Polymérisation anionique de l'acroléine, 2. Influence de la nature du contre-ion et de la température sur la cinétique de la réaction

In tetrahydrofuran, with Na⁺ and Li⁺ as counter-ions, the kinetic order of the anionic polymerization of acrolein is unity for monomer and for initiator. These results indicate that the living ends are not associated at the studied concentrations of initiator. The polymerization rate depends on the nature of the counter-ion. Transfer reactions to monomer do not affect the polymerization rate but greatly change the molecular weights M _n of polyacroleins. The experimental M are much lower than the theoretical M . The propagation constants k_pr and the transfer constant h_m are determined using these experimental values of M . From these results, we can conclude that with Li⁺ as counter ion, transfer reactions are much more numerous than with Na⁺. Furthermore, the polymerization rate increases with temperature. The activation energies of the propagation (E_a,pr) and transfer reactions (E_a,t) can be determined separately. When the temperature increases the propagation reaction is promoted in comparison to the transfer reaction to monomer, and simultaneously transfer reactions to polymer take place. This last phenomenon restricts the upper value of the polymerization temperature.     

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.     

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

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

PLP‐SEC Study into the Free‐Radical Propagation Rate Coefficients of Partially and Fully Ionized Acrylic Acid in Aqueous Solution

Summary: Propagation rate coefficients, k_p, for acrylic acid (AA) polymerization at 6 °C in aqueous solution were measured via pulsed laser polymerization (PLP) with the degree of ionization, α, varied over the entire range between 0 and 1. These measurements were carried out in conjunction with aqueous‐phase size‐exclusion chromatography (SEC). Strictly speaking, the reported k_p's are “apparent” propagation rate coefficients deduced from the PLP‐SEC data under the assumption that the local monomer concentration at the radical site is identical to overall monomer concentration. At an AA concentration of 0.69 mol · L^?1, the apparent k_p decreases from 111 000 L · mol^?1 · s^?1 at α = 0 to 13 000 L · mol^?1 · s^?1 at α = 1.0. The significant lowering of k_p with higher α is attributed to the repulsion between both monomer molecules and macroradicals becoming negatively charged. Addition of up to 10 mol‐% (with respect to AA) sodium hydroxide to the fully ionized aqueous AA solution leads to an enhancement of k_p up to 57 000 L · mol^?1 · s^?1.

Dependence of apparent k_p values on the degree of ionization of acrylic acid (a) and on pH (b) for aqueous polymerizations of acrylic acid.     

Kinetic studies of the anionic polymerization of methyl methacrylate in tetrahydrofuran with Na+ as counter ion,using monofunctional initiators

A newly designed automatically controlled stirred reactor suitable for kinetic measurements of reactions with half lives ≥2s has been applied to follow the anionic polymerization of methyl methacrylate in THF with Na⁺ as a counter ion in the presence of an excess of NaB(C₆H₅)₄. As initiators were used: benzylsodium reacted with α-methylstyrene (I), fluorenylsodium (II), and 9-methylfluorenylsodium (III). With I the initiation is fast as compared with the polymerization reaction which is first order in monomer concentration. Within the range of ?50°C to ?100°C an almost unperturbed “living” polymerization is observed. The Arrhenius plot of the rate constants results in a straight line with activation energy E_a = 4,4kcal·mol^?1 (= 18kJ·mol^?1) and frequency exponent A = 7,0.II and III are slow initiators, II giving rise to side reactions because of the “acidic” proton in 9-position after initiation, III exhibiting a rate constant of initiation k_i = 1l·mol^?1·s^?1 at ?72°C. The termination reaction is becoming increasingly important with increasing temperature and seems to be a unimolecular reaction with E_a,t = 11,5kcal·mol^?1 (= 48 kJ·mol^?1) and A_t = 10. Since the basic feature of the reactor is the possibility of drawing samples, polymers from each state of the reaction were available to be investigated also with respect to their tacticity. The monomer addition was shown to follow Bernoullian statistics. A structure of the “living” end being in harmony with the results observed is discussed.     

Phénomènes cinétiques associés à la transition vitreuse du polyisoprène de structure 1,4 prépondérante

The thermal behavior of polyisoprene with a high content of 1,4 structures prepared by anionic polymerization has been investigated in the glass transition interval by means of differential scanning calorimetry (DSC). This polymer is of particular interest since it has a low glass transition temperature T_g and shows a substantial increase in heat capacity in the glass transition interval. When the thermal history of the polymer is fixed by linear cooling, the dependence of T_g (measured at the inflexion point of the experimental curve) on heating rate q, can be expressed by q=constant × exp{?E/(RT_g)} where E varies from 127 to 144 kJ/mol when the cooling rate decreases from 80 to 1.25 K/min. It is shown that this behavior is consistent with a kinetic model for glass transition involving a simple relaxation process characterized by an energy of activation close to E.     

