Synthèse par voie radicalaire de polymères à extrémités hydroxylées 4. Polymérisation et copolymérisation de butènes

The homopolymerization of 1-butene, 2-butene, and isobutene in methanol initiated by hydrogen peroxide affords low molecular weight hydroxylated oligomers in low polymerization yields. The copolymerization of these monomers with a diene monomer such as butadiene can easily be carried out. The reactivity ratios were found to depend on the structure of the monomers; the polymerization and copolymerization rate of 2-butene being higher than those of isobutene, but lower than those of 1-butene.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 2 Synthèse de polybutadiènes

The polymerization of butadiene with aqueous hydrogen peroxide as initiator in an alcoholic medium, gives oligomers of low molecular weight (≈500) and liquid polymers with hydroxy end groups and average molecular weights between 1500 and 11000. The obtained products show that the monomeric units have mainly 1,4 structures (trans). The polymers contain two or three, in certain cases up to six hydroxy groups per molecule. Systematic studies were carried out varying the proportions of alcohol, hydrogen peroxide, and monomer in the reaction mixture.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 12. Etude de la copolymérisation du méthacrylate de méthyle avec divers acrylates et méthacrylates. Détermination des microstructures

Methyl methacrylate was copolymerized with butyl or isobutyl acrylates, and butyl, isobutyl, or 2,3-epoxypropyl methacrylates, by hydrogen peroxide, in the presence of ethanol under UV irradiation (at 254 nm) at room temperature. The analysis of the microstructures was based on resonance splitting of the methoxy protons of MMA, depending on their environment. This splitting was not obtained with isobutyl and 2,3-epoxypropyl methacrylates. All the products were found to be predominantly syndiotactic.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 10. Synthèse de poly(méthacrylate de méthyle)s par le rayonnement UV: étude de l'influence de la nature du solvant mutuel sur la polymolécularité

Methyl methacrylate was polymerized under UV irradiation (254 nm) at room temperature by hydrogen peroxide in order to give hydroxytelechelic polymers. The polymerization was carried out in the presence of ethanol. An alcohol may be used as a diluent, as a mutual solvent of hydrogen peroxide and the monomer, and as a solvent or nonsolvent of the polymer. The influence of the alcohol is pointed out on the various characteristics of the polymerization; the results are compared with those obtained in methanol.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 1, synthèse de polyisoprènes

Aqueous hydrogen peroxide decomposes by heat into two hydroxyl radicals which initiate the polymerization process. With isopren as monomer, two main products are obtained: liquid hydroxytelechelic polymers (1,4, principally trans) and oligomers composed of dimers, trimers and tetramers. The addition of alcohol to the polymerization medium modifies deeply the conversion yield in oligomers and polymers, and the molecular weight. The kinetics and the influence of the temperature of the reaction are studied.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 14. Synthèse de copolymères butadiène-vinylferrocène

Hydrogen peroxide, thermally cleaved into hydroxyl radicals, was used as initiator of butadiene-vinylferrocene copolymerization. The influence of different parameters like temperature, pressure, proportion of hydrogen peroxyde and addition of a solvent with weak transfer capability was studied.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 9. Synthèse de polybutadiènes: étude des microstructures

Butadiene polymerization with hydrogen peroxide resulted in the simultaneous formation of oligomers, polymers, and high polymers. Analyses of their microstructures showed that oligomers have a higher content of 1,2-structures (28%) than the polymers (22%). The nature of the chain ends was determined with low molecular weight compounds. The content of 1,2-units is distinctly higher in the oligomers, which shows that initiation takes place preferably in 1,2- and propagation in 1,4-position. Besides hydroxyl end groups, other functional groups were detected in small quantities in the low molecular weight products: aldehydes, ketones, acids, hydroperoxides, and epoxides. These functions result from secondary reactions such as transfer, initiation, or termination reactions with alcohol releasing radicals.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 3. Synthèse de poly(acétate de vinyle)

