André Collet

Fluorocarbon associative polymers

Fluorocarbon associative polymers modified along the backbone or at the extremities by hydrophobic groups are reviewed with respect to their association and rheological properties in aqueous solutions. Above a threshold concentration corresponding to the formation of a reversible network structure, the solutions behave as physical gels. In this review, it is shown that the viscoelasticity of fluorocarbon associative polymer gels is enhanced with respect to that of hydrocarbon analogues. For polymers substituted at the extremities (telechelics), significant progresses have been made in recent years concerning the microstructure, the phase behavior and the rheology of the gel state. Telechelics in solutions are forming multiconnected structures, which dynamical features are in good agreement with those of transient network models.

Kinetics of homopolymerization of fluorinated acrylates, 5. Influence of the spacer between the fluorinated chain and the ester group

The synthesis of various fluorinated acrylates CH 2 =CHCOO(CH 2 ) p C n F 2n+1 and their kinetics of radical homopolymerization are presented. The fluoroacrylated monomers have been prepared in two steps by acrylation of the corresponding halogenated alcohols produced by radical addition of perfluoroalkyl iodides(C n F 2n+1 I) to ω-hydroxylated alkenes. The fluorinated acrylates differ from each other in the nature (branched or linear) and the length (n ranging from I to 8) of the fluorinated chain and in the nature of the spacer between this fluorinated chain and the ester group (p ranging from I to 11). The kinetics of polymerization led to the determination of k 2 p /k te . These values were comparcd with those of commercially available fluorinated acrylates and were found to depend upon both the spacer length and the nature of the fluorinated group.

Characterization of natural rubber using size-exclusion chromatography with online multi-angle light scattering: Study of the phenomenon behind the abnormal elution profile

Natural and synthetic poly(cis-1,4-isoprene) were characterized by size-exclusion chromatography coupled with an online multi-angle light scattering detector (SEC-MALS). Unlike synthetic poly(cis-1,4-isoprene) (SR), natural rubber (NR) samples showed anomalous elution profiles. The beginning of elution was very similar to SR but, after a certain elution volume, the molar masses of the eluting macromolecules increased with elution volume instead of continuing to decrease, which resulted in an upturn curve profile. Adding tetrabutylammonium bromide (TBABr) to THF (solvent and mobile phase) removed this phenomenon. In addition, using different concentrations of TBABr showed that TBABr had two simultaneous actions. TBABr reduced the abnormal elution profiles and the quantity of aggregates (insoluble part or gel). These results mean that the main phenomenon involved in abnormal elution was delayed entities adsorbing on the column packing. Their delayed elution was responsible for the artificial increase in molar masses, especially at high elution volumes. The results obtained suggest that these entities are very compact and have a sphere-like structure.

Synthesis and characterization of model fluoroacylated poly(ethylene oxide)

Abstract The modification of hydroxytelechelic poly(ethylene oxide)s (PEO) of molecular weights 10.000, 20.000 by a fluorinated acid leading to fluoroacylated poly(ethylene oxide)s (FA-PEO) is described. The one pot process involving the in situ generation of a fluorinated anhydride by reaction with N , N -dicyclohexylcarbodiimide (DCC) leads to complete modification of hydroxy end-groups. The reaction is catalyzed by dimethylaminopyridine (DMAP). A method, based on 19 F-NMR spectroscopy, has been developed for the detection and titration of residual PEO hydroxy end-groups.