Cinétique de télomérisation, 3. Détermination des constantes de tranfert en catalyse rédox

Three methods were used for the determination of transfer constants to the metallic complex in the telomerization reaction with redox catalysis. The first one consists in the determination of DP _n as a function of the mole ratio of telogen to monomer at the beginning of the reaction. The second one is based on the variation of the conversion degree of telogen to monomer. The last one requires the knowledge of the cumulated DP _n and the conversion degree of monomer samples during the reaction. The proposed laws were checked following the methyl acrylate telomerisation with CCl₄ as a telogen and CuCl₂ as a catalyst at 120°C. The transfer constant to CuCl₂ was found to be about 600 according to the three methods.     

Télomérisation de l'isobutylène

The telomerization of isobutene was investigated using redox catalysis, free radical, and particularly cationic initiation. The influence of the initiator on the degree of polymerization and the structure of the telomers was studied. Redox and free radical telomerization with CCl₄ and CCl₃Br were found to permit synthesis and identification of the monoadduct structure. Cationic telomerization gives regular structure compounds and the molecular weights are higher than those obtained by other methods of telomerization.     

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.     

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.     

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 de composées photoréticulables, 7. Télomères des acides acrylique et méthacrylique gréffés par méthacrylate d'époxy-2,3 propyle

Telomers were prepared from acrylic or methacrylic acid and CCl₃Br, C₁₂H₂₅SH, C₁₈H₃₇SH or C₈F₁₇C₂H₄SH by initiation with 2,2'-azoisobutyronitrile. The transfer constant of CCl₃Br and the thiols, which are about 0,03 and 0,5, respectively, were determined. These telomers were used as supports of photopolymerizable functions, which were introduced by grafting of 2,3-epoxypropyl methacrylate, catalysed with dodecyldimethylamine. The reactions were followed by ¹H NMR, elemental analyses, tonometrie, and especially by GPC and titration of the acid functions. The grafting telomers, holding many acrylic functions which react upon UV and electron irradiation, give photoreticulated varnish coatings with very interesting properties.     

Etude de la télomérisation de l'acide acrylique par les mercaptans, 1 Télomérisation de l'acide acrylique par l'acide thioglycolique; Influence de la nature du solvant sur la valeur de la constante de transfert et de kp/√kte

The telomerization of acrylic acid (AA) with thioglycolic acid (TGA) initiated with 2,2′‐azoisobutyronitrile (AIBN) was first investigated in organic medium (THF, 65°C). The kinetic study of this telomerization led to the determination of the TGA transfer constant (C_T = 3.2) and to the ratio k_p/√k_te equal to 0.48 L^1/2·mol^–1/2·s^–1/2. Then, the same study was performed both in aqueous medium and in water/THF mixture in order to investigate the solvent effect on the transfer constant. From these works it is emphasised that the nature of the solvent plays an important role on the kinetics parameters. First, this research underlined an increase of the k_p/√k_te value by raising the water proportion in water/THF mixtures. Then, the kinetic study showed the highest value for the k_p/√k_te constant, equal to 2.48 L^1/2·mol^–1/2·s^–1/2 when the telomerization proceeded in water. Consequently, the value of C_T, which is directly influenced by the k_p/√k_te constant, presented a decrease from C_T = 3.2 in THF to a value equal to 0.5 in water. By this way, the « ideal » case of telomerization (C_T = 1) was reached for a mixture of solvents; 80% water/20% THF (v/v).     

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.     

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.     

Télomères monofonctionnels du chlorure de vinyle, 3. Cinétique par catalyse rédox

A kinetic study of the redox telomerization of vinyl chloride with carbon tetrachloride was carried out. Transfer constants of PVC to the metallic ion (C_Feⁿ), initiation rate (k_i), and functionnality of the resulting telomers were measured. Instantaneous and cumulated polymerization degrees, (DP_n )_i and (DP_n )_cum were determined with the help of a theoretical study. These constants provide a rigorous control of the telomerization of vinyl chloride with RCCl₃, (R containing an alcohol or ester group).     

Cinétiques de télomérisation, 1. Determination des lois applicables à la synthèse des télomères à DPn moyens en télomérisation radicalaire

The kinetics of free radical telomerization was studied. The theoretical relations that can be applied in reactions of this type, were evaluated. When transfer predominates, the equations giving the variations of monomer, telogen and initiator as a function of time were established. Moreover, instantaneous and cumulated number and weight average degrees of polymerization were calculated. The resulting relations were checked on the example of the telomerization of 2,3-epoxypropyl methacrylate with bromotrichloromethane in the presence of two initiators and two different temperatures. Comparison of the experimental results with the theoretical ones revealed the scope of application of the general formulae giving the average degrees of polymerization.     

