Roger Fayt

New developments in block polymerization

Preparation de copolymeres sequences par polymerisation radicalaire. Preparation de copolymeres sequences par polymerisation anionique. Preparation de copolymeres sequences par polymerisation cationique. Preparation de copolymeres sequences par polymerisation par coordination. Preparation de copolymeres sequences par polymerisation en croissance par etapes. Conclusions generales. References

Shear thickening of halato-telechelic polymers in apolar solvents

Abstract Short-length polymers selectively end-capped with a metal carboxylato group at both ends, i.e. metal carboxylato-telechelic polymers, exhibit an unusual shear-thickening behaviour in apolar solvents, depending on the main experimental parameters that control the ion-pair association, such as metal cation, concentration and temperature. In contrast to the non-ionic precursors, metal carboxylato-telechelics are indeed responsible for a marked increase in the solution viscosity in a range of shear rates between 0.1 and 1000 s −1 . The shear-rate dependence of the solution viscosity has been analysed in a close relationship to metal counterion, polymer concentration, temperature and addition of polar compounds to the apolar solvent. As a rule, the dilatant behaviour depends strongly on the formation of polymer aggregates in relation to the mutual interactions of the ion pairs. A consensus is now emerging on the origin of the shear-thickening effect, which should be found in inter-aggregate associations rather than in a transition from intramolecular to intermolecular associations of the individual chains.

The Anionic Polymerization of Alkyl Acrylates : A Challenge

Kinetics and mechanism of anionic polymerization processes can be modified on purpose by ligands specific of the active anionic species. The reactivity enhancement promoted by cation-binding agents is well-documented, whereas complexing the well-known alkyllithium initiators to non reactive alkyl metals or metal alkoxides can affect the kinetics and improve the stereoregulation of the polymerization. Quite interestingly, some inorganic salts, such as lithium chloride, exhibit an important regulating effect in the anionic polymerization of alkyl acrylates. Indeed, side-reactions are now controlled to such an extent that the propagation is a living process and leads to polymers with an unimodal and narrow molecular weight distribution.

Dispersions of carbon black in a non-polar medium stabilized by poly(styrene-b-stearyl methacrylate) amphipathic block copolymers

Well characterized poly(styrene-b-stearyl methacrylate) copolymers were synthesized by a living anionic copolymerization process. The polystyrene block of these amphipathic copolymers dissolved in a selective solvent of the poly(stearyl methacrylate) block adsorbs onto carbon black. An experimental isotherm in agreement with the Langmuir equation is observed. Considerations about the area occupied by the copolymers at the carbon black surface in isododecane are in favour of steric stabilization. These copolymers are thus able to stabilize fine and stable carbon black dispersions in isododecane; thus there is a possibility of application in liquid toner electrophotography.