Effect of the degree of neutralization on the micellization of block ionomers

Abstract

Abstract:The effect of neutralization on the micellization of polystyrene-b-poly(acry1ic acid) (PS-b-PAA) was investigated by static light scattering (SLS) and small-angle X-ray scattering (SAXS). The block copolymers, present initially in single chain form in either dioxane or benzene-methanol (90110 (vlv)), were neutralized to different degrees by the addition of cesium hydroxide dissolved in methanol. The solutions were simultaneously monitored by SLS. It was found that micelle formation began near 5% neutralization. The normalized scattered light intensity at 90' (19dc) increased dramatically in the neutralization range between ca. 10 and 60%. For neutralization degrees between 60 and ca. loo%, 19dc did not change significantly with a further increase in the percent of neutralization. In the second part of the study, two block copolymers, PS(600)-b-PAA(34) and PS(600)-b-PAA(45) (the number of monomer units is given in parentheses), were prepared from benzenemethanol (90110 (vlv)) with different degrees of neutralization: 5, 25, 60, 100, and 150%. The resulting solutions were freeze-dried and the dried samples were redissolved in toluene. These samples were investigated by SLS and SAXS. By SLS, the aggregation numbers (fl were found to be the same between 5 and 60% neutralization. An increase in f was observed in going from 60 to 100%; i.e., f increased from 82 to 92 for PS(600)-b-PAA(34), and from 79 to 110 for PS(600)-b-PAA(45). The f values for the two block copolymers at 150% neutralization were found to be the same as those for 100% neutralization. The core radii values (R,,,) were measured for the neutralized PS(600)-b-PAA(45) samples at 0.05 g1mL in toluene by SAXS. The R,,,, values increased from 5 to 60% neutralization, remained constant from 60 to loo%, and increased again in the range from 100 to 150%. The results are explained by dynamic considerations. For low percent neutralization, between 5 and 60%, the micelles and single chains are proposed to be in a dynamic equilibrium state. For higher percent neutralization, between 60 and 10070, the dynamics are probably much slower.Key words: block copolymers, micelles, ionomers, light scattering, small angle X-ray scattering (or SAXS).RCsume : Faisant appel A la diffusion statique de la lumitre (SLS) et la diffusion des rayons X A petit angle (SAXS), on a Ctudit l'effet de la neutralisation sur la micellisation du polystyrtne-b-poly(acide acrylique) (PSb-PAA). Les copolymtres A blocs, qui sont prisents initialement sous la forme d'une chaine simple dans le dioxane ou dans un melange benztne-mtthanol(90110 (vlv)), se neutralisent A des degrts divers par l'addition d'hydroxyde de ctsium dissous dans le mCthanol. On a examink les solutions simultaniment par SLS. On a trouvt que la formation de micelles commence prts d'environ 5% de neutralisation. L'intensitC.normalisCe de la lumitre diffuste A 90 ' (19dc) This paper is dedicated to Professor J.E. (Jim) Guillet in recognition of his contributions to Canadian chemistry.

Scaling Relations and Size Control of Block Ionomer Microreactors Containing Different Metal Ions

“…As previously stated, it has been found that block ionomer micelles, in their final state, are kinetically-frozen aggregates that do not exhibit dynamic equilibrium, even under high-temperature conditions . However, it is believed that rapid exchange between micelles and unimers does exist in the early stages of micellization, when the ion content of the insoluble blocks is relatively low and micelle lability is enhanced by solvent swelling . As the degree of neutralization increases, solvent is expelled from the micelle and the core becomes increasingly viscous and compact.…”

Aggregation and Critical Micelle Concentrations of Polystyrene-b-poly(sodium acrylate) and Polystyrene-b-poly(acrylic acid) Micelles in Organic Media

“…It should be noted that the trends which are observed in the aggregation numbers for these samples which have relatively short insoluble block lengths (0.4−3 mol %) may not necessarily be indicative of the behavior for higher ionic block lengths. For instance, a recent paper probed the effect of different degrees of neutralization on the micellization of two block copolymer samples, PS(600) -b- PAA(34) and PS(600) -b- PAA(45) . In that study, the aggregation numbers in toluene for the acid block copolymers were found to be lower than those of the sodium neutralized samples.…”

“…Micellization of block ionomers has been studied extensively in this laboratory ,− as well as in others. − Block ionomer micelles have been shown to possess several characteristic features. For instance, they have been found to be extremely stable. , This stability allows for the characterization of the micelles by SEC. , In general, two peaks could be identified from the SEC chromatograms, one corresponding to the micellized block copolymer and the other due to block copolymers present as single chains.…”

“…It was found that segments near the core had a restricted mobility compared to those further from the core or to single chains in solution. The effect of different degrees of neutralization of the block forming the micelle core on the micellization was also probed by SAXS and SLS …”

Poly(N‐hydroxyethyl acrylamide)‐b‐polystyrene by combination of ATRP and aminolysis processes

“…Solution‐ and micelle‐forming behaviors of the block copolymers constituting with hydrophilic poly(ethylene oxide) and hydrophobic poly(propylene oxide) blocks have also been studied in detail 9. Self‐assembling and nanocomposite formation of polystyrene‐ b ‐poly(4‐vinyl pyridine),10 polystyrene‐ b ‐poly(acrylic acid),11 and poly(ethylene oxide)‐ b ‐poly(butylene oxide)12 have been investigated in various solvent systems.…”