Jean-Pierre Vairon

Functionalized latexes as substrates for atom transfer radical polymerization

The application of atom transfer radical polymerization (ARTP) to the homopolymerization of 2-hydroxyethyl acrylate and 2-(methacryloyloxy) ethyl trimethylammonium chloride at the surface of a crosslinked polystyrene latex functionlalized with alkyl bromide groups is reported. Polimerization was carried out using the surface groups of the dialyzed latex as initiators. The resulting hydrophobic core, hydrophilic shell latexes, were analyzed by FTIR, 13 C-NMR spectroscopy, and dynamic light scattering.

Pulsed‐laser radical polymerization and propagation kinetic parameters of some alkyl acrylates

Pulsed-laser photoinitiated polymerization was used to determine, in toluene solution, the propagation kinetic parameters of a series of acrylates with increasing size of the alkyl side group. Transfer to monomer and to toluene did not occur significantly in our PLP conditions and our temperature range since no broadening of the MMD was observed, allowing generally to work with two inflection points. In contrast, depending on the nature of the acrylate and on the PLP conditions, transfer to polymer, and thus long chain branching, can critically interfere. Indeed, the Mark-Houwink-Sakurada parameters, which are used to calculate the absolute molar mass at the inflection point, strongly depend on the polymer structure and thus, should be carefully measured for each PLP sample. Although still preliminary, the results show that the k p s measured in toluene solution present a tendency to continuously decrease when increasing the size of the side group. This observation is conflicting with the reported behaviour for PLP experiments in bulk, revealing a possible solvent effect.

Synthesis of amphiphilic polyelectrolyte block copolymers using “living” radical polymerization. Application as stabilizers in emulsion polymerization

This paper describes the synthesis of amphiphilic block copolymers composed of an ionic poly(styrenesulfonate) first segment and a hydrophobic polystyrene second one, using TEMPO-mediated “living” radical polymerization. These copolymers proved to be efficient stabilizers in the emulsion polymerization of styrene.

Polystyrene-block-poly(butyl acrylate) and polystyrene-block-poly[(butyl acrylate)-co-styrene] block copolymers prepared via controlled free-radical miniemulsion polymerization using degenerative iodine transfer

Polystyrene-block-poly(butyl acrylate) and polystyrene-block-poly[(butyl acrylate)-co-styrene] block copolymers were prepared in an aqueous dispersed system via controlled free-radical miniemulsion polymerization using degenerative iodine transfer. The first step is batch miniemulsion polymerization of styrene in the presence of C 6 F 13 I as transfer agent. The second step consists of the addition of butyl acrylate to this seed latex, either in one shot or continuously. The addition was started before the consumption of styrene was complete in order to perform a copolymerization reaction able to moderate the rate of propagation in the butyl acrylate polymerization step and, therefore, to favor the transfer reaction. Kinetics of polymerization and control of the molar masses were examined according to the experimental conditions and particularly to the rate of butyl acrylate addition. The formed block copolymers were analyzed by size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). formula chim. Evolution of M n with conversion for the second block (straight line: theoretical M n )

Synthesis of water‐soluble nitroxides and their use as mediators in aqueous‐phase controlled radical polymerization

Water-soluble nitroxides with different struc- tures were tested as mediators in the controlled free-radical polymerization of sodium 4-styrenesulfonate carried out in water at 130 °C. Nitroxides based on 1,1,3,3-tetramethyl- isoindolin-2-oxyl and 1,1,3,3-tetraethylisoindolin-2-oxyl with an ionic group on the aromatic ring (either a quaternary ammonium or a sulfonate substituent) exhibited better efficiency than water-soluble derivatives of 2,2,6,6-tetramethyl-1- piperidinyloxy radical (TEMPO). The steric hindrance at the nitroxide site (ethyl or methyl substituent) had a much larger influence on the activation-deactivation equilibrium than the type of ionic group. With nitroxides bearing four ethyl substituents, the equilibrium constant was one order of magnitude larger than that obtained for nitroxides with four methyl substituents. Final molar masses matched the predicted values, with narrow distribution. Livingness of the poly(sodium 4-styrenesulfonate)s was confirmed by successful reinitiation of sodium acrylate in water at 130 °C.

Mucoadhesion of copolymers and mixtures containing polyacrylic acid

Water-soluble polymers were synthesized from dextran and polyacrylic acid and their ocular mucoadhesion was evaluated. One series had polyacrylic acid grafted onto the polysaccharide backbone of dextran, and another series had dextran grafted onto the polyacrylic acid backbone. Mucoadhesion of these copolymers was investigated using a tensile apparatus and compared with that of polyacrylic acid/dextran mixtures prepared in different proportions. Whatever the copolymer structure, no synergistic effects were seen and mucoadhesion was not markedly increased compared to dextran. The adhesion of copolymers was the same as that of mixtures having a similar polyacrylic acid content and was always less than that of polyacrylic acid alone. Formation of an interpolymer complex occurred at concentrations up to 60% polyacrylic acid, and only above this value did bioadhesion increase above that of dextran. When this complex was dissociated by neutralization of the carboxyl groups of polyacrylic acid, the mucoadhesion of the copolymers and the mixtures was improved. These experiments demonstrated that copolymers and mixtures of dextran and polyacrylic acid did not produce polymers with improved ocular mucoadhesion.

