Étude de la solvatation préférentielle des poly(méthacrylates de méthyle) dans quelques mélanges de solvants

The behavior of some poly(methyl methacrylate)s in solvent-mixtures (benzene-methanol, carbone tetrachloride-methanol and dioxane-methanol) was investigated. The dependence of microstructure and molecular weight of the polymer on the preferential solvation was determined. The existence of a conformational transition for syndiotactic poly(methyl methacrylate) in dioxane and in dioxane-methanol could be shown.     

Photochimie de la polyacrylophénone en solution, 2. Courbe d'inhibition à fortes concentrations en inhibiteur. Désactivation statique et solvatation préférentielle

Static quenching performed on the type II cleavage of polyacrylophenone, poly(1-benzoylethylene), (PAP) in 1-methylnaphthalene, (MeN) as solvent and as quencher, has allowed us to evaluate the rate constant of electronic triplet-triplet energy transfer K_el for the system PAP-MeN. This value is similar with the value determinated for the system valerophenone-MeN. indicating that K_el is independant of the carbonyl position free or bound to a polymer chain. The aspect of the quenching curve at high concentration of MeN in benzene has been associated with phenomenona of preferential solvation of benzene in the ternary system PAP-MeN-benzene which has been determinated by the method of dialysis equilibrium.     

Etude du comportement d'une série de polystyrènes linéaires dans des mélanges de solvants

The preferential solvation of anionically polymerised polystyrene by different solvent/non solvent mixtures (CCl₄/CH₃OH, C₆H₆/CH₃OH, dioxane/CH₃OH, C₆H₆/Heptane) was studied by light scattering. The parameter λ′ of preferential solvation depends on molecular weight M according to where λ′_∞ is the preferential solvation at infinite molecular weight and A a quantity characteristic for the composition of the mixed solvent. A increases with decreasing thermodynamic goodness of the solvent mixture. The above equation can be derived semi-empirically by assuming that the solvent composition near the chain depends on the density of chain segments. This hypothesis furthermore explains the observed anomalous behavior of the intrinsic viscosity/molecular weight relationship below molecular weights of about 160,000 in solvent/non solvent mixtures.     

Influence de la masse moléculaire,de la polydispersité et de la température sur les phénomènes de solvatation préférentielle de polystyrènes linéaires dans différents mélanges de solvant

This paper describes the study of preferential adsorption of polystyrene in a solvent mixture as a function of different parameters. In the first place the influence of the density of intramolecular segments (the effect of the molecular weight and the polydispersity of the polymer) on this phenomenon was examined. The effect of the temperature on the solvation coefficient was also considered. Certain experimental results were found to be in good agreement with the thermodynamic theories of preferential adsorption. The lack of the knowledge concerning the variation of the thermodynamic interaction parameters, with the density of intramolecular segments and the temperature, did not permit a rigorous quantitative study.     

Incréments d'indice de réfraction de polymères en solution: Étude des lois de mélange. Influence de la masse moléculaire et de la structure

The variation of the refractive index increment (dn/dc) with the molecular weight and the structure of series of linear and branched well-defined polystyrenes dissolved in benzene was studied. Testing the Lorenz-Lorentz and Onsager-Böttcher mixture rules, we were able to show that:

• 1 Below a critical molecular weight of about 2·10⁴, the linear correlation dn/dc=f(1/M_n) is well explained by the influence of chemical heterogeneities included in the polymer chain (end-groups, branching points etc.).
• 2 These rules do not account for specific polymer-solvent interactions and are not quite rigorous.
• 3 The variations of (dn/dc) and the partial specific volume of the polymer, v?_p, observed already for molecular weights higher than 2·10⁴ are accompagnied by a change in the partial specific refractivity. These effects are related to the influence of intramolecular segment density in the interior of the linear or branched coil.

A homologous series of polyoxyethylene-glycols (α-hydro-ω-hydroxypoly(oxyethylene)s) in benzene presents the same behaviour.     

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.     

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.     

Copolymérisation de la N-acryloyl-L-valine et de la N-acryloyl-L-phénylalanine avec l'acrylamide

The synthesis of N-acryloyl-L -valine (NAVAL) and N-acryloyl-L -phenylalanine (NAPHE) have been carried out from L-valine and L-phenylalanine. The chiral compounds have been characterized by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy and polarimetry. The copolymerization of NAVAL salt, (NAVAL Na, monomer A) or NAPHE salt (NAPHENa, monomer A′) with acrylamide (AM, monomer B) has been investigated using K₂S₂O₈ as initiator, over a range of the feed compositions for NAVALNa (or NAPHENa) from 10 to 100 mol-%. The compositions of copolymers have been systematically assessed through ¹³C NMR. The reactivity ratios for the couple A, B were determined as r_A = 0,67, r_B = 0,91 and for the couple A′, B they have been evaluated to be: r_A′ = 0,40, r_B = 0,91. The azeotropic composition is located at 21 mol-% for the couple A, B and at 13 mol-% for the couple A′, B. Drag reduction effects are obtained with these polymers.     

