement with the experimental data.

The possibility of cationic grafting through a termination reaction of the active species with an aromatic backbone (“grafting onto”) has been considered. When the polymerization of styrene is initiated with AlEt2Cl and C6H5CH2Cl at −50°, in a methylene chloride methylcyclohexane mixture in the presence of poly(isobutylene-co-styrene), no graft copolymer is formed during the reaction. Grafting occurs subsequently, probably through a slow reaction with the aromatic rings of the backbone. In the case of backbones containing benzyl chloride groups [poly(isobutene-co-p-chloromethylstyeren)] the graft copolymer formed during the polymerization results mainly from initiation grafting (“grafting from”). Grafting onto, if it eventually occurs at high conversion or high monomer concentration, is only a side reaction.

Resume L'homopolymerisation cationique du chloro-1 butadiene et sa copolymerisation avec l'isobutene ont ete realisees en solution dans le chlorure de methylene. Les couples catalyseur-cocatalyseur etaient AlEt2Cl, tBuCl et AlEtCl2, tBuCl (dans ce dernier cas la presence de tBuCl n'etait pas necessaire pour amorcer la polymerisation). Selon les conditions operatoires les polymeres obtenus sont de M n elevee (200.000) et insolubles dans CH2Cl2 ou de faible M n (20.000)et solubles dans CH2Cl2. L'homopolymere du Cl1Bu est, quant a lui, toujours de faible M n (10.000) et soluble. La structure des unites Cl1Bu resulte d'un enchainement presque exclusivement 3,4 (essentiellement trans). Cette methode ne convient donc pas pour la preparation d'elastomeres renfermant des unites 1,4 de structure analogue a celles presentes dans le caoutchouc butyl chlore.

Methyl methacrylate (MMA) and organochloroaluminium dimers (Al)2 form strong complexes. An investigation by cryometry and 1H-NMR led to the conclusion that the association can be formulated thus: (Al) 2 +2MMA⇄2(Al, MMA) . The value of the equilibrium constant, in bulk at 20°, is 25 l mol−1 for AlEt2Cl and 70 l mol−1 for Al2Et3Cl3. In the case of AlEtCl2, the constant is too high to be measured, the association being practically quantitative. No ternary association of styrene with the Al-MMA complex could be detected using these methods; in any case, the formation constant of such a complex would be lower than 0.1 l mol−1.

Resume Les constantes d'association K4 et k4 des paires d'ions et des ions triples au sein des solutions de polymeres vivants de la vinyl-2 pyridine ont ete determinees en utilisant la methode des moindres carres. Les resultats a 0° dans le tetrahydrofuranne sont KA = 4.6·108 et kA- 5.2·104 dans le cas du contre ion Na+ et KA = 6.6·108 et kA = 1.6·108 dans le cas du contre ion Cs+. Ces valeurs sont compatibles avec les resultats cinetiques recemment publies. Pour determiner KA et kA avec plus de precision, les coefficients de diffusion de translation de la polyvinylpyridine vivante et hydrolysee ont ete determines en mesurant le gradient de concentration le long d'une cellule optique. Pour un DP de 8, la valeur de 0.336 cm2/sec a ete trouvee dans les deux cas, ce qui correspond pour l'anion p 2 VP a une conductivite equivalente limite notablement inferieure a celle d'une chaine de polystyrolene de meme degre de polymerisation.

Resume Des copolymeres greffes ont ete prepares en amorcant la polymerisation de l'indene par du monochlorodiethylaluminium et du chlorure de tertiobutyle en presence de terpolymeres d'ethylene, de propylene et d'un diene. Dans le cas des terpolymeres dont le motif insature est peu encombre, tels ceux derives de l'hexadiene-1,4 et du dicyclopentadiene, l'accroissement du M n est du principalement a des reactions de pontage entre les chaines d'elastomere, et l'efficacite de greffage de l'indene est faible. Les polymere-troncs dont les groupements insatures presentent un fort encombrement sterique, comme ceux derives de l'ethylidene norbornene, conduisent a des copolymeres greffes avec des efficacites de greffage elevees, pouvant atteindre 50%. Dans ce dernier cas, une reaction de greffage par amorcage a partir des sites insatures est proposee pour rendre compte des differences entre ces deux types de reactions.

The kinetics of the photoinitiated copolymerization of styrene and methyl methacrylate in the presence of ethylaluminium sesquichloride, in toluene solution, has been investigated by dilatometry. The data are in agreement with a statistical copolymerization mechanism involving styrene and complexed MMA. The strong alternating tendency is due to an enhancement of the cross-propagation reactions, although homopolymerization may occur in the presence of a large excess of one of the monomers. The ternary complex, if formed, seems not to play a major role in propagation. A reaction scheme is proposed and some of the rate constants have been estimated.

Resume Les copolymeres greffes prepares par greffage cationique de l'indene sur du caoutchouc butyl chlore ont des structures regulieres en peigne. Leurs proprietes mecaniques, qui peuvent etre reliees au nombre de greffons par chaine, sont conservees en partie jusqu'a 100° (a 100° resistance a la rupture; 50 kg/cm 2 , allongement a la rupture: 330%). Les copolymeres prepares par greffage sur des terpolymeres ethylene-propylene-diene ont des structures moins bien definies et des proprietes mecaniques mediocres, meme a temperature ambiante.