Caesium as counter-ion in the anionic polymerization of ethylene oxide, 3. Dimethyl sulfoxide as solvent

The anionic polymerization of ethylene oxide in dimethyl sulfoxide using the caesium 3,6-dioxa-1-octanolate as initiator was studied at 50°C. Conductivity measurements have shown that the living polymer exists as free ion or contact ion pair. The reaction rates were found to be first order with respect to monomer and 1,9 order with respect to initiator with a mean value for the propagation rate constant of 60 mol ^{?1, 9}l^{1, 9}s^?1. Based on the experimental findings a polymerization mechanism is proposed.     

Cationic copolymerization of norbornadiene with styrene by AlEtCl2/tert-butyl chloride catalyst system, 2. Effect of polymerization conditions on “crosslinking” and “polymer linking” reactions

The cationic copolymerization of norbornadiene (NBD) and styrene (St) was carried out with the AlEtCl₂/tert-butyl chloride catalyst system under various conditions. Detailed analyses were focused on the effect of reaction conditions on the two types of intermolecular reactions, that is, the “crosslinking” reaction to form an insoluble polymer and the “polymer linking” reaction to form a soluble polymer with a molecular weight higher than that of the non-crosslinked polymer. The two types of crosslinking processes can explain the unique dependency of the polymer solubility on the NBD/St feed ratio. The “polymer linking” reaction is initiated after complete consumption of the monomers and is strongly affected by the polymerization conditions. For example, longer polymerization time, lower temperature, an initial monomer concentration [M]₀ around 1,0–1,5 mol/L, a [t-BuCl]₀/[AlEtCl₂]₀ ratio around 0,75–1,0 and increasing [AlEtCl₂]₀ are the factors that facilitate the “polymer linking”.     

A kinetic study of the emulsion copolymerization of N,N′-methylenebis(acrylamide) and an unsaturated polyester

The emulsion copolymerization of N,N′-methylenebis(acrylamide) (MBA) and an unsaturated polyester (UP) initiated by potassium peroxodisulfate was kinetically investigated at 50°C by conventional gravimetric and dilatometric methods. The rate of polymerization, the size of latex particles and the number of polymer particles were determined as a function of MBA concentration. The rate of MBA polymerization was found to be proportional to the 0,8th (at 0–15% conversion) and 0,9th (at 20–40% conversion) order with respect to [MBA] at 0,0231 mol · dm^?3 of UP. The values of the reaction order on the monomer concentration are discussed in terms of homogeneous and emulsion polymerization and crosslinking effects. The rate of UP polymerization in the emulsion copolymerization of MBA and UP does not depend on the total monomer concentration. The specific rate of MBA (or UP) polymerization increases with increasing monomer concentration and reaches a maximum at a certain concentration of monomer. The size of polymer particles decreases and the number of particles increases with increasing UP fraction. The stability of polymer particles increases with increasing UP fraction in the monomer feed. The ratio (k_p/k_t^0,5)₀ of the relative rate constants for propagation k_p and termination k_t calculated for the MBA or UP polymerizations at zero conversion increases with increasing MBA concentration. The growth of the polymer particles proceeds via polymerization in particles and by interparticle crosslinking reactions.     

Kinetic study of the polymerization of N,N′-methylenebis(acrylamide) in aqueous dispersion systems

The aqueous-phase polymerization of N,N′-methylenebis(acrylamide) initiated by potassium peroxodisulfate in the absence and in the presence of the anionic emulsifier sodium dodecylsulfate was kinetically investigated at 50°C by conventional gravimetric and dilatometric methods. The rate of polymerization is found to be proportional to the 0,75 and 0,24 oder with respect to potassium peroxodisulfate and N,N′-methylenebis(acrylamide) concentrations, respectively. On the other hand, it is independent of the concentration of sodium dodecylsulfate. This agrees with the polymerization of a monomer soluble in water. Therefore, the equations for a homogeneous polymerization were applied to evaluate the experimental results. The calculated ratio k_p/k_t^0,5 of the rate constants of propagation k_p and termination k_t for the N,N′-methylenebis(acrylamide) polymerization at zero conversion in the absence of emulsifier are scattered in the interval between 3,1 and 3,4 dm^1,5 · mol^?0,5 · s^?0,5 and in the presence of emulsifier in the interval between 2,4 and 3,5 dm^1,5 · mol^?0,5 · s^?0,5. They are close to those obtained for the homogeneous polymerization of acrylamide in the aqueous phase. The lower values of k_p/k_t^0,5 ≈ 0,3–0,6 dm^1,5 · mol^?0,5 · s^?0,5 determined for the polymerization of N,N′-methylenebis(acrylamide) for conversions between 30 and 60% follow from the hindered termination reaction within the polymer particles. The polymer dispersions formed are unstable. The growth of the polymer particles proceeds predominantly by coalescence. This suggests a kinetics which does not follow the Smith-Ewart theory but is characterized by a continuous particle nucleation and agglomeration. The interval 1 occurs at the beginning of the dispersion polymerization when polymer particles are being formed. Interval 2 follows, once the number of polymer particles has been fixed.     

