Synthèse et caractérisation de copolymères coordinés par des sels métalliques

The anionic block copolymerisation of isoprene and 2-vinylpyridine (2VP) followed by a coordination with iron (III) chloride, leads to thermoreversibly crosslinked copolymers. These copolymers are character+ed by a low polydispersity (M?_w/M?_w≈1,1) between the coordination nodules of poly(2-vinylpyridine). The study of the swelling ratio at the equilibrium in benzene shows that such a polymeric network does not reach the equilibrium state expected from the thermodynamic analysis of the system. The presence of 2VP in the copolymer induces a screening effect which prevents the solvent diffusion through the polyisoprene network.     

Cinétiques de télomérisation, 7. Calcul de k/kTe en polymérisation radicalaire de divers monomères

In contrast to the usual method of determination of the principle ratio in radical polymerization, k/k_Te, which is based on the comparison of the rate of polymerization with the concentration of initiator, a method was used consisting in the representation of log_e([M]₀/[M]) versus (1 ? e^?kd^t/2). The results obtained with styrene, vinyl acetate, acrylic acid, methacrylic acid, and 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl acrylate ( 1 ) were found to be in good agreement with those already obtained by the other method.     

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.     

Détermination des masses et des distributions moléculaires d'un poly(aryléthercétone-co-sulfone) semi-cristallin (HTX) à l'aide d'une méthode de dérivatisation chimique, 1. Caractérisation moléculaire du HTX en solution dans l'acide sulfurique concentre

HTX, a poly(aryletherketone-co-sulfone), is characterized in solution in concentrated sulfuric acid. Upon dissolution in concentrated H₂SO₄, HTX is chemically modified by sulfonation of phenyl rings. The modification of the chemical structure is studied with a model compound by means of IR spectroscopy. The increase of the molar mass corresponding to a complete sulfonation is determined by means of mass spectrometry. Light scattering and ¹⁹F NMR measurements are performed in order to obtain the weight- (M?_w)_s and number-average (M?_n)_s molar masses of sulfonated HTX samples. (M?_w)s values allow the determination of the Mark-Houwink-Sakurada relationship for HTX in 99,5% H₂SO₄ at 25°C.     

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.     

Polymérisation anionique de l'acroléine, 3. Analyse des microstructures par 1H NMR et 13C NMR et mécanisme de polymérisation

We have synthesized anionic polyacroleins using various initiators (naphthalene complex, tert-butyllithium) in different solvents (tetrahydrofuran, toluene). We have studied the ¹H NMR and ¹³C NMR spectra of the polymers and assigned monomeric units and diads by comparison with spectra of four compounds corresponding to the different microstructure arrangements. By this method, we have clearly proved the presence of 1,4- as well as 3,4- and 1,2-units. But numerous cyclisations occur on the 1,2-units. Using only the ¹H NMR method, a first estimation of the microstructure was obtained. ¹³C NMR gave further information and permitted the estimation of the (1,4-cis)/(1,4-trans) ratio. Furthermore the presence of hydroxyl groups along the chains has also been established. A satisfactory determination of the 1,2,3,4- and 1,4-structure percentages of several polyacroleins has been obtained using ¹H NMR and ¹³C NMR simultaneously. A mechanism of acrolein polymerization, based on two different living ends is proposed. The microstructure indicates the existence of several complexation phenomena. When the living end/metal and monomer/metal complexations are weak (with Na⁺ e.g.), the polymer consists mainly of 1,4- and 3,4-units. On the other hand, with Li⁺, the microstructure has a high 1,2-content. Moreover, the living end/Li⁺ complexation would decrease with the chain length, because of the increasing attraction of the cation by the other complexing sites on this chain.     