Resume La copolymerisation de l'indene et du methacrylate de methyle (MAM), amorcee photochimiquement par un rayonnement u.v., en presence de sesquichlorure d'ethylaluminium (SCEA) comme agent complexant conduit a des copolymeres alternes lorsque [indene] ⩾ [MAM] ⩾ [SCEA]. Les masses moleculaires des copolymeres varient de 32.000 a 900.000, en fonction des concentrations des reactifs, de la temperature de la reaction et de l'intensite de la lumiere incidente. Les resultats de l'etude cinetique peuvent etre interpretes simplement en envisageant une copolymerisation statistique entre l'indene et le methacrylate de methyle complexe par le SCEA. Toutefois l'intervention d'un complexe ternaire SCEA-MAM indene ne peut pas etre totalement ecartee. Pour les fortes concentrations en MAM, le monomere libre intervient dans le schema reactionnel.

Resume L'eventualite d'une competition entre les reactions de greffage par amorcage et par terminaison est examinee et discutee dans le cas du greffage de l'indene et du styrene sur un polymere-tronc isobutyl e ne -p- chloromethylstyr e ne . Pour des reactions effectuees a -55°, en presence de monochlorodiethylaluminium, le greffage par amorcage intervient pratiquement seul dans le cas de l'indene. La separation de l'homopolyindene forme permet alors de preciser le mecanisme des reactions de transfert.

Resume Les reactivites des ions libres intervenant au cours de la polymerisation anionique de monomeres vinyliques ont ete calculees. Les constantes de copolymerisation k AB donnees par la litterature ont ete comparees avec l'energie de stabilisation mise en jeu lors de la reaction d'un certain nombre de carbanions avec un meme monomere. En particulier les reactivites des carbanions des polymeres vivants de la vinyl-2 pyridine, du styrolene et de quelques de substitution de ce dernier vis-a-vis du diphenyl-1,1 ethylene ont ete determinees. Les constantes d'homopolymerisation ont ete comparees avec la variation d'energie π entre l'“etat monomere” et l'“etat carbanion” de ces memes derives vinyliques. La possibilite de l'intervention de reactions secondaires au cours de la polymerisation des vinyl-pyridines a ete aussi examinee par les methodes de chimie quantique.

Resume Une etude du greffage cationique de l'indene sur le caoutchoue butyl chlore (CBC), amorce par le monochlorodiethylaluminium, en solution dans un melange en volumes egaux de chlorure de methylene et de methylcyclohexane, a - 50, a permis d'obtenir des efficacites de greffage voisines de 100% avec une conversion totale de l'indene. La vitesse de polymerisation de l'indene obeit a une loi d'ordre un vis a vis du monomere et a une loi d'ordre 0,5 vis-a-vis de AlEt2Cl comme dans les polymerisations effectuees en presence de chlorure d'alkyle comme cocatalyseur. Il n'apparait pas d'ordre simple vis-a-vis du chlore cocatalytique. L'influence des concentrations des reactifs sur la nature des produits obtenus en particulier celle des rapports (CBC) (indene) (AlEt 2 Cl) et (AlEt 2 Cl) a ete precisee. Comme la reaction de polymerisation a ete realisee dans des conditions ou se produisent des reactions de transfert, les tres fortes efficacites de greffage observees sont dues a un regreffage des chaines de polyindene provenant du transfert.

Resume La conductivite des solutions de polymeres vivants de la vinyl-2 pyridine dans le tetrahydrofuranne est beaucoup plus faible que celles des polymeres vivants de la vinyl-4 pyridine et du styrolene. Ce phenomene est attribue aux possibilites de chelation du contre-ion sodium avec l'atome d'azote du cycle pyridinique, lorsqu'il est situe en 2.

Resume Le spectre d'absorption electronique des carbanions de la polyvinyl-2 pyridine presente un maximum d'absorption a 315 nm et un epaulement situe entre 380 et 500 nm (en fonction de la nature du cation alcalin). Cet epaulement correspond a des maximums secondaires situes entre 460 et 500 nm. Cette absorption est due a la presence dun carbanion trienyle formea la suite d'une reaction secondaire ayant lien lors de la phase d'amorcage de la polymerisation.

Resume La conductivite des polymeres vivants de la vinyl-2 pyridine dans le tetrahydrofuranne (cas des contre-ions Na+, K+ et Cs+) est notablement inferieure a celle des solutions correspondantes de polystyrolene. Les amorceurs utilises ont conduit soit a des macromolecules monofonctionnelles, soit a des macromolecules bifonctionnelles et les valeurs des constantes de dissociation, mesurees entre 23° et −43°, sont sensiblement les mames. A 23° par exemple, les valeurs de KD sont egales a 8,3-10−10 (contre-ion Na+), 2,45- 10−9 (contre-ion K+), 1,05- 10−9 (contre-ion Cs+). Les faibles conductivites observees sont attribuees a la solvatation du cation par les groupements pyridiniques du motif terminal et du motif penultieme de la chaine. L'abaissement de la conductivite, par rapport aux solutions de polymeres vivants du styrolene, est beaucoup moins sensible dans le cas d'un gros cation comme le cesium. La presence d'especes ioniques secondaires (carbanions trienyles ou nitranions) au sein de la solution de polymeres vivants entraine une erreur absolue sur les valeurs de KD mais ne modifie pas les conclusions precedentes.