Cinétiques de télomérisation, 4. Nouvelle méthode de détermination des constantes de transfert en catalyse radicalaire

For the determination of transfer constants C_T to the telogen in telomerization reactions started with free radicals we used three methods. The first one is the method of Mayo, the second one is based on the variation of the conversion degree of telogen to monomer and the last method requires the knowledge of the cumulated number-average degree of polymerization DP _n and monomer conversion α_M of the samples during the reaction. Verifications of the proposed laws are made for methacrylic acid telomerization with CCl₃Br and methyl methacrylate telomerization with benzenethiol as a telogen and 2,2′-azoisobutyronitrile as the initiator at 70°C. The transfer constant to CCl₃Br is ca. 0,03 and that to C₆H₅SH ca. 1,5.     

Mise au point sur l'analyse par chromatographie par exclusion stérique en milieu aqueux de télomères de l'acide acrylique

In the case of water soluble polymers, the use of size exclusion chromatography (SEC) for the determination of the molecular weight involves numerous difficulties. In order to analyse and determine the molecular weight of acrylic acid telomers we have first tried to obtain a satisfactory and reproducible separation. In this particular case, low-molecular-weight standards are not commercially available. Therefore, we decided to prepare standards based on acrylic acid, either by telomerization with a fluorinated telogen or by polymerization with an initiator bearing a fluorinated group. A calibration curve was obtained from the standards. Telomers of acrylic acid with thioglycolic acid were analysed. This is a general method for determination of DP _n by SEC when there is no standard for the polymers. It can be used in a wide range of DP _n from 1 to 700.     

Télomérisation en milieu aqueux, 2. Étude cinétique de la télomérisation de l'acide acrylique avec l'acide thioglycolique

The telomerization of acrylic acid with thioglycolic acid initiated with hydrogen peroxide in aqueous medium is presented. In order to better control this reaction, the decomposition of H₂O₂ was first investigated by means of differential scanning calorimetry (DSC), leading to a very high value of the dissociation rate constant (k_d), and then studied by volumetry in the presence of a mercaptan. This second method gave a higher value of k_d (by about 6 orders of magnitude at 50°C). From the latter value, the ratio fk_P²/k_Te and the transfer constant of thiogiycolic acid, C_t, were determinated and compared with those reported in the literature. The kinetical parameters, obtained from theoretical and experimental values of DP _n and the conversion of the monomer are in good agreement and allow to prepare telomers of acrylic acid with controlled chain length.     

Synthèse et copolymérisation avec l'acrylamide de macromonomères d'acrylate de dodécyle

Graft copolymers of well-defined structure and composition were prepared by radical copolymerization of acrylamide and poly(dodecyl acrylate) macromonomers. The macromonomers were prepared by telomerization of dodecyl acrylate in the presence of 2-mercaptoethanol as a transfer agent, followed by reaction with acryloyl chloride. Poly(dodecyl acrylate) macromonomers with M _n = 1100, 1100, 2200 and 4600 were synthesized. The kinetics of the radical telomerization of dodecyl acrylate with 2-mercaptoethanol and AIBN was studied at 66°C in THF. Under these conditions we obtained the transfer constant C_T = 0,9. The graft copolymerization of acrylamide with the poly(dodecyl acrylate) macromonomer was carried out in the presence of the transfer agent C₆F₁₃C₂H₄SH. If C₀ = [AIBN]/[Acrylamide] = 0,01 and R₀ = [C₆F₁₃C₂H₄SH]/[Acrylamide] = 0,01, for acrylamide a DP _n = 160 was obtained in all cases, for the macromonomer of M _n = 1100 a DP _n = 2,5, and for the macromonomer of M _n > 1100 a DP_n = 1.     

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.     

Télomérisation en milieu aqueux, 1. Télomérisation de l'acide acrylique avec l'acide thioglycolique

The telomerization of acrylic acid with thioglycolic acid (mercaptoacetic acid) in aqueous medium, with various initiators (H₂O₂,Na₂S₂O₈,K₈ thermal initiation and 2,2′-azobis (2-amidiniopropane) dihydrochloride) has been achieved. Thus, we were able to point out the limitation of the chain length due to the transfer agent, which is characteristic of a telomerization reaction. Mono-, di-and tri-adducts were isolated and characterized after esterification of the reaction medium with ethanol, then hydrolized. These various adducts were used as standards for size-exclusion chromatography, and the influence of the reaction parameters (initiator, temperature, quality of solvent, amount of telogen was investigated). We also determined the transfer constant of thioglycolic acid (C_T = 0,47). It is worth to note that knowing this value, it is possible to control precisely the number -average degree of polymerization of this type of reaction. This allowed us to prepare telomers with a 50% final weight concentration in the dry extract, as it was recommended for their use in paper industry.     

