Alain Brembilla

Synthesis of new amphiphilic cationic block copolymers and study of their behaviour in aqueous medium as regards hydrophobic microdomain formation

Abstract Block copolymers of N -hexadecyl-4-vinylpyridinium bromide (4VPC 16 Br) and N , N -dimethylacrylamide (DMAA) were synthesised by nitroxide-mediated radical polymerisation using 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) as a control agent. The behaviour of such block copolymers in aqueous medium was then investigated in relation to the respective size of both the amphiphilic and the hydrophobic block. Viscosimetry, surface tension measurements, and fluorescence spectroscopy revealed that intramolecular hydrophobic microdomains were spontaneously formed by the pendent long alkyl chains. The properties of the corresponding microdomains were determined in terms of polarity and local cohesion, and were revealed to depend on the relative length of the blocks in the copolymer.

Detection of hydrophobic microdomains in aqueous solutions of amphiphilic polymers using fluorescent molecular rotors

Homopolymers and random copolymers derived from 3-vinylpyridium salts form compact coils in aqueous solutions. The resulting hydrophobic microdomains were characterized by both the hypsochromic shift of the wavelength emission band and the fluorescence quantum yield increase of a molecular rotor used as a fluorescence probe.

Behavior of 3-vinylpyridine in nitroxide-mediated radical polymerization: The influence of nitroxide concentration, solvent, and temperature

The influence of nitroxide concentration, solvent, and temperature on the nitroxide-mediated radical polymerization of 3-vinylpyridine (3VP) was examined. Long-chain poly(3-vinylpyridine)s with low polydispersities were synthesized. The initial 2,2,6,6-tetramethylpiperidin-1-oxyl concentration had no influence on the kinetics of the polymerization but was responsible for the obtained molar weights. Compared with the polymerization of styrene, the polymerization of 3VP proved quite fast. The influence of temperature on the reaction rate was also demonstrated, and the polymerization could be controlled even at 110 °C. Some polymerizations were also performed in solution to test the influence of a solvent such as ethylene–glycol, whose effect on the polymerization of 3VP was dependent on temperature.

Synthesis and behaviour study of amphiphilic polyvinylimidazolium salts in aqueous media: Effects of the microdomains on a bimolecular reaction involving hydrophobic reactants

Abstract Homopolymers of 3-alkyl-1-vinylimidazolium bromides series have been prepared by free radical polymerization in aqueous solution or in benzene. The tendency of aggregation of these water soluble polymers was studied by viscosity measurements and fluorescence probes which have revealed the formation of hydrophobic microdomains. These polymers were tested in water media as a macromolecular matrix for the introduction of a microenvironment able to induce an acceleration effect for a bimolecular reaction involving two hydrophobic reactants. The reaction rates of 5(6)-decylbenzimidazole on the hydrolysis of 4′-nitrophenyl-5-alkoxypicolinates in the presence of the poly(3-hexadecyl-l-vinylimidazolium bromide) or its low molecular weight analogue at pH = 7.09, T = 30° C were estimated and compared.

1-Methyl-2-Pyrrolidinone : A Well-Adapted Solvent in the Benzothiazoles Synthesis

Abstract We describe the synthesis of a series of 2-aryl and 2-alkyl benzothiazoles with high yields using 1-Methyl-2-pyrrolidinone as reaction solvent.

Influence of initiator in controlled radical polymerization using nitroxide capping: the case of N,N-dimethylacrylamide.: Synthesis of block copolymers of 4-vinylpyridine and N,N-dimethylacrylamide

Abstract The behaviour of N,N-dimethylacrylamide (DMAA), when involved in a nitroxide-mediated radical polymerization, depends on the initiator. 2,2′-azobis (isobutyronitrile) triggers a fast reaction which cannot be proved to be controlled. On the contrary, when benzoyl peroxide is used, the reaction proceeds slowly and chain-growth control can be evidenced by studying the evolution of both conversion vs. time and number average molar weight vs. conversion. In the present case, poly(N,N-dimethylacrylamide)s were synthesized, whose polydispersities revealed to be much lower than the indices ever reached so far with 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO). Copolymers of DMAA were then obtained using TEMPO-terminated poly(4-vinylpyridine) as a macroinitiator.

N-alkyl-3-vinylpyridinium salts: homopolymerization of the hexadecyl derivative and behaviour study of the polymer in aqueous media

SummaryWe report on the preparation and the characterization of R-alkylated quaternary salts (with RCCH3, C12H25, C16H33, X=Br-) derived from 3-vinylpyridine (3-VP). Our first attempts on free radical polymerization of 1-hexadecyl-3-vinylpyridinium bromide in benzene solution were described. The viscosimetric behaviour and binding of dye (Methyl Orange) to this homopolymer in aqueous media were interpreted as the formation of compact coils resulting in the presence of hydrophobic microdomains.

Solvent effects on TEMPO-mediated radical polymerizations: behaviour of 3-vinylpyridine in a protic solvent

Abstract Solvents can strongly influence the equilibrium between dormant and active species which is involved in 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-mediated radical polymerizations. At 110°C, the overall polymerization rate of 3-vinylpyridine in pyridine was logically found lower than that in bulk, due to dilution. However, in ethylene-glycol, the opposite behaviour was observed. According to infrared spectroscopy, this unexpected increase in the overall polymerization rate was attributed to hydrogen bonding between ethylene-glycol and the pyridine rings, which weakens the C–O–N bond of the TEMPO-terminated polymers. Semi-empirical molecular orbital calculations were used to support the FTIR results and to calculate the decrease in the dissociation enthalpy of the polymer–nitroxide bond.

Microstructure study of new amphiphilic copolymers from 3-alkyl-1-vinylimidazolium salts

Abstract The surface active monomer 3-hexadecyl-1-vinylimidazolium bromide was copolymerized free-radically with N -vinyl-pyrrolidone or 3-methyl-1-vinylimidazolium bromide in ethanol solution at low conversion copolymerization. The reactivity ratios were determined by the Fineman-Ross and Kelen-Tudos methods. The non-linear regression of the copolymer composition variations vs the comonomer composition, using reactivity ratios as adjustable parameters was also employed. Their microstructures were examined in terms of instantaneous and average copolymer compositions as a function of conversion, diads fractions and average monomer lengths at initial polymerization.

Poly(N-alkylacrylamide-co-vinylpyridinium): synthesis and aqueous solution properties

Copolymers of 4-vinylpyridine and N-alkylacrylamides (alkyl chain bearing 6, 10 and 12 carbon atoms) were prepared by bulk free radical copolymerization using 2,2′-azobisisobutyronitrile and 2,2′-azobis(2,4-dimethylvaleronitrile) as initiators. Poly(N-alkylacrylamide-co-4-vinylpyridine)s were then converted into cationic copolymers by quaternization of the pyridine rings with methylbromide. Their amphiphilic properties in dilute aqueous media were studied by viscosimetry, fluorescence and tensiometry. In selected solvents (water + methanol), the association phenomenon was investigated as a function of the solvent composition and the chemical structure of the copolymers.