Effect of Poly(acrylic acid) Block Length Distribution on Polystyrene-b-poly(acrylic acid) Block Copolymer Aggregates in Solution. 2. A Partial Phase Diagram

Abstract

The first paper of the series, which focused on the effect of polydispersity on the self-assembly of block copolymer vesicles, showed that an increase in the width of the poly(acrylic acid) (PAA) block length distribution resulted in a decrease in the size of the vesicles formed. In this paper, the rest of the phase diagram is explored. For the present study, a series of polystyrene-b-poly(acrylic acid) copolymers of an identical polystyrene length of 325 units but of varying degrees of polymerization of PAA was synthesized. Mixtures of the copolymers were made to artificially broaden the molecular weight distribution of PAA at a constant number average of 48 in the polydispersity index (PDI) range of 1.1-3.3. The mixtures were dissolved in dioxane, and water was added slowly to predetermined amounts. Transmission electron microscopy was used to observe aggregate morphologies at different water contents and PAA PDIs. At low water contents, dynamic light scattering was also used to measure the sizes of the aggregates. A partial phase diagram as a function of the water content and PAA PDI was obtained. Large compound micelles and spherical micelles (average diameter of 40 nm) were found at low water contents; however, at a water content of 12% (w/w), a continuum of morphologies from spheres to rods to vesicles was found with increasing PAA PDI. In addition, each copolymer was investigated by itself under identical conditions to those used for the mixtures to determine if there was any segregation of the individual polymers into separate aggregates. No evidence for such segregation was found.

Formation and catalytic activity of spherical composites with surfaces coated with gold nanoparticles

“…In addition, the micelle clusters or large compound micelles may also cause the size from the DLS to be larger than that from the TEM, because the TEM result is only a partial reflection of the micelle size. A similar result is also reported by Eisenberg and co-workers [24]. In their study on the self-assembly of polystyrene-block-poly(acrylic acid) (PS-b-PAA), both the DLS and TEM results show a very broad distribution size range of the spherical micelles as large compound micelles are formed.…”

Self‐Assembled Block Copolymer Aggregates: From Micelles to Vesicles and their Biological Applications

“…At first it was speculated that polymer vesicles were non-equilibrium structures because of the glassy nature of the PS membrane, but their thermodynamic stability was subsequently established. [37][38][39][40] Further work confirmed that vesicular morphologies are not dictated by the kinetically frozen glassy nature of the hydrophobic block, since vesicles could be formed with low glass transition temperature (T g ) hydrophobes such as PBD [41,42] and poly(propylene oxide) (PPO). [43] Since these initial reports, there have been hundreds of papers that describe the formation of polymer vesicles and a number of excellent reviews.…”

Recent trends in the tuning of polymersomes’ membrane properties

“…This phenomenon is a particularity of the self-assembly of amphiphilic block copolymers even though it may occur also for pegylated phospholipids, having a macromolecular polar head. Moreover, Eisenberg et al demonstrated, by blending a series of PS-b-PAA block copolymer presenting similar PS molecular weight but variable PAA molecular weight, that vesicle size tends to decrease when the polymolecularity of the hydrophilic chains increases, due to this segregation phenomenon that tends to increase the membrane curvature [30,31]. Interestingly the vesicle size polydispersity has also been reported to decrease in the meantime, leading to this counter-intuitive result that more polydisperse chains lead to more mono-disperse assemblies!…”