Polymérisation et copolymérisation de l'acétoxy-1 butadiène

1-Acetoxybutadiene ( 1a, b ) can be polymerized under radical conditions as well in bulk, in benzene solution or in an aqueous emulsion. Polymers consist of ca. 80% 1, 4-units ( 4 ) and 20% 3,4-units ( 5 ), as determined by use of model compounds ( 2 and 3 ). Important chain transfer reactions to monomer, which have been measured, account for low number-average molecular weights (M?_n ≈ 5000). Radical copolymerisations with acrylic, vinyl, and diene monomers indicate 1a, b to be quite similar to isoprene in these reactions. Copolymers with M?_n ≈ 20 000 are readily obtained. 1-Acetoxybutadiene polymers prepared via cationic catalysts are unstable unless careful purified. Anionic reagents are destroyed by this monomer even at ?80°C.     

Cinétiques de télomérisation, 6. Détermination des degrés de polymérisation a partir de la répartition moléculaire

It is shown that the kinetic laws established for polymerization reactions can be applied for telomerization reactions provided the number-average degrees of polymerization DP _n are greater than ten. For DP _n > 10 it is necessary to calculate the molecular distributions. Values of DP _n obtained with the method of Mayo and the molecular distribution method are compared and an experimental application is given by the radical-initiated telomerization of glycidyl methacrylate (2,3-epoxypropyl methacrylate) with bromotrichloromethane.     

Cinétique de télomérisation, 2. Détermination des lois applicables à la synthèse des télomères à DPn moyens par catalyse rédox

Some theoretical relations concerning the kinetics of redox catalysed telomerization were studied. Assuming that the transfer termination reaction to the metallic cation is the main termination reaction, equations were established giving, as a function of time, monomer and telogen concentrations. Moreover, instantaneous and cumulated number- and weight-average degrees of polymerization could be calculated. As an example the telomerization of ethyl acrylate with carbon tetrachloride as telogen and with ferric chloride/benzoin as catalyst at four concentrations were carried out. The theoretical and the experimental results are in good agreement with the predictions.     

Recherche de télomères à activité pharmacologique potentielle, 2. Télomères de l'acide acrylique et greffage de composés hydroxylés

Several telomers of acrylic acid with carbone tetrachloride were prepared. Their average degree of polymerization, which was between 10 and 50, was determined by several analytical methods (elemental analysis, viscosimetry, and GPC). From the kinetic equations of telomerization a relation between DP _n of these telomers and the experimental conditions is established. Fixation of hydroxylic compounds through direct esterification was studied and it was found that the prepared telomers can be used as hydrosoluble carriers for drugs containing primary alcohol or phenol functions.     

Télomères monofonctionnels du chlorure de vinyle, 2. Cinétique par amorçage radicalaire

Radical telomerizations of vinyl chloride with telogens R? CCl₃, containing alcohol and acid functions in the R group, were carried out. The molecular weights of the obtained products are between 1000 and 10 000. Transfer constants (C_T) were calculated for each case by studying the DP_n (10 to 50) variation as a function of the mole ratio (R) of telogen to monomer. In addition, the functionality of the resulting poly(vinyl chloride) was evaluated from the values of C_T and R.     

Phénomènes d'inversion de la stéréoélection dans les polymérisations de l'épithio-1,2 propane

Polymerization of racemic 1,2-epithiopropane ( 6 ) with initiators resulting from the reaction of an organometallic compound (Zn(C₂H₅)₂, Cd(CH₃)₂ or Cd(C₂H₅)₂) with a chiral mono or dihydroxy compound (optically active alcohol or 1,2-diol) leads to an optically active polymer by preferential incorporation of one of the enantiomers. The residual unreacted monomer is enriched in the opposite enantiomer. Stereoelectivity ratios (r) (corresponding to the preferential choice of the initiator for one of the enantiomers during the polymerization) as high as 2,4 are obtained. Such a reaction represents a kinetic resolution of a monomer resulting in optical purities up to 65%. The choice of a peculiar enantiomer depends on the absolute configuration of the chiral agent used, on the nature of the organometallic compound and on the conditions of the preparation of the initiator. It can be shown that for a given organometallic compound/chiral hydroxy compound system, the choice of one or the other enantiomer depends on the relative composition of the initiator in the alkylmetal alcoholate and dialcoholate species. Two types of stereoelections have been observed: when the absolute configuration of the monomer chosen corresponds to that of the chiral agent used for initiation, it is called “homosteric”. In the opposite case the stereoelection is called “antisteric”. The composition of several soluble homosteric and antisteric initiators can be determined from their NMR spectra.     