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.     

Cinétiques de télomérisation, 5. Détermination des degrés de polymérisation moyens cumulés dans les réactions de télomérisation et de polymérisation radicalaires

Two principal methods are described for the determination of the cumulative number-average and weight-average degrees of polymerization in polymerization and telomerization reactions. The first method for the calculation of both quantities uses the ratio of monomer concentration and concentration of radicals created. In the second the instantaneous number-average degrees of polymerization of short intervals of monomer conversion are added up. A comparison of the two methods is given and an application is studied for redox telomerization of ethyl acrylate with carbon tetrachloride.     

Synthèse et transformations chimiques des télomères de l'undécène-10 oate de méthyle, 1

Redox of radical telomerizations of methyl 10-undecenoate (1) with different telogens such as CCl₄, CCl₃Br, CCl₃CF₃, HPO (OEt)P₂ or different adducts of CCI₄, on vinylidene chloride and chlorotrifluoroethylene, were studied. Chemical transformation of the end of the chains led to the corresponding difunctional compounds. Starting with these last compounds, polycondensation reactions were carried out.     

Etude de la diaddition de l'acétate d'allyle sur les télogènes chlorofluorés possédant deux groupements CCl3 en extrémité de chaîne

The redox catalyzed addition of compounds such as Cl₃C? CF₂? CCl₃ and Cl₃C? CF₂? CCl₂? CH₂? CHCl? CH₂? OCOCH₃ to allyl acetate was studied with the purpose of obtaining telechelic products. RuCl₂[P(C₆H₅)₃]₃ was used as catalyst, and its action was compared to that of cooper- or iron-based catalysts. The products were isolated and their structures studied by means of ¹³C, ¹⁹F and ¹H NMR spectroscopy. The reaction mechanism was studied to improve the yield of the diaddition product for its utilisation as monomer in polycondensation reactions. It was found that the low reactivity for a second addition is not due to the presence of a chlorine atom in β-position of the acetate function. When allyl acetate was replaced by allyl bromide or chloride in the first addition, the second addition to allyl acetate occurred normally.     

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.     

Radical telomerization of vinyl acetate with chloroform. Application to the synthesis of poly(vinyl acetate)‐block‐polystyrene copolymers by consecutive telomerization and atom transfer radical polymerization

This paper demonstrates that radical telomerization and atom transfer radical polymerization (ATRP) can be combined in a two‐step procedure to prepare poly‐(vinyl acetate)‐block‐polystyrene (PVOAc‐b‐PSt) diblock copolymers. The first step consists in telomerizing VOAc with chloroform, leading to trichloromethyl‐terminated VOAc telomers CCl₃(VOAc)_nH. A detailed ¹H NMR analysis shows that nearly pure telomer structures are obtained over a broad range of DP_n values (up to at least 60 units). When ATRP of styrene is initiated with a model telomer adduct (CCl₃CH₂CH₂OAc), molecular weights increase linearly with monomer conversion and match theoretical values. Moreover, polydispersities are consistently low (1.22 < M_w/M_n < 1.38) throughout polymerization. Similarly, VOAc telomers (DP_n = 9 and 62) are good ATRP macroinitiators. The high purity of the resulting diblock copolymers is confirmed by GPC using RI/UV dual detection.     

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.     

Etude de la télomérisation du méthacrylate de méthyle par l'acide thioglycolique. Application à la détermination des probabilités de structures des télomères synthétisés

This paper presents a new theoretical method for the determination of the PMMA telomers functionality in order to better control the telomerization reaction. Telomers bearing a functional end‐group are obtained by telomerization of methyl methacrylate with thioglycolic acid, initiated either with 2,2′‐azoisobutyronitrile (AIBN) or with 4,4′‐azocyanopentanoic acid (ACPA). In both cases of initiation, the transfer constants of thioglycolic acid are determined and are respectively equal to 0.672 and 0.674. Then, these results were applied to this new method so as to predict and quantify the several structures of telomers obtained above. This method is based on both contribution of termination and transfer to mercaptan in Mayo's law and allows to quantify all the kinds of macromolecules with their both extremities. The influence of the telogen amount vs the functionality of telomers, that of the initiator concentration and that of the nature of the initiator are investigated and underlined the importance of each factor. Finally, theoretical telomer functionalities are compared with experimental ones by titration of acid functions and are in good agreement.     

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.