Étude viscosimétrique de solutions de polyélectrolytes par dilution isoionique. Effet de la densité de charge sur la conformation du polyion

The reduced viscosity η_sp/c of dilute solutions of carboxymethylcelluloses (CMC) was studied, keeping the total ionic strength of the solution constant; the variation of η_sp/c with concentration is often linear and the Huggins constant k′ increases with decreasing ionic strength. So it is possible to obtain the intrinsic viscosity [η]_{I = 0} at zero ionic strength I and to calculate the corresponding molecular dimensions. The variation of [η]_{I = 0} with the degree of substitution of CMC is explained by a progressive change from a zig-zag conformation to a rod when the linear charge of the polyion increases.     

Etude comparée des propriétés mécaniques dynamiques des formes I et II du polybutène-1. Cinetique de transformation II → I

The behaviour of the molecular motion in synthetic cis- and trans-1,4-polyisoprenes was studied by nuclear magnetic resonance. The line-widths (ΔH_pp), second (M₂) and fourth moments (M₄) of the absorption curves were measured at 77, 4.2, and 1.3 K. The obtained values of ΔH_pp and M₂ for cis-polyisoprene indicate that the molecular motions are apparently not completely quenched at 77 K since there is a further increase in the values of M₂ and ΔH_pp when decreasing the temperature from 77 to 4.2 K. It was found also that the value of M₂ at 4.2 and 1.3 K (? 20 G²) was larger than the previously computed one for a rigid lattice (18.5 G²). The temperature dependence of M₂ and ΔH_pp for trans-polyisoprene is different from that for cis-polyisoprene. The values of M₂ are constant in the range from 77 to 1.3 K (? 19.5 G²), which suggests that the molecular motion is presumably stopped in this polymer already at 77 K.     

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).     

Contribution à l'étude de la métallation de structures polyisoprène, 1. Mèthode de dosage

Squalene, as a model compound, and polyisoprene were metalated by the complex of sec-butyllithium (sec-BuLi) with N,N,N′,N′-tetramethylenediamine. The rate of metalation was determined indirectly by further reaction with a deactivating reagent. Amongst the various agents tested, a solution of chlorotrimethylsilane (Me₃SiCl) in diethyl ether was preferred, as deactivation by this reagent does not lead to secondary reactions. The rate of silylation of sec-BuLi by Me₃SiCl was found to be influenced by the solvent and the temperature. The presence of diethyl ether, as solvent of silylation, and a reaction temperature of 0°C are suitable conditions for the reaction between lithiated polymers and Me₃SiCl.     

Terpolymérisation acrylonitrile/styrène/acrylate de méthyle, 3. Etude du mécanisme de la copolymérisation en emulsion

Emulsion copolymerization appears to be very suitable for mechanistic investigations in emulsion polymerization. A study of the emulsion copolymerization under various conditions (batch, semi-continuous, composition controlled reactor) of the styrene (S)/acrylonitrile (A) system is presented, which may have model character due to the very different monomer solubilities both in water and in their polymers. Comparison of copolymer composition with monomer mixture composition in the various phases (determine by gas chromatography analysis after the emulsion has been centrifuged) confirms that the monomer/polymer particles are the main loci of polymerization. The monomier / water ratio and the amount of emulsifier sodium dodecylsulfate influence the polymerization rate (R_p) as well as the particle size (D?_p). The existance of a monomer droplet phase seems also to be determinant for many features of such as a copolymerization as, e. g., the evolution of R_p, D?_p, number of particles (N_p) etc. In addition, in a batch process, the composition drift versus conversion modified the monomer solubilities within the particles, the emulsifier adsorption, the particle growth which appeared to reach a limiting size, mainly due to electrostatic hindrance. It is also observed, Whatever may be the emulsion polymerization process, that R_p is not proportional towards N_p, but towards dN_p/dt; this might be related to the particle growth rate. A. mechanism is derived, based on experimental data and thermodynamic considerations, which allows to take into account molecular interactions (χ), coplymer composition, D_p, interfacial tension (γ), and above all, the actual monomer feed composition within the polymerization loci, as the copolymerization proceeds.     