Synthesis of di- and triblock copolymers of styrene and butyl acrylate by controlled atom transfer radical polymerization

Di- and triblock copolymers of styrene and butyl acrylate with controlled molar masses (Mn up to ≈ 105) were sequentially prepared by radical atom transfer polymerization in a homogeneous medium using chlorine end capped polymers as initiators and the copper(I) chloride/bipyridine complex as catalyst, in the presence of dimethylformamide. Random poly(styrene-co-butyl acrylate) was synthesized and the cross-over reactions between Cl end capped polystyrene and poly(butyl acrylate) to the opposite monomers were examined.

Influence of crystallization conditions on the location of side-chain branches in ethylene copolymers as studied by high-resolution solid-state 13C N.M.R.

High-resolution solid-state 13C N.M.R. experiments have been carried out on a series of Ziegler-Natta ethylene copolymers containing a small amount of side chain branches. Selective observations of the amorphous and crystalline phases of these compounds have shown that a small quantity of methyl branches can be accomodated in the crystalline zones, in a way which is independent of the thermal history of the sample. On the contrary, branches longer than methyl appear to be mainly located in the amorphous and interfacial areas and the composition of each phase depends on the thermal treatment undergone by the sample. In polyethylenes and ethylene copolymers, the accomodation of some side groups in the crystalline phase of the material has been investigated by several techniques. From the analysis of the melting temperature/composition relations in ethylene-type copolymers from diazoalkenes containing varying amounts of either methyl or n-propyl side groups arranged in random sequence distribution, it has been concluded (RICHARDSON et al., 1963) that while small quantities of the methyl side groups are incorporated into the crystalline phase at equilibrium, the larger side groups are excluded. These conclusions appear to be disputed by wide-angle X-ray diffraction studies of ethylene copolymers. The unit cell dimensions are known to expand and distort as the concentrations of either methyl, ethyl, n-propyl or n-butyl side groups are increased (WALTER and REDING 1956, EICHORN 1958, COLE and HOLMES 1960, SWANN 1962, BAKER and MANDELKERN 1966). However these unit cell variations do not necessarily demonstrate the incorporation of the branches into the lattice, as the unit cell dimensions may be affected by the crystallite size (RICHARDSON et al., 1963). They can also be affected by the details of folds, fold surface and the interior defect in crystals (DAVIS et al., 1968). Moreover the results appear generally dependent on the crystallization conditons. A detailed study (BAKER and MANDELKERN, 1966) has shown that in the methyl copolymers, a proportion of the side groups enters the lattice as an equilibrium condition, while, in the n-propyl copolymer containing small concentrations of side groups, the lattice spacings are close to those of the homopolymer. These conclusions can be compared with the interpretation of crystalline lattice dimension data reported by SHIRAYAMA et al. (1972): Branches smaller than C3 would be accomodated in the lattice, whereas branches larger than C4 would be excluded from the lattice, enter the amorphous domain and produce smaller relative side group composition of the fast relaxing (T1(13C)) amorphous regions, although it increases the crystallinity of the sample (Table 1). In the same way, the comonomer 13C lines can be observed in the spectra taken with the delayed contact pulse sequence (Fig.2) and their relative intensities with respect to the polyethylene main peak do not depend on the thermal treatment (quenching or slow cooling) undergone by the sample. These last results lead to the conclusion that a small number of methyl branches can be accomodated in the crystalline zones of the material independently of the thermal history of the copolymer, even if the treatment increases the crystallinity.

Cationic polymerization of cyclopentadiene initiated by bifunctional trityl salts evidence for a direct addition of the initiator and application to block copolymerization

A chemical evidence for the fixation of triphenylmethyl cation in the initiation step is given in the case of cyclopentadiene polymerization initiated by stable trityl salts. With SbCl6 as counter ion, negligible transfer reaction takes place at 0°C. The situation is more complex with SbCl5OH−. Mono and bifunctional trityl salts have also been used for the synthesis of AB and ABA block copolymers.

Stable carbocationic species observed during the oligomerization of p-isopropyl-α-methyistyrene initiated by CH3SO3H in CH2CI2 solution

The cationic oligomerization of p-isopropyl-α-methylstyrene by CF3SO3H in dichloromethane has been investigated. The electronic spectrum of the corresponding active species showed two absorption maxima at 362 and 490 nm. The reaction did not give high polymers but rather dimers and trimers as major products, the proportion of olefinic dimers and trimers increasing at lower temperatures compared with the indanic products. Oligomers with ¯Dn ≃ 20 were obtained at −58°C for a monomer to initiator ratio greater than 1800.