Poly{[(Chloro-2 éathyl)-4 phéanyl]-1 éathylène}: Synthèse,caractérisations,dégradation thermique et modifications chimiques

Poly{1-[4-(2-chloroethyl)phenyl]ethylene} ( 3 ) was synthesized by bulk polymerization of 4-(2-chloroethyl)styrene ( 6 ) in two steps from commercial products. The polymer was characterized by means of GPC (weight-average molecular weight M?_w = 85 000 and number-average molecular weight M?_n = 63 500), ¹H NMR and ¹³C NMR spectroscopy. The first stage of thermal degradation begins at 290°C and ends at about 410°C. The overall activation energy was calculated to be 43 kcal · mol^?1 (180 kJ · mol^?1). The solid residue was crosslinked and insoluble. The volatile products, identified by gas chromatography-mass spectroscopy (GC-MS), were chiefly hydrogen chloride, dichloromethane and monomer. In a strongly basic medium, nucleophilic substitution of chlorine was achieved without elimination.     

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.     

Mechanismus der NCA-Polymerisation, 3. Über die Amin katalysierte Polymerisation von Sarkosin-NCA und -NTA

Sarcosine-NTA ( 6b ), a hitherto unknown and—contrary to sarcosine-NCA ( 6a )—distillable liquid, was prepared from N-ethoxythiocarbonyl sarcosine ( 8 ). The polymerization of the NCA 6a and the NTA 6b in pyridine leads to higher polymerization degrees P?_n than with other tertiary amines. The polysarcosine resulting from the NTA shows thereby always lower molecular weights than that resulting from the NCA. During the pyridine catalysed polymerization of the NTA, 1,4-dimethyl-2,5-dioxopiperazine ( 3a ) is formed as byproduct and its amount increases with decreasing monomer concentration. The polymerization of sarcosine-NCA with pyridine or γ-picoline shows the greatest increase of P?_n in the range from 90–100% conversion, whereas with triethylamine as catalyst P?_n decreases in this range. Various reaction mechanisms are discussed; in the case of pyridine catalysis, initiation and propagation via “zwitterions” is the most probable mechanism. The NCA 6a was also polymerized with tert-butylamine as initiator at various monomer/initiator-ratios. P?_n, of the resulting polysarcosine was measured by ¹H-NMR-spectroscopy and an (η_sp/c)/M?_n relationship was established.     

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.     

Living cationic polymerization of styrene by 1-chloroethylbenzene/tin(IV) chloride in chloroform

Living cationic polymerization of styrene in the presence of 1-chloroethylbenzene (1-CEB)/SnCl₄ as an initiating system has been investigated in chloroform at -15 to +20°C. The best results were obtained at -15°C. Under these conditions, the number-average molecular weight (M?_n) of the products increases linearly with increasing monomer conversion. The molecular weight of the polymer produced could be further increased by adding additional monomer. The molecular weights are in good agreement with the calculated values assuming that one living polymer chain is formed per one 1-CEB molecular. The molecular weight distributions of the polymers obtained are narrow (ratio of weight- to number-average molecular weights 1,07 ≤ M?_w/M?_n ≤ 1,17). The living character of these polymerizations depends on the polarity of the solvent and on temperature.     

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.     

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.     

4-(α,α-dimethylbenzyl)phenyl methacrylate, 2. Polymerization in N,N-dimethylformamide

The polymerization rate of 4-(α,α-dimethylbenzyl)phenyl methacrylate in DMF at 70°C is of the order 1,6 in [monomer] and first order in [AIBN], which deviates from classical kinetics. This could be reconciled by a reaction scheme in which dimeric monomer associates and a spontaneous termination are postulated. The scheme is supported by the dependence of the kinetic chain length, v, on the 1,6-th power in [monomer] and zeroth power in [AIBN]. The degree of polymerization is smaller than v, which indicates some chain transfer. A remarkable feature is the constancy of the dispersion degree, M?_w/M?_n, of the polymers of about 1,4 up to high degrees of conversion. The overall activation energy of the polymerization, E_a, is 60,1 kJ · mol^?1, and the preexponential factor ln A ≈ 15,5 (A in (mol · dm^?3)^?1,5 · s^?1). The polymer chains seem to have a rod-like character in THF as deduced from the Mark-Houwink exponent of 1,46. In toluene the polymer tends to form associates.     