Polymérisation de thiirannes différemment substitués à l'aide du système chiral ZnEt2/(S)-dihydroxy-2,2′ binaphtyl-1,1′, 1. Stéréoélectivité de la polymérisation

Differently substituted thiiranes were polymerized using an atropoisomeric chiral initiator: ZnEt₂/(S)-2,2′-dihydroxy-1,1′-binaphthyl (DHBN) (mole ratio 1/1). It was observed that high stereoelectivities are obtained with monomers bearing small alkyl substituents and that the resolution efficiency of the initiator decreases as the bulkiness of the substituent increases. From the comparison of the results obtained with another initiator system, ZnEt₂/(R)-3,3-dimethyl-1,2-butanediol (DMBD) (mole ratio 1/1), the use of ZnEt₂/(S)-DHBN could be shown to be more suitable for the polymerization of thiiranes with linear alkyl substituents. Contrary to the case of polymerization initiated by the system ZnEt₂/(R)-DMBD, the polymerization reaction of thiiranes with ZnEt₂/(S)-DHBN was usually accompanied by the production of the corresponding olefins in various amounts.     

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.     

Polyoxirannes et polythiirannes comportant un centre chiral dans la chaine latérale, 2. Polymérisation de (2RS,3S)- et (2S,3S)-époxy-1,2 méthyl-3 pentanes

1,2-Epoxy-3-methylpentanes ( 1 ) of different diastereoisomeric compositions were polymerized using anionic (tert-BuOK, KOH), stereospecific (ZnEt₂/H₂O, ZnEt₂/MeOH), or stereoelective (ZnEt₂/R(?) 3,3-dimethyl-1,2-butanediol (R( ? ) DMBD)) catalysts. In all the cases a preferential incorporation of the (2R,3S) diastereoisomer in the polymer chain was observed. With anionic and coordinated anionic achiral catalysts the election was low but significant, whereas with the chiral ZnEt₂/R( ? ) DMBD system, in the case of the polymerization of the (2RS,3S) monomer, the election was high and corresponded to a stereoelectivity ratio of r = 4, the highest one obtained up to now for oxiranes. The observed effects are due to the presence of a chiral centre in the side chain of the monomer.     

Compatibilité de polymères porteurs de groupements amides tertiaires avec le poly(difluoro-1,1 éthylène). Etude par enthalpimétrie différentielle

The miscibility of poly(1,1-difluoroethylene) ( 1 ) with poly(N-vinyl-2-pyrrolidone) poly(N-methyl-N-vinylacetamide) and poly(N,N-dimethylacrylamide), containing tert-amido groups, was investigated by differential scanning calorimetry. Amorphous homogeneous blends were obtained whenever the weight fractions of polymer 1 is less than 0,7. The dependence of the single glass transition temperature (T_g) versus composition may be readily analyzed either through the Gordon-Taylor equation (high values of the k parameter, suggesting strong specific interactions between the homopolymers) or by means of the Couchman relation (no adjustable parameter). The broadening of the glass transition range and the variation of the increment of specific heat at T_g for the blends are discussed.     

Synthèse de polyquinazolones à chaîne latérale fluorée

Bis(4H-3,1-benzoxazin-4-one) substituted in 2- and 2′-position with ? CH₂CH₂R_F, where R_F is a perfluorinated alkyl group, have been prepared. Polycondensation with 4,4′-oxydianiline and with 4,4′-methylenedianiline led to polyquinazolones which have different inherent viscosities according to the solvent of polycondensation and to the proportions of reactants used. The thermal behavior of these polymers characterized by differential scanning calorimetry or thermogravimetry was studied. The polyquinazolones are thermostable and exhibit a fluorine content of 50 mass-%.     

Preferential solvation of polystyrene by an excimer-forming fluorophore in the system polystyrene/cyclohexane

Fluorescence spectroscopy is used to study the preferential solvation of the polymer and the mobility of the fluorophore in the highly diluted ternary system polystyrene/ethyl 1-naphthoate/cyclohexane under theta-conditions. The ratio of the excimer to monomer fluorescence intensity I_exc/I_mon of the fluorophore is correlated with the concentration and the mobility of the fluorophore in the two phases, inside and outside the polymer coil; the limits of this model are discussed in detail. In the selected system preferential solvation increases the I_exc/I_mon ratio whereas the reduced mobility of the fluorophore inside the coil acts in the opposite manner. The model allows to calculate the distribution coefficient K for the distribution of the fluorophore between the two phases and the ratio q of the mobilities for the fluorophore in the two phases. The values of K obtained indicate a strong preferential solvation of polystyrene by the ethyl 1-naphthoate fluorophore. The mobility ratio q depends on the molar mass of the polymer in such a way that it reflects segmental density.