On heating, hydrogen peroxide is cleaved into hydroxyl radicals, which can be used as initiators of polymerization in order to give hydroxylated polymers of low molecular weight. The conversion and the number average molecular weights are influenced by the presence of an alcohol in the reaction medium, and the results depend on the solubility of the polymer in the applied alcohol. The following characteristics of the polymerisation of vinyl acetate in methanol are studied: distribution of molecular weights, microstructures, proportion of hydroxyl groups in the macromolecule. The influence of several parameters as reaction time, temperature, proportion of hydrogen peroxyde and solvent, is also investigated.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 6. Etude des réactions de transfert

Radical polymerizations in an alcohol, initiated by hydrogen peroxide were found to afford polymers with hydroxyl end groups. The constants of chain transfer to the initiator and to the alcohol were determined for the polymerization of vinyl acetate, isoprene, and butadiene. The results show the influence of the initiator and the nature of the alcohol in the polymerization mechanism.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 11. Etude de la copolymérisation du méthacrylate de méthyle avec divers acrylates et méthacrylates. Détermination des rapports de réactivité

Methylmethacrylate (MMA) was polymerized in an oxygen or argon atmosphere with butyl or isobutyl acrylates, and butyl, isobutyl, or 2,3-epoxypropyl methacrylates, by hydrogen peroxyde in the presence of ethanol under UV irradiation (254 nm) at room temperature. The reactivity ratios were determined. MMA shows a higher reactivity than its comonomers, in good agreement with the results of the literature, except for isobutyl and 2,3-epoxypropyl methacry-lates.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 7. Synthèse de polybutadiènes: Études cinétiques

It could be shown that radical polymerizations of butadiene in methanol, initiated by hydrogen peroxide, cleaved in two hydroxyl radicals by thermal reaction, give three types of products: oligomers formed predominantly during the two first hours, polymers formed by an autoacceleration phenomenon, mainly during the two first hours, and polymers of high molecular weight, formed after two hours of reaction. The results show that the reaction order is about 1,6. In addition, thermal initiation was also observed.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 8. Synthèse de polybutadiènes: Etude de différents paramètres influençant la polymolécularité

It was shown that radical polymerization of butadiene in 1-butanol and 2-butanol, initiated by hydrogen peroxide cleaved into two hydroxyl radicals by heat, leads to three types of polymers according to their respective polydispersity. It was found that the formation of these products — oligomers, polymers, and high polymers — can be influenced by modifying the experimental conditions. Thus, it is possible to obtain selectively oligomers free of polymers and polymers free of low molecular weight oligomers.     

Polymères thiocarboxyliques, 1. Synthèse et étude de la polymérisation radicalaire de monomères dithiocarboxyliques

The syntheses and free-radical polymerizations of methyl and carboxymethyl 4-vinyldithiobenzoates are described as well as various copolymers. Copolymerisation parameters were determined for the copolymerizations of the methyl dithioester with styrene and with methyl methacrylate.     

Oligomères amphiphiles obtenus par voie radicalaire, 1. Synthèse et caractérisation d'oligomères de l'acide acrylique à extrémité dodécylthio

Oligomeric emulsifiers were prepared by the technique described by Roe, with special care of composition and molecular weight. Acrylic acid was polymerized in 2-propanol with lauroyl peroxide as initiator in the presence (at various ratios) of 1-dodecanethiol ( 8 ) as transfer agent to control the chain length. A good agreement was found between the various methods used for kinetic determination and oligomer characterization (¹H NMR, sulfur analysis, vapor pressure osmometry, acidimetry, GPC). Values of k_pk_t^-1/2, transfer constants for thiol 8 and solvent, nature of chain ends, polydispersity, and molecular weight were determined. Polymer fractionation was successfully performed using different solvents for recovery.     