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.     

Synthesis of 2,3,4-tri-O-benzyl-[1→6]-α-D-glucopyranan and [1→6]-α-D-glucopyranan with high molecular weight by polymerization of 1,6-anhydro-2,3,4-tri-O-benzyl-β-D-glucopyranose

The polymerization mechanism of 1,6-anhydro-2,3,4-tri-O-benzyl-β-D -glucopyranose ( 1 ) was investigated in order to synthesize 2,3,4-tri-O-benzyl-[1→6]-α-D -glucopyranan ( 2a ) and [1→6]-α-D -glucopyranan ( 2b ) (dextran) with high molecular weight. It was found that the optimum polymerization time to obtain high molecular weights was 40min when the monomer was polymerized in methylene chloride at ?60°C. Stereoregular 2a with a \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {DP} _{\rm n} $ of 1800 (M?_n = 777000), which was about twice as high as the highest \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {DP} _{\rm n} $ previously reported, was obtained in 77% yield by polymerizing the monomer with 0.8 mole-% PF₅ as catalyst applying a monomer-to-solvent weight/volume ratio of 50%. 2a with a high molecular weight was debenzylated to give 2b with a \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {DP} _{\rm n} $ of 446 (M?_n = 72300). The α-stereospecificity and the solid state of the synthetic dextran were investigated by means of optical rotation, NMR spectroscopy, and X-ray diffraction pattern.     

Transition-metal-catalyzed vinyl addition polymerizations of norbornene derivatives with ester groups

Norbornene derivatives containing ester substituents were submitted to Pd(II)-catalyzed vinyl addition polymerization. The transition metal catalyst was found to tolerate the ester functionality. However, the rate of polymerization was reduced in comparison to the polymerization of norbornene. The polymerization of the pure exo-isomers produced substantially higher yields than reactions of monomers containing a high proportion of the corresponding endo-isomer. By varying the ester substituent, amorphous polymers with glass transition temperatures over the range of ?40 to 268°C were synthesized. An approximately linear relationship of molecular weight to monomer conversion was established, and the non-uniformity remained narrow (M?_w/M?_n ≈ 1,15 – 1,25) until high conversions for several of the exo-isomers studied. This indicates that both chain transfer and chain termination are rare.     

Synthesis of Branched Polymers by Means of Living Anionic Polymerization, 9. Radical Coupling Reaction of 1,1‐Diphenylethylene‐Functionalized Polymers with Potassium Naphthalenide and Its Application to Syntheses of In‐Chain‐Functionalized Polymers and Star‐Branched Polymers

Radical coupling reactions of both 1,1‐diphenylethylene (DPE)‐chain‐end‐ and DPE‐in‐chain‐functionalized polymers with potassium naphthalenide have been studied under the conditions mainly in THF at –78°C. Chain‐end‐functionalized polymers having M̄_n values of less than 10 kg/mol were very efficiently coupled in more than 90% yield to afford the polymeric dianion that were dimeric coupled products with two 1,1‐diphenylalkyl anions in the middle of the chains. However, the dimer yield decreased with increasing the molecular weight. The dimer was obtained in 59% yield with use of the chain‐end‐functionalized polymer having M̄_n of 33.9 kg/mol. Well‐defined in‐chain‐functionalized polymers with two benzyl bromide and DPE moieties each have been successfully synthesized by the reaction of the polymeric dianion thus obtained with 1‐(4‐bromobutyl)‐4‐(tert‐butyldimethylsilyloxymethyl)benzene and 1‐[4‐(4‐bromobutyl)phenyl]‐1‐phenylethylene, respectively. The radical coupling reaction of in‐chain‐functionalized polymers with DPE (M̄_n ca. 20 kg/mol) with potassium naphthalenide also proceeded efficiently to afford the coupled products that were A₂A′₂ and A₂B₂ four‐arm star‐branched polymers with well‐defined structures (M̄_n ca. 40 kg/mol).     

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.