Micelle formation of poly(acrylic acid)-block-poly(methyl methacrylate) block copolymers in mixtures of water with organic solvents

Abstract

SUMMARY: The micelle formation of poly(acrylic acid)-block-poly(methyl methacrylate) (AA-MMA) block copolymers in mixtures of water with organic solvents was investigated by non-radiative energy transfer (NRET). In the case of block copolymers with 70 hydrophobic MMA units, which form strongly aggregated micelles in pure water, the addition of a non-selective organic solvent (methanol or 1,4-dioxane) induces a micelle-unimer transition within a relatively small range of solvent composition without significantly increasing the rate of chain exchange between micelles close to this transition region. The addition of 2 vol.-% dimethyl adipate (a solvent with chemical similarity to the PMMA block and only limited solubility in water) does not speed up the chain exchange in this system either. In contrast, this solvent promotes the aggregation of smaller block copolymers (20 or 40 MMA units) which are mainly present as single chains in pure water. In the case of the block copolymer with 40 MMA units the so formed micelles show a very slow chain exchange extending over many days. These observations prompt us to assume that the rate of the micelle-unimer exchange equilibrium is not kinetically hindered (i. e., determined by the T g of the core material of the micelle) but controlled by a strong thermodynamic preference for the aggregated state.

Micellization of block copolymers

“…Similar studies were carried out by Wegner et al [119] on fluorescent labelled PMMA -PAA copolymers in mixtures of water with organic solvents such as methanol or dioxane. From their fluorescence and NMR measurements these authors came to the conclusion that the block copolymer multimerization is preceded by the collapse of the hydrophobic block and that the micelle-unimer exchange equilibrium might not be kinetically hindered under given conditions, such as by the glassy state of the micellar core, but could be controlled by a strong thermodynamic preference for the aggregated state.…”

“…It can be noticed that for these copolymers with a constant PB sequence, the association number Z decreases as expected from theory with increasing PEO content. A similar study for PMMA -PAA diblock copolymers in methanol and mixtures of water with organic solvents was performed by Wegner and co-workers [119].…”

“…Rager et al [119] have recently studied by nonradiative energy transfer techniques the micelle formation of PAA -PMMA -(F) block copolymers, tagged with pyrene or naphthalene, in mixtures of water with organic solvents. By addition of dimethyladipate to the micellar system, acting as a plasticizer of the PMMA core, these authors concluded that under their experimental conditions, the micelleunimer exchange equilibrium is not kinetically hindered, e.g.…”

Fundamental Studies & Recent Advances in Anionic Polymerization. 6. Creation of Functional Nano-Materials via Self Organization of Block Co-Polymers

“…Conversely, when the polystyrene content was increased, crew-cut micelles were observed. A similar investigation has been made of block copolymers in which the polystyrene was replaced with poly(methyl methacrylate) and a fl uorescer was introduced [31]. When a cationic quaternised polyvinylpyridine was used, the block copolymers with polystyrene became soluble in water and crew-cut micelles were observed at a high content of polystyrene segments [32].…”

Effects of polydispersity on the phase coexistence diagrams in multiblock copolymers with Laser block length distribution

“…Recently several publications have been appeared in connection with block copolymer systems from both theoretical [1,2,3] and experimental [4,5,6] aspects. In AB multiblock copolymer melts, the immiscibility between A and B blocks induces self-assembly into various ordered microstructures.…”