Terpolymérisation acrylonitrile-styène-acrylate de méthyle, 2. Synthèse de terpolymères homogènes en composition par polymérisation en émulsion

Previous Kinetic studies of the emulsion polymerisation of the three component system acrylonitrile (A) — styrene (S) — methyl acrylate (M) have shown that S is much more reactive than A and M, which have practically the same reactivities. As a consequence, in batch process a large copolymer composition drift is observed versus conversion. To avoid this damageable drift, two techniques were investigated, to get homogeneous macromolecules. (1) Application of the well known “semi-continuous technique” which appeared not to be totally satisfactory, since the initial batch polymer fraction generally has a composition different from the further polymer when the monomer feed is added under starving conditions; a mixture of various macromolecules is the result. (2) The use of the composition controlled reactor, developed in this laboratory, which consists in a continuous monitored readjustment of monomer feed composition. However, due to the heterogeneous medium of an emulsion copolymerization, the copolymer exerts a small chemical heterogeneity which may be practically negligible at high monomer/water ratio. It is finally proposed that a thermodynamic approach might overcome such a behaviour and insure an actual control of the copolymer composition.     

Polymères thiocarboxyliques, 2. Synthèse par modification de polymères préformés

Dithioester groups were introduced into linear or crosslinked polystyrenes by Friedel-Crafts reaction with ClCH₂Si(CH₃)₃/CS₂ or with ethyl chlorodithioformate, as well as thioamide groups by reaction with ethoxycarbonyl isothiocyanate. Treatment of several copolymers of acrylonitrile with ethanethiol and hydrogen chloride and subsequently with H₂S led to copolymers with dithioester and thioamide groups in the side chains without cyclization. Most of these reactions occur without crosslinking.     

Synthèse de polymères étoiles par réaction de polymères ω-fonctionnels sur des polyisocyanates

The present investigation was undertaken to study further the synthesis of networks with viscoelastic properties. This involves two stages: synthesis of functional polymers with reactive chain ends and selective condensation reaction with polyfunctional crosslinking agents. In order to determine the conditions of crosslinking reaction, a preliminary study was realised on the branched star polymer synthesis. These polymers are obtained by reaction of ω-functional polymer with tri-, tetra-, and pentaisocyanates. Polymers used in this work were polyisoprene, polybutadiene, polystyrene, block copolymers from diene and styrene with hydroxylic end groups. The reaction of the liquid polymer having hydroxylic end groups with isocyanates leads to a branched star polymer with formation of an urethane group, the average branching depending on the functionality of the polyisocyanates. Structures of this star polymer are confirmed by NMR analysis and by determination of the rel. mol. mass.     

Polymères photoréticulables à unités cinnamiques, 1 Synthèse des monomères et polymérisation

The synthesis of cinnamic acid derivatives with a carbon-carbon double bond in para position was studied by a Knoevenagel reaction with p-chloromethylstyrene. The latter was obtained via a several-step reaction from 2-phenylethanol. The monomers can be polymerized by a free-radical process without affecting the cinnamic group. Copolymerization is effective only with monomers such as maleic anhydride, p-vinylbenzaldehyde or methyl methacrylate, having a π-acid character like the cinnamic acid derivatives used in our study.     

Oligomères amphiphiles obtenus par voie radicalaire, 3. Simulation et contrôle de la synthèse d'oligomères de i'acide acrylique et de i'acrylamide à extrémité thio

The synthesis of amphiphilic oligomers through radical initiated polymerization of hydrophilic monomers in the presence of long hydrocarbon chain thiols as transfer agents was simulated using a model based on a kinetic scheme similar to that proposed by Ikada. Taking into account the solvent as a secondary transfer agent, the weight fractions of different oligomer molecules and the average degrees of polymerization versus conversion were determined as a function of the mole ratio [thiol]/[monomer] and the solvent transfer constant. A relatively good agreement was found between the theoretical and the experimental values for acrylic acid (AA) and acrylamide (Am) oligomerizations. Oligomers terminated by the solvent could complete with thiol-terminated oligomers. It is interesting that by modifying the simulation model, it is possible to estimate the amount of thiol necessary to keep the composition of the reactant mixture constant during synthesis, thereby eliminating the drift in the oligomer composition at high conversion.