Interfacial Properties of a Diblock Amphiphilic Copolymer: Poly(isobutylvinyl ether-b-2-methyl-2-oxazoline)

Abstract

Novel amphiphilic diblock copolymers, poly(isobutylvinyl ether-b-2-methyl-2-oxazoline) (PIBVE-b-POXZ), were synthesized by cationic polymerization. The molar ratio of IBVE in the copolymers was varied from 20% to 50%. Their molecular weights were over the range from 1000 to 4000. The associations of these copolymers have been studied by small-angle neutron scattering (SANS) in two selective solvents: water which solubilizes the POXZ block and cyclohexane which solubilizes the PIBVE block. In 1% solutions, all the soluble copolymers formed micellar aggregates. The copolymers have been adsorbed on porous silica particles from selective and nonselective solvents. The adsorbed layers have been studied by SANS. In the case of a nonselective solvent of the two sequences (dichloromethane) copolymers have shown comparable adsorption as the homopolymers. Influence of concentration of solutions has been studied in adsorption from aqueous solutions. For dilute watery solutions, the adsorbed chains were in mushroom configuration and the adsorbed amounts were low. On the opposite, stable and very dense copolymer layers corresponding to extended brushes have been obtained in the presence of concentrated watery solutions. The copolymer chains are anchored by the PIBVE blocks which are collapsed on the surface while the POXZ blocks are in a very extended conformation. The influence of the hydrophilic/lipophilic balance has been studied by varying the chemical composition. The amounts of adsorbed polymer were increased with amount of IBVE in the copolymer. The thicknesses of the adsorbed layers have been found to follow qualitatively the theoretical model of Marques and Joanny for the adsorption of diblock copolymers in selective solvents. Adsorption from cyclohexane which is a selective solvent of the PIBVE block at different copolymer compositions has shown thick adsorbed layers which could correspond to direct adsorption of the micelles on the surface.