Anionic polymerization of one-ended “living” strontium-polystyrene in tetrahydropyran in the presence of tetraglyme and in benzene

The anionic polymerization of the strontium salt of one-ended living polystyrene (SrS₂) was investigated at 20°C in tetrahydropyran (THP) in the presence of two different concentrations of added tetraglyme. Similarly to BaS₂ in tetrahydrofuran (THF) and to SrS₂ in THF and in pure THP, the observed pseudo-first-order rate constant of propagation, k_obs, was nearly independent of the total concentration of salt, their values being 7,5.10^?3 s^?1 and 9 · 10^?3 s^?1, respectively, i. e. about 100 to 120 times higher than in pure THP. This indicates that the propagation occurs mainly via an increased but constant amount of free S^? anions resulting from the two already known equilibria SrS₂ ? (SrS)⁺ + S^?(K₁) and 2 SrS₂ ? (SrS)⁺ + (SrS₃)^? (K₂) and the equilibrium of glymation (SrS⁺) + G ? G, (SrS)⁺ (K_i). A small not exactly determinable contribution of glymated ion-pairs and/or triple ions, whose rate constants would then probably be of the order of 18 l · mol^?1 · s^?1 and 80 l · mol^?1 · s^?1, respectively, could not be excluded. The glymation constant K_i was found to be about 3 · 10⁶ 1 · mol^?1, i.e., approximately 17 times greater than for the Na⁺ cation. Finally, a kinetic experiment with SrS₂ at 20°C in pure benzene (contaminated, however, with some remaining THP from the preparation of SrS₂) indicated that propagation by ion-pairs is possible with a bimolecular apparent rate constant K_app = 1,1 · 10^?1 l · mol^?1 · s^?1.     

Aqueous polymerization of acrylamide initiated by acidic permanganate/thiourea redox system

The polymerization of acrylamide, initiated by acidic permanganate/thiourea redox system, was studied in aqueous media at 30 ± 0,2 °C in nitrogen. The rate of polymerization (R_p) was found to be proportional to nearly the first power of the catalyst (KMnO₄) concentration, within the range of 0,5 · 10^?2 to 1,4 · 10^?2 mol dm^?3, and independent of the thiourea concentration. However, the rate of polymerization varies with the first power of the hydrochloric acid concentration within the range of 2,85 · 10^?2 to 11,4 · 10^?2 mol dm^?3, and increases linearly up to certain extent by varying the monomer concentration from 2,5 · 10^?2 to 12,5 · 10^?2 mol dm^?3. A deviation from the linear behaviour is observed, however, above a concentration of 12,5 · 10^?2 mol dm^?3. The initial rate of polymerization (R_i) as well as the maximum conversion increases by increasing the temperature up to 35 °C, but the maximum conversion falls as the temperature rises above 35 °C. The overall energy of activation is found to be 47,70 kJ mol^?1 (11,48 kcal/mol^?1) within the temperature range of 25–45 °C. Addition of salts, except manganous salts, was found to be associated with a depression in the R_p and maximum conversion. The effect of cationic and anionic surfactants has been found to increase and decrease the R_p respectively; non-ionic detergents, however, have no effect on the R_p.     

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.     