Chain‐Growth Polycondensation in Solid‐Liquid Phase with Ammonium Salts for Well‐Defined Polyesters

Polycondensation of a potassium 4‐bromomethylbenzoate derivative dispersed in organic solvent was carried out with tetrabutylammonium iodide as a phase transfer catalyst (PTC) and a reactive benzyl bromide as an initiator to yield polyesters having a defined molecular weight and a narrow molecular weight distribution (M̄_w/M̄_n < 1.3). Polymerization involves the transfer of monomer to organic solvent layer with the PTC and the reaction of monomer with the initiator and the polymer end benzyl bromide moiety in a chain polymerization manner, as evidenced by polymerization behavior; increase of the molecular weight in proportion to monomer conversion and equal amount of the initiator unit and the end group in polymer irrespective of monomer conversion. Furthermore, the molecular weight increased in proportion to feed ratio ([monomer]₀/[initiator]₀), and the polydispersity index M̄_w/M̄_n stayed less than 1.3 over the whole range of feed ratio.     

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.     

Télomères et cotéloméres d'intérêt biologique et biomédical, 7. Synthèse, évaluations physico-chimiques et biologiques de télomères amphiphiles de type acryloylamino-acide

New ionic telomeric surfactants derived from acryloylamino acids were synthesized and their tensioactive properties compared to those of non-ionic analogs previously reported. We also compared their anti HIV behavior with that of other polymeric polyanionic derivatives. Acryloyl monomers of various amino acids such as glycine, alanine, aspartic, glutamic and γ-aminobutyric acid were prepared and telomerized in the presence of various alkanes or perfluoroalkanethiols as chain transfer reagents. For a given amino acid, the critical micellar concentration (CMC) was shown to depend upon the nature and the length of the hydrophobic tail and not the size of the hydrophilic head, i.e., the number average degree of polymerization (DP _n). None of the telomeric polyanionic derivatives reported herein induced HIV inhibition.     

Synthèse de composéas photoréticulables, 8. Réaction des téalomères du méthacrylate d'époxy-2,3 propyle avec l'acide acrylique et cinnamique

The addition reaction of methacrylic acid ( 6 ) to the telomer 3 , resulting from 2,3-epoxypropyl methacrylate ( 1 ) and dodecanethiol ( 2 ), (DP _n = 6) was studied. The percentage of addition at 60°C was found to be 32 after 24 h. When using an epoxide/methacrylic acid mole ratio of 2:1 Products were obtained which can easily be crosslinked by UV irradiation and which stick to aluminium to give water-resistant products.     

Recherche de télomères à activité pharmacologique potentielle, 3. Préparation et toxicologie de supports télomères à fonctions hydroxyles

Several telomers of vinyl alcohol with chloroform and diethyl phosphonate were prepared. Their DP _n were measured by several analytical methods (elemental analysis, NMR spectroscopy, viscosimetry). Their small molecular size, their good water-solubility, and their very low acute toxicity allow to use them as drug-carriers in pharmacological applications.     

Controlled/“living” radical polymerization of styrene catalyzed by FeCl2/succinic acid

A new ligand, succinic acid, was successfully used for atom transfer radical polymerization. The reaction was carried out at 40 to 100°C in bulk with α‐bromoethyl benzene as the initiator and FeCl₂/(succinic acid) as the catalyst system. The molecular weight of the resulting polymer increases with increasing monomer conversion, however, it is somewhat lower than the theoretical value. The polydispersity index is relatively low (M_w/M_n = 1.30) even though there may be a possible chain transfer reaction during the polymerization. The enthalpy of the equilibrium between active species and dormant ones was calculated to be 2.15 kcal/mol.     

New ester and lactone end‐functionalized N‐vinyl‐2‐pyrrolidinone oligomers

New oligomers of N‐vinyl‐2‐pyrrolidinone functionalized at one end with either ester or lactone functions were obtained by radical polymerization in the presence of different ester (methyl isobutyrate and methyl phenylacetate) and lactone (ε‐caprolactone, δ‐valerolactone and γ‐butyrolactone) compounds as chain transfer agents. The oligomeric samples obtained were characterized in terms of molecular weight and molecular weight distribution by means of analytical size exclusion chromatography (SEC), using purposely synthesized poly(N‐vinyl‐2‐pyrrolidinone) standards. The chain transfer constant C_T of either methyl isobutyrate, δ‐valerolactone, or γ‐butyrolactone towards N‐vinyl‐2‐pyrrolidinone were determined with the help of the known cumulative number‐average degree of polymerization X_n and monomer conversion Y_t of the samples during the reaction.     

Etude de la réaction de télomérisation d'un monomère tensioactif cationique

A polymerizable methacrylic surfactant is synthetized from methacryloyl chloride and 11-bromoundecanol. The obtained cationic monomer is telomerized with a fluorinated thiol, and the transfer constant C_T is calculated. This value is in the same range as transfer constants of classical methacrylic monomers. The obtained k_p²/k_T is low because of the long chain ester. Polymers were prepared in homogeneous solution with an average molecular weight of 25 000.