On the kinetics of hydrolytic degradation of native cellulose

The kinetics of the hydrolytic degradation of celluloses the molecular properties of which still correspond largely to those of the native state are studied. The hydrolytic agent has been 0,5 mol/l aqueous solution of KHSO₄. The degrees of polymerization were determined viscosimetrically in copper ethylene diamine (CuEn) as solvent under standard conditions. In order to convert viscosity-average and weight-average degrees of polymerization DP_η and DP_w in the corresponding number-average DP_n, a DP_w/DP_n calibration curve had been elaborated using polymer analogeous nitrates of a series of samples degraded under the same conditions. The results reveal that hydrolytic degradation of native cellulose takes place by two simultaneously occurring kinetic mechanisms, for which the following rate constants were derived: k₁ = 0,12 h^?1, k₂ = 3,88·10^?6 h^?1, and k₁ = 0,79 h^?1; k₂ = 38,35 · 10^?6 h^?1, corresponding to a degradation temperature of 40°C and 60°C, respectively, and related to an initial degree of polymerization DP₀ = 13 000. The number of faster cleaving bonds per molecule (β₁) and the number average of normally splitting bonds being between two “weak links” (β₂) resulted in β₁ ≈ 3,5 and β₂ ≈ 3 600. The activation energies of the rapid and the slower reaction were found to be 20 kcal/mol (83,7 kJ/mol) and 24 kcal/mol (100,4 kJ/mol), respectively. Additional degradation experiments on the same, but pre-swollen or pre-reduced samples did not provoke any variations in the results. It can be excluded, therefore, that the simultaneous occurrence of two kinteic mechanisms is a consequence either of facts which involve diffusion control, or the existence of “stressed” bonds. The found relatively high activation energies rather permit to assume native modifications in the chemical structure of the cellulose molecule as the most probable reason for the faster bond splitting reaction.     

Terpolymérisation acrylonitrile-styrène-acrylate de méthyle, 4. Copolymérisation en emulsion styrène-acrylate de méthyle en réacteur fermé (batch) en présence de persulfate de potassium

To improve the knowledge of emulsion copolymerization of monomers both swelling their copolymers, but which are of quite different polarity (water solubility), a series of styrene (S)/methyl acrylate (MeA) copolymerizations was carried out in batch at 50°C with potassium persulfate as initiator. The overall rates of copolymerization increase with the amount of MeA in the monomer feed. Copolymer composition follows the usual copolymerization equation if bulk/solution reactivity ratios (r_ij) and monomer partition between aqueous and organic phase are taken into account (simulation). However, accurate kinetic data at low conversion (gas chromatography) put in evidence an enhanced polymerization of the more hydrophilic monomer (MeA), which can be attributed to polymerization in the water phase. Particle sizes increase with conversion and tend to a limiting value, the higher the MeA content is. Particle number (N_p), which is practically constant with conversion of S homopolymerization, tends to increase with MeA content as polymerization proceeds. This trend is enhanced if the emulsifier (sodium dodecanesulfonate, SDS) concentration is increased. Overall propagation rate constants were estimated as function of the experimental conditions and monomer concentration within the particles. From kinetic data (rate of polymerization) and N_p, it was found that the average number of radicals per particle, ñ, remains close to 0,5. It was then possible considering S(k_p = 125 1 · mol^?1 · s^?1) as a standard monomer, to estimate the polymerization rate constant for MeA (335 1 · mol^?1 · s^?1). Since adsorption of emulsifier was shown to be closely related to particle surface composition, the specific area A_s of SDS was measured on latices at various conversions and initial monomer feeds. As conversions increases, the particle surface appears to be richer and richer in MeA, which corresponds to a particle structuration. Strong and weak acid group titration is also in quite good agreement with the colloidal behaviour.     

Nature des espèces «vivantes» en polymérisation anionique des diènes conjugués

The nature of “living” propagating species in the anionic polymerization of conjugated dienes was studied by nuclear magnetic resonance. A judicious choice of monomers affords a glimpse of electronic and steric effects on the observed structures. It is shown that the “living” oligomers contain only 4,1 and/or 1,4 (cis and trans) structures, and that the active species can be described by a delocalized π-allyl structure. Association seems to be the fundamental point in the mechanism of the reaction of the initiator with the diene. The internal association of the lithium organic compound disappears or alters to an external association with any electron donating agent. The nucleophilic function can also be taken by the diene itself. A mechanism is proposed based on the concept of association.     

Kinetic Studies of the Copolymerization of Ethylene with Norbornene by ansa‐Zirconocene/Methylaluminoxane Catalysts: Evidence of a Long‐Lasting “Quasi‐Living” Initial Period

Copolymers of ethylene (E) with norbornene (N) were synthesized using the catalysts rac‐Et(Ind)₂ZrCl₂/MAO ( 1 ), 90%rac/10%meso‐Et(4,7‐Me₂Ind)₂ZrCl₂/MAO ( 2 ), and rac‐H₂C(3‐t‐BuInd)₂ZrCl₂/MAO ( 3 ). Catalyst activity, molar mass (MM), and copolymer composition were studied as a function of time. The polymers showed an unusually narrow molar mass distribution (MMD) and a significant increase of their MM with time for up to one hour, suggesting a “quasi‐living” polymerization at 30 °C. The experimental data were fitted to kinetic equations and the propagation and transfer reactions were described in quantitative terms. Norbornene greatly depressed the propagation rate, along with the chain transfer rate. The more sterically hindered catalysts of the series showed lower propagation and chain transfer turnover frequency than 1 and yielded polymers with a low ( 2 ) to very low ( 3 ) norbornene content. The presence of norbornene in solution seemed to be one of the main factors responsible for the observed “quasi‐living” character of the copolymerization, probably due to coordination of norbornene to the active site. Time‐resolved kinetic studies also allowed for the calculation of the fraction of active metal centers, ranging from 56% ( 3 ) and 66–68% ( 1 ) to 94% ( 2 ) of the total zirconium present, depending on catalyst structure.

Left: molar mass (top) and polydispersity (bottom) as a function of the normalized polymer yield. The dashed line is the theoretical curve for ideal living polymerization. Catalysts 1 (□), 2 (?), and 3 (○) at N/E ratio 12.5 and catalyst 1 (?) at N/E ratio 28.4. Right: enlargement of the low yield section.     

Novel Features of 9‐Methylene‐9H‐thioxanthene (MTAE) in Living Anionic Polymerization

For this study, a new epithio‐1,1‐diphenylethylene (DPE) derivative, namely, 9‐Methylene‐9H‐thioxanthene (MTAE), is synthesized, and its copolymerization reactions are investigated, showing distinctive features in living anionic copolymerization. At room temperature and hydrocarbon solvents, MTAE cannot be copolymerized with styrene (St) but can be copolymerized with 1,4‐divinylbenzene (DVB), forming a linear alternating copolymer. Based on this finding, ter‐polymerization of MTAE, DVB and St is conducted to generate a special alternating structure. Additionally, MTAE is found to exhibit fairly high reactivity in copolymerization with Isoprene (Ip) under the same conditions. An alternating sequence of alt‐MTAE/Ip containing high trans‐geometric Ip content (76% of trans‐1,4) and a di‐block sequence of alt‐MTAE/Ip‐b‐Ip are easily obtained. Its experimental reactivity ratio with Ip is investigated via the in situ ¹H NMR method (r_Ip = 0.28), and the corresponding kinetic behaviors and sequence structure are elucidated. Finally, the origin of the effect of MTAE on the isomerism of Ip during chain propagation is investigated by density functional theory (DFT) calculations, and it is found that the bridge sulfur atom in MTAE interacts strongly with living species. This special finding provides a novel approach for the sequence regulation, precise functionalization, and stereo‐structure control in living anionic polymerization originating from monomer structure design.     

Polybutadiènes hydroxytéléchéliques, 2 Microstructure et fonctionnalité des polyméres obtenus par voie anionique. Etude par résonance magnétique nucléaire du proton et du carbon 13

The examination, by ¹H NMR, of anionic hydroxytelechelic polybutadienes in conjunction with accurately measured M _n values allows the simultaneous determination of the number average functionality and the identification of the nature of the chain ends bearing the functional groups. The microstructure of the polymer chains has been studied by ¹³C NMR. A high proportion of isolated vinyl units has been found only if the percentage of vinyl is less than 70%, whereas the vinyl sequences are atactic. During the functionalization, if lithium is utilized as catalyst, only one molecule of ethylene oxide is added at each end of the polymer chain. With potassium, ethylene oxide polymerizes. Owing to the chain ends, reaction mechanisms of the addition of ethylene oxide onto the living polymer have been proposed.     

Synthèse et polymérisation de monomères acryliques fluorés substitués en position α, 4. Applications à l'α-acétoxyacrylate et à l'α-propionyloxyacrylate de 2-perfluorooctyléthyle

The synthesis of the two monomers 2-perfluorooctylethyl α-acetoxyacrylate ( 1 ) and 2-perfluorooctylethyl α-propionyloxyacrylate ( 2 ) was performed in two steps starting from ethyl pyruvate and 2-perfluorooctylethanol with overall yields of about 56% and 50%, respectively. Transesterification of ethyl pyruvate with the adequate fluorinated alcohol followed by enol acylation gave 1 and 2 , respectively. The kinetic study of polymerization of monomers 1 and 2 , led to the determination of the values of the ratio of the square of the rate constant of propagation over the rate constant of termination k²_p/k_te equal to 9,2 · 10^?3 and 9,1 · 10^?3 L · mol^?1 ·s^?1, respectively, and were compared to those of commercially available fluorinated acrylates